Patent Publication Number: US-2021186572-A1

Title: Articulating implant connectors and related methods

Description:
RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 15/926,051, filed on Mar. 20, 2018. U.S. patent application Ser. No. 15/926,051 is a continuation-in-part of U.S. patent application Ser. No. 15/471,075, filed on Mar. 28, 2017, and now issued as U.S. Pat. No. 10,561,454. The entire contents of each of these applications are incorporated herein by reference. 
    
    
     FIELD 
     Articulating implant connectors and related methods are disclosed herein. 
     BACKGROUND 
     Fixation systems can be used in orthopedic surgery to maintain a desired spatial relationship between multiple bones or bone fragments. For example, various conditions of the spine, such as fractures, deformities, and degenerative disorders, can be treated by attaching a spinal fixation system to one or more vertebrae. Such systems typically include a spinal fixation element, such as a rigid or flexible rod or plate, that is coupled to the vertebrae by attaching the element to various anchoring devices, such as screws, hooks, or wires. Once installed, the fixation system holds the vertebrae in a desired position until healing or spinal fusion can occur, or for some other period of time. 
     There are many instances in which it may be desirable to connect multiple implants to each other. For example, some revision surgeries involve extending a previously-installed construct to additional vertebral levels by coupling a newly-installed spinal rod to a previously-installed rod. By way of further example, aspects of the patient&#39;s anatomy, the surgical technique used, or the desired correction may require that multiple spinal rods be connected to one another. As yet another example, coupling multiple rods to one another can improve the overall strength and stability of an implanted construct. 
     There can be various difficulties associated with connecting multiple implants to each other. The available space for the implanted construct can often be very limited, particularly in the cervical area of the spine. Also, aligning and positioning implants and connectors in the surgical wound may be challenging or cumbersome for the surgeon. There is a continual need for improved implant connectors and related methods. 
     SUMMARY 
     Articulating implant connectors and related methods are disclosed herein. Exemplary connectors can include first and second bodies that are rotatable relative to one another about a rotation axis and selectively lockable to resist or prevent such rotation. Each of the bodies can be configured to couple to a rod or other fixation component, and the connector can be used to lock first and second rods together even when the rods are obliquely angled with respect to one another. 
     In some embodiments, a connector can include a first body that defines a first rod-receiving recess, the first body having proximal and distal ends that define a proximal-distal axis extending therebetween; a second body that defines a second rod-receiving recess, the second body having proximal and distal ends that define a proximal-distal axis extending therebetween; a hinge pin that couples the first body to the second body, a central longitudinal axis of the hinge pin defining a rotation axis about which the first and second bodies rotate relative to one another; and a fastener movable with respect to at least one of the first and second bodies to urge the first and second bodies towards one another along the rotation axis and thereby lock relative rotation of the first and second bodies about the rotation axis. 
     The fastener can secure a rod to one of the first and second rod-receiving recesses. The fastener can be a first fastener configured to secure a first rod within the first rod-receiving recess. The connector can include a second fastener configured to secure a second rod in the second rod-receiving recess. The hinge pin can be formed integrally with the first body. The hinge pin can be rotatable relative to both of the first and second bodies. The first and second bodies can include respective bearing surfaces configured to bear against one another to lock relative rotation of the first and second bodies about the rotation axis. The bearing surfaces can be defined by complementary male and female structures of the first and second bodies. The first body can include a conical male projection, an outer surface of which defines the bearing surface of the first body. The second body can include a conical female recess, an inner surface of which defines the bearing surface of the second body. The bearing surfaces can each include teeth or splines. The hinge pin can be received within a cavity formed in the first body or the second body. The hinge pin can translate longitudinally within the cavity as the fastener is moved relative to said at least one of the first and second bodies. The proximal-distal axes of the first and second bodies can be obliquely angled with respect to one another. A force applied by the fastener can be transferred to the hinge pin through a saddle. The saddle can include a conical surface that engages and bears against a corresponding conical surface of the hinge pin to pull the first and second bodies towards one another. The saddle can include a keel extending distally therefrom. The keel can be received within a slot formed in the hinge pin. The keel can have a bearing surface that engages and bears against a corresponding bearing surface of the slot to pull the first and second bodies towards one another. The bearing surfaces of the keel and the slot can lie in planes that are obliquely angled with respect to the rotation axis. The saddle can include first and second keels defining a space therebetween in which a central rib of the hinge pin is received. The first and second keels can have bearing surfaces that engage and bear against corresponding bearing surface of the hinge pin. The hinge pin can include a rod seat formed therein. The rod seat can be configured such that urging a rod against the rod seat causes the hinge pin to translate relative to at least one of the first and second bodies along the rotation axis. The rod seat can be positioned relative to the first rod-receiving recess such that a lateral sidewall of the rod seat interferes with a rod as the rod is seated in the first rod-receiving recess. The rod seat can be curved in multiple planes. 
     In some embodiments, a connector can include a first body that defines a first rod-receiving recess; a hinge pin formed integrally with the first body and extending laterally therefrom to a free end; a second body that defines a second rod-receiving recess, the second body having a cavity in which the free end of the hinge pin is received to couple the second body to the first body such that the first and second bodies rotate relative to one another about a rotation axis; a first fastener configured to secure a first rod within the first rod-receiving recess; and a second fastener configured to secure a second rod within the second rod-receiving recess and to urge the first and second bodies towards one another along the rotation axis to lock relative rotation of the first and second bodies about the rotation axis. 
     The second fastener can be configured to bear against a saddle disposed within the second rod-receiving recess to urge a bearing surface of the saddle against a bearing surface of the hinge pin to move the first and second bodies towards one another. The second fastener can be configured to bear against a rod disposed within the second rod-receiving recess to urge the rod against a rod seat of the hinge pin to move the first and second bodies towards one another. 
     In some embodiments, a surgical method can include inserting a first rod into a first rod-receiving recess of a first body of a connector; inserting a second rod into a second rod-receiving recess of a second body of the connector, the second body being coupled to the first body by a hinge pin; rotating the first body relative to the second body about a rotation axis defined by the hinge pin; moving a fastener with respect to at least one of the first and second bodies to urge the first and second bodies towards one another along the rotation axis and thereby lock relative rotation of the first and second bodies about the rotation axis; and securing the first and second rods to an anatomy of a patient. 
     The first rod can be secured to a cervical spine of the patient by one or more bone anchors and the second rod can be secured to a thoracic spine of the patient by one or more bone anchors. Rotating the first body relative to the second body can cause the first and second rods to be obliquely angled with respect to one another. Moving the fastener can be effective both to secure one of the first and second rods to the connector and to lock rotation of the connector. 
     In some embodiments, a connector can include a first body that defines a first rod-receiving recess; a hinge pin extending laterally from the first body to a free end; a second body that defines a second rod-receiving recess, the second body having a cavity in which the free end of the hinge pin can be received to couple the second body to the first body such that the first and second bodies rotate relative to one another about a rotation axis of the hinge pin; a first fastener configured to secure a first rod within the first rod-receiving recess; and a second fastener configured to secure a second rod within the second rod-receiving recess. The hinge pin can have planar surfaces that intersect to form one or more corners. The corners of the hinge pin can apply a force against the cavity of the second body that locks the hinge pin in place when the second fastener secures the second rod within the second rod-receiving recess. 
     A cross section of the hinge pin can have a polygonal profile. The connector can further include a saddle disposed within the second rod-receiving recess. The saddle can include a saddle protrusion extending distally therefrom. The saddle protrusion can be received within a slot formed in the hinge pin. The force applied by one or more corners of the hinge pin can be transferred from a force applied by the second fastener through the saddle. The saddle protrusion can limit a rotation of the hinge pin within the cavity of the second body when a terminal end of the slot of the hinge pin engages and bears against the saddle protrusion. The saddle can have a bearing surface adjacent to the saddle protrusion that engages and bears against a corresponding bearing surface of the hinge pin adjacent to the slot. The slot of the hinge pin can be formed radially about a central rib of the hinge pin. The saddle protrusion of the saddle can define a depression in which the central rib of the hinge pin is received. 
     In some embodiments, the connector can include a first body that defines a first rod-receiving recess; a hinge pin extending laterally from the first body to a free end; a second body that defines a second rod-receiving recess, the second body having a cavity in which the free end of the hinge pin can be received to couple the second body to the first body such that the first and second bodies rotate relative to one another about a rotation axis of the hinge pin; a saddle defining a rod seat disposed within the second rod-receiving recess, the saddle including a saddle protrusion extending distally therefrom, the saddle protrusion being received within a slot formed in the hinge pin; a first fastener configured to secure a first rod within the first rod-receiving recess; and a second fastener configured to secure a second rod on the rod seat of the saddle. The slot of the hinge pin can have an angled cam surface that can engage and bear against a corresponding angled bearing surface of the saddle protrusion to lock the hinge pin in place when the second fastener secures the second rod within the second rod-receiving recess. 
     The angled cam surface of the slot can be oriented at an oblique angle with respect to the longitudinal axis of the hinge pin. The angled bearing surface of the saddle protrusion can be oriented at an oblique angle with respect to the longitudinal axis of the hinge pin. The angled bearing surface of the saddle protrusion can be oriented to match the oblique angle of the angled cam surface of the slot in the hinge pin. The saddle protrusion can have a wedge-shaped cross section that can apply a force against the angled cam surface of the slot of the hinge pin to lock the hinge pin in place when the second fastener secures the second rod within the second rod-receiving recess. 
     In some embodiments, the connector can include a first body that defines a first rod-receiving recess; a hinge pin extending laterally from the first body to a free end; a second body that defines a second rod-receiving recess, the second body having a cavity in which the free end of the hinge pin can be received to couple the second body to the first body such that the first and second bodies rotate relative to one another about a rotation axis of the hinge pin; a first fastener configured to secure a first rod within the first rod-receiving recess; and a second fastener configured to secure a second rod within the second rod-receiving recess. The free end of the hinge pin can extend through the cavity and into an opening defined in the second body. The opening can have a cross sectional shape that limits rotation of the free end of the hinge pin relative to the second body about the rotation axis. 
     The free end of the hinge pin can have a cross sectional shape configured to rotate within the opening of the second body. The cross sectional shape of the free end of the hinge pin and the cross sectional shape of the opening can define a degree of rotation of the free end of the hinge pin. The cross sectional shape of the opening of the second body and the cross sectional shape of the free end of the hinge pin can be D-shaped. The D-shaped cross section of the opening of the second body can have an area greater than an area of the D-shaped cross section of the free end of the hinge pin. 
     The second fastener can be configured to bear against a saddle disposed within the second rod-receiving recess to urge a bearing surface of the saddle against a corresponding bearing surface of the hinge pin. The saddle can include a saddle protrusion extending distally from an edge of the saddle adjacent to the bearing surface of the saddle. The saddle protrusion can be received within a slot formed in the hinge pin adjacent to the bearing surface of the hinge pin. The slot of the hinge pin can be aligned with an edge of the second rod-receiving recess when the free end of the hinge pin is inserted into the through hole opening of the second body. The bearing surface of the hinge pin can bear against the bearing surface of the saddle for a continuous length that is greater than half the width of the second rod-receiving recess. 
     In some embodiments, the connector can include a first body that defines a first rod-receiving recess; a hinge pin extending laterally from the first body to a free end; a second body that defines a second rod-receiving recess, the second body having a cavity in which the free end of the hinge pin can be received to couple the second body to the first body such that the first and second bodies rotate relative to one another about a rotation axis of the hinge pin; a saddle defining a rod seat disposed within the second rod-receiving recess, the saddle including a saddle protrusion extending distally therefrom, the saddle protrusion being received within a slot formed in the hinge pin; a first fastener configured to secure a first rod within the first rod-receiving recess; and a second fastener configured to secure a second rod on the rod seat of the saddle. The slot of the hinge pin can be aligned with an edge of the second rod-receiving recess when the free end of the hinge pin is inserted into the cavity of the second body. 
     The saddle protrusion can extend distally from an edge of the saddle adjacent to a bearing surface of the saddle. The saddle protrusion can be received within the slot of the hinge pin. The bearing surface of the saddle can bear against a bearing surface of the hinge pin for a continuous length that can be greater than half the width of the second rod-receiving recess. 
     In some embodiments, a surgical method can include inserting a first rod into a first rod-receiving recess of a first body of a connector, the first body including a hinge pin that extends laterally therefrom to a free end; inserting a second rod onto a rod seat formed in a saddle disposed in a second rod-receiving recess of a second body of the connector, the hinge pin of the first body being inserted into a cavity formed in the second body and thereby coupling the first body of the connector to the second body of the connector; rotating the first body relative to the second body about a rotation axis defined by the hinge pin, such that a slot formed in the hinge pin rotates about a saddle protrusion extending distally from the saddle; moving a fastener with respect to the second body to secure the second rod within the second rod-receiving recess and thereby lock relative rotation of the first and second bodies about the rotation axis; and securing the first and second rods to an anatomy of a patient. 
     Moving the fastener with respect to the second body can urge a bearing surface of the saddle against a corresponding bearing surface of the hinge pin and thereby cause one or more corners of the hinge pin to apply a force against the cavity of the second body. Rotating the first body relative to the second body about a rotation axis defined by the hinge pin can include rotating the first body with respect to the second body such that the saddle protrusion can limit a rotation of the hinge pin when a terminal end of the slot of the hinge pin engages and bear against the saddle protrusion. The slot of the hinge pin can have an angled cam surface and the saddle protrusion can have a corresponding angled bearing surface. Moving the fastener with respect to the second body can wedge the angled bearing surface of the saddle protrusion into the angled cam surface of the slot. Rotating the first body relative to the second body about a rotation axis defined by the hinge pin can include rotating the first body such that the free end of the hinge pin rotates within an opening defined in the second body of the connector. The opening can have a cross sectional shape that limits rotation of the free end of the hinge pin. Rotating the first body relative to the second body about a rotation axis defined by the hinge pin can include rotating the first body such that the slot of the hinge pin rotates about the saddle protrusion that extends distally from an edge of the saddle and can be aligned with an edge of the second rod-receiving recess. Moving the fastener with respect to the second body can urge a bearing surface of the saddle against a corresponding bearing surface of the hinge pin for a continuous length that is greater than half the width of the second rod-receiving recess. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a perspective view of a connector, shown with first and second rods; 
         FIG. 1B  is an exploded perspective view of the connector of  FIG. 1A ; 
         FIG. 1C  is a sectional side view of the connector and rods of  FIG. 1A ; 
         FIG. 1D  is a partial exploded view of the connector of  FIG. 1A ; 
         FIG. 1E  is a perspective view of a first body of the connector of  FIG. 1A ; 
         FIG. 1F  is another perspective view of the first body of  FIG. 1E ; 
         FIG. 1G  is a perspective view of a first saddle of the connector of  FIG. 1A ; 
         FIG. 1H  is another perspective view of the first saddle of  FIG. 1G ; 
         FIG. 1I  is a perspective view of a hinge pin of the connector of  FIG. 1A ; 
         FIG. 1J  is an end view of the hinge pin of  FIG. 1I ; 
         FIG. 1K  is a side view of the hinge pin of  FIG. 1I ; 
         FIG. 1L  is a top view of the hinge pin of  FIG. 1I ; 
         FIG. 2A  is a perspective view of a connector, shown with first and second rods; 
         FIG. 2B  is an exploded perspective view of the connector of  FIG. 2A ; 
         FIG. 2C  is a sectional side view of the connector and rods of  FIG. 2A ; 
         FIG. 2D  is a perspective view of a second body of the connector of  FIG. 2A ; 
         FIG. 2E  is another perspective view of the second body of  FIG. 2A ; 
         FIG. 3A  is a perspective view of a connector, shown with first and second rods; 
         FIG. 3B  is an exploded perspective view of the connector of  FIG. 3A ; 
         FIG. 3C  is a sectional side view of the connector and rods of  FIG. 3A ; 
         FIG. 3D  is a perspective view of a saddle of the connector of  FIG. 3A ; 
         FIG. 3E  is a side view of the saddle of  FIG. 3D ; 
         FIG. 3F  is another perspective view of the saddle of  FIG. 3D ; 
         FIG. 3G  is a perspective view of a first body of the connector of  FIG. 3A ; 
         FIG. 3H  is a perspective view of a second body of the connector of  FIG. 3A ; 
         FIG. 3I  is a top view of an alternate first body of the connector of  FIG. 3A ; 
         FIG. 3J  is an end view of an alternate saddle of the connector of  FIG. 3A   
         FIG. 3K  is a side view of the alternate first body of  FIG. 3I ; 
         FIG. 3L  is a side view of the alternate saddle of  FIG. 3J ; 
         FIG. 4A  is a perspective view of a connector, shown with first and second rods and with first and second fasteners of the connector omitted; 
         FIG. 4B  is an exploded perspective view of the connector of  FIG. 4A ; 
         FIG. 4C  is a sectional side view of the connector of  FIG. 4A ; 
         FIG. 4D  is a perspective view of a second body of the connector of  FIG. 4A ; 
         FIG. 4E  is a side view of a first body of the connector of  FIG. 4A ; 
         FIG. 4F  is a perspective sectional view of the first body of the connector of  FIG. 4A ; 
         FIG. 5A  is a perspective view of a connector, shown with first and second spinal rods; 
         FIG. 5B  is an exploded perspective view of the connector of  FIG. 5A ; 
         FIG. 5C  is a perspective view of a first body of the connector of  FIG. 5A ; 
         FIG. 5D  is another perspective view of the first body of  FIG. 5C ; 
         FIG. 5E  is an end view of the first body of  FIG. 5C ; 
         FIG. 5F  is a top view of the connector of  FIG. 5A , shown with the saddle of the connector omitted; 
         FIG. 5G  is a perspective view of a second body of the connector of  FIG. 5A ; 
         FIG. 5H  is another perspective view of the second body of  FIG. 5G ; 
         FIG. 5I  is a perspective view of the saddle of the connector of  FIG. 5A ; 
         FIG. 5J  is a sectional side view of the connector of  FIG. 5A , shown with the fasteners of the connector omitted; 
         FIG. 5K  is another perspective view of the saddle of  FIG. 5I ; 
         FIG. 5L  is an end view of the saddle of  FIG. 5I ; 
         FIG. 5M  is another perspective view of a connector, shown with the second body as transparent; 
         FIG. 5N  is a sectional end view of the connector of  FIG. 5A , shown with the fasteners of the connector omitted; 
         FIG. 5O  is another sectional end view of the connector of  FIG. 5A , shown with the fasteners of the connector omitted; 
         FIG. 6A  is a perspective view of a connector, shown with the fasteners of the connector omitted; 
         FIG. 6B  is an exploded perspective view of the connector of  FIG. 6A ; 
         FIG. 6C  is a perspective view of a first body of the connector of  FIG. 6A ; 
         FIG. 6D  is top view of the connector of  FIG. 6A , shown with the saddle of the connector omitted; 
         FIG. 6E  is a perspective view of the saddle of the connector of  FIG. 6A ; 
         FIG. 6F  is another perspective view of the saddle of  FIG. 6E ; 
         FIG. 6G  is another perspective view of the saddle of  FIG. 6E ; 
         FIG. 6H  is another perspective view of the connector of  FIG. 6A , shown with the second body of the connector as transparent; 
         FIG. 6I  is a sectional side view of the connector of  FIG. 6A , shown with the fasteners omitted; 
         FIG. 6J  is bottom view of the connector of  FIG. 6A , shown with the second body of the connector as transparent; 
         FIG. 7A  is a perspective view of a connector, shown without the fasteners of the connector; 
         FIG. 7B  is an exploded perspective view of the connector of  FIG. 7A ; 
         FIG. 7C  is a side view of a first body of the connector of  FIG. 7A ; 
         FIG. 7D  is a top view of the first body of  FIG. 7C ; 
         FIG. 7E  is an end view of the first body of  FIG. 7C ; 
         FIG. 7F  is a side view of a second body of the connector of  FIG. 7A ; 
         FIG. 7G  is a perspective view of the second body of  FIG. 7F ; 
         FIG. 7H  is another perspective view of the second body of  FIG. 7F ; 
         FIG. 7I  is a side view of the saddle of the connector of  FIG. 7A ; 
         FIG. 7J  is a perspective view of the saddle of  FIG. 7I ; 
         FIG. 7K  is another perspective view of the saddle of  FIG. 7I ; 
         FIG. 7L  is another perspective view of the connector of  FIG. 7A , shown with the saddle and the fasteners of the connector omitted; 
         FIG. 7M  is a sectional side view of the connector of  FIG. 7A ; 
         FIG. 7N  is an end view of the connector of  FIG. 7A ; 
         FIG. 7O  is a sectional end view of the connector of  FIG. 7A , shown with the fasteners of the connector omitted; and 
         FIG. 8  is a perspective view of a human spine with a fixation system attached thereto. 
     
    
    
     DETAILED DESCRIPTION 
     Articulating implant connectors and related methods are disclosed herein. Exemplary connectors can include first and second bodies that are rotatable relative to one another about a rotation axis and selectively lockable to resist or prevent such rotation. Each of the bodies can be configured to couple to a rod or other fixation component, and the connector can be used to lock first and second rods together even when the rods are obliquely angled with respect to one another. 
     Certain exemplary embodiments will now be described to provide an overall understanding of the principles of the structure, function, manufacture, and use of the devices and methods disclosed herein. One or more examples of these embodiments are illustrated in the accompanying drawings. Those skilled in the art will understand that the devices and methods specifically described herein and illustrated in the accompanying drawings are non-limiting exemplary embodiments. The features illustrated or described in connection with one exemplary embodiment may be combined with the features of other embodiments. 
       FIGS. 1A-1L  illustrate an exemplary embodiment of a connector  100 . As shown, the connector  100  can include a first body  102  that defines a first rod-receiving recess or channel  104  and a second body  106  that defines a second rod-receiving recess or channel  108 . The first and second bodies  102 ,  106  can be connected to one another at least in part by a hinge pin  110 . The hinge pin  110  can define a rotation axis A 1  about which the first and second bodies  102 ,  106  can rotate relative to one another. The connector  100  can include first and second fasteners  112 ,  114  configured to secure respective first and second rods R 1 , R 2  or other fixation elements to the connector  100 . 
     At least one of the fasteners  112 ,  114  can further be configured to urge the first and second bodies  102 ,  106  towards one another and thereby lock relative rotation of the first and second bodies about the rotation axis A 1 . For example, the first fastener  112  can be tightened to secure a first rod R 1  within the first body  102  and to apply a force to a first ramped, curved, or otherwise tapered surface  116  of the hinge pin  110  to draw the first and second bodies  102 ,  106  towards one another, locking rotation therebetween. In the illustrated embodiment, a force applied by the first fastener  112  is transferred to the hinge pin  110  through the first rod R 1  and through a first saddle  118  disposed between the first rod and the hinge pin. In other arrangements, the saddle  118  can be omitted and the first rod R 1  can bear directly against the hinge pin  110 . In still further arrangements, the first fastener  112  can bear directly against the saddle  118 . For example, the first fastener  112  can include an outer set screw that bears against the saddle  118  to lock relative rotation of the bodies  102 ,  106 , and an inner set screw that bears against the first rod R 1  to secure the first rod to the connector  100 . 
     Similarly, the second fastener  114  can be tightened to secure a second rod R 2  within the second body  106  and to apply a force to a second ramped, curved, or otherwise tapered surface  120  of the hinge pin  110  to draw the first and second bodies  102 ,  106  towards one another, locking rotation therebetween. In the illustrated embodiment, a force applied by the second fastener  114  is transferred to the hinge pin  110  through the second rod R 2  and through a second saddle  122  disposed between the second rod and the hinge pin. In other arrangements, the saddle  122  can be omitted and the second rod R 2  can bear directly against the hinge pin  110 . In still further arrangements, the second fastener  114  can bear directly against the saddle  122 . For example, the second fastener  114  can include an outer set screw that bears against the saddle  122  to lock relative rotation of the bodies  102 ,  106 , and an inner set screw that bears against the second rod R 2  to secure the second rod to the connector  100 . 
     The geometries of the various components of the connector  100  can be configured such that tightening either of the fasteners  112 ,  114  individually is effective to lock relative rotation between the bodies  102 ,  106 , or such that both fasteners  112 ,  114  must be tightened before relative rotation between the bodies  102 ,  106  is locked. 
     The ability to rotate the first and second bodies  102 ,  106  relative to one another about the rotation axis A 1  can advantageously allow first and second rods R 1 , R 2  to be locked together even when the rods are obliquely angled with respect to one another, e.g., in the sagittal plane or in the coronal plane. The connector  100  can be particularly useful in connecting tandem rods of a spinal fixation construct across the cervical-thoracic (CT) junction of a patient. For example, the connector  100  can secure the rods R 1 , R 2  in a laterally-offset arrangement to accommodate the different screw trajectories that may occur at the CT junction. By way of further example, the ability of the connector  100  to articulate can allow a cervical rod and a thoracic rod to be locked to one another at an oblique angle in the sagittal plane, e.g., to restore natural lordosis or kyphosis. The connector  100  can also be particularly useful in spinal deformity correction and other procedures in which multiple angled rods are to be coupled to one another. 
     The first body  102  is shown in greater detail in  FIGS. 1C, 1E, and 1F . The first body  102  can include proximal and distal ends  102   p ,  102   d  that define a proximal-distal axis A 2 . The proximal end  102   p  of the body  102  can include a pair of spaced apart arms  124 ,  126  that define the first rod-receiving recess  104  therebetween. A rod R 1  disposed in the first rod-receiving recess  104  can have a central longitudinal rod axis A 3 . The first rod-receiving recess  104  can be open in a proximal direction, such that a rod R 1  can be inserted into the recess by moving the rod distally with respect to the connector  100 . Alternatively, the first rod-receiving recess  104  can be open in distal direction, open in a lateral direction, or closed such that the rod R 1  must be translated along the axis A 3  to insert the rod into the recess  104 . 
     Each of the arms  124 ,  126  can extend from the distal portion  102   d  of the body  102  to a free end. The outer surfaces of each of the arms  124 ,  126  can include a feature (not shown), such as a recess, dimple, notch, projection, or the like, to facilitate coupling of the connector  100  to various instruments. For example, the outer surface of each arm  124 ,  126  can include an arcuate groove at the respective free end of the arms for attaching the connector  100  to an extension tower or retractor. The arms  124 ,  126  can include or can be coupled to extension or reduction tabs (not shown) that extend proximally from the body  102  to functionally extend the length of the arms  124 ,  126 . The extension tabs can facilitate insertion and reduction of a rod or other implant, as well as insertion and locking of the first fastener  112 . The extension tabs can be configured to break away or otherwise be separated from the arms  124 ,  126 . 
     The inner surfaces of each of the arms  124 ,  126  can be configured to mate with the first fastener  112 . For example, the inner surfaces of the arms  124 ,  126  can include threads that correspond to external threads formed on the first fastener  112 . Accordingly, rotation of the first fastener  112  with respect to the body  102  about the axis A 2  can be effective to translate the first fastener with respect to the body axially along the axis A 2 . 
     The inner surfaces of each of the arms  124 ,  126  can include features for retaining the first saddle  118  within the first body  102  and/or for limiting or preventing certain movement of the saddle with respect to the body. For example, the arms  124 ,  126  can each include a recess  128  configured to receive a corresponding projection  144  formed on the saddle  118 . Each recess  128  can define a distal-facing upper surface configured to limit proximal travel of the saddle  118  along the axis A 2  and a proximal-facing lower surface configured to limit distal travel of the saddle  118  along the axis A 2 . The recess  128  can extend through less than an entire width of the arm in which the recess is formed, such that rotation of the saddle  118  relative to the body  102  about the axis A 2  is limited or prevented when the projections  144  of the saddle are received within the recesses. 
     It will be appreciated that the illustrated retention features are exemplary, and that various other retention features can be used instead or in addition. For example, the structures can be reversed such that the body  102  includes projections received within corresponding recesses formed in the saddle  118 . As another example, the saddle  118  and the body  102  can include opposed grooves in which a snap ring or C-clip is received to retain the saddle to the body. As yet another example, the saddle  118  and the hinge pin  110  can include opposed grooves in which a snap ring or C-clip is received to retain the saddle to the hinge pin. 
     The first body  102  can include an outer bearing surface  130  configured to contact and bear against a corresponding bearing surface  140  of the second body  106 . The respective bearing surfaces  130 ,  140  of the bodies  102 ,  106  can bear against one another to lock relative rotation between the bodies as they are urged towards one another. In the illustrated embodiment, the bearing surfaces  130 ,  140  of the first and second bodies  102 ,  106  are opposed planar surfaces configured to frictionally-engage one another when the connector  100  is locked. It will be appreciated, however, that various other arrangements can be used instead or in addition. For example, the bearing surfaces  130 ,  140  can include or can be defined by complementary male and female structures of the first and second bodies  102 ,  106 . In some embodiments, the first body  102  can include a conical male projection, an outer surface of which defines the bearing surface  130  of the first body, and the second body  106  can include a conical female recess, an inner surface of which defines the bearing surface  140  of the second body. As the projection of the first body  102  is urged into the recess of the second body  106 , the conical surfaces wedge against one another to form a taper-lock connection. While conical surfaces are described in the example above, the male and female features can include concave or convex spherical surfaces, stepped surfaces, and so forth. 
     One or both of the bearing surfaces  130 ,  140  can include surface features for enhancing grip between the surfaces. For example, one or both surfaces can include teeth, grooves, roughening, surface textures or coatings, etc. In some embodiments, as shown in  FIG. 1D , each bearing surface  130 ,  140  can include a plurality of teeth that extend radially outward from the rotation axis A 1 . The teeth can selectively interlock to maintain the bodies  102 ,  106  in one of a plurality of discrete rotational positions relative to one another. 
     The distal end  102   d  of the body  102  can define an interior cavity  132  in which a first end of the hinge pin  110  can be received. The cavity  132  can be open to the bearing surface  130  of the first body  102  and open to the first rod-receiving recess  104  as shown. In some embodiments, the cavity  132  can be a blind bore formed in the bearing surface  130  of the body  102  and intersecting with the first rod-receiving recess  104 . At least one dimension of the cavity  132  can be greater than a corresponding dimension of the hinge pin  110  to allow the hinge pin to translate within the cavity along the rotation axis A 1 . As described further below, the cavity  132  can be dimensioned to limit the degree to which the body  102  can rotate relative to the hinge pin  110  about the axis A 1 . 
     The second body  106  can be identical or substantially identical to the first body  102 , or can have any of the features or variations described above with respect to the first body  102 . Accordingly, only a brief description of the second body  106  is provided here for the sake of brevity. The second body  106  can include proximal and distal ends  106   p ,  106   d  that define a proximal-distal axis A 4 . The proximal end  106   p  of the body  106  can include a pair of spaced apart arms  134 ,  136  that define the second rod-receiving recess  108  therebetween. A rod R 2  disposed in the second rod-receiving recess  108  can have a central longitudinal rod axis A 5 . The second rod-receiving recess  108  can be open in a proximal direction, such that a rod R 2  can be inserted into the recess by moving the rod distally with respect to the connector  100 . Alternatively, the second rod-receiving recess  108  can be open in distal direction, open in a lateral direction, or closed such that the rod R 2  must be translated along the axis A 5  to insert the rod into the recess  108 . 
     Each of the arms  134 ,  136  can include features  138  for retaining the saddle  122  within the body  106 . The second body  106  can include an outer bearing surface  140  configured to contact and bear against the outer bearing surface  130  of the first body  102 . The distal end  106   d  of the second body  106  can define an interior cavity  142  in which a second end of the hinge pin  110  can be received. The cavity  142  can be open to the bearing surface  140  of the second body  106  and open to the second rod recess  108  as shown. In some embodiments, the cavity  142  can be a blind bore formed in the bearing surface  140  of the body  106  and intersecting with the second rod recess  108 . At least one dimension of the cavity  142  can be greater than a corresponding dimension of the hinge pin  110  to allow the hinge pin to translate within the cavity along the rotation axis A 1 . As described further below, the cavity  142  can be dimensioned to limit the degree to which the body  106  can rotate relative to the hinge pin  110  about the axis A 1 . 
     The bodies  102 ,  106  of the connector  100  can include various features for decreasing or increasing the center-to-center offset between the first and second rods R 1 , R 2  when the rods are locked to the connector. In the illustrated embodiment, the bearing surfaces  130 ,  140  of the first and second bodies  102 ,  106  are obliquely angled with respect to the bodies&#39; respective proximal-distal axes A 2 , A 4 . Accordingly, the rods R 1 , R 2  move towards one another as they are advanced distally into the connector  100 . This can advantageously reduce the center-to-center offset of the rods R 1 , R 2 , while preserving sufficient material thickness at the proximal ends of the bodies  102 ,  106  to withstand the relatively high forces subjected to the connector  100  during rod reduction, fastener tightening, and/or post-operative patient movement. 
     As another example, the bearing surfaces  130 ,  140  of the bodies  102 ,  106  can be parallel to the proximal-distal axes A 2 , A 4 , and instead the rod recesses  104 ,  108  can be obliquely angled or can follow a curved path with respect to the proximal-distal axes to bring the rods R 1 , R 2  closer together. 
     As another example, the axis along which the first fastener  112  advances as it is tightened can be offset laterally from the first rod axis A 3  when the first rod R 1  is fully seated in the recess  104 , or can be obliquely angled with respect to the proximal-distal axis A 2  of the first body  102 . Alternatively, or in addition, the axis along which the second fastener  114  advances as it is tightened can be offset laterally from the second rod axis A 5  when the second rod R 2  is fully seated in the recess  108 , or can be obliquely angled with respect to the proximal-distal axis A 4  of the second body  106 . 
     The rotation axis A 1  of the connector  100  can be perpendicular to the rod axis A 3  and perpendicular to the rod axis A 5 . The rotation axis A 1  can be perpendicular to the proximal-distal axis A 2  of the first body, or can be obliquely angled with respect to the axis A 2 . The rotation axis A 1  can be perpendicular to the proximal-distal axis A 4  of the second body, or can be obliquely angled with respect to the axis A 4 . The proximal-distal axes A 2 , A 4  of the bodies  102 ,  106  can be parallel to one another or can extend at an oblique angle with respect to one another. 
     The first saddle  118  is shown in greater detail in  FIGS. 1C, 1G, and 1H . The saddle  118  can be positioned within the body  102 . The saddle  118  can be configured to translate within the body  102  along the axis A 2 , e.g., between proximal and distal limits defined by the interaction between the recesses  128  of the body  102  and projections  144  formed on the saddle. 
     The saddle  118  can be generally cylindrical with first and second arms  146 ,  148  extending in a proximal direction to respective free ends of the arms. The first and second arms  146 ,  148  can be aligned with the first and second arms  124 ,  126  of the body  102  such that a recess defined therebetween is aligned with the first rod-receiving recess  104 . Accordingly, the first rod R 1  can be simultaneously cradled between the arms  146 ,  148  of the saddle  118  and the arms  124 ,  126  of the body  102  when the rod is disposed in the first rod-receiving recess  104 . The first and second arms  146 ,  148  of the saddle  118  can include projections  144  extending radially outward therefrom and configured to be received within the recesses  128  of the first body  102 . 
     The distal-facing surface of the saddle  118  can define a recess  150  configured to receive at least a portion of the hinge pin  110 . In the illustrated embodiment, the recess  150  is semi-cylindrical. The depth of the recess  150  can increase along the length of the recess as shown to account for a body geometry in which the proximal-distal axis A 2  of the body is obliquely angled with respect to the rotation axis A 1  of the hinge pin  110 . 
     The saddle  118  can include one or more ramped, curved, or otherwise tapered surfaces configured to contact and bear against a counterpart surface of the hinge pin  110 . For example, a depression formed in the outer surface of the first arm  146  of the saddle  118  can define a first bearing surface  152  that is a section of a cone. A depression formed in the outer surface of the second arm  148  of the saddle  118  can define a second bearing surface  154  that is a section of a cone. 
     The second saddle  122  can be identical or substantially identical to the first saddle  118 , or can have any of the features or variations described above with respect to the first saddle  118 . Accordingly, only a brief description of the second saddle  122  is provided here for the sake of brevity. The second saddle  122  can be positioned within the body  106 . The saddle  122  can be configured to translate within the body  106  along the axis A 4 , e.g., between proximal and distal limits defined by the interaction between the recesses  138  of the body and projections  156  formed on the saddle. 
     The saddle  122  can be generally cylindrical with first and second arms  158 ,  160  extending in a proximal direction to respective free ends of the arms. The first and second arms  158 ,  160  can be aligned with the first and second arms  134 ,  136  of the body  106  such that a recess defined therebetween is aligned with the second rod-receiving recess  108 . Accordingly, the second rod R 2  can be simultaneously cradled between the arms  158 ,  160  of the saddle  122  and the arms  134 ,  136  of the body  106  when the rod is disposed in the second rod-receiving recess  108 . The first and second arms  158 ,  160  of the saddle  122  can include projections  156  extending radially outward therefrom and configured to be received within the recesses  138  of the second body  106 . 
     The distal-facing surface of the saddle  122  can define a recess  162  configured to receive at least a portion of the hinge pin  110 . In the illustrated embodiment, the recess  162  is semi-cylindrical. The depth of the recess  162  can increase along the length of the recess as shown to account for a body geometry in which the proximal-distal axis A 4  of the body  106  is obliquely angled with respect to the rotation axis A 1  of the hinge pin  110 . 
     The saddle  122  can include one or more ramped, curved, or otherwise tapered surfaces configured to contact and bear against a counterpart surface of the hinge pin  110 . For example, a depression formed in the outer surface of the first arm  158  of the saddle  122  can define a first bearing surface  164  that is a section of a cone. A depression formed in the outer surface of the second arm  160  of the saddle  122  can define a bearing surface  166  that is a section of a cone. 
     The first fastener  112  can include an exterior thread configured to mate with the interior threads formed on the arms  124 ,  126  of the body  102  to allow the first fastener to be advanced or retracted along the axis A 2  with respect to the body by rotating the first fastener about the axis A 2 . The first fastener  112  can include a driving interface  168  configured to receive a driver for applying a rotational force to the first fastener about the axis A 2 . The distal surface of the first fastener  112  can be configured to contact and bear against a rod R 1  disposed in the first rod-receiving  104  recess to lock the rod to the connector  100 . When tightened against the rod R 1 , the first fastener  112  can prevent the rod from translating relative to the connector  100  along the axis A 3  and/or from rotating with respect to the connector about the axis A 3 . While a unitary set screw  112  is shown, it will be appreciated that other fasteners can be used instead or addition, such as a closure cap that advances and locks by quarter-turn rotation, a closure cap that slides in laterally without rotating, a nut that threads onto an exterior of the body, or a dual-component set screw with independently-rotatable inner and outer members, the inner member acting on the rod R 1  and the outer member acting on the saddle  118 . 
     The second fastener  114  can include an exterior thread configured to mate with the interior threads formed on the arms  134 ,  136  of the second body  106  to allow the second fastener to be advanced or retracted along the axis A 4  with respect to the body by rotating the second fastener about the axis A 4 . The second fastener  114  can include a driving interface  170  configured to receive a driver for applying a rotational force to the second fastener  114  about the axis A 4 . The distal surface of the second fastener  114  can be configured to contact and bear against a rod R 2  disposed in the second rod-receiving  108  recess to lock the rod to the connector  100 . When tightened against the rod R 2 , the second fastener  114  can prevent the rod from translating relative to the connector  100  along the axis A 5  and/or from rotating with respect to the connector about the axis A 5 . While a unitary set screw  114  is shown, it will be appreciated that other fasteners can be used instead or addition, such as a closure cap that advances and locks by quarter-turn rotation, a closure cap that slides in laterally without rotating, a nut that threads onto an exterior of the body, or a dual-component set screw with independently-rotatable inner and outer members, the inner member acting on the rod R 2  and the outer member acting on the saddle  122 . 
     The hinge pin  110  is shown in greater detail in  FIGS. 1I-1L . As shown, the hinge pin  110  can include opposed first and second ends that define a central longitudinal axis A 6  extending therebetween. The longitudinal axis A 6  can be collinear with the rotation axis A 1  of the connector  100 . The hinge pin  110  can be formed as a substantially cylindrical shaft with one or more protrusions  172  extending radially outward therefrom. One or both side surfaces of the protrusions  172  can be ramped, curved, or otherwise tapered and configured to contact and bear against counterpart surfaces of the saddles  118 ,  122  or, in embodiments in which the saddles are omitted, against counterpart surfaces of the rods R 1 , R 2 . The illustrated hinge pin  110  includes at least first and second protrusion surfaces  116 ,  120  that each form sections of respective cones. The middle protrusion  172  of the hinge pin  110  can help keep the hinge pin centered in the cavities  132 ,  142  and maintain the bodies  102 ,  106  in a position in which the bearing surfaces  130 ,  140  are parallel. 
     The protrusions  172  can extend around less than an entire circumference of the hinge pin  110 , such that the protrusions have a non-cylindrical cross-section in a plane transverse to the axis A 6 . For example, as shown in  FIG. 1J , each protrusion can define a lobe shape with first and second flat segments  172 A,  172 B joined by an arc  172 C. The cavities  132 ,  142  formed in the bodies  102 ,  106  can have a corresponding shape, only with an arc that extends a greater degree about the circumference of the hinge pin  110 . Accordingly, when the protrusions  172  are received within the cavities  132 ,  142 , the degree to which the bodies  102 ,  106  are able to rotate relative to the hinge pin  110  about the axis A 1  is limited to the difference between the arc length of the protrusions and the arc length of the cavity. 
     The connector  100  can be assembled by inserting one end of the hinge pin  110  into the cavity  132  of the first body  102  and the other end of the hinge pin into the cavity  142  of the second body  106 . The saddles  118 ,  122  can be inserted into the proximal ends of the bodies  102 ,  106  and advanced distally until the projections  144 ,  156  of the saddles snap into the grooves  128 ,  138  of the bodies to retain the saddles therein. At this stage of assembly, even before locking rods within the connector  100 , the saddles  118 ,  122  can interfere with the protrusions  172  of the hinge pin  110  to prevent the hinge pin from being removed from either of the first and second bodies  102 ,  106 . 
     A first rod R 1  can be seated in the first rod recess  104  and secured to the connector  100  by tightening the first fastener  112 . As the first fastener  112  is tightened, the first rod R 1  can be urged distally against the saddle  118 , in turn urging the saddle distally against the hinge pin  110 . As the saddle  118  is urged distally, the female conical surface  152  of the saddle bears against the male conical surface  116  of the hinge pin protrusion  172 , applying a force to the hinge pin  110  that urges the hinge pin deeper into the cavity  132 . 
     A second rod R 2  can be seated in the second rod recess  108  and secured to the connector  100  by tightening the second fastener  114 . As the second fastener  114  is tightened, the second rod R 2  can be urged distally against the saddle  122 , in turn urging the saddle distally against the hinge pin  110 . As the saddle  122  is urged distally, the female conical surface  166  of the saddle bears against the male conical surface  120  of the hinge pin protrusion  172 , applying a force to the hinge pin  110  that urges the hinge pin deeper into the cavity  142 . 
     Before fully tightening one or both fasteners  112 ,  114 , the bodies  102 ,  106  can be rotated relative to one another about the axis A 1  as desired by the user. The fasteners  112 ,  114  can then be tightened to lock such relative rotation. In particular, the opposing forces applied to the hinge pin  110  by the saddles  118 ,  122  as the fasteners  112 ,  114  are tightened can cause the bodies  102 ,  106  to translate relative to one another along the axis A 1 , urging the bearing surfaces  130 ,  140  of the bodies into engagement with each other. Friction, mechanical interlock, or other forces between the bearing surfaces  130 ,  140  can be effective to lock relative rotation of the bodies  102 ,  106  about the axis A 1 . 
       FIGS. 2A-2E  illustrate an exemplary embodiment of a connector  200 . As shown, the connector  200  can include a first body  202  that defines a first rod-receiving recess or channel  204  and a second body  206  that defines a second rod-receiving recess or channel  208 . The first and second bodies  202 ,  206  can be connected to one another at least in part by a hinge pin  210 . The hinge pin  210  can define a rotation axis A 1  about which the first and second bodies  202 ,  206  can rotate relative to one another. The connector  200  can include first and second fasteners  212 ,  214  configured to secure respective first and second rods R 1 , R 2  or other fixation elements to the connector  200 . 
     At least one of the fasteners  212 ,  214  can further be configured to urge the first and second bodies  202 ,  206  towards one another and thereby lock relative rotation of the first and second bodies about the rotation axis A 1 . For example, the first fastener  212  can be tightened to secure a first rod R 1  within the first body  202  and to apply a force to a first ramped, curved, or otherwise tapered surface  216  of the hinge pin  210  to draw the first and second bodies  202 ,  206  towards one another, locking rotation therebetween. In the illustrated embodiment, a force applied by the first fastener  212  is transferred to the hinge pin  210  through the first rod R 1 . In other arrangements, a saddle of the type described above can be disposed between the first rod R 1  and the hinge pin  210 . In still further arrangements, the first fastener  212  can bear directly against a saddle. For example, the first fastener  212  can include an outer set screw that bears against a saddle to lock relative rotation of the bodies  202 ,  206 , and an inner set screw that bears against the first rod R 1  to secure the first rod to the connector  200 . 
     The second fastener  214  can be tightened to secure a second rod R 2  within the second body  206 . The second fastener  214  can bear directly against the second rod R 2 , or against an intermediate rod pusher  222  as shown. 
     The ability to rotate the first and second bodies  202 ,  206  relative to one another about the rotation axis A 1  can advantageously allow first and second rods R 1 , R 2  to be locked together even when the rods are obliquely angled with respect to one another, e.g., in the sagittal plane or in the coronal plane. The connector  200  can be particularly useful in connecting tandem rods of a spinal fixation construct across the cervical-thoracic (CT) junction of a patient. For example, the connector  200  can secure the rods R 1 , R 2  in a laterally-offset arrangement to accommodate the different screw trajectories that may occur at the CT junction. By way of further example, the ability of the connector  200  to articulate can allow a cervical rod and a thoracic rod to be locked to one another at an oblique angle in the sagittal plane, e.g., to restore natural lordosis or kyphosis. The connector  200  can also be particularly useful in spinal deformity correction and other procedures in which multiple angled rods are to be coupled to one another. 
     The first body  202  can include proximal and distal ends  202   p ,  202   d  that define a proximal-distal axis A 2 . The proximal end  202   p  of the body  202  can include a pair of spaced apart arms  224 ,  226  that define the first rod-receiving recess  204  therebetween. A rod R 1  disposed in the first rod-receiving recess  204  can have a central longitudinal rod axis A 3 . The first rod-receiving recess  204  can be open in a proximal direction, such that a rod R 1  can be inserted into the recess by moving the rod distally with respect to the connector  200 . Alternatively, the first rod-receiving recess  204  can be open in distal direction, open in a lateral direction, or closed such that the rod R 1  must be translated along the axis A 3  to insert the rod into the recess  204 . 
     Each of the arms  224 ,  226  can extend from the distal portion  202   d  of the body  202  to a free end. The outer surfaces of each of the arms  224 ,  226  can include a feature (not shown), such as a recess, dimple, notch, projection, or the like, to facilitate coupling of the connector  200  to various instruments. For example, the outer surface of each arm  224 ,  226  can include an arcuate groove at the respective free end of the arms for attaching the connector  200  to an extension tower or retractor. The arms  224 ,  226  can include or can be coupled to extension or reduction tabs (not shown) that extend proximally from the body  202  to functionally extend the length of the arms  224 ,  226 . The extension tabs can facilitate insertion and reduction of a rod or other implant, as well as insertion and locking of the first fastener  212 . The extension tabs can be configured to break away or otherwise be separated from the arms  224 ,  226 . 
     The inner surfaces of each of the arms  224 ,  226  can be configured to mate with the first fastener  212 . For example, the inner surfaces of the arms  224 ,  226  can include threads that correspond to external threads formed on the first fastener  212 . Accordingly, rotation of the first fastener  212  with respect to the body  202  about the axis A 2  can be effective to translate the first fastener with respect to the body axially along the axis A 2 . 
     The first body  202  can include an outer bearing surface  230  configured to contact and bear against a corresponding bearing surface  240  of the second body  206 . The respective bearing surfaces  230 ,  240  of the bodies  202 ,  206  can bear against one another to lock relative rotation between the bodies as they are urged towards one another. In the illustrated embodiment, the bearing surfaces  230 ,  240  of the first and second bodies  202 ,  206  are defined by complementary male and female structures of the first and second bodies  202 ,  206 . As shown, the first body  202  can include a conical male projection, an outer surface of which defines the bearing surface  230  of the first body, and the second body  206  can include a conical female recess, an inner surface of which defines the bearing surface  240  of the second body. As the projection of the first body  202  is urged into the recess of the second body  206 , the conical surfaces  230 ,  240  wedge against one another to form a taper-lock connection. While conical surfaces are described in the example above, the male and female features can include concave or convex spherical surfaces, stepped surfaces, and so forth. It will be appreciated that various other arrangements can be used instead or in addition, such as opposed planar surfaces configured to frictionally-engage one another as in the connector  100  described above. 
     One or both of the bearing surfaces  230 ,  240  can include surface features for enhancing grip between the surfaces. For example, one or both surfaces can include teeth, grooves, roughening, surface textures or coatings, etc. In some embodiments, each bearing surface  230 ,  240  can include a plurality of teeth that extend radially outward from the rotation axis A 1 . The teeth can selectively interlock to maintain the bodies  202 ,  206  in one of a plurality of discrete rotational positions relative to one another. 
     The distal end  202   d  of the body  202  can define an interior cavity  232  in which a first end of the hinge pin  210  can be received. The cavity  232  can be open to the bearing surface  230  of the first body  202  and open to the first rod-receiving recess  204  as shown. In some embodiments, the cavity  232  can be a blind bore formed in the bearing surface  230  of the body  202  and intersecting with the first rod-receiving recess  204 . At least one dimension of the cavity  232  can be greater than a corresponding dimension of the hinge pin  210  to allow the hinge pin to translate within the cavity along the rotation axis A 1 . 
     The second body  202  is shown in greater detail in  FIGS. 2C, 2D, and 2E . The second body  206  can include proximal and distal ends  206   p ,  206   d  that define a proximal-distal axis A 4 . The body  206  can include a pair of spaced apart arms  234 ,  236  that define the second rod-receiving recess  208  therebetween. A rod R 2  disposed in the second rod-receiving recess  208  can have a central longitudinal rod axis A 5 . The second rod-receiving recess  208  can be open in a lateral direction, as shown, such that a rod R 2  can be inserted into the recess by moving the rod laterally with respect to the connector  200 . Alternatively, the second rod-receiving recess  208  can be open in a proximal direction, open in a distal direction, or closed such that the rod R 2  must be translated along the axis A 5  to insert the rod into the recess  208 . 
     The second body  206  can include an outer bearing surface  240  configured to contact and bear against the outer bearing surface  230  of the first body  202 . The second body  206  can define an interior cavity  242  in which a second end of the hinge pin  210  can be received. The cavity  242  can be open to the bearing surface  240  of the second body  206  and open to the second rod recess  208  as shown. The cavity  242  can include a shoulder  274  configured to limit translation of the hinge pin  210  relative to the body  206  along the axis A 1 . 
     A rod pusher  222  can be disposed within the cavity  242  and can be configured to bear against the second rod R 2 . The rod pusher  222  can be coupled to the second body  206  by a bias element configured to bias the rod pusher towards the rod R 2 , e.g., to provide a “snap and drag” effect when seating the rod in the second recess  208 . Further details on such features can be found in U.S. application Ser. No. 15/158,127 filed on May 18, 2016 and entitled “IMPLANT CONNECTORS AND RELATED METHODS,” which is hereby incorporated by reference in its entirety. 
     At least one of the arms  234 ,  236  of the second body  206  can include an opening  276  configured to receive the second fastener  214  therein. For example, as shown, the first arm  234  can include a threaded opening  276  in which the second fastener  214  can be advanced to urge the rod pusher  222  against a second rod R 2  seated in the second rod-receiving recess  208 . 
     The bodies  202 ,  206  of the connector  200  can include various features for decreasing or increasing the center-to-center offset between the first and second rods R 1 , R 2  when the rods are locked to the connector. In the illustrated embodiment, the outer surface of the first body  202  that opposes the second body  206  is obliquely angled with respect to the proximal-distal axis A 2 . Accordingly, the rods R 1 , R 2  move towards one another as they are advanced into the connector  200 . This can advantageously reduce the center-to-center offset of the rods R 1 , R 2 , while preserving sufficient material thickness at the proximal end of the first body  202  to withstand the relatively high forces subjected to the connector  200  during rod reduction, fastener tightening, and/or post-operative patient movement. 
     As another example, the opposing outer surfaces of the bodies  202 ,  206  can be parallel to the proximal-distal axes A 2 , A 4 , and instead the rod recesses  204 ,  208  can be obliquely angled or can follow a curved path with respect to the proximal-distal axes to bring the rods R 1 , R 2  closer together. 
     As another example, the axis along which the first fastener  212  advances as it is tightened can be offset laterally from the first rod axis A 3  when the first rod R 1  is fully seated in the recess  204 , or can be obliquely angled with respect to the proximal-distal axis A 2  of the first body  202 . Alternatively, or in addition, the axis along which the second fastener  214  advances as it is tightened can be offset laterally from the second rod axis A 5  when the second rod R 2  is fully seated in the recess  208 , or can be obliquely angled with respect to the proximal-distal axis A 4  of the second body  206 . 
     The rotation axis A 1  of the connector  200  can be perpendicular to the rod axis A 3  and perpendicular to the rod axis A 5 . The rotation axis A 1  can be perpendicular to the proximal-distal axis A 2  of the first body, or can be obliquely angled with respect to the axis A 2 . The rotation axis A 1  can be perpendicular to the proximal-distal axis A 4  of the second body, or can be obliquely angled with respect to the axis A 4 . The proximal-distal axes A 2 , A 4  of the bodies  202 ,  206  can be parallel to one another or can extend at an oblique angle with respect to one another. 
     The first fastener  212  can include an exterior thread configured to mate with the interior threads formed on the arms  224 ,  226  of the body  202  to allow the first fastener to be advanced or retracted along the axis A 2  with respect to the body by rotating the first fastener about the axis A 2 . The first fastener  212  can include a driving interface  268  configured to receive a driver for applying a rotational force to the first fastener about the axis A 2 . The distal surface of the first fastener  212  can be configured to contact and bear against a rod R 1  disposed in the first rod-receiving  204  recess to lock the rod to the connector  200 . When tightened against the rod R 1 , the first fastener  212  can prevent the rod from translating relative to the connector  200  along the axis A 3  and/or from rotating with respect to the connector about the axis A 3 . While a unitary set screw  212  is shown, it will be appreciated that other fasteners can be used instead or addition, such as a closure cap that advances and locks by quarter-turn rotation, a closure cap that slides in laterally without rotating, a nut that threads onto an exterior of the body, or a dual-component set screw with independently-rotatable inner and outer members, the inner member acting on the rod R 1  and the outer member acting on a saddle of the type described above. 
     The second fastener  214  can include an exterior thread configured to mate with the interior threads formed in the first arm  234  of the second body  206  to allow the second fastener to be advanced or retracted along the axis A 4  with respect to the body by rotating the second fastener about the axis A 4 . The second fastener  214  can include a driving interface  270  configured to receive a driver for applying a rotational force to the second fastener  214  about the axis A 4 . The distal surface of the second fastener  214  can be configured to contact and bear against the rod pusher  222  or, in embodiments in which the rod pusher is omitted, against a rod R 2  disposed in the second rod-receiving  208  recess to lock the rod to the connector  200 . When tightened, the second fastener  214  can prevent the rod R 2  from translating relative to the connector  200  along the axis A 5  and/or from rotating with respect to the connector about the axis A 5 . While a unitary set screw  214  is shown, it will be appreciated that other fasteners can be used instead or addition, such as a closure cap that advances and locks by quarter-turn rotation, a closure cap that slides in laterally without rotating, or a nut that threads onto an exterior of the body. 
     The hinge pin  210  can include opposed first and second ends that define a central longitudinal axis A 6  extending therebetween. The longitudinal axis A 6  can be collinear with the rotation axis A 1  of the connector  200 . The hinge pin  210  can be formed as a substantially cylindrical shaft. The portion of the hinge pin  210  received within the first body  202  can include a rod seat  278 . The portion of the hinge pin  210  received within the second body  206  can include a protrusion  272  extending radially outward therefrom. 
     The protrusion  272  can be seated in and can bear against the shoulder  274  formed in the second body  206 . Accordingly, lateral translation of the hinge pin  210  along the axis A 1 , e.g., as the first rod R 1  is urged against the hinge pin, can cause the second body  206  to be urged towards the first body to lock relative rotation therebetween. The rod seat  278  can be ramped, curved, or otherwise tapered and configured to contact and bear against the first rod R 1 . The rod seat  278  can have a width parallel to the axis A 1  that is greater than the diameter of the first rod R 1  and/or greater than the width of the first rod-receiving recess  204 . The rod seat  278  can be located along the length of the hinge pin  210  at a position in which a lateral sidewall  216  of the rod seat interferes with a rod R 1  as the rod is seated in the first rod-receiving recess  204 . As the rod R 1  is advanced into the first rod-receiving recess  204 , it can bear against the lateral sidewall  216  of the rod seat  278  to cause the hinge pin  210  to translate laterally along the axis A 1 , pulling the second body  206  towards the first body  202  to lock relative rotation therebetween. The hinge pin  210  can be rotatable relative to the first and second bodies  202 ,  206  about the axis A 1 , such that the floor of the rod seat  278  remains aligned with a floor of the first rod-receiving recess  204  or is moved into such alignment automatically as a rod R 1  is seated therein. Prior to seating the first rod R 1 , the hinge pin  210  can be retained within the cavity  232  of the first body  202  using various techniques, such as swaging or a retention pin that limits axial translation of the hinge pin  210  relative to the body without limiting rotation of the hinge pin relative to the body about the axis A 1 . 
     The connector  200  can be assembled by inserting the hinge pin  210  through the cavity  242  of the second body  206  to seat the protrusion  272  of the hinge pin against the shoulder  274  and then installing the rod pusher  222  within the second body to retain the hinge pin therein. The free end of the hinge pin  210  can then be inserted into the cavity  232  of the first body  202  and retained therein with a retention feature of the type described above. At this stage of assembly, even before locking rods within the connector  200 , the hinge pin  210  can be prevented from being removed from either of the first and second bodies  202 ,  206 . 
     A second rod R 2  can be seated in the second rod recess  208  and secured to the connector  200  by tightening the second fastener  214 . As the second fastener  214  is tightened, the rod pusher  222  can be urged distally against the second rod R 2  to lock the rod to the connector  200 . The second body  206  can remain free to rotate relative to the first body  202  about the axis A 1  even after the second rod R 2  is locked to the connector  200 . 
     A first rod R 1  can be seated in the first rod recess  204  and secured to the connector  200  by tightening the first fastener  212 . As the first fastener  212  is tightened, the first rod R 1  can be urged distally against the rod seat  278  of the hinge pin  210 , applying a force to the hinge pin that urges the hinge pin deeper into the cavity  232 . 
     Before fully tightening one or both fasteners  212 ,  214 , the bodies  202 ,  206  can be rotated relative to one another about the axis A 1  as desired by the user. The fastener  212  can then be tightened to lock such relative rotation. In particular, the force applied to the hinge pin  210  by the first rod R 1  when the fastener  212  is tightened can cause the bodies  202 ,  206  to translate relative to one another along the axis A 1 , urging the bearing surfaces  230 ,  240  of the bodies into engagement with each other. Friction, mechanical interlock, or other forces between the bearing surfaces  230 ,  240  can be effective to lock relative rotation of the bodies  202 ,  206  about the axis A 1 . It will be appreciated that the connector  200  can allow locking of the second rod R 2  to the connector and locking of the rotational degree-of-freedom of the connector to be performed independently of one another. 
       FIGS. 3A-3L  illustrate an exemplary embodiment of a connector  300 . As shown, the connector  300  can include a first body  302  that defines a first rod-receiving recess or channel  304  and a second body  306  that defines a second rod-receiving recess or channel  308 . The first and second bodies  302 ,  306  can be connected to one another at least in part by a hinge pin  310 . The hinge pin  310  can define a rotation axis A 1  about which the first and second bodies  302 ,  306  can rotate relative to one another. The connector  300  can include first and second fasteners  312 ,  314  configured to secure respective first and second rods R 1 , R 2  or other fixation elements to the connector  300 . 
     At least one of the fasteners  312 ,  314  can further be configured to urge the first and second bodies  302 ,  306  towards one another and thereby lock relative rotation of the first and second bodies about the rotation axis A 1 . For example, the second fastener  314  can be tightened to secure a second rod R 2  within the second body  306  and to apply a force to a ramped, curved, or otherwise tapered surface  320  of the hinge pin  310  to draw the first and second bodies  302 ,  306  towards one another, locking rotation therebetween. In the illustrated embodiment, a force applied by the second fastener  314  is transferred to the hinge pin  310  through the second rod R 2  and through a saddle  322  disposed between the second rod and the hinge pin. In other arrangements, the saddle  322  can be omitted and the second rod R 2  can bear directly against the hinge pin  310 . In still further arrangements, the second fastener  314  can bear directly against the saddle  322 . For example, the second fastener  314  can include an outer set screw that bears against the saddle  322  to lock relative rotation of the bodies  302 ,  306 , and an inner set screw that bears against the second rod R 2  to secure the second rod to the connector  300 . 
     The first fastener  312  can be tightened to secure a first rod R 1  within the first body  302 . The first fastener  312  can bear directly against the first rod R 1  as shown, or against an intermediate rod pusher of the type described above with respect to the connector  200 . 
     The ability to rotate the first and second bodies  302 ,  306  relative to one another about the rotation axis A 1  can advantageously allow first and second rods R 1 , R 2  to be locked together even when the rods are obliquely angled with respect to one another, e.g., in the sagittal plane or in the coronal plane. The connector  300  can be particularly useful in connecting tandem rods of a spinal fixation construct across the cervical-thoracic (CT) junction of a patient. For example, the connector  300  can secure the rods R 1 , R 2  in a laterally-offset arrangement to accommodate the different screw trajectories that may occur at the CT junction. By way of further example, the ability of the connector  300  to articulate can allow a cervical rod and a thoracic rod to be locked to one another at an oblique angle in the sagittal plane, e.g., to restore natural lordosis or kyphosis. The connector  300  can also be particularly useful in spinal deformity correction and other procedures in which multiple angled rods are to be coupled to one another. 
     The first body  302  is shown in greater detail in  FIGS. 3C and 3G . The first body  302  can include proximal and distal ends  302   p ,  302   d  that define a proximal-distal axis A 2 . The proximal end  302   p  of the body  302  can include a pair of spaced apart arms  324 ,  326  that define the first rod-receiving recess  304  therebetween. A rod R 1  disposed in the first rod-receiving recess  304  can have a central longitudinal rod axis A 3 . The first rod-receiving recess  304  can be open in a proximal direction, such that a rod R 1  can be inserted into the recess by moving the rod distally with respect to the connector  300 . Alternatively, the first rod-receiving recess  304  can be open in distal direction, open in a lateral direction, or closed such that the rod R 1  must be translated along the axis A 3  to insert the rod into the recess  304 . 
     Each of the arms  324 ,  326  can extend from the distal portion  302   d  of the body  302  to a free end. The outer surfaces of each of the arms  324 ,  326  can include a feature (not shown), such as a recess, dimple, notch, projection, or the like, to facilitate coupling of the connector  300  to various instruments. For example, the outer surface of each arm  324 ,  326  can include an arcuate groove at the respective free end of the arms for attaching the connector  300  to an extension tower or retractor. The arms  324 ,  326  can include or can be coupled to extension or reduction tabs (not shown) that extend proximally from the body  302  to functionally extend the length of the arms  324 ,  326 . The extension tabs can facilitate insertion and reduction of a rod or other implant, as well as insertion and locking of the first fastener  312 . The extension tabs can be configured to break away or otherwise be separated from the arms  324 ,  326 . 
     The inner surfaces of each of the arms  324 ,  326  can be configured to mate with the first fastener  312 . For example, the inner surfaces of the arms  324 ,  326  can include threads that correspond to external threads formed on the first fastener  312 . Accordingly, rotation of the first fastener  312  with respect to the body  302  about the axis A 2  can be effective to translate the first fastener with respect to the body axially along the axis A 2 . 
     The first body  302  can include an outer bearing surface  330  configured to contact and bear against a corresponding bearing surface  340  of the second body  306 . The respective bearing surfaces  330 ,  340  of the bodies  302 ,  306  can bear against one another to lock relative rotation between the bodies as they are urged towards one another. In the illustrated embodiment, the bearing surfaces  330 ,  340  of the first and second bodies  302 ,  306  are defined by complementary male and female structures of the first and second bodies  302 ,  306 . As shown, the first body  302  can include a conical male projection, an outer surface of which defines the bearing surface  330  of the first body, and the second body  306  can include a conical female recess, an inner surface of which defines the bearing surface  340  of the second body. As the projection of the first body  302  is urged into the recess of the second body  306 , the conical surfaces  330 ,  340  wedge against one another to form a taper-lock connection. While conical surfaces are described in the example above, the male and female features can include concave or convex spherical surfaces, stepped surfaces, and so forth. It will be appreciated that various other arrangements can be used instead or in addition, such as opposed planar surfaces configured to frictionally-engage one another as in the connector  100  described above. 
     One or both of the bearing surfaces  330 ,  340  can include surface features for enhancing grip between the surfaces. For example, one or both surfaces can include teeth, grooves, roughening, surface textures or coatings, etc. In some embodiments, each bearing surface  330 ,  340  can include a plurality of teeth that extend radially outward from the rotation axis A 1 . The teeth can selectively interlock to maintain the bodies  302 ,  306  in one of a plurality of discrete rotational positions relative to one another. 
     As described further below, the hinge pin  310  can be formed integrally with the first body  302 . The hinge pin  310  can project laterally from the distal end  302   d  of the first body  302  along the axis A 1 . The bearing surface  330  of the first body  302  can be an exterior surface of the integrally-formed hinge pin  310 . 
     The second body  302  is shown in greater detail in  FIGS. 3C and 3H . Except as described below, the second body  306  can be identical or substantially identical to the first body  302 , or can have any of the features or variations described above with respect to the first body  302 . Accordingly, only a brief description of the second body  306  is provided here for the sake of brevity. The second body  306  can include proximal and distal ends  306   p ,  306   d  that define a proximal-distal axis A 4 . The proximal end  306   p  of the body  306  can include a pair of spaced apart arms  334 ,  336  that define the second rod-receiving recess  308  therebetween. A rod R 2  disposed in the second rod-receiving recess  308  can have a central longitudinal rod axis A 5 . The second rod-receiving recess  308  can be open in a proximal direction, such that a rod R 2  can be inserted into the recess by moving the rod distally with respect to the connector  300 . Alternatively, the second rod-receiving recess  308  can be open in distal direction, open in a lateral direction, or closed such that the rod R 2  must be translated along the axis A 5  to insert the rod into the recess  308 . 
     Each of the arms  334 ,  336  can include features  338  for retaining the saddle  322  within the body  306 , e.g., of the type described above with respect to the connector  100 . The second body  306  can include an outer bearing surface  340  configured to contact and bear against the outer bearing surface  330  of the first body  302 . The distal end  306   d  of the second body  306  can define an interior cavity  342  in which a free end of the hinge pin  310  can be received. The cavity  342  can be open to the bearing surface  340  of the second body  306  and open to the second rod recess  308  as shown. In some embodiments, the cavity  342  can be a blind bore formed in the bearing surface  340  of the body  306  and intersecting with the second rod recess  308 . At least one dimension of the cavity  342  can be greater than a corresponding dimension of the hinge pin  310  to allow the hinge pin to translate within the cavity along the rotation axis A 1 . 
     The bodies  302 ,  306  of the connector  300  can include various features for decreasing or increasing the center-to-center offset between the first and second rods R 1 , R 2  when the rods are locked to the connector. For example, one or both of the outer surfaces of the bodies  302 ,  306  that oppose one another can be obliquely angled with respect to the respective proximal-distal axes A 2 , A 4 . Accordingly, the rods R 1 , R 2  can move towards one another as they are advanced into the connector  300 . This can advantageously reduce the center-to-center offset of the rods R 1 , R 2 , while preserving sufficient material thickness at the proximal ends of the bodies  302 ,  306  to withstand the relatively high forces subjected to the connector  300  during rod reduction, fastener tightening, and/or post-operative patient movement. 
     As another example, the opposing outer surfaces of the bodies  302 ,  306  can be parallel to the proximal-distal axes A 2 , A 4 , and instead the rod recesses  304 ,  308  can be obliquely angled or can follow a curved path with respect to the proximal-distal axes to bring the rods R 1 , R 2  closer together. 
     As another example, the axis along which the first fastener  312  advances as it is tightened can be offset laterally from the first rod axis A 3  when the first rod R 1  is fully seated in the recess  304 , or can be obliquely angled with respect to the proximal-distal axis A 2  of the first body  302 . Alternatively, or in addition, the axis along which the second fastener  314  advances as it is tightened can be offset laterally from the second rod axis A 5  when the second rod R 2  is fully seated in the recess  308 , or can be obliquely angled with respect to the proximal-distal axis A 4  of the second body  306 . 
     The rotation axis A 1  of the connector  300  can be perpendicular to the rod axis A 3  and perpendicular to the rod axis A 5 . The rotation axis A 1  can be perpendicular to the proximal-distal axis A 2  of the first body, or can be obliquely angled with respect to the axis A 2 . The rotation axis A 1  can be perpendicular to the proximal-distal axis A 4  of the second body, or can be obliquely angled with respect to the axis A 4 . The proximal-distal axes A 2 , A 4  of the bodies  302 ,  306  can be parallel to one another or can extend at an oblique angle with respect to one another. 
     The saddle  322  is shown in greater detail in  FIGS. 3C, 3D, 3E, and 3F . The saddle  322  can be positioned within the body  306 . The saddle  322  can be configured to translate within the body  306  along the axis A 4 , e.g., between proximal and distal limits defined by the interaction between the recesses  338  of the body  306  and projections  356  formed on the saddle. 
     The saddle  322  can be generally cylindrical with first and second arms  358 ,  360  extending in a proximal direction to respective free ends of the arms. The first and second arms  358 ,  360  can be aligned with the first and second arms  334 ,  336  of the body  306  such that a recess defined therebetween is aligned with the second rod-receiving recess  308 . Accordingly, the second rod R 2  can be simultaneously cradled between the arms  358 ,  360  of the saddle  322  and the arms  334 ,  336  of the body  306  when the rod is disposed in the second rod-receiving recess  308 . The first and second arms  358 ,  360  of the saddle  322  can include projections  356  extending radially outward therefrom and configured to be received within the recesses  338  of the second body  306 . 
     The distal-facing surface of the saddle  322  can define a recess  362  configured to receive at least a portion of the hinge pin  310 . In the illustrated embodiment, the recess  362  is semi-cylindrical. The depth of the recess  362  can increase along the length of the recess to account for a body geometry in which the proximal-distal axis A 4  of the body  306  is obliquely angled with respect to the rotation axis A 1  of the hinge pin  310 . 
     The saddle  322  can include one or more ramped, curved, or otherwise tapered surfaces configured to contact and bear against a counterpart surface of the hinge pin  310 . For example, a keel projection  380  extending distally from the recess  362  of the saddle  322  can define a first bearing surface  366 . The first bearing surface  366  can be planar. The first bearing surface  366  can lie in a plane that is obliquely angled with respect to the rotation axis A 1 . As shown in  FIG. 3F , the first bearing surface  366  can include first and second planar portions that are obliquely angled relative to one another and relative to the axis A 1 , and that meet at a central ridge. This can facilitate smoother ramping when the connector bodies  302 ,  306  are rotated relative to one another from a neutral position. 
     The first fastener  312  can include an exterior thread configured to mate with the interior threads formed on the arms  324 ,  326  of the body  302  to allow the first fastener to be advanced or retracted along the axis A 2  with respect to the body by rotating the first fastener about the axis A 2 . The first fastener  312  can include a driving interface  368  configured to receive a driver for applying a rotational force to the first fastener about the axis A 2 . The distal surface of the first fastener  312  can be configured to contact and bear against a rod R 1  disposed in the first rod-receiving  304  recess to lock the rod to the connector  300 . When tightened against the rod R 1 , the first fastener  312  can prevent the rod from translating relative to the connector  300  along the axis A 3  and/or from rotating with respect to the connector about the axis A 3 . While a unitary set screw  312  is shown, it will be appreciated that other fasteners can be used instead or addition, such as a closure cap that advances and locks by quarter-turn rotation, a closure cap that slides in laterally without rotating, or a nut that threads onto an exterior of the body. 
     The second fastener  314  can include an exterior thread configured to mate with the interior threads formed on the arms  334 ,  336  of the second body  306  to allow the second fastener to be advanced or retracted along the axis A 4  with respect to the body by rotating the second fastener about the axis A 4 . The second fastener  314  can include a driving interface  370  configured to receive a driver for applying a rotational force to the second fastener  314  about the axis A 4 . The distal surface of the second fastener  314  can be configured to contact and bear against a rod R 2  disposed in the second rod-receiving  308  recess to lock the rod to the connector  300 . When tightened against the rod R 2 , the second fastener  314  can prevent the rod from translating relative to the connector  300  along the axis A 5  and/or from rotating with respect to the connector about the axis A 5 . While a unitary set screw  314  is shown, it will be appreciated that other fasteners can be used instead or addition, such as a closure cap that advances and locks by quarter-turn rotation, a closure cap that slides in laterally without rotating, a nut that threads onto an exterior of the body, or a dual-component set screw with independently-rotatable inner and outer members, the inner member acting on the rod R 2  and the outer member acting on the saddle  322 . 
     The hinge pin  310  can include opposed first and second ends that define a central longitudinal axis A 6  extending therebetween. The longitudinal axis A 6  can be collinear with the rotation axis A 1  of the connector  300 . The hinge pin  310  can be formed integrally or monolithically with the first body  302  as shown, or can be fixedly attached thereto, e.g., by welding or other processes. A free end of the hinge pin  310  can be received within the second body  306 . The portion of the hinge pin  310  received within the second body  306  can include a slot  382  formed therein in which the keel  380  of the saddle  322  can be received. One or more sidewalls of the slot  382  can be ramped, curved, or otherwise tapered and configured to contact and bear against a counterpart surface of the saddle  322  or, in embodiments in which the saddle  322  is omitted, against a counterpart surface of the second rod R 2 . The illustrated hinge pin  310  includes a ramped bearing surface  320  configured to contact and bear against the bearing surface  366  of the saddle  322  as the second fastener  314  is tightened. The bearing surface  320  can be planar. The bearing surface  320  can lie in a plane that is obliquely angled with respect to the rotation axis A 1 . 
     As the second fastener  314  is tightened, the saddle  322  can be urged distally to translate the keel  380  distally within the slot  382 . As the keel  380  moves within the slot  382 , the bearing surface  366  of the keel can be urged along the counterpart bearing surface  320  of the hinge pin  310 , causing the hinge pin to translate laterally within the cavity  342  of the second body  306  along the axis A 1 , thereby pulling the first body  302  towards the second body to lock relative rotation therebetween. 
     The distal end of the keel  380  can be tapered or bulleted to facilitate insertion of the keel into the slot  382 . Insertion of the keel  380  into the slot  382  of the hinge pin  310  can prevent the hinge pin from being removed from the second body  306 , thereby retaining the first and second bodies  302 ,  306  to one another, even before one or both rods R 1 , R 2  are locked to the connector  300 . Interaction between the keel  380  and the slot  382  can also be effective to limit the range of articulation between the first and second bodies  302 ,  306 . For example, the slot  382  can have a width in a direction perpendicular to the axis A 1  and perpendicular to the axis A 4  that is greater than a corresponding width of the keel  380 . The degree to which the bodies  302 ,  306  can rotate relative to one another about the axis A 1  can be limited by the difference between the width of the slot  382  and the width of the keel  380 . 
     The connector  300  can be assembled by inserting the free end of the hinge pin  310  into the cavity  342  of the second body  306 . The saddle  322  can be inserted into the proximal end of the second body  306  and advanced distally until the projections  356  of the saddle snap into the grooves  338  of the second body  306  to retain the saddle therein. At this stage of assembly, even before locking rods within the connector  300 , the saddle  322  can interfere with the slot  382  of the hinge pin  310  to prevent the hinge pin from being removed from the second body  306 . 
     A first rod R 1  can be seated in the first rod recess  304  and secured to the connector  300  by tightening the first fastener  312 . The second body  306  can remain free to rotate relative to the first body  302  about the axis A 1  even after the first rod R 1  is locked to the connector  300 . 
     A second rod R 2  can be seated in the second rod recess  308  and secured to the connector  300  by tightening the second fastener  314 . As the second fastener  314  is tightened, the second rod R 2  can be urged distally against the saddle  322 , in turn urging the saddle distally against the hinge pin  310 . As the saddle  322  is urged distally, the ramped surface  366  of the saddle bears against the ramped surface  320  of the slot  382  in the hinge pin  310 , applying a force to the hinge pin that urges the hinge pin deeper into the cavity  342 . 
     Before fully tightening one or both fasteners  312 ,  314 , the bodies  302 ,  306  can be rotated relative to one another about the axis A 1  as desired by the user. The fastener  314  can then be tightened to lock such relative rotation. In particular, the force applied to the hinge pin  310  by the saddle  322  when the fastener  314  is tightened can cause the bodies  302 ,  306  to translate relative to one another along the axis A 1 , urging the bearing surfaces  330 ,  340  of the bodies into engagement with each other. Friction, mechanical interlock, or other forces between the bearing surfaces  330 ,  340  can be effective to lock relative rotation of the bodies  302 ,  306  about the axis A 1 . It will be appreciated that the connector  300  can allow locking of the first rod R 1  to the connector and locking of the rotational degree-of-freedom of the connector to be performed independently of one another. 
     While a single, centrally-mounted keel  380  is described above, it will be appreciated that other configurations are possible. For example, as shown in  FIGS. 3I-3L , the saddle  322  can include first and second keels  380 A,  380 B spaced apart from one another in the width dimension of the saddle. As also shown, the slot of the hinge pin  310  can be replaced with first and second slots  382 A,  382 B that form a reduced-width portion or central rib  384  of the hinge pin configured to be received between the keels  380 A,  380 B of the saddle  322  when the connector  300  is assembled. Each keel  380 A,  380 B can include a ramped, curved, or otherwise tapered bearing surface that contacts and bears against a corresponding surface of the hinge pin  310  adjacent the central rib  384 . The relative widths of the rib  384  and the space between the keels  380 A,  380 B can be selected to limit the degree to which the first body  302  can rotate relative to the second body  306  about the axis A 1 . 
       FIGS. 4A-4F  illustrate an exemplary embodiment of a connector  400 . As shown, the connector  400  can include a first body  402  that defines a first rod-receiving recess or channel  404  and a second body  406  that defines a second rod-receiving recess or channel  408 . The first and second bodies  402 ,  406  can be connected to one another at least in part by a hinge pin  410 . The hinge pin  410  can define a rotation axis A 1  about which the first and second bodies  402 ,  406  can rotate relative to one another. The connector  400  can include first and second fasteners  412 ,  414  configured to secure respective first and second rods R 1 , R 2  or other fixation elements to the connector  400 . 
     At least one of the fasteners  412 ,  414  can further be configured to urge the first and second bodies  402 ,  406  towards one another and thereby lock relative rotation of the first and second bodies about the rotation axis A 1 . For example, the second fastener  414  can be tightened to secure a second rod R 2  within the second body  406  and to apply a force to a ramped, curved, or otherwise tapered surface  420  of the hinge pin  410  to draw the first and second bodies  402 ,  406  towards one another, locking rotation therebetween. In the illustrated embodiment, a force applied by the second fastener  414  is transferred to the hinge pin  410  through the second rod R 2 . The first fastener  412  can be tightened to secure a first rod R 1  within the first body  402 . The first fastener  412  can bear directly against the first rod R 1  as shown, or against an intermediate rod pusher of the type described above with respect to the connector  200 . 
     Except as indicated below and as will be readily appreciated by one having ordinary skill in the art in view of the present disclosure, the structure and operation of the connector  400  is the same as the connector  300  described above, and therefore a detailed description is omitted here for the sake of brevity. 
     As shown, the connector  400  can omit a saddle component, such that the second rod R 2  bears directly against a rod seat  420  formed in the hinge pin  410 . The rod seat  420  can be ramped, curved, or otherwise tapered. The rod seat  420  can have a width parallel to the axis A 1  that is greater than the diameter of the second rod R 2  and/or greater than the width of the second rod-receiving recess  408 . The rod seat  420  can be located along the length of the hinge pin  410  at a position in which a lateral sidewall of the rod seat interferes with a rod R 2  as the rod is seated in the second rod-receiving recess  408 . As the rod R 2  is advanced into the second rod-receiving recess  408 , it can bear against the lateral sidewall of the rod seat  420  to cause the hinge pin  410  to translate along the axis A 1 , pulling the second body  406  towards the first body  402  to lock relative rotation therebetween. 
     The rod seat  420  can be curved in multiple planes to allow the above-described bearing action to occur at any of a plurality of relative rotational positions about the axis A 1  of the hinge pin  410  and the second body  406 . For example, the rod seat  420  can be curved in a first plane defined by the axes A 1 , A 2  and in a second plane defined by the axes A 2 , A 3 . As shown in  FIG. 4E , the rod seat can have a circular cross section in a first plane P 1 . As shown in  FIG. 4F , the rod seat  420  can have a cross section in a plane P 2  perpendicular to the first plane P 1  that is defined by first and second straight segments angled relative to one another and joined by an arcuate segment. 
     The rod seat  420  can be configured such that approximately the same ramp geometry is presented to the rod R 2 , regardless of the articulation angle of the first and second bodies  402 ,  406 . The degree of curvature of the rod seat  420  in the second plane P 2  can be configured to limit articulation of the first and second bodies  402 ,  406 . 
     The hinge pin  410  can be retained within the second body  406  using various techniques, such as swaging or a retention pin that limits axial translation of the hinge pin relative to the body while still permitting rotation of the hinge pin relative to the second body. In the illustrated embodiment, the free end of the hinge pin  410  includes a post or rivet tail  486  that projects axially therefrom. The post  486  can be received within a through-hole  488  formed in the second body  406  and thereafter swaged, deformed, flattened, or otherwise modified such that the post cannot be freely removed from the through-hole. The terminal end of the post  486  can be cupped or hollowed to facilitate deformation of the post during the swaging process. 
       FIGS. 5A-5O  illustrate an exemplary embodiment of a connector  500 . As shown, the connector  500  can include a first body  510  that defines a first rod-receiving recess or channel  512  and a second body  580  that defines a second rod-receiving recess or channel  582 . The first and second bodies  510 ,  580  can be connected to one another at least in part by a hinge pin  514  that defines a rotation axis A 1  about which the bodies can rotate relative to one another. The hinge pin  514  can project laterally from the first body  510  to a free end. The free end of the hinge pin  514  can be received within an interior cavity  584  formed in the second body  580 , thereby coupling the first and second bodies  510 ,  580 . The connector  500  can include first and second fasteners  520 ,  522  configured to secure first and second rods R 1 , R 2  or other fixation elements to the connector  500  within the respective rod-receiving recesses  512 ,  582 . The second fastener  522  can also be configured to apply a force on the hinge pin and thereby lock the relative rotation of the first and second bodies  510 ,  580 . As shown in the illustrated embodiment, the force applied by the second fastener  522  can be transferred to the hinge pin  514  through a saddle  550 . 
     As discussed further below, to increase the locking strength of the connector  500 , the exterior surface of the hinge pin  514  can include sharp corners  516  or other surface features that bear against the inner wall of the cavity  584  of the second body  580 . As force is applied by the second fastener  522  to the hinge pin  514 , the corners  516  of the pin may cut into or otherwise deform the inner wall of the cavity  584 , and thereby increase the resistance of the connector bodies  510 ,  580  to rotation. The hinge pin  514  of the first body  510  can include a slot  518  configured to receive a distal projection of a saddle  550  disposed in the second rod-receiving recess  582 , thereby preventing disassembly of the first and second bodies  510 ,  580  and limiting the relative rotation between the first and second bodies  510 ,  580 . 
     The first body  510  of the connector  500 , including the hinge pin  514 , is shown in greater detail in  FIGS. 5C through 5F . The first body  510  can include proximal and distal ends  510   p ,  510   d  that define a proximal-distal axis A 2 . The proximal end  510   p  of the body  510  can include a pair of spaced apart arms  524 ,  526  that extend from the distal portion  510   d  of the body  510  to a free end. The spaced apart arms  524 ,  526  can define the first rod-receiving recess  512  therebetween. The first rod-receiving recess  512  can be open in a proximal direction, such that a rod R 1  can be inserted into the recess by moving the rod distally with respect to the connector  500 . Alternatively, the first rod-receiving recess  512  can be open in distal direction, open in a lateral direction, or closed such that the rod R 1  must be translated along the axis A 3  to insert the rod into the recess  512 . 
     The hinge pin  514  can project along the rotation axis A 1  from an outer surface  528  of the arm  526 . As shown in the illustrated embodiment, the outer surface  528  of the arm  526  can extend vertically from the distal end  510   d  of the first body  510 . The hinge pin  514  can extend perpendicular from a distal end portion of the outer surface  528  of the arm  526 . The hinge pin  514  can include opposed first and second ends that define a central longitudinal axis A 6  extending therebetween. The longitudinal axis A 6  can be collinear with the rotation axis A 1  of the connector  500 . The hinge pin  514  can be formed integrally or monolithically with the first body  510  as shown, or can be fixedly attached thereto, e.g., by welding or other processes. 
     The hinge pin  514  can have an exterior surface that includes sharp corners  516  radially disposed at least partially about a perimeter of the pin. As discussed further below, when the hinge pin is locked down, the sharp corners  516  of the pin can cut into and/or deform an inner wall of the cavity  584  of the second body  580 , thereby increasing the locking strength of the connector  500  through edge loading. For example, through such edge loading, the sharp corners  516  of the hinge pin  514  can create additional friction, mechanical interlock, or increase the radial force applied by the pin against the second body  580  to effectively lock relative rotation of the bodies  510 ,  580  about the axis A 1 . The corners  516  of the hinge pin  514  can be formed by planar surface segments  530  that extend longitudinally at least partially around the pin. Each of the planar surface segments  530  can be obliquely angled with respect to one or more adjacent planar surface segments, such that the planar surface segments  530  intersect with each other to form the sharp corners  516  of the hinge pin  514 . 
     As shown in  FIG. 5E , the hinge pin  514  can have five (5) planar surface segments  530  that form the lateral and distal surfaces of the pin. The planar segments  530  can intersect obliquely at their respective edges such that the corners  516  of hinge pin  514  form a cross sectional profile of a partial octagon. The proximal surface  532  of the hinge pin  514  can have a rounded, curved, ramped or other contoured shape. It will be appreciated that, in some embodiments, the planar surface segments  530  can form the exterior surface of the hinge pin  514 , such that the sharp corners  516  are radially disposed about the entire circumference of the pin. In some embodiments, more than five (5) planar surface segments  530  can be used to form the corners  516  of the hinge pin  514  with a cross sectional profile of a polygon or portion thereof. In some embodiments, less than five planar surface segments can be used to form the corners  516  of the hinge pin  514  with a cross sectional profile of a polygon or portion thereof. 
     As shown in  FIGS. 5C and 5F , a slot  518  can be formed in the proximal surface  532  of the hinge pin  514 . The slot  518  can be an arcuate or rectangular shaped slot. The length of the slot  518  can be defined between a first pair of opposing sidewalls  540 ,  542 . Each of the opposing sidewalls  540 ,  542  can lie in a plane perpendicular to the rotation axis A 1 . The width of the slot  518  can be defined between a second pair of sidewalls  544 ,  546  disposed between the first pair of opposing sidewalls. Each of the sidewalls  544 ,  546  can lie in a plane perpendicular or oblique to the opposing sidewalls  540 ,  542  of the slot. A rib  548  can be formed in the slot  518  between the sidewalls  544 ,  546 . As discussed further below, the slot  518  can be configured to receive a distal projection of a saddle  550  disposed in the second rod-receiving recess  582 , thereby preventing disassembly of the first and second bodies  510 ,  580  and limiting the relative rotation between the first and second bodies  510 ,  580 . 
     The second body  580  is shown in greater detail in  FIGS. 5G and 5H . The second body  580  can include proximal and distal ends  580   p ,  580   d  that define a proximal-distal axis A 4 . The proximal end  580   p  of the body  580  can include a pair of spaced apart arms  586 ,  588  that define the second rod-receiving recess  582  therebetween. A rod R 2  disposed in the second rod-receiving recess  582  can have a central longitudinal rod axis A 5 . The second rod-receiving recess  582  can be open in a proximal direction, such that a rod R 2  can be inserted into the recess by moving the rod distally with respect to the connector  500 . Alternatively, the second rod-receiving recess  582  can be open in distal direction, open in a lateral direction, or closed such that the rod R 2  must be translated along the axis A 5  to insert the rod into the recess  582 . Each of the arms  586 ,  588  can include recesses or grooves  590  for retaining the saddle  550  within the body  580 . The second body  580  can include an outer surface  592  that opposes the outer surface  528  of the first body  510 . 
     The distal end  580   d  of the second body  580  can define an interior cavity  584  in which a free end of the hinge pin  514  can be received. The cavity  584  can be open from the outer surface  592  of the second body  580  and open to the second rod recess  582 . As shown in the illustrated embodiment, the cavity  584  can be a blind bore formed in the outer surface  592  of the body  580  and intersecting with the second rod recess  582 . In some embodiments, the cavity  584  can be a through bore. At least one dimension of the cavity  584  can be greater than a corresponding dimension of the hinge pin  514  to allow the hinge pin to translate within the cavity along the rotation axis A 1 . 
     The saddle  550  is shown in greater detail in  FIGS. 5I through 5L . The saddle  550  can be positioned within the second body  580 . The saddle  550  can be generally cylindrical with first and second arms  554 ,  556  extending in a proximal direction to respective free ends of the arms. The first and second arms  554 ,  556  can define a rod-receiving recess or rod seat  558  therebetween. The first and second arms  554 ,  556  of the saddle  550  can be aligned with the first and second arms  586 ,  588  of the second body  580  such that rod seat  558  is aligned with the second rod-receiving recess  582 . Accordingly, the second rod R 2  can be simultaneously cradled between the arms  554 ,  556  of the saddle  550  and the arms  586 ,  588  of the second body  580  when the rod R 2  is disposed in the second rod-receiving recess  582 . The first and second arms  554 ,  556  of the saddle  550  can include projections  560  (e.g., spring tabs) extending radially outward therefrom and configured to be received within the grooves or other recesses  590  of the second body  580 . The saddle  550  can be configured to translate within the body  580  along the axis A 4 , e.g., between proximal and distal limits defined by the interaction between the grooves or recesses  590  of the second body  580  and the radial projections  560  of the arms  554 ,  556 . 
     As shown in  FIGS. 5J through 5L , the saddle  550  can have a recessed distal-facing bearing surface  562  and a saddle projection  552  extending distally therefrom. The recessed bearing surface  562  can have a curved or other suitable shape configured to contact and bear against a semi-cylindrical, exterior surface of the hinge pin  514 . The distal saddle projection  552  can be configured to be received within the slot  518  of the hinge pin  514 , and thereby maintain coupling of the first body  510  and the second body  580 . The distal saddle projection  552  can also be configured to interfere with the slot  518  as the hinge pin  514  rotates, thereby limiting the rotation range of the first body  510  relative to the second body  580 . 
     As shown in the illustrated embodiment, the distal saddle projection  552  can be centrally disposed within the recessed bearing surface  562 . The distal saddle projection  552  can have lateral-facing bearing surfaces  564 ,  566  extending distally from the recess. The lateral-facing bearing surfaces  564 ,  566  of the saddle projection can lie in a plane that is perpendicular with respect to the recessed bearing surface  562  and the rotation axis A 1 . The lateral-facing bearing surfaces  564 ,  566  of the saddle projection can be planar or curved. The lateral-facing bearing surfaces  564 ,  566  of the saddle projection can be configured to respectively contact and bear against the opposing sidewalls  540 ,  542  of the slot  518  of the hinge pin  514  perpendicular to the rotation axis A 1 , and thereby prevent disassembly of the first and second bodies  510 ,  580 . 
     The lateral-facing bearing surfaces  564 ,  566  of the saddle projection can meet at a ridge  570  having a distal-facing bearing surface. The ridge  570  of the saddle projection  552  can extend perpendicular with respect to the proximal-distal axis A 4  of the second body  580 . In the illustrated embodiment, the ridge  570  can include a recess  572  formed in the distal-facing bearing surface. The recess  572  can be sized to accommodate the rib  548  formed in the slot  518 . As discussed further below, the distal-facing bearing surface of the ridge  570  adjacent to the recess  572  can be configured to interfere with the side walls  544 ,  546  of the slot  518  as the hinge pin  514  rotates, thereby limiting the rotation range of the first body  510  relative to the second body  580 . 
     As shown in  FIG. 5M through 5O , the connector  500  can be assembled by inserting the free end of the hinge pin  514  through the opening in the outer bearing surface  592  and into the cavity  584  of the second body  580 . The hinge pin  514  can be oriented within the cavity  584 , such that the slot  518  of the pin is aligned with the second rod-receiving recess  582 . The saddle  550  can be inserted into the proximal end  580   p  of the second body  580  and distally advanced until the distal saddle projection  552  is received in the slot  518  of the hinge pin  514 . The radial projections  560  of the saddle arms  554 ,  556  can snap into the grooves or recesses  590  of the second body  580  to retain the saddle  550 . 
     At this stage of assembly, even before locking rods within the connector  500 , the saddle  550  can interfere with the slot  518  of the hinge pin  514  to prevent the pin from being removed from the second body  580 . For example, when the saddle projection  552  is received in the slot  518 , the lateral-facing surfaces  564 ,  566  of the saddle projection can bear against the opposing sidewalls  540 ,  542  of the slot to prevent removal of the pin, and thereby maintain coupling of the first and second bodies  510 ,  580 . The distal saddle projection  552  can also interfere with the slot  518  of the hinge pin  514  to limit the relative rotation of the connector bodies  510 ,  580 . For example, as shown in  FIG. 5N , when the hinge pin  514  rotates clockwise or counter clockwise about the rotation axis A 1 , the extent of such rotation can be restricted by one of the sidewalls  544 ,  546  of the slot  518  contacting the ridge  570  of the saddle projection  552 . 
     In the illustrated embodiment, the ridge  570  of the saddle projection  552  can have a distal-facing contact surface that lies in a plane perpendicular with respect to the proximal-distal axis A 4  of the second body. As shown, the sidewalls  544 ,  546  of the slot  518  can lie in a common plane. When the saddle projection  552  is disposed within the slot  518 , a gap can be formed between the planar contact surfaces of the ridge  570  and the slot  518 , thereby enabling the hinge pin  514  to rotate within the limits defined therebetween. 
     In some embodiments, a recess  572  can be formed in the ridge  570  that is sized to at least partially receive a rib  548  disposed between the sidewalls  544 ,  546  of the slot. Such embodiments can facilitate an increase in the range of rotation of the hinge pin  514  without a corresponding increase in the width of the gap. Alternatively or additionally, such embodiments can facilitate a decrease the width of the gap without a corresponding decrease in the range of rotation of the hinge pin. In some embodiments, the sidewalls  544 ,  546  of the slot can lie in respective planes that intersect obliquely to increase or decrease the range of rotation of the pin. 
     In some embodiments, the interaction between the slot  518  of the hinge pin  514  and the saddle projection  552  can limit the range of rotation of the pin symmetrically with respect to the rotation axis A 1 . For example, in some embodiments, the range of rotation of the hinge pin  514  can be limited to ±30 degrees, ±60 degrees, ±180 degrees, or other symmetrical range suitable depending on the surgical procedure. In some embodiments, the interaction between the slot  518  of the hinge pin  514  and the saddle projection  552  can limit the range of rotation of the pin asymmetrically with respect to the rotation axis A 1 . Limiting the range of rotation of the pin  514  by forming a smaller slot  518  can allow more material to be retained on the pin, thereby increasing the strength of the pin. 
     A first rod R 1  can be seated in the first rod receiving recess  512  of the first body  510  and secured to the connector  500  by tightening the first fastener  520 . The first fastener  520  can include an exterior thread configured to mate with the interior threads formed on the arms  524 ,  526  of the first body  510  to allow the first fastener to be advanced or retracted along the axis A 2  with respect to the body by rotating the first fastener about the axis A 2 . The first fastener  520  can include a driving interface configured to receive a driver for applying a rotational force to the first fastener about the axis A 2 . While a unitary set screw  520  is shown, it will be appreciated that other fasteners can be used instead or addition, such as a closure cap that advances and locks by quarter-turn rotation, a closure cap that slides in laterally without rotating, or a nut that threads onto an exterior of the body. 
     The distal surface of the first fastener  520  can be configured to contact and bear against a rod R 1  disposed in the first rod-receiving recess  512  to lock the rod to the connector  500 . When tightened against the rod R 1 , the first fastener  520  can prevent the rod from translating relative to the connector  500  along the axis A 3  and/or from rotating with respect to the connector about the axis A 3 . The first rod R 1  can be seated in the first rod-receiving recess  512 , while the second body  580  can remain free to rotate relative to the first body  510  about the rotation axis A 1  even after the first rod R 1  is locked to the connector  500 . 
     A second rod R 2  can be seated in the rod seat  558  of the saddle  550  disposed in the second rod receiving recess  582  of the second body  580 . The second rod R 2  can be secured to the connector  500  by tightening the second fastener  522 . The second fastener  522  can include an exterior thread configured to mate with the interior threads formed on the arms  586 ,  588  of the second body  580  to allow the second fastener to be advanced or retracted along the axis A 4  with respect to the body by rotating the second fastener about the axis A 4 . The second fastener  522  can include a driving interface configured to receive a driver for applying a rotational force to the second fastener  522  about the axis A 4 . 
     The distal surface of the second fastener  522  can be configured to contact and bear against the rod R 2  disposed in the saddle  550  to lock the rod to the connector  500 . When tightened against the rod R 2 , the second fastener  522  can prevent the rod from translating relative to the connector  500  along the axis A 5  and/or from rotating with respect to the connector about the axis A 5 . While a unitary set screw  522  is shown, it will be appreciated that other fasteners can be used, instead or in addition, such as a closure cap that advances and locks by quarter-turn rotation, a closure cap that slides in laterally without rotating, a nut that threads onto an exterior of the body, or a dual-component set screw with independently-rotatable inner and outer members, the inner member acting on the rod R 2  and the outer member acting on proximal free ends of the saddle arms  554 ,  556 . 
     As the second fastener  522  is tightened, the second rod R 2  can be urged distally against the saddle  550 , thereby causing the saddle to urge distally against the hinge pin  514 . As shown in  FIG. 5O , the recessed distal-facing bearing surface  562  of the saddle  550 , adjacent to the distal saddle projection  552 , can bear against a counter bearing surface of the hinge pin  514 . The downward force applied by the saddle  550  can urge the pin  514  against the inner wall of the cavity  582  of the second body  580 . 
     Before fully tightening one or both fasteners  520 ,  522 , the bodies  510 ,  580  can be rotated relative to one another about the axis A 1  as desired by the user. The second fastener  522  can then be tightened to lock such relative rotation. In particular, when the fastener  522  is tightened, the force applied to the hinge pin  514  by the saddle  550  can urge the sharp corners  516  of the pin to cut and/or deform the inner wall of the cavity  584  of the second body  580 . Through such edge loading, the sharp corners  516  of the hinge pin  514  can create additional friction, mechanical interlock, or increase the radial force applied by the pin against the second body  580  to effectively lock relative rotation of the bodies  510 ,  580  about the axis A 1 . It will be appreciated that the connector  500  can allow locking of the first rod R 1  to the connector and locking of the rotational degree-of-freedom of the connector to be performed independently of one another. 
     In other arrangements, the second fastener  522  can bear directly against the saddle  550 . For example, the second fastener  522  can include an outer set screw that bears against the saddle arms  554 ,  556  to lock relative rotation of the bodies  510 ,  580 , and an inner set screw that bears against the second rod R 2  to secure the second rod to the connector  500 . In still further arrangements, the saddle  522  can be omitted and the second rod R 2  can bear directly against the hinge pin  514 . 
     The ability to rotate the first and second bodies  510 ,  580  relative to one another about the rotation axis A 1  can advantageously allow first and second rods R 1 , R 2  to be locked together even when the rods are obliquely angled with respect to one another, e.g., in the sagittal plane or in the coronal plane. The connector  500  can be particularly useful in connecting tandem rods of a spinal fixation construct across the cervical-thoracic (CT) junction of a patient. For example, the connector  500  can secure the rods R 1 , R 2  in a laterally-offset arrangement to accommodate the different screw trajectories that may occur at the CT junction. By way of further example, the ability of the connector  500  to articulate can allow a cervical rod and a thoracic rod to be locked to one another at an oblique angle in the sagittal plane, e.g., to restore natural lordosis or kyphosis. The connector  500  can also be particularly useful in spinal deformity correction and other procedures in which multiple angled rods are to be coupled to one another. 
     In some embodiments, the bodies  510 ,  580  of the connector  500  can include various features for decreasing or increasing the center-to-center offset between the first and second rods R 1 , R 2  when the rods are locked to the connector. For example, one or both of the outer surfaces of the bodies  510 ,  580  that oppose one another can be obliquely angled with respect to the respective proximal-distal axes A 2 , A 4 . Accordingly, the rods R 1 , R 2  can move towards one another as they are advanced into the connector  500 . This can advantageously reduce the center-to-center offset of the rods R 1 , R 2 , while preserving sufficient material thickness at the proximal ends of the bodies  510 ,  580  to withstand the relatively high forces subjected to the connector  500  during rod reduction, fastener tightening, and/or post-operative patient movement. 
     As another example, the opposing outer surfaces of the bodies  510 ,  580  can be parallel to the proximal-distal axes A 2 , A 4 , and instead the rod recesses  512 ,  582  can be obliquely angled or can follow a curved path with respect to the proximal-distal axes to bring the rods R 1 , R 2  closer together. 
     As another example, the axis along which the first fastener  520  advances as it is tightened can be offset laterally from the first rod axis A 3  when the first rod R 1  is fully seated in the recess  512 , or can be obliquely angled with respect to the proximal-distal axis A 2  of the first body  510 . Alternatively, or in addition, the axis along which the second fastener  522  advances as it is tightened can be offset laterally from the second rod axis A 5  when the second rod R 2  is fully seated in the recess  582 , or can be obliquely angled with respect to the proximal-distal axis A 4  of the second body  580 . 
     The arms  524 ,  526  can include or can be coupled to extension or reduction tabs (not shown) that extend proximally from the body  510  to functionally extend the length of the arms  524 ,  526 . The extension tabs can facilitate insertion and reduction of a rod or other implant, as well as insertion and locking of the first fastener  520 . The extension tabs can be configured to break away or otherwise be separated from the arms  524 ,  526 . The inner surfaces of each of the arms  524 ,  526  can be configured to mate with the first fastener  520 . For example, the inner surfaces of the arms  524 ,  526  can include threads that correspond to external threads formed on the first fastener  520 . Accordingly, rotation of the first fastener  520  with respect to the body  510  about the axis A 2  can be effective to translate the first fastener with respect to the body axially along the axis A 2 . The arms  586 ,  588  can similarly include or be coupled to extension or reduction tabs. 
     In some embodiments, the connector  500  can include various features of a unilateral locking interface, including but not limited to one or more grooves  594  and surface projections  596 . The unilateral locking interface enables a surgical instrument that includes a unilateral locking mechanism (not shown) to rigidly hold onto one side of the connector  500 . Exemplary unilateral locking interfaces that can be included in the connector  500  are disclosed in U.S. patent application Ser. No. 15/843,618, filed on Dec. 15, 2017, entitled “Unilateral Implant Holders and Related Methods” (now published as US-2019-0183541-A1), the entire contents of which are hereby incorporated by reference. 
       FIGS. 6A-6J  illustrate an exemplary embodiment of a connector  600 . As shown, the connector  600  can include a first body  610  that defines a first rod-receiving recess or channel  612  and a second body  680  that defines a second rod-receiving recess or channel  682 . The first and second bodies  610 ,  680  can be connected to one another at least in part by a hinge pin  614  that defines a rotation axis A 1  about which the bodies can rotate relative to one another. In the illustrated embodiment, the hinge pin  614  can project laterally from the first body  610  to a free end. The free end of the hinge pin  614  can be received within an interior cavity  684  formed in the second body  680 . The connector  600  can include first and second fasteners  620 ,  622  configured to secure first and second rods R 1 , R 2  or other fixation elements to the connector  600  within the respective rod-receiving recesses  612 ,  682 . The hinge pin  614  of the first body  610  can include a slot  618  configured to receive a distal projection  652  of a saddle  650  disposed in the second rod-receiving recess  682 , thereby preventing disassembly of the first and second bodies  610 ,  680  and limiting the relative rotation between the first and second bodies  610 ,  680 . 
     As discussed further below, to increase the locking strength of the connector  600 , the slot  618  of the pin can be obliquely angled with respect to the rotation axis A 1  of the pin. The angled slot  618  can be configured to receive the distal projection  652  of a saddle  650  disposed in the second rod-receiving recess  682 . The distal saddle projection  652  can be oriented at an oblique angle to match or coincide with the angled slot  618  of the hinge pin  614 . The distal saddle projection  652  can have a wedge-shaped cross section with tapered bearing surfaces that facilitate wedging of the saddle projection in the slot  618  in response to a force applied by the second fastener  622  against the rod R 2  and/or saddle  650  itself. Wedging the distal saddle projection  652  into the angled slot  618  of the hinge pin  614  can create additional friction, mechanical interlock, or increased force applied by the pin against the second body  680  to effectively lock relative rotation of the bodies  610 ,  680  about the axis A 1 . 
     Except as described below or as will be readily appreciated by one having ordinary skill in the art, the first body  610 , the second body  680 , the first fastener  620 , and the second fastener  622  of the connector  600  are substantially similar to the first body  510 , the second body  580 , the first fastener  520 , and the second fastener  522  of the connector  500  described above with respect to  FIGS. 5A-5O . A detailed description of the structure and function thereof is thus omitted here for the sake of brevity. The connector  600  can include any combination of the features of the connector  500  described above. 
     The first body  610  of the connector  600 , including the hinge pin  614 , is shown in greater detail in  FIGS. 6C and 6D . The first body  610  can include proximal and distal ends  610   p ,  610   d  that define a proximal-distal axis A 2 . The proximal end  610   p  of the body  610  can include a pair of spaced apart arms  624 ,  626  that extend from the distal portion  610   d  of the body  610  to a free end. The spaced apart arms  624 ,  626  can define the first rod-receiving recess  612  therebetween. 
     The hinge pin  614  can project along the rotation axis A 1  from an outer surface  628  of the arm  626 . The hinge pin  614  can extend perpendicular from a distal end portion of the outer surface  628  of the arm  626 . The hinge pin  614  can include opposed first and second ends that define a central longitudinal axis A 6  extending therebetween. The longitudinal axis A 6  can be collinear with the rotation axis A 1  of the connector  600 . As discussed above with respect to  FIGS. 5A-5O , the exterior surface of the hinge pin  614  can include sharp corners  616  or other surface features that can bear against the inner wall of the cavity  684  of the second body  680  to increase the locking strength of the connector  600 . 
     The slot  618  can be formed in the proximal surface of the hinge pin  614 . The slot  618  of the pin can be oriented at an oblique angle with respect to the rotation axis A 1  of the pin and a central longitudinal rod axis A 5  of the second rod-receiving recess  682 . In some embodiments, the slot  618  can be oriented at an oblique angle of approximately 7 degrees with respect to the rod axis A 5 . When the bodies are rotated, the oblique angle causes the bodies to move further or closer apart in relation to each other in the lateral direction. This additional motion creates drag and thereby increases rotational resistance in axis A 1  when the first body is locked down. In some embodiments, the slot  618  can be oriented at an oblique angle within an approximate range between 5 and 10 degrees with respect to the rod axis A 5 , inclusively. 
     The length of the slot  618  can be defined between a first pair of opposing sidewalls  640 ,  642  that form angled cam surfaces. Each of the opposing sidewalls  640 ,  642  can lie in a plane that is oblique to the rotation axis A 1  and the rod axis A 5  of the second rod-receiving recess  682 . The opposing sidewalls  640 ,  642  can lie in substantially parallel planes or can be obliquely angled with respect to one another. The width of the slot  618  can be defined by a proximal-facing surface  644  disposed between the first pair of opposing sidewalls  640 ,  642  of the slot. As discussed further below, the slot  618  can be configured to receive the distal projection  652  of the saddle  650  disposed in the second rod-receiving recess  682 , and thereby prevent disassembly of the first and second bodies  610 ,  680  and increase the locking strength of the connector  600  to resist relative rotation between the first and second bodies  610 ,  680 . 
     The saddle  650  is shown in greater detail in  FIGS. 6E through 6J . The saddle  650  can be generally cylindrical with first and second arms  654 ,  656  extending in a proximal direction to respective free ends of the arms. The first and second arms  654 ,  656  of the saddle  650  can define a rod seat  658  therebetween. The first and second arms  654 ,  656  of the saddle  650  can include projections  660  (e.g., spring tabs) extending radially outward therefrom. The radial projections  660  can be configured to snap into or otherwise be received within grooves or other recesses  690  of the second body  680  to retain the saddle  650  therein. 
     The saddle  650  can have a distal-facing bearing surface  662 . The distal-facing bearing surface  662  can have a planar, ramped, curved or other suitable contour configured to contact and bear against a counterpart bearing surface of the hinge pin  614 . The saddle  650  can include a saddle projection  652  that extends distally from the distal-facing bearing surface  662  to maintain coupling of the first and second bodies  610 ,  680  and to increase the locking strength of the connector  600  to resist relative rotation of the bodies. In some embodiments, only the saddle projection  652  is configured to contact and bear against the hinge pin  614 . 
     As shown in the illustrated embodiment, the distal saddle projection  652  can be obliquely angled with respect to a central longitudinal rod axis A 5  defined by the rod seat  658 . The distal saddle projection  652  can be oriented at an oblique angle to match or coincide with the angle of the slot  618  of the hinge pin  614 . Thus, when disposed in the second body  680 , the distal saddle projection  652  can be oriented at an oblique angle with respect to the rotation axis A 1  of the pin and a central longitudinal rod axis A 5  of the second rod-receiving recess  682 . The obliquely angled geometry of the saddle projection  652  and the slot  618  can provide increased resistance to relative rotation between the bodies  610 ,  680  about the axis A 1  when the connector  600  is locked. 
     The distal saddle projection  652  can have tapered bearing surfaces  665 ,  667  configured to facilitate wedging of the saddle projection in the slot  618  in response to a downward force applied against the saddle  650 . To facilitate wedging, the tapered bearing surfaces  665 ,  667  of the distal saddle projection  652  can be angled or ramped to intersect with the sidewalls  640 ,  642  of the slot  618  of the hinge pin  614  at a mismatched angle. Put another way, the tapered bearing surfaces  665 ,  667  of the distal saddle projection can lie in respective planes that are skewed relative to the opposing sidewalls  640 ,  642  of the slot  618 . Wedging the distal saddle projection  652  into the angled slot  618  of the hinge pin  614  can create additional friction, mechanical interlock, or increased force to effectively lock relative rotation of the bodies  610 ,  680  about the axis A 1 . 
     As shown in  FIGS. 6H through 6J , the connector  600  can be assembled by inserting the free end of the hinge pin  614  through the opening in the outer surface  692  and into the cavity  684  of the second body  680 . The hinge pin  614  can be oriented within the cavity  684 , such that the slot  618  of the pin is aligned with the second rod-receiving recess  682 . The saddle  650  can be inserted into the proximal end  680   p  of the second body  680 . The saddle  650  can be configured to translate within the body  680  along the axis A 4  and can thus be distally advanced until the distal saddle projection  652  is received in the slot  618  of the hinge pin  614 . 
     In some embodiments, the saddle  650  can be configured to translate between proximal and distal limits defined by the interaction between the grooves or recesses  690  of the second body  680  and the radial projections  660  of the arms  654 ,  656 . When disposed in the second body  680 , the first and second arms  654 ,  656  of the saddle  650  can be aligned with the first and second arms  686 ,  688  of the second body such that rod seat  658  is aligned with the second rod-receiving recess  682 . Accordingly, the second rod R 2  can be simultaneously cradled between the arms  654 ,  656  of the saddle  650  and the arms  686 ,  688  of the second body  680  when the rod R 2  is disposed in the second rod-receiving recess  682 . 
     At this stage of assembly, even before locking rods within the connector  600 , the saddle  650  can interfere with the slot  618  of the hinge pin  614  to prevent the pin from being removed from the second body  680 . For example, when the saddle projection  652  is received in the slot  618 , the tapered bearing surfaces  665 ,  667  of the saddle projection can bear against the opposing sidewalls  640 ,  642  of the slot to prevent removal of the pin, and thereby maintain coupling of the first and second bodies  610 ,  680 . 
     The distal saddle projection  652  can also interfere with the slot  618  of the hinge pin  614  to limit the relative rotation of the connector bodies  610 ,  680 . For example, when the hinge pin  614  rotates clockwise or counter clockwise about the rotation axis A 1 , the extent of such rotation can be restricted by an outer edge  668  of the proximal-facing surface  644  of the slot  618  contacting a ridge  670  of the saddle projection  652 . In the illustrated embodiment, the ridge  670  of the saddle projection  652  can have a distal-facing contact surface that lies in a plane perpendicular with respect to the proximal-distal axis A 4  of the second body. When the saddle projection  622  is disposed within the slot  618 , a gap can be formed between the ridge  670  and the proximal-facing surface  644  of the slot  618 , thereby enabling the hinge pin  614  to rotate within the limits defined therebetween. 
     In some embodiments, the interaction between the slot  618  of the hinge pin  614  and the saddle projection  652  can limit the range of rotation of the pin symmetrically with respect to the rotation axis A 1 . For example, in some embodiments, the range of rotation of the hinge pin  614  can be limited to ±30 degrees, ±60 degrees, ±180 degrees, or other symmetrical range suitable depending on the surgical procedure. In some embodiments, the interaction between the slot  618  of the hinge pin  614  and the saddle projection  652  can limit the range of rotation of the pin asymmetrically with respect to the rotation axis A 1 . 
     A first rod R 1  can be seated in the first rod receiving recess  612  of the first body  610  and secured to the connector  600  by tightening the first fastener  620 . The first fastener  620  can include an exterior thread configured to mate with the interior threads formed on the arms  624 ,  626  of the first body  610  to allow the first fastener to be advanced or retracted along the axis A 2  with respect to the body by rotating the first fastener about the axis A 2 . The distal surface of the first fastener  620  can be configured to contact and bear against a rod R 1  disposed in the first rod-receiving recess  612  to lock the rod to the connector  600 . When tightened against the rod R 1 , the first fastener  620  can prevent the rod from translating relative to the connector  600  along the axis A 3  and/or from rotating with respect to the connector about the axis A 3 . The first rod R 1  can be seated in the first rod-receiving recess  612 , while the second body  680  can remain free to rotate relative to the first body  610  about the rotation axis A 1  even after the first rod R 1  is locked to the connector  600 . 
     A second rod R 2  can be seated in the rod seat  658  of the saddle  650  disposed in the second rod receiving recess  682  of the second body  680 . The second rod R 2  can be secured to the connector  600  by tightening the second fastener  622 . The second fastener  622  can include an exterior thread configured to mate with the interior threads formed on the arms  686 ,  688  of the second body  680  to allow the second fastener to be advanced or retracted along the axis A 4  with respect to the body by rotating the second fastener about the axis A 4 . The distal surface of the second fastener  622  can be configured to contact and bear against the rod R 2  disposed in the saddle  650  to lock the rod to the connector  600 . When tightened against the rod R 2 , the second fastener  622  can prevent the rod from translating relative to the connector  600  along the axis A 5  and/or from rotating with respect to the connector about the axis A 5 . 
     As the second fastener  622  is tightened, the second rod R 2  can be urged distally against the saddle  650 , thereby causing the saddle projection  652  to be urged distally into the slot  618  of the hinge pin  614  and lock relative rotation of the bodies  610 ,  680 . In other arrangements, the second fastener  622  can bear directly against the saddle  650 . For example, the second fastener  622  can include an outer set screw that bears against the saddle arms  654 ,  656  to lock relative rotation of the bodies  610 ,  680 , and an inner set screw that bears against the second rod R 2  to secure the second rod to the connector  600 . 
     Before fully tightening one or both fasteners  620 ,  622 , the bodies  610 ,  680  can be rotated relative to one another about the axis A 1  as desired by the user. The second fastener  622  can then be tightened to lock such relative rotation. In particular, the force applied by the second fastener  622  to the saddle  650  can wedge the saddle projection  652  into the slot  618  of the hinge pin  614 . For example, as shown in  FIG. 6I , the distal saddle projection  652  can be wedged into the slot  618  of the hinge pin  614  such that the tapered bearing surfaces  665 ,  667  intersect with the sidewalls  640 ,  642  of the slot  618  at a mismatched angle. The downward force applied by wedging the distal saddle projection  652  into the angled slot  618  of the hinge pin  614  can urge the pin  614  against the inner wall of the cavity  684  of the second body  680 , and thereby effectively lock relative rotation of the bodies  610 ,  680  about the axis A 1 . 
     In some embodiments, the force applied to the hinge pin  614  by wedging the saddle  650  into the slot  618  of the pin can urge the sharp edges or corners  616  of the pin to cut and/or deform the inner wall of the cavity  684  of the second body  680 . Through such edge loading, the sharp corners  616  of the hinge pin  614  can create additional friction, mechanical interlock, or increase the radial force applied by the pin against the second body  680  to effectively lock relative rotation of the bodies  610 ,  680  about the axis A 1 . It will be appreciated that the connector  600  can allow locking of the first rod R 1  to the connector and locking of the rotational degree-of-freedom of the connector to be performed independently of one another. 
     The ability to rotate the first and second bodies  610 ,  680  relative to one another about the rotation axis A 1  can advantageously allow first and second rods R 1 , R 2  to be locked together even when the rods are obliquely angled with respect to one another, e.g., in the sagittal plane or in the coronal plane. The connector  600  can be particularly useful in connecting tandem rods of a spinal fixation construct across the cervical-thoracic (CT) junction of a patient. For example, the connector  600  can secure the rods R 1 , R 2  in a laterally-offset arrangement to accommodate the different screw trajectories that may occur at the CT junction. By way of further example, the ability of the connector  600  to articulate can allow a cervical rod and a thoracic rod to be locked to one another at an oblique angle in the sagittal plane, e.g., to restore natural lordosis or kyphosis. The connector  600  can also be particularly useful in spinal deformity correction and other procedures in which multiple angled rods are to be coupled to one another. 
       FIGS. 7A-7O  illustrate an exemplary embodiment of a connector  700 . As shown, the connector  700  can include a first body  710  that defines a first rod-receiving recess or channel  712  and a second body  780  that defines a second rod-receiving recess or channel  782 . The first and second bodies  710 ,  780  can be connected to one another at least in part by a hinge pin  714  that defines a rotation axis A 1  about which the bodies can rotate relative to one another. In the illustrated embodiment, the hinge pin  714  can project laterally from the first body  710  to a free end. The free end of the hinge pin  714  can be received within an interior cavity  784  formed in the second body  780 . The connector  700  can include first and second fasteners  720 ,  722  configured to secure first and second rods R 1 , R 2  or other fixation elements to the connector  700  within the respective rod-receiving recesses  712 ,  782 . The hinge pin  714  of the first body  710  can include a retention slot  718  configured to receive a distal projection  752  of a saddle  750  disposed in the second rod-receiving recess  782 , thereby preventing disassembly of the first and second bodies  710 ,  780 . 
     As discussed further below, the structural integrity of the connector  700  can be improved to reduce the risk of the hinge pin  714  breaking under an applied shear force between the first and second bodies  710 ,  780 . For example, as shown in the illustrated embodiment, the structural integrity of the hinge pin  714  can be improved by forming the retention slot  718  in close proximity to the free end of the hinge pin  714 , such that the slot can be exposed through the second rod-receiving recess  782  while providing the hinge pin with a maximum cross sectional area for a significant portion of its length. Alternatively or in addition, in some embodiments, the locking strength of the connector  700  can be increased by maximizing the contact surface area between the saddle  750  and the hinge pin  714 . Alternatively or in addition, in some embodiments, the free end of the hinge pin  714  can be configured to interact with a through hole opening  798  defined in the second body  780  to limit the degree of rotation by the pin, and thereby limit the relative rotation permitted between the bodies  710 ,  780 . 
     The first body  710  of the connector  700 , including the hinge pin  714 , is shown in greater detail in  FIGS. 7C through 7E . The first body  710  can include proximal and distal ends  710   p ,  710   d  that define a proximal-distal axis A 2 . The proximal end  710   p  of the body  710  can include a pair of spaced apart arms  724 ,  726  that extend from the distal portion  710   d  of the body  710  to a free end. The spaced apart arms  724 ,  726  can define the first rod-receiving recess  712  therebetween. The first rod-receiving recess  712  can be open in a proximal direction, such that a rod R 1  can be inserted into the recess by moving the rod distally with respect to the connector  700 . Alternatively, the first rod-receiving recess  712  can be open in distal direction, open in a lateral direction, or closed such that the rod R 1  must be translated along the axis A 3  to insert the rod into the recess  712 . 
     The hinge pin  714  can project along the rotation axis A 1  from an outer surface  728  of the arm  726 . As shown in the illustrated embodiment, the outer surface  728  of the arm  726  can extend vertically from the distal end  710   d  of the first body  710 . The hinge pin  714  can extend perpendicular from a distal end portion of the outer surface  728  of the arm  726 . The hinge pin  714  can include opposed first and second ends that define a central longitudinal axis A 6  extending therebetween. The longitudinal axis A 6  can be collinear with the rotation axis A 1  of the connector  700 . The hinge pin  714  can be formed integrally or monolithically with the first body  710  as shown, or can be fixedly attached thereto, e.g., by welding or other processes. 
     The hinge pin  714  can have a first portion  730 , a second portion  732  and an intermediate portion or rib  734  that connects the first and second portions. The first portion  730  of the hinge pin  714  can have a cylindrical or other suitable shape that allows the pin to freely rotate within the cavity  784  of the second body  780 . The second portion  732  of the hinge pin  714  can have a semi-cylindrical or other suitable shape having a cross section that can interact with the second body  780  to limit rotation of the pin within the cavity  784 . In some embodiments, the second portion  732  of the pin  714  can have a semi-circular or D-shaped cross section. The rib  734  of the hinge pin  714  can have a cylindrical or other suitable shape to form the retention slot  718  between the first portion  730  and the second portion  732  of the pin. The length of the slot  718  can be defined by the length of the rib  734  disposed between a sidewall  740  of the first portion  730  and an opposing sidewall  742  of the second portion  732 . Each of the opposing sidewalls  740 ,  742  can lie in a plane perpendicular to the rotation axis A 1 . As discussed further below, the slot  718  can be configured to receive a distal projection of a saddle  750  disposed in the second rod-receiving recess  782 , thereby preventing disassembly of the first and second bodies  710 ,  780 . 
     The second body  780  is shown in greater detail in  FIGS. 7F through 7H . The second body  780  can include proximal and distal ends  780   p ,  780   d  that define a proximal-distal axis A 4 . The proximal end  780   p  of the body  780  can include a pair of spaced apart arms  786 ,  788  that define the second rod-receiving recess  782  therebetween. A rod R 2  disposed in the second rod-receiving recess  782  can have a central longitudinal rod axis A 5 . The second rod-receiving recess  782  can be open in a proximal direction, such that a rod R 2  can be inserted into the recess by moving the rod distally with respect to the connector  700 . Alternatively, the second rod-receiving recess  782  can be open in distal direction, open in a lateral direction, or closed such that the rod R 2  must be translated along the axis A 5  to insert the rod into the recess  782 . Each of the arms  786 ,  788  can include recesses or grooves  790  for retaining the saddle  750  within the body  780 . The second body  780  can include an outer surface  792  that opposes the outer surface  728  of the first body  710 . 
     The distal end  780   d  of the second body  780  can define an interior cavity  784  in which a free end of the hinge pin  714  can be received. As shown in the illustrated embodiment, the cavity  784  be a through hole that extends from a first opening  794  formed in the outer surface  792  to a second opening  798  formed in the opposite outer surface  796  of the second body  780 . As discussed further below, the second opening  798  formed in the outer surface  796  of the second body  780  can be configured to at least partially receive and interact with the free end portion  732  of the hinge pin  714  and thereby limit rotation of the pin within the cavity  784 . As shown in  FIG. 7H , the second opening in the outer surface  796  of the second body can have a semi-circular or D-shaped cross section. At least one dimension of the cavity  784  can be greater than a corresponding dimension of the hinge pin  714  to allow the hinge pin to translate within the cavity along the rotation axis A 1 . 
     The saddle  750  is shown in greater detail in  FIGS. 7I through 7K . The saddle  750  can be generally cylindrical with first and second arms  754 ,  756  extending in a proximal direction to respective free ends of the arms. The first and second arms  754 ,  756  of the saddle  750  can define a rod seat  758  therebetween. The first and second arms  754 ,  756  of the saddle  750  can include projections  760  (e.g., spring tabs) extending radially outward therefrom. The radial projections  760  can be configured to snap into or otherwise be received within grooves or other recesses  790  of the second body  780  to retain the saddle  750  therein. 
     The saddle  750  can have a recessed distal-facing bearing surface  762  and a saddle projection  752  extending therefrom. The recessed distal-facing bearing surface  762  can have a planar, ramped, curved or other suitable contour configured to contact and bear against an exterior surface of the hinge pin  714 . As shown in the illustrated embodiment, the recessed bearing surface  762  of the saddle  750  can be curved to contact and bear against the cylindrical-shaped surface of the first portion  730  of the hinge pin  714 . The saddle projection  752  can extend distally from the distal-facing bearing surface  762  to maintain coupling of the first and second bodies  710 ,  780 . 
     As shown in the  FIGS. 7J and 7K , the distal saddle projection  752  can be aligned with an arm  756  of the saddle  750 . For example, as shown in the illustrated embodiment, the distal saddle projection  752  can extend distally along an edge of the saddle  750  coplanar with the saddle arm  756 . In some embodiments, the distal saddle projection  752  can extend distally from the recessed bearing surface  762  of the saddle, such that the projection is disposed adjacent to the edge of the saddle  750  in a plane parallel to the saddle arm  756 . 
     As discussed further below, by disposing the distal saddle projection  752  at the edge or adjacent to the edge of the saddle  750 , the contact surface area can be maximized between the first portion  730  of the hinge pin  714  and the distal-facing bearing surface  762  of the saddle  750 . Maximizing the contact surface area between the hinge pin  714  and the saddle  750  can increase the locking strength of the connector  700  to resist rotation between the first and second bodies  710 ,  780 . In some embodiments, the saddle projection  752  can define a recess  754  sized to partially receive the intermediate portion (or rib)  734  of the hinge pin  714  and thereby allow the rib to rotate within the recess. 
     As shown in  FIG. 7L through 7O , the connector  700  can be assembled by inserting the hinge pin  714  through the first opening  794  of the outer surface  792  of the second body  780  and into the cavity  784  until the free end portion  732  of the pin is received in the second opening  798  of the outer surface  796 . When the free end portion  732  of the hinge pin  714  is received in the second opening  798  of the second body  780 , the retention slot  718  of the pin can be exposed proximally through the second rod-receiving recess  782 , such that the slot is aligned with the edge of the recess  782  closest to the arm  788  of the second body  780 . In some embodiments, the slot  718  can be offset from the edge of the second rod-receiving recess  782  between the central longitudinal rod axis A 5  and the arm  788  of the second body  780 . 
     By forming the retention slot  718  in close proximity to the free end of the hinge pin  714 , e.g., such that the slot is exposed at or adjacent to the edge of the second rod-receiving recess  782 , the hinge pin can have a maximum cross sectional area for a significant portion of its length, and thereby improve the structural integrity of the connector  700 . For example, in some embodiments, the first portion  730  of the hinge pin  714  can have a maximum cross sectional area that extends longitudinally from the outer bearing surface  728  of the first body  710  to more than halfway across the width of the second rod-receiving recess  782 . In such embodiments, the risk of the hinge pin  714  breaking under an applied shear force between the first and second bodies  710 ,  780  can be reduced. 
     As shown in  FIG. 7M , the saddle  750  can be inserted into the proximal end  780   p  of the second body  780  and distally advanced until the distal saddle projection  752  is received in the slot  718  of the hinge pin  714 . The radial projections  760  of the saddle arms  754 ,  756  can snap into the grooves or recesses  790  of the second body  780  to retain the saddle  750 . When disposed in the second body  780 , the first and second arms  754 ,  756  of the saddle  750  can be aligned with the first and second arms  786 ,  788  of the second body such that rod seat  758  is aligned with the second rod-receiving recess  782 . Accordingly, the second rod R 2  can be simultaneously cradled between the arms  754 ,  756  of the saddle  750  and the arms  786 ,  788  of the second body  780  when the rod R 2  is disposed in the second rod-receiving recess  782 . 
     At this stage of assembly, even before locking rods within the connector  700 , the saddle  750  can interfere with the slot  718  of the hinge pin  714  to prevent the pin from being removed from the second body  780 . For example, when the saddle projection  752  is received in the slot  718 , the lateral-facing surfaces of the projection can bear against the opposing sidewalls  740 ,  742  of the slot to prevent removal of the pin, and thereby maintain coupling of the first and second bodies  710 ,  780 . The depth of the slot  718  can be configured to be greater than the height of the distal saddle projection  752  to ensure that the distal-facing surface  762  of the saddle bears against the first portion  730  of the pin during locking. 
     A first rod R 1  can be seated in the first rod receiving recess  712  of the first body  710  and secured to the connector  700  by tightening the first fastener  720 . The first fastener  720  can include an exterior thread configured to mate with the interior threads formed on the arms  724 ,  726  of the first body  710  to allow the first fastener to be advanced or retracted along the axis A 2  with respect to the body by rotating the first fastener about the axis A 2 . The distal surface of the first fastener  720  can be configured to contact and bear against a rod R 1  disposed in the first rod-receiving recess  712  to lock the rod to the connector  700 . When tightened against the rod R 1 , the first fastener  720  can prevent the rod from translating relative to the connector  700  along the axis A 3  and/or from rotating with respect to the connector about the axis A 3 . The first rod R 1  can be seated in the first rod-receiving recess  712 , while the second body  780  can remain free to rotate relative to the first body  710  about the rotation axis A 1  even after the first rod R 1  is locked to the connector  700 . 
     A second rod R 2  can be seated in the rod seat  758  of the saddle  750  disposed in the second rod receiving recess  782  of the second body  780 . The second rod R 2  can be secured to the connector  700  by tightening the second fastener  722 . The second fastener  722  can include an exterior thread configured to mate with the interior threads formed on the arms  786 ,  788  of the second body  780  to allow the second fastener to be advanced or retracted along the axis A 4  with respect to the body by rotating the second fastener about the axis A 4 . The second fastener  722  can include a driving interface configured to receive a driver for applying a rotational force to the second fastener  722  about the axis A 4 . 
     The distal surface of the second fastener  722  can be configured to contact and bear against the rod R 2  disposed in the saddle  750  to lock the rod to the connector  700 . When tightened against the rod R 2 , the second fastener  722  can prevent the rod from translating relative to the connector  700  along the axis A 5  and/or from rotating with respect to the connector about the axis A 5 . While a unitary set screw  722  is shown, it will be appreciated that other fasteners can be used, instead or in addition, such as a closure cap that advances and locks by quarter-turn rotation, a closure cap that slides in laterally without rotating, a nut that threads onto an exterior of the body, or a dual-component set screw with independently-rotatable inner and outer members, the inner member acting on the rod R 2  and the outer member acting on proximal free ends of the saddle arms  754 ,  756 . 
     Before fully tightening one or both fasteners  720 ,  722 , the bodies  710 ,  780  can be rotated relative to one another about the axis A 1  as desired by the user. The degree of rotation of the hinge pin  714 , and thereby the relative rotation permitted between the bodies  710 ,  780 , can be limited by the interaction between the free end portion  732  of the hinge pin  714  and the opening  798  in the outer surface  796  of the second body  780 . 
     As shown in  FIG. 7N , the through hole opening  798  in the outer surface  796  of the second body  780  and the free end portion  732  of the hinge pin  714  can be configured to have respective cross sectional profiles, perpendicular to the rotation axis A 1 , that allow the pin to rotate clockwise and counter-clockwise between a predetermined range of angles about the rotation axis A 1 . For example, in the illustrated embodiment, the free end portion  732  of the pin and the through hole opening  798  of the second body  780  can both have semi-circular or D-shaped cross sectional profiles. As shown, the semi-circular profile of the through hole opening  798  is larger than the semi-circular profile of the free end portion  732  of the pin to allow the free end portion of the pin to rotate about the rotation axis A 1  within the through hole opening of the second body. When the hinge pin  714  rotates clockwise or counter clockwise about the rotation axis A 1 , the extent of such rotation can be restricted by bearing surfaces  735 ,  737  of the free end portion  732  contacting an inner wall of through hole opening  798 . In some embodiments, the interaction between the through hole opening  798  and the free end portion  732  of the hinge pin  714  can limit the range of rotation of the pin symmetrically with respect to the rotation axis A 1 . For example, in some embodiments, the range of rotation of the hinge pin  714  can be limited to ±30 degrees, ±60 degrees, ±180 degrees, or other symmetrical range suitable depending on the surgical procedure. In some embodiments, the interaction between the through hole opening  798  and the free end portion  732  of the hinge pin  714  can limit the range of rotation of the pin asymmetrically with respect to the rotation axis A 1 . 
     Once the first and second bodies  710 ,  780  are rotated to the desired orientation, the second fastener  722  can then be tightened to lock the relative rotation of the first and second bodies  710 ,  780 . As the second fastener  722  is tightened, the second rod R 2  can be urged distally against the saddle  750 , thereby causing the saddle to urge distally against the hinge pin  714 . For example, as shown in the illustrated embodiment of  FIG. 7O , the distal-facing bearing surface  762  of the saddle  750  can urged to contact and bear against the counter bearing surface of the first portion  730  of the hinge pin  714 . By forming the slot  718  as close as possible to the free end portion  732  of the pin, the contact surface area between the distal-facing bearing surface  762  of the saddle  750  and the counter bearing surface of the hinge pin  714  can be maximized. For example, in some embodiments, the contact surface area between the saddle  750  and the hinge pin  714  can extend in the direction of the longitudinal axis A 6  for a continuous length that is greater than half the width of the second rod-receiving recess  782 . In some embodiments, the contact surface area between the saddle  750  and the pin  714  can extend for a continuous length between 70% and 90% of the width of the second rod-receiving recess  782 . By maximizing the contact surface area between the saddle  750  and the pin  714 , the locking force and thus the locking strength of the connector  700  can be increased to resist relative rotation of the first and second bodies  710 ,  780 . 
     In other arrangements, the second fastener  722  can bear directly against the saddle  750 . For example, the second fastener  722  can include an outer set screw that bears against the saddle arms  754 ,  756  to lock relative rotation of the bodies  710 ,  780 , and an inner set screw that bears against the second rod R 2  to secure the second rod to the connector  700 . 
     It will be appreciated that the connector  700  can allow locking of the first rod R 1  to the connector and locking of the rotational degree-of-freedom of the connector to be performed independently of one another. 
     In some embodiments, the connector  700  can include various features of a unilateral locking interface, including but not limited to one or more grooves  702  and surface projections  704 . The unilateral locking interface enables a surgical instrument that includes a unilateral locking mechanism (not shown) to rigidly hold onto one side of the connector  700 . Exemplary unilateral locking interfaces that can be included in the connector  700  are disclosed in U.S. patent application Ser. No. 15/843,618, filed on Dec. 15, 2017 and entitled “Unilateral Implant Holders and Related Methods” (now published as US-2019-0183541-A1), the entire contents of which are hereby incorporated by reference. 
     The connector  700  can include any combination of the features of the connector  500  described above. For example, as discussed above with respect to  FIGS. 5A-5O , the exterior surface of the hinge pin  714  can include sharp corners or other surface features (now shown) that can bear against the inner wall of the cavity  784  of the second body  780  to increase the locking strength of the connector  700 . 
     The ability to rotate the first and second bodies  710 ,  780  relative to one another about the rotation axis A 1  can advantageously allow first and second rods R 1 , R 2  to be locked together even when the rods are obliquely angled with respect to one another, e.g., in the sagittal plane or in the coronal plane. The connector  500  can be particularly useful in connecting tandem rods of a spinal fixation construct across the cervical-thoracic (CT) junction of a patient. For example, the connector  500  can secure the rods R 1 , R 2  in a laterally-offset arrangement to accommodate the different screw trajectories that may occur at the CT junction. By way of further example, the ability of the connector  500  to articulate can allow a cervical rod and a thoracic rod to be locked to one another at an oblique angle in the sagittal plane, e.g., to restore natural lordosis or kyphosis. The connector  500  can also be particularly useful in spinal deformity correction and other procedures in which multiple angled rods are to be coupled to one another. 
     Any of the connectors  100 ,  200 ,  300 ,  400 ,  500 ,  600 , and  700  described above can include a taper-lock mating between the first and second bodies. The taper lock can be formed by a conical male feature wedged into a conical female feature. The cone angle of the male feature can be in the range of about 5 degrees to about 35 degrees. The cone angle of the male feature can be about 20 degrees. The cone angle of the female feature can be in the range of about 5 degrees to about 35 degrees. The cone angle of the female feature can be about 20 degrees. The male and female cone features can have the same cone angle or different cone angles. The connector geometry can be selected such that there is a space between the first and second bodies along the axis A 1  when the connector is fully tightened, which can ensure that the taper lock bears most or all of the locking force. The male and female features can be flat cones, or can include surface features such as axial splines. 
     The degree to which the first and second bodies can rotate relative to one another can vary in any of the connectors  100 ,  200 ,  300 ,  400 ,  500 ,  600 , and  700  described above. The first body can be rotatable up to 360 degrees with respect to the second body. The first body can be rotatable up to about 180 degrees with respect to the second body. The first body can be rotatable up to about 60 degrees with respect to the second body. 
     The geometries of the rod-receiving recesses of any of the connectors  100 ,  200 ,  300 ,  400 ,  500 ,  600 , and  700  described above can vary. One or both recesses can include a V-shaped seat configured to accommodate rods of different diameters. 
     An exemplary method of using the connectors disclosed herein is described below. 
     The procedure can begin by forming an open or percutaneous incision in the patient to access a target site. The target site can be one or more vertebrae, a long bone or multiple portions of a long bone, or any other bone or non-bone structure of the patient. As shown in  FIG. 8 , the target site can be multiple vertebrae in the patient&#39;s cervical and thoracic spine. 
     Bone anchors can be driven into one or more of the vertebrae and spinal rods can be attached thereto using known techniques. In the illustrated example, bilateral spinal rods R 1 , R 2  are coupled to four adjacent vertebrae V 1 -V 4  using eight bone anchors S 1 -S 8 . In addition, bilateral rods R 3 , R 4  are coupled to two additional vertebrae V 5 -V 6  using four bone anchors S 9 -S 12 . The rods R 1 , R 2  can be connected to the rods R 3 , R 4 , respectively, using two connectors C 1 -C 2  of the type described herein (e.g., any of the connectors  100 ,  200 ,  300 ,  400 ,  500 ,  600 ,  700  or combinations or variations thereof). 
     The connectors C 1 -C 2  can be articulated and locked in an articulated position as shown. This can allow the principal longitudinal axes of the rods R 1 , R 3  to be obliquely angled with respect to each other, and/or for the principal longitudinal axes of the rods R 2 , R 4  to be obliquely angled with respect to each other. 
     All of the rods R 1 -R 4 , the connectors C 1 -C 2 , and the bone anchors S 1 -S 12  can be installed in a single procedure. 
     Alternatively, the rods R 1 , R 2  and the bone anchors S 1 -S 8  may have been installed in a previous procedure, and the current procedure can be a revision procedure in which the rods R 3 , R 4 , the connectors C 1 -C 2 , and the bone anchors S 9 -S 12  are installed to extend the previously-installed construct to additional levels. 
     The connectors C 1 -C 2  can be attached to position the rods R 1 -R 4  such that they overlap in a lateral view. One or both connectors C 1 -C 2  can also be rotated 90 degrees from the orientation shown to position one or both rod pairs R 1 , R 3  and R 2 , R 4  such that they overlap in a posterior or anterior view. 
     The above steps can be repeated to install additional rods and/or connectors at the same or at different vertebral levels. Final tightening or other adjustment of the construct can be performed and the procedure can be completed using known techniques and the incision closed. 
     It should be noted that any ordering of method steps expressed or implied in the description above or in the accompanying drawings is not to be construed as limiting the disclosed methods to performing the steps in that order. Rather, the various steps of each of the methods disclosed herein can be performed in any of a variety of sequences. In addition, as the described methods are merely exemplary embodiments, various other methods that include additional steps or include fewer steps are also within the scope of the present disclosure. 
     While the methods illustrated and described herein generally involve attaching spinal rods to multiple vertebrae, it will be appreciated that the connectors and methods herein can be used with various other types of fixation or stabilization hardware, in any bone, in non-bone tissue, or in non-living or non-tissue objects. The connectors disclosed herein can be fully implanted, or can be used as part of an external fixation or stabilization system. The devices and methods disclosed herein can be used in minimally-invasive surgery and/or open surgery. 
     The devices disclosed herein and the various component parts thereof can be constructed from any of a variety of known materials. Exemplary materials include those which are suitable for use in surgical applications, including metals such as stainless steel, titanium, or alloys thereof, polymers such as PEEK, ceramics, carbon fiber, and so forth. The various components of the devices disclosed herein can be rigid or flexible. One or more components or portions of the device can be formed from a radiopaque material to facilitate visualization under fluoroscopy and other imaging techniques, or from a radiolucent material so as not to interfere with visualization of other structures. Exemplary radiolucent materials include carbon fiber and high-strength polymers. 
     Although specific embodiments are described above, it should be understood that numerous changes may be made within the spirit and scope of the concepts described.