Patent Publication Number: US-2022233215-A1

Title: Anti-splay head and set screw for spinal fixation

Description:
FIELD 
     The present technology is related generally to spinal fixation systems and processes and, more particularly, to an anti-splay head and set-screw arrangement. 
     BACKGROUND 
     Surgical screws and rods are used commonly in surgically correcting spinal abnormalities. Pedicle screw assemblies are used to facilitate placement and attachment of a spinal rod relative to the spine. Such pedicle screw assemblies include at least a bone screw section or anchor and at least one receiver portion attached to the bone screw. The bone screw sections are anchored to the vertebrae in the surgical procedure. 
     The receiver portions have arms between which portions of the spinal rod is received. The arms are often configured with internal threading corresponding to threading on a set screw. Following screw anchoring in the bone, and placement of the rod between the arms of the receiver, a set screw is threaded between the arms to secure the rod in the receiver. 
     The receiver portions of typical pedicle screws can be angularly or fixedly positionable with respect to the screw sections to facilitated desired attachment of the spinal rod between vertebrae. 
     Outward forces on the receiver arms over time following implantation try to splay the arms away from each other. One manner of limiting splay is by receiver and set-screw threads configured, such as with sloping thread faces, such that the set screw holds the arms inward, against the set screw. 
     Other attempted solutions for splaying include using a cap installable around at least a portion an exterior of the receiver arms, to hold the arms from moving away from each other. 
     These and other prior efforts to avoid splaying have various shortcomings. Shortcomings include undesirable cost, form factor (e.g., implant size or fit within the patient), and strength over time. 
     SUMMARY 
     The systems, process, and techniques of this disclosure relate generally to an anti-splay head and set-screw arrangement. 
     In one aspect, the present disclosure provides an anti-splaying system. The system includes a receiver having a base, a first arm, a second arm, a first locking channel, and a second locking channel. The first arm and the second arm each extend from the base defining a rod-receiving cavity between the arms. The first and second arms include first and second inner threads formed in respective inner surfaces of the first and second arms. The first locking channel is formed in the inner surface of the first arm and extending from a proximal opening to a proximal bottom at or adjacent a first proximal beginning of the first inner thread. The second locking channel is formed in the inner surface of the second arm and extending from a proximal opening to a proximal bottom at or adjacent a second proximal beginning of the second inner thread. 
     Further in this aspect, the system includes a set screw having a driving portion, a body portion, external threads extending from the body portion, and an intermediate locking component connected rotatably to the body portion. 
     The intermediate locking component of the set screw and the locking channels of the receiver are configured such that the locking component can, in operation of the system, be moved into a securing position in the locking channels and, when in the secured position, fixes the two arms from splaying away from each other. 
     The intermediate locking component is connected rotatably to the body portion intermediate the driving portion and the external threads of the set screw. 
     The locking component comprises opposing lateral ends sized and shaped corresponding to size and shape of the locking channel, for mating engagement between the locking component and the locking channels. 
     A first lateral end of the lateral ends comprises opposing shoulders sized and shaped to engage opposing shoulders of a first locking channel of the locking channels 
     The lateral ends include first and second lateral ends, and the connecting component includes first and second arms connecting the first and second lateral ends respectively to the ring. 
     The locking channel has a depth that is about twice as deep as the locking ends are tall or less. 
     The locking component includes a ring surrounding a portion of the set screw body. The body has a reduced diameter where the ring surrounds the body. 
     In another aspect, the system further includes a bone anchor connectable with the receiver, and the spinal rod. 
     In still another aspect, the technology includes methods of making any of the anti-splaying systems or anti-splay components described above. 
     Details of one or more aspects of the disclosure are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the techniques described in this disclosure will be apparent from the description, drawings, and claims. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  shows perspective views of an anti-splaying system partially disassembled, the system including an anti-splay receiver and an anti-splay set screw, according to embodiments of the present disclosure; 
         FIG. 2  is a cross section of the anti-splay set screw taken along line F 2 -F 2  of  FIG. 1 ; 
         FIG. 3  is a side view of the anti-splaying system of  FIG. 1 ; 
         FIG. 4  is a perspective view of the anti-splay set screw being lowered for insertion to the receiver; 
         FIG. 5  is the perspective view of  FIG. 4  with the anti-splay set screw being threaded toward a final position within the anti-splay receiver; 
         FIG. 6  is a bottom view of the anti-splay set screw; 
         FIG. 7  is a top view of the anti-splay receiver; 
         FIG. 8  is the top view of  FIG. 7 , with the anti-splay set screw inserted into the anti-splay receiver; and 
         FIG. 9  is a cross section of the anti-splaying system, assembled, taken along line F 9 -F 9  of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     Turning now to the drawings, and more particularly to the first figure,  FIG. 1  shows a perspective view of components of an anti-splay system, indicated generally by reference numeral  100 . 
     The system  100  includes an anti-splay head, or receiver  110 , and an anti-splay set screw  120 , according to embodiments of the present disclosure. 
     The receiver  110  has arms  112  extending up, or proximally, from a base  113 . The arms  112  define a rod cavity  114  between them, for receiving a spinal-fusion rod. A rod  300  is shown schematically, disposed in the cavity  114 , in  FIGS. 3 and 8 . 
     The set screw  120  extends from a driving, or proximal, end having a driving portion  122 . The driving portion  122  includes a driving port  123 . The driving port  123  may be a cavity sized and shaped corresponding to any available set-screw driver (now shown). 
     The set screw  120  further includes a shaft, or body  125  extending to a distal end of the screw  120 . In a contemplated embodiment, the driving portion  122  can be formed integrally or monolithically with or in the body  125  of the set screw  120 . 
     The body  125  has a threaded exterior  126 . The threaded surface  126  corresponds in size and shape to a thread  116  of the receiver  110 , for being threaded into the receiver. 
     The set screw  120  further includes a locking component  124 . The locking component  124  is connected rotatably to the body  125 , as indicated by arrows in  FIG. 1 . 
     The locking component  124  is in various embodiments connected to the body  125  intermediate the driving portion  122  and the screw threads  126 . The locking component  124  can be referred to in such cases as an intermediate locking component, an intra-screw locking component, or the like. 
     While the arrows in  FIG. 1  indicate a first direction of rotation, the connecting features are in various embodiments configured so that the locking component  124  can rotate in both direction, or in one direction or the other, only. 
     The locking component  124  extends between opposing ends  128 . The ends  128  of the locking component  124  are connected by a central connector  130 . The connector in various embodiments is shaped as a ring  130 . The ring  130  surrounds a portion of the body  125  extending up to the driving portion  122 , as shown well in  FIG. 2 . In various embodiments, the body  125  has a reduced diameter to accommodate the ring, as shown in  FIG. 2 . 
     The connection in various embodiments includes features facilitating the relative rotation between the ring  130  and the body  125 , such as ball-bearings or a medical lubricant. 
     The ends  128  can extend by arms  127  connecting the ends  128  to the central connecting structure  130 , e.g., connecting ring  130 . 
     With further reference to the anti-splay receiver  110 , each arm  112  has an internal thread set  116 . As shown in  FIG. 1 , each thread set  116  is interrupted or separated by an anti-splay, or locking, channel  118  at a proximal end of the receiver threads  116 . The threads  116  oppose each other across the cavity  114 , and can be referred to as opposing threads or thread sections. 
     Each locking channel  118  extends distally from a proximal opening  117  (referenced in  FIG. 1 ) to a distal stop or bottom. In operation of the system  100 , the anti-splay set screw  120  is threaded into the anti-splay receiver  110  until the locking component  124  enters the locking channel  118 . The threading can be performed until the locking component  124  engages with the channel stop  119  ( FIG. 7 ) and/or the distal end of the body engages the spinal rod  300  ( FIGS. 3 and 8 ). Engaging the rod is in most embodiments the priority. 
     The locking channel  118  is sized and shaped, and the anti-splay set screw  120  is sized and shaped, such that the set screw  120  extends distally in being threaded into the receiver  110  until the rod is contacted by the distal end of the rod. At that time, or after a certain small amount of further threading, such as a quarter, half, or full turn of the screw  120 , the locking component  124  bottoms out at stop  119  of the channel  118 . The system  100  is in some embodiments designed, and the rod sized, such that the locking end  128  enters the channel  118  completely, even if it doesn&#39;t bottom out. 
     The locking channel must be sufficiently deep. If the locking channel  118  is not deep enough, the locking component  124  would bottom out, at the stop  119 , before the set screw  120  is able to thread sufficiently into the receiver  110 . 
     In various embodiments, the stop  119  is at or adjacent a top of the corresponding inner thread  116 . The stop  119  may be at or adjacent a first, second, or third level of inner threading  116 , for instance. In the example of  FIG. 1 , the channel extends through a single level of inner thread from the top or opening  117 , with the stop  119  being generally at start of a second level of inner thread from the top or opening  117 . These areas, including the first one or few threads, can be referred to generally as a proximal beginning of the inner thread. 
     In various embodiments, the channel depth is at least equal to a height of the locking component  124 , or a height of the ends  128  of the locking component  124 . 
     In contemplated embodiments, the system  100 , or a kit in which the system is provided, includes any of the components referenced. The system or kit can include any suitable components for performing the surgical procedures, including but not limited to implantable components and instruments for effecting the surgery. The system  100  can include, for instance, any of the anti-splay receiver  110 , the anti-splay set screw  120 , and the rod  300 . The system  100  or kit can include the driver referenced, but not shown. And the system  100  or kit can include any number and size of these parts, including multiple anti-splay set screws and receivers  120 ,  110 . 
     Turning to the second figure,  FIG. 2  illustrates a cross section of the set screw  120 , taken along line F 2 -F 2  of  FIG. 1 . 
     In operation of the system  100  ( FIG. 1 ), the locking component  124  is aligned into the locking channel  118  of the receiver  110 , by a surgeon or surgical robot. As the anti-splay set screw  120  is threaded into the receiver  110 , by the surgeon or robot turning a driver (or, driving instrument; not shown) against a driving portion  220  of the driving portion  122 , the locking component  124  enters the channel  118 . 
       FIG. 3  is a side view of the anti-splay receiver  110  and anti-splay set screw  120  of  FIG. 1 . Rotatability of the locking component  124  relative to the set-screw body  125  is indicated again by arrow. 
       FIG. 3  also shows schematically an end view of the rod  300  positioned in the cavity  114  of the receiver  110 . 
       FIG. 4  is a perspective view of the anti-splay set screw  120  being positioned for lowering for insertion to the anti-splay receiver  110 . The movement is indicated generally by arrow in  FIG. 4 . 
     Prior to the movement of  FIG. 4 , the receiver  110  is secured to a patient vertebra, by a bone screw connected to the receiver  110 . The bone screw (not shown) can be any conventional or available type. The receiver  110  can be configured for top-loading or bottom-loading of the bone screw into the receiver  110 . The receiver  110  may in such ways be connected or connectable to the bone anchor readily—e.g., easily in the usual course of a surgery. 
     The anti-splay receiver  110  and anti-splay bone screw  120  can be further configured to allow desired relative motion, such as uniaxial or multiaxial motion. In some embodiments, the bone screw and the receiver  110  are fixed together, either by being formed integrally or monolithically, or by being fixedly connected to each other. 
     In operation of the anti-splaying system  100 , before and/or as the set-screw  120  is moved toward the receiver  110 , care is taken such that the locking ends  128  of the locking component  124  are aligned with the anti-splay channels  118  of the arms  112  of the receiver  110 . 
     The anti-splay channels  118  receive ends  128  of the locking component  124 . In various embodiments the locking component  124  is sized such that the ends extend further laterally than a maximum diameter of the screw body  125 , and in some cases farther than a maximum diameter than the thread  126 , as shown in the figures, and best seen in  FIG. 2 . 
       FIG. 5  shows the anti-splay set screw  120  having been threaded to a final position within the anti-splay receiver  110 . In this position, the locking component  124  would seat against the rod  300 , which is shown in  FIGS. 3 and 8 . Motion of threading, transitioning the set screw  120  toward the final position, is indicated by arrow in  FIG. 5 . 
       FIG. 6  is a bottom view of the anti-splay set screw  120 . Relative rotatability between the set screw body  125  and the locking component  124  is indicated by arrow in  FIG. 6 , as in  FIG. 1 . 
     The ends  128  of the locking component  124  are configured such that, when engaged with the arms  112  of the receiver  110 , being slid into the anti-splay channels  118 , keep the arms  112  from moving away from each other. The connection keeps each arm  112  from moving away from the other arm—i.e., keeps the arms  118  from splaying. 
     The ends  128  of the locking component  124  include first engagement or locking features  600 , such as shoulders. The shoulders  600 , which may be referred to as external shoulders, engage second, corresponding, engagement or locking features  700  ( FIG. 7 ) of the receiver  110 . The shoulders  600  of the locking component  124  can be referred to as external shoulders, corresponding to internal shoulders  800  of the receiver  110 . 
     The configuration of each end  128  can be referred to as a double-dovetail, corresponding to the opposing shoulders  600 . 
     In contemplated embodiments (not shown in detail), the locking or engaging features are configured in any of a variety of other ways. The features may include the locking component  124  having at each end  128  opposing internal shoulders. In this case, the internal shoulders of the locking component  124  form a locking-component void, for engaging with opposing external shoulders of a protrusion extending from or on an inner surface of each arm  112  of the receiver  110 , for instance. In this case, the locking component  124  is aligned so that the protrusion of the receiver  112  is received in the void of the locking component  124 , as the internal shoulder of the locking component  124  is slid down along the external shoulder of the protrusion of the receiver arms  112 . 
       FIG. 7  illustrates a plan view of the anti-splay receiver  110 . The view shows a top-down, or proximately looking, view of the receiver including anti-splay channels  118 . 
       FIG. 8  is the top view of  FIG. 7 , with the anti-splay set screw  120  inserted into the anti-splay receiver  110 , yielding the anti-splaying system  100  assembled. Full assembly in some embodiments includes the anti-splay set screw and receiver  120 ,  110  being connected to the bone anchor (not shown). 
     The rod  300  is shown seated in the anti-splay receiver  110 . The rod  300  is secured in place there by the receiver  110  and the anti-splay set screw  120  threaded to the receiver  110 , with the ends  128  of the locking component  124  secured in the anti-splay channel  118  of the receiver  110 . 
     It should be understood that various aspects disclosed herein may be combined in combinations other than the combinations presented specifically in the description and the accompanying drawings. It should also be understood that, depending on the example, certain acts or events of any of the processes or methods described herein may be performed in other sequence, added, merged, or left out altogether (e.g., all described acts or events may not be necessary to carry out the techniques). 
     Any disclosure or claim herein referencing direction is not meant to limit interpretation of the disclosure, unless the disclosure or claim requires expressly such limitation. Reference, for instance, to movement up or down herein is not limited to movement in any certain direction during surgery or system assembly, as the surgery or assembly can be performed with any of a wide variety or orientations or in any suitable reference frame. 
     In addition, while certain aspects of this disclosure are described as being performed by a single module or unit for purposes of clarity, it should be understood that the techniques of this disclosure may be performed by a combination of units or modules associated with, for example, a medical device. 
     Unless defined specifically otherwise herein, all terms are to be given their broadest possible interpretation including meanings implied from the specification as well as meanings understood by those skilled in the art and/or as defined in dictionaries, treatises, etc. It must also be noted that, as used in the specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless otherwise specified, and that the terms “comprises” and/ or “comprising,” when used in this specification, specify the presence of stated features, elements, and/or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and/or groups thereof. 
     It will be understood that various modifications may be made to the embodiments disclosed herein. Therefore, the above description should not be construed as limiting, but merely as exemplification of the various embodiments. Those skilled in the art will envision other modifications within the scope and spirit of the claims appended hereto.