Abstract:
A lateral connector assembly for connecting a bone engaging fastener to an elongated member, such as a spinal rod includes a lateral connector having an opening for receiving a portion of the bone engaging fastener therethrough. The lateral connector includes a plate portion and an integral yoke portion, which yoke portion is attached to the elongated member by way of a clamp. The lateral connector assembly can include variable angle means between the clamp and the yoke portion of the lateral connector that permits rotation of the lateral connector about an axis projecting outward from the spinal rod. The clamp includes a tapering channel to capture the elongated member and lock the connector assembly.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates generally to spinal fixation systems, such as systems for use in the fixation of the spine for the treatment of various spinal deformities. Specifically, the present invention contemplates a lateral connector assembly for interconnecting an elongated member, such as a rod or tether, with a bone engaging fastener such as a hook, screw or bolt.  
         [0002]     The treatment of spinal deformities and injuries has evolved significantly over the last 30 years. Spinal deformities, such as scoliosis and kyphosis, as well as fractures, spondylolisthesis, and other medical indications have been treated using a system of relatively rigid elongated members spanning the vertebral column. In one type of system, the elongated members constitute a plate that has a number of openings or slots through which bone bolts or bone screws extend. The bone engaging fasteners are threaded into different aspects of the vertebra and fixed to the plate to achieve fixation of the elongated plate. In other procedures, elongated rigid rods are joined to screws or hooks embedded in the spine to fix the relative position of each vertebra. In yet further procedures for dynamic stabilization, an at least partially flexible elongate member is joined to bone engaging fasteners embedded in the spine.  
         [0003]     In the implantation of any spinal instrumentation, one goal of the surgeon is to minimize the intrusion into the patient, whether by the amount of implants that must be used, the size of the surgical access opening or by the length of time required to fix the implants within the patient. Further, the system must be easy to use and provide the surgeon with confidence that it will provide the desired stabilization after implantation.  
         [0004]     While connectors have been provided that offer various degrees of freedom of movement between the elongated member and the bone fastener, there remains a need for providing an improved connection between the bone fastener and the elongated member.  
       SUMMARY OF THE INVENTION  
       [0005]     The present invention provides a connector assembly for connecting a bone engaging fastener to an elongated member. In one aspect the invention includes a connector for joining the bone engaging fastener to a clamp having a channel for holding the elongated member. A compression member is provided to hold the elongated member in the channel and a mechanism is included in the channel to translate the compression force on the elongated member into a locking force to lock the connector to the clamp. In one embodiment, a locking member is provided with an oblique bearing surface that engage the elongated member. In another embodiment, the channel includes an oblique bearing surface that forces the elongated member against a portion of a locking member that locks the connector to the clamp.  
         [0006]     In another aspect, the present invention provides a lateral connector assembly for connecting a bone engaging fastener to an elongated member. In one embodiment, the connector assembly includes a lateral connector having a plate portion and a first connection portion, the plate portion defines an opening configured to receive the bone engaging fastener therethrough and the first connection portion defines a first locking surface. The assembly further includes a clamp having a body defining a channel therethrough sized to receive the elongated member therein and a second connection portion defining a connection axis and configured for engagement with the first connection portion of the lateral connector. A variable angle locking member is disposed between the first connection portion and the second connection portion, the variable angle locking member has a second locking surface for engaging the first locking surface of the lateral connector at a plurality of angular orientations, and the variable angle locking member includes a locking member bearing surface opposite the second locking surface. The locking member bearing surface is disposed at least in part within the channel for engaging the elongated member and disposed at an oblique angle with respect to the connection axis. The system further includes a compression member extending between the clamp and the elongated member, the compression member acting to urge the elongated member against the bearing surface.  
         [0007]     Further aspects, forms, embodiments, objects, features, benefits, and advantages of the present invention shall become apparent from the detailed drawings and descriptions provided herein.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]      FIG. 1  is an exploded perspective view of a connector assembly according to one aspect of the present invention.  
         [0009]      FIG. 2  is a partially exploded perspective of the connector assembly of  FIG. 1  in combination with an elongated member and a bone engagement member.  
         [0010]      FIG. 3A  is a perspective view of the connector of  FIG. 2  in an assembled form.  
         [0011]      FIG. 3B  is a partial cross-sectional view of the connector of  FIG. 3A  taken along line  3 B- 3 B.  
         [0012]      FIG. 4  is a partial cross-sectional view of an alternative embodiment of a connector assembly according to another aspect of the present invention.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0013]     For the purposes of promoting an understanding of the principles of the present invention, reference will now be made to the embodiments illustrated in the drawings, and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is intended. Any alterations and further modifications in the described devices, instruments, methods, and any further application of the principles of the invention as described herein are contemplated as would normally occur to one skilled in the art to which the invention relates.  
         [0014]     Referring now to  FIG. 1 , there is shown a connector assembly  100  according to the present invention. Connector assembly  100  includes a plate portion  110 , a clamp body  150 , a variable angle locking washer  130  and a retaining clip  160 . The plate portion includes an elongated opening  112  and a connection flange  114  with a locking face  116  having a series of radially emanating splines  115  surrounding connection opening  118 . As shown in  FIG. 3B , internal connection opening  118  includes an annular groove defining an internal shoulder  120 . The variable angle locking washer  130  includes a locking face  132  having a series of radially emanating splines surrounding opening  138  and configured for interdigitating engagement with splines  115  of locking face  116 . Locking washer  130  further includes a pair of tapering rod bearing surfaces  134  and  136  spaced on either side of opening  138 . Extending between bearing surfaces  134  and  136 , is recessed shoulder  140 .  
         [0015]     Clamp body  150  includes a threaded opening  152  extending into a through channel  154 . Extending away from through channel  154  at a substantial perpendicular angle is the connection extension  157 . In the illustrated embodiment, the connection extension extends along a connection axis L 1  and is divided by gap  155  into upper and lower branches. An upper projection  158  is formed on the upper branch and a lower projection  162  is formed on the lower branch. A retaining clip  160  is adapted to slide along gap  155  and engage internal shoulder  120  of the plate portion  110 .  
         [0016]     Referring now to  FIGS. 2, 3A , and  3 B, the connector assembly  100  is shown is an assembled form. Its assembly with be further described below. In  FIG. 2 , locking washer  130  has been placed about connection extension  157  of the clamp body  150 . The connection extension  157  extends through opening  138  in locking washer  130  and has been positioned in connection opening  118 . It will be appreciated that gap  155  allows the upper and lower branches of the connection extension  157  to flex inwardly to allow projections  158  and  162  to pass beyond internal shoulder  120 . In the illustrated embodiment, the upper and lower branches are formed such that they have a tendency to resiliently return to the position shown in  FIG. 3B , with the projections  158  and  162  disposed in the annular groove behind shoulder  120 . In this manner, the projections  158  and  162  cooperate with shoulder  120  to retain the connection extension in mated contact with the plate portion  110  as shown in  FIG. 3B . With the clamp body  150 , locking washer  130  and plate portion  110  in the position shown in  FIG. 2 , the retaining clip  154  is passed along gap  155  until its legs are seated behind internal should  120  on plate portion  110 . In this manner, the retaining clip  154  fills gap  155  to lock the assembly together and thereby prevents the upper and lower branches from flexing inward to release the projections  158  and  162  from the annular groove behind shoulder  120 . It will be appreciated that the connection extension  157 , lock washer  130  and plate portion  110  are configured such that in the retained position shown in  FIG. 2 , the plate portion  110  may swivel with respect to the lock washer  130  and clamp body  150 . The interconnection between the rectangular shaped shoulder  140  on the lock washer and the rectangular enlarged portion of the connection extension  157  maintains the angular relationship of the lock washer substantially constant with respect to the clamp body  50 . In a one aspect, the connector assembly  100  is preassembled into the retained position of  FIG. 2  during the manufacturing process and packaged for use.  
         [0017]     In the retained positioned the connector assembly  100  is ready for implantation in a patient. In use, a bone fastener, such as bone screw  210  is implanted in the desired position in the patient. Although not illustrated, it is contemplated that bone screw  210  is implanted into the pedicle of a vertebral body along axis L 3  for a posterior fixation procedure. Further, a plurality of bone screws  210  are implanted in adjacent spinal levels to complete a posterior fixation procedure. Once the bone screws  210  have been implanted, an elongated spinal rod  240  is selected and cut to a length sufficient to span the plurality of bone screws  210 . At least one connector assembly  100  is placed on the rod  240 . The connector assembly  100  is in the retained position such that the plate portion  110  may be rotated with respect to the rod clamp body  150 . The plate portion  110  is rotated such that the opening  112  is in substantial alignment with the bone screw  210 . The upper portion of bone screw  210  is passed through opening  112  in the plate portion  110 . An internally threaded nut  220  is connected to the externally threaded post of the bone screw  210  and is advanced to engage the bone screw to the plate portion  110 .  
         [0018]     The externally threaded set screw  230  is threadedly engaged with the internally threaded side walls of opening  152 . Set screw  230  advances along compression axis L 2  as shown in  FIG. 3B . As set screw  230  advances along compression axis L 2 , the rod  240  is urged in the direction of compression axis L 2 . In the embodiment shown in  FIG. 3B , bearing wall  156  of the clamp channel  154  extends in a plane aligned with axis L 5  that is in substantially parallel alignment with axis L 2 . As rod  240  moves in the direction L 2  along bearing surface  156 , the rod  240  engages a portion of locking member bearing surfaces  134  and  136  that extend into channel  154 . Locking member bearing surfaces  134  and  136  extend in a locking member bearing plane in substantial alignment with axis L 4 . In the illustrated embodiment, axis L 5  of the clamp bearing surface and axis L 4  of the locking member bearing surface intersect to form an acute angle within the channel  154 . In this manner, the channel  154  has a first width substantially aligned with connection axis L 1  adjacent the set screw and opening  152 , and a second width substantially aligned with connection axis L 1  and disposed opposite the set screw  230 . The first width is greater than the second width. The first width is greater than the diameter of rod  240  while the second width is less than the diameter of rod  240 .  
         [0019]     In the illustrated embodiment, the sloping wall  156  and corresponding sloping walls  134  and  136  form a channel with side walls that taper from the top, adjacent the set screw, to the bottom of the channel. As the set screw  230  pushes rod  240  into the tapered channel  154 , the set screw compression force is translated by the sloping bearing walls  156 , and locking member bearing walls  134  and  136  into a locking force applied along axis L 1 . In the illustrated embodiment the locking member bearing surfaces  134  and  136  are disposed at an oblique angle with respect to the connection axis L 1  and the compression axis L 2 . The clamp bearing surface is also positioned oblique to connection axis L 1 . This locking force applied against bearing walls  134  and  136  urges the locking member  130  splines into locking engagement with the projecting splines  115  of the connection portion  114  of the plate  110 . It will be appreciated that the set screw compression force on rod  240  causes movement of the locking washer  130  along the locking axis L 1 . Further, movement of the set screw moves rod  240  along bearing surfaces  134  and  136 , and clamp bearing surface  156  toward the bottom of the channel. It will be appreciated that rod  240  is positionable in an infinite number of positions along the bearing surfaces. Moreover, with the locking member  130  fully engaged with the connection portion  114 , further compression force applied by set screw  230  tends to tighten the locking force applied along axis L 1  and to hold rod  230  in a three point contact lock to inhibit movement of the clamp  150  along the rod  240 . The tightened set screw holds the connector assembly in a locked position as shown in  FIGS. 3A and 3B . The three point contact lock is formed by the engagement between the rod  240  with the set screw  230 , the clamp bearing wall  156  and the split locking member bearing wall defined by surfaces  134  and  136 . Also, in a plane taken along axis L 1 , the rod is held in a three point lock position between clamp bearing wall  156  and the locking member bearing walls defined by surfaces  134  and  136  that are spaced wider than the width transverse to axis L 1  of the bearing surface  156 .  
         [0020]     In a further embodiment shown in  FIG. 4 , the clamp body  310  has an internally threaded bore  312  extending along an axis L 6  that is in substantial alignment with axis L 3  of the bone fastener and substantially perpendicular to the locking axis L 2 . Externally threaded set screw  330  is positioned in the bore  312  and exerts a compression force along axis L 6 . The channel of the clamp body is formed substantially as described above. As rod  350  is advanced along axis L 6  into the tapered channel, the rod  350  bears against clamp bearing surface  316  causing the rod to translate along the locking axis L 2  as it slides along the bearing surfaces. Continued compression force along axis L 6  forces the rod  330  against locking member bearing surface  334  and results in translation of the locking member along the locking axis to lock against the connection portion of the plate. It will be appreciated that in the embodiment illustrated in  FIG. 4 , the clamp channel is configured to transfer the compressive force of the locking member into a locking force in a substantially perpendicular direction. Further, in the illustrated embodiment, the set screw  330  and axis L 6  extend in a direction that substantially bisects the acute angle between oblique clamp bearing surface  316  extending along axis L 5  and the oblique locking member bearing surface  334  extending along axis L 4 .  
         [0021]     Although the above illustrated embodiments have been described in detail for the purpose of illustration and understanding of the principles of the present invention, it is contemplated that the invention may be applied in a variety of spinal stabilization assemblies. For example, in one embodiment the clamp body and locking washer combination of the present invention may be applied to the lateral connector of U.S. Pat. No. 5,976,135 to Sherman et al., incorporated herein by reference in its entirety. In another embodiment the connection portion of the plate member is moveable with respect to the portion of the plate member engaging the bone fastener. The moveable connection portion translates along the connection axis in response to the transmission of the set screw compressive force being translated by a clamp body assembly according to the present invention to translate the rod along the locking axis and thereby move the assembly to a locked position. As set forth in U.S. Pat. Nos. 6,579,292 to Taylor and 5,885,285 to Simonson, incorporated herein by reference in their entirety, the moveable connection portion slides along the plate member to capture and hold the bone screw without the need for a separate locking nut. Still further, in another embodiment, the plate member may be substantially ring shaped such that it is joined to a shaft of a bone fastening element.  
         [0022]     Although a set screw has been shown as the compression member in the illustrated embodiment, in another embodiment, the compression member is an external nut with internal threading that engages an externally threaded portion of the clamp body. In still a further embodiment, the compression member is one or more tapered sleeves that slide along the rod to lock the rod in the channel.  
         [0023]     The connector assembly is useful for rigid rods and flexible connectors. For example, in one embodiment, rod  240  is formed of a rigid material such as titanium or stainless steel. In another embodiment, rod  240  is flexible. In such an embodiment, rod  240  is formed of plastic or a flexible metal. In still a further embodiment, the elongate member is not a rod but a flexible cable or cord that may be tensioned between adjacent spinal levels and connectors. Still further, lateral refers to the connection of the elongated member along one side of the shaft of the bone fixation element such as screw  210  as opposed to fixing the elongated member in line with the axis of the bone screw.  
         [0024]     The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions and alterations herein without departing from the spirit and scope of the present disclosure.