Abstract:
A clamp for attaching a cross connecting device to a spinal fixation system comprising an outer body and an inner body. The outer body defines an internally threaded bore and an outer body cavity, and the inner body defines an inner body cavity. The inner body is at least partially disposed within the outer body. A pin is provided for connecting the inner and outer bodies to each other, while allowing for a limited amount of movement therebetween. A set screw suitable for being driven into the internally threaded bore is provided for securing the inner body to the spinal fixation system.

Description:
PRIORITY TO RELATED APPLICATIONS 
     The present application claims priority to U.S. Provisional Patent Application No. 61/473,004 entitled “CLAMP FOR SPINAL CROSS CONNECTION DEVICE,” which was filed on Apr. 7, 2011, and is hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     1. Technical Field 
     The present application relates to connection systems for spinal fixation devices, including cross connecting devices for spinal fixation bone anchors such as bone screws and hooks. 
     2. Related Art 
     The bones and connective tissue of an adult human spinal column includes more than twenty vertebrae coupled sequentially to one another by a tri-joint complex. The complex includes an anterior disc and two posterior facet joints. The anterior discs of adjacent bones are cushioned by cartilage spacers referred to as intervertebral discs. The vertebrae are each anatomically categorized into one of four classifications: cervical, thoracic, lumbar, and sacral. The cervical portion of the spine, which comprises the top of the spine up to the base of the skull, includes the first seven vertebrae. The intermediate twelve vertebrae are thoracic vertebrae, and connect to the lower spine comprising five lumbar vertebrae. The base of the spine includes the sacral bones (including the coccyx). 
     The spinal column is highly complex in that it includes over twenty vertebrae coupled to one another for housing and protecting critical elements of the nervous system. These elements of the nervous system have seemingly innumerable peripheral nerves and circulatory bodies in close proximity to each other. Despite its complexity, the spine is a highly flexible structure, capable of a high degree of curvature and twisting in many different directions. 
     However, genetic or developmental irregularities, trauma, chronic stress, tumors and disease can result in spinal pathologies that either limit this range of motion, or threaten the critical elements of the nervous system protected by the spinal column. A variety of systems have been disclosed in the art which provide some degree of immobilization of the spine by implanting artificial assemblies in or onto the spinal column. These assemblies include anterior, posterior, and lateral assemblies. Lateral and anterior assemblies can be coupled to the anterior portion of the spine, typically between vertebral bodies. Posterior spinal fixation systems generally include a pair of rods, which can be aligned along an axis to which the bones are to be disposed, and which are then attached to the spinal column by spinal fixation bone anchors, such as pedicle hooks and/or pedicle screws. Hooks can be coupled to the lamina or attached to transverse processes, while screws can be inserted through pedicles. In order to provide enhanced torsional rigidity, these structures can include cross-connecting devices for coupling the rods together in a direction that is generally transverse with respect to the axis of the rods. These cross-connecting devices can be coupled directly to the rods themselves, or can be attached to the bone anchors. 
     A number of improvements to prior cross-connecting devices are desirable. For example, it is desirable to provide clamps for cross-connecting devices that are highly adjustable in several degrees of freedom. 
     SUMMARY 
     Spinal fixation devices, cross connecting devices for spinal fixation devices, and components thereof, including clamps for cross connecting devices, are described herein. 
     According to one aspect of the present disclosure, a clamp for attaching a cross connecting device to a spinal fixation system comprises an outer body that defines an internally threaded bore and an outer body cavity, an inner body that is at least partially disposed within the outer body cavity, the inner body defining an inner body cavity, a pin for connecting the outer and inner bodies to each other, and a set screw suitable for being driven into the internally threaded bore for securing the inner body to the spinal fixation system. 
     The spinal fixation system can include a rod, and the outer body can include a clearance slot for allowing the rod to extend through the outer body cavity. The inner body can include a slotted rod-receiving interface. The slotted rod-receiving interface can include a rod-receiving portion configured to snap onto the rod. The rod-receiving portion of the slotted rod-receiving interface can be configured to be tightened onto the rod as the set screw is driven into the internally threaded bore. The slotted rod-receiving interface can further include at least one expansion portion. 
     The outer body can include a slot that extends between the internally threaded bore and the outer body cavity. The inner body can include a lever portion that extends through the slot into the internally threaded bore. 
     The clamp can further comprise a stop feature for limiting pivoting movement between the outer and inner bodies about the pin. The stop feature can include a tab and a mating groove. 
     According to another aspect of the present disclosure, a spinal fixation system can comprise a spinal fixation device, a rod connected to the spinal fixation device, a cross-connecting device, and a clamp for connecting the cross-connecting device to the rod. The clamp can comprise an outer body that defines an internally threaded bore and an outer body cavity, an inner body that is at least partially disposed within the outer body cavity, the inner body defining an inner body cavity configured to receive at least a portion of the spinal fixation device body, a pin for connecting the outer and inner bodies to each other, and a set screw suitable for being driven into the internally threaded bore for securing the inner body to the rod. 
     The outer body of the clamp can include a clearance slot for allowing the rod to extend through the outer body cavity. The inner body of the clamp can include a slotted rod-receiving interface. The slotted rod-receiving interface includes a rod-receiving portion can be configured to snap onto the rod. The rod-receiving portion of the slotted rod-receiving interface can be configured to be tightened onto the rod as the set screw is driven into the internally threaded bore. The slotted rod-receiving interface can further include at least one expansion portion. 
     The outer body of the clamp can include a slot that extends between the internally threaded bore and the outer body cavity. The inner body of the clamp can include a lever portion that extends through the slot into the internally threaded bore. 
     The clamp of the spinal fixation system can further comprise a stop feature for limiting pivoting movement between the outer and inner bodies about the pin. The stop feature can include a tab and a mating groove. 
     The spinal fixation device can include a spinal fixation device body, and the inner body can be configured to receive at least a portion of the spinal fixation device body. 
     These and other features, aspects, and embodiments of the invention are described below in the section entitled “Detailed Description.” 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Features, aspects, and embodiments of the inventions are described in conjunction with the attached drawings, in which: 
         FIGS. 1A and 1B  show a spinal fixation system having a cross connecting device that is attached to rods using clamps according to the present disclosure; 
         FIG. 2  shows an enlarged perspective view of the clamp attached to a body and rod of the spinal fixation device shown in  FIGS. 1A and 1B ; 
         FIG. 3  shows an exploded view of the clamp shown in  FIG. 2 ; 
         FIG. 4  shows a cross-sectional view of the clamp shown in  FIGS. 2 and 3 ; and 
         FIG. 5  shows a cross-sectional view of the clamp shown in  FIGS. 2-4  attached to a body and rod of the spinal fixation device shown in  FIGS. 1A and 1B . 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 1A and 1B  show a spinal fixation system  10  that includes a plurality of spinal fixation devices  12  and a pair of rods  14 . A cross connecting device  20  is also provided for connecting opposing rods  14  and spinal fixation devices  12 . 
     The spinal fixation devices  12  can include pedicle screws as shown, and can include other types of bone anchors, including hooks. Each fixation device  12  includes a body  12   a , a shank  12   b , and a set screw  12   c . There are various known body styles, including the open style shown. Alternative styles include closed, reduction, and offset body styles. The shank  12   b  can be cannulated or non-cannulated. The shank  12   b  can be monoaxial or mutliaxial relative to the body  12   a . Each shank  12   b  can include a single-lead thread as shown, or can include multiple-lead threads, where there are two or more threads that wind along the shank, usually equally spaced apart from each other. Instead of a shank  12   b , one or more of the bodies  12   a  can include, or be attached to, a hook that can be attached to vertebrae, for example in the cervical area where vertebrae are small. 
     Once the spinal fixation devices  12  are secured to bone, the rods  14  can be placed along the bodies  12   a  and secured in place by the set screws  12   c . Then, once the rods  14  are secured to the spinal fixation devices  12 , the cross connecting device  20  can be placed over bodies  12   a  of a pair of spinal fixation devices  12  as shown in  FIGS. 1A and 1B . 
     The cross connecting device  20  includes a fixable pivot junction  22 , a first connection member  24 , a second connection member  26 , and clamps  28 . The cross connecting device  20  can be lengthwise and angularly adjusted, thereby accommodating for translational, rotational, and angular misalignments between the connected spinal fixation devices  12 . More specifically, the first and second connection members  24  and  26  are connected by the fixable pivot junction  22  such that the fixable pivot junction  22  allows the first and second connection members  24  and  26  to be translationally, rotationally, and angularly repositioned relative to each other. Once desired adjustments are made, the fixable pivot junction  22  can be locked, and the clamps  28  can be secured to the rods  14  as described in greater detail below. 
       FIG. 2  shows an enlarged perspective view of a clamp  28  attached to the body  12   a  and rod  14  of the spinal fixation device  12 .  FIG. 3  shows an exploded view of the clamp  28 , and  FIG. 4  shows a cross-sectional view of the clamp  28 . The clamp  28  includes an outer body  30 , an inner body  32 , a pin  34 , and a set screw  36 . 
     The outer body  30  includes an outer-body cavity  38  within which the inner body  32  resides. The outer body  30  also has a clearance slot  40  to allow the rod  14  to connect to the inner body  32 . The outer body  30  also has an internally-threaded bore  42  for receiving the correspondingly-threaded set screw  36 . 
     The outer body  30  and the inner body  32  are secured together by the pin  34 . The outer and inner bodies  30  and  32  include pin holes  44  that are aligned and receive the pin  34 . The pin holes  44  can be sized such that the pin  34  is press-fit into one or more of the pin holes  44  so that once the pin  34  is installed into the holes  44 , it cannot easily be removed from the holes  44 . An alternative type of connecting element can be used in place of the pin  34 , such as a bolt or rivet. 
     The clamp  28  preferably includes a stop feature for preventing, or at least limiting, pivoting movement between the outer and inner bodies  30  and  32  about the pin  34 . In the illustrated embodiment, a tab  46  on the underside of the outer body  30  engages a mating groove  48  of the inner body  32 , thereby restricting the outer and inner bodies  30  and  32  from pivoting about the pin  34 . Thus, the combination of the tab  46  and mating groove  48  constitute an embodiment of a stop feature. Alternatively, the tab  46  can be provided on the inner body  30  and the mating groove can be provided on the outer body  32 , opposite the configuration shown. Other alternative embodiments can include a pin, rivet, bolt, or other device that can be used for restricting pivoting about the pin  34 . Such alternatives can be used with, or in place of, the combination of the tab  46  and mating groove  48 . 
     The inner body  32  has a slotted rod receiving interface  50 . The interface  50  includes a rod-receiving portion  50   a , a first expansion portion  50   b , and a second expansion portion  50   c . The rod-receiving portion  50   a  is defined by an at least somewhat circular geometry that is slightly smaller than the diameter of the rod  14  and is configured to snap onto the rod  14 . The expansion portions  50   b  and  50   c  are provided above the rod-receiving portion  50   a . The expansion portions  50   b  and  50   c  allow the rod-receiving portion  50   a  to expand without permanently deforming the inner body  32  as the clamp  28  is snapped onto a rod  14 . The slightly undersized rod-receiving portion  50   a  results in a friction fit with the rod  14 . 
     The inner body  32  has an inner-body cavity  52  that is configured to fit over a body  12   a  of a spinal fixation device  12 . The fit between the inner body  32  and the body  12   a  of the spinal fixation device  12  is preferably such that a relatively small amount of clearance exists between them along the longitudinal axis of the rod  14 , and that more substantial clearance exists in the medial region  52   a  and lateral region  52   b  (shown in  FIG. 5 ) of the inner-body cavity  52 . The additional clearance in the medial and lateral regions  52   a  and  52   b  allows for some variation in the orientation of the body  12   a , for example in a plane perpendicular to the longitudinal axis of the rod  14 . 
     The outer body  30  includes a slot  54  that extends between the threaded bore  42  and the outer-body cavity  38 . The slot  54  provides an opening for a lever portion  56  of the inner body  32 . The lever portion  56  is a protruding tapered geometry that extends into the threaded bore  42  through the slot  54 . 
     Referring now also to  FIG. 5 , during a surgical procedure the spinal fixation devices  12  and rods  14  are placed in a configuration such as is shown in  FIGS. 1A and 1B . The cross connecting device  20  is then placed over two spinal fixation devices  12  and each clamp  28  is snapped onto a construct rod  14 . In order for this to occur, the set screw  36  is partially backed out of the threaded bore  42  to allow the inner body  32  to spring open to accept the rod  14  into the rod-receiving portion  50   a  of the rod receiving interface  50 . The set screw  36  can then be tightened by driving the set screw  36  into the threaded bore  42 . As the set screw  36  is threaded into the outer body  30 , it eventually contacts the lever portion  56  of the inner body  32 . Once the set screw  36  contacts the lever portion  56 , the continued driving of the set screw  36  causes the set screw  36  to drive against the lever portion  56  and urge the lever portion  56  to cause the inner body  32  to pivot relative to the outer body  30  about the pin  34 . However, the pivoting motion is restricted due to the limiting action of the tab  46  of the outer body  30  against the mating groove  48  of the inner body  32 . Thus, continued tightening of the set screw  36  against the lever portion  56  causes the rod-receiving portion  50   a  to tighten against the rod  14 , thereby clamping the clamp  28  onto the rod  14 . 
     The inner body  32  also includes a tapered surface  58  opposite the lever portion  56 . The tapered surface  58  includes connection-member-receiving region  60 . The connection-member-receiving region  60  is provided for attaching the clamp  28  to a connection member such as one of the first and second connection members  24  and  26  shown in  FIGS. 1A and 1B . The mechanism used for attaching a connection member to the clamp  28  can vary, but examples can include press-fitting the connection member into the connection-member-receiving region  60 ; securing the connection member into the connection-member-receiving region  60  using a set screw, pin, or bolt; and providing corresponding threaded surfaces on the connection member and connection-member-receiving region  60  so that the connection member can be threaded into the connection-member-receiving region  60 . 
     While various embodiments in accordance with the disclosed principles have been described above, it should be understood that they have been presented by way of example only, and are not limiting. Thus, the breadth and scope of the invention(s) should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the claims and their equivalents issuing from this disclosure. Furthermore, the above advantages and features are provided in described embodiments, but shall not limit the application of such issued claims to processes and structures accomplishing any or all of the above advantages. 
     Additionally, the section headings herein are provided for consistency with the suggestions under 37 C.F.R. 1.77 or otherwise to provide organizational cues. These headings shall not limit or characterize the invention(s) set out in any claims that may issue from this disclosure. Specifically and by way of example, although the headings refer to a “Technical Field,” such claims should not be limited by the language chosen under this heading to describe the so-called technical field. Further, a description of a technology in the “Background” is not to be construed as an admission that technology is prior art to any invention(s) in this disclosure. Neither is the “Summary” to be considered as a characterization of the invention(s) set forth in issued claims. Furthermore, any reference in this disclosure to “invention” in the singular should not be used to argue that there is only a single point of novelty in this disclosure. Multiple inventions may be set forth according to the limitations of the multiple claims issuing from this disclosure, and such claims accordingly define the invention(s), and their equivalents, that are protected thereby. In all instances, the scope of such claims shall be considered on their own merits in light of this disclosure, but should not be constrained by the headings set forth herein.