Abstract:
A facet support assembly including at least one rod including an upper portion rigidly fixed to a spinal fastener, and a lower portion configured to support an inferior articular process, wherein when the spinal fastener is secured to a pedicle of a lumbar vertebra, the lower portion of the at least one rod abuts against and supports the inferior articular process of the same lumbar vertebra.

Description:
FIELD OF THE INVENTION 
     The present invention is generally related to apparatus and methods for spinal prostheses or implants, and particularly to a posterior-medial facet support assembly. 
     BACKGROUND OF THE INVENTION 
     Through the course of life, disease or injury, the spinal canal, the laminae, or facets of one or more vertebral bodies can degenerate or become damaged, such that the spinal cord and/or nerve roots become compressed. This can result in an undesired anatomy, loss of mobility, and pain or discomfort. For example, spinal stenosis, as well as spondylosis, spondylolisthesis, osteoarthritis and other degenerative phenomena may cause back and leg pain. Such phenomena may be caused by a narrowing of the spinal canal by a variety of causes that result in the pinching of the spinal cord and/or nerves in the spine. 
     Decompression and fusion of two or more adjacent vertebrae are common options for treating these problems. However, it is known that fusion tends to cause the degeneration to migrate to adjacent vertebral levels. Thus, non-fusion solutions are desirable for the treatment of the above mentioned degenerative problems. 
     SUMMARY OF THE INVENTION 
     The present invention seeks to provide an improved posterior-medial facet support assembly, as described in more detail further below. The present invention provides a posterior and medial support for the native facets after a bony decompression procedure. The present invention seeks to provide a minimal invasive, motion preserving, novel spinal implant. The assembly is mainly advantageous for the posterior portion of the spine, but is not limited to this specific area. 
     One of the chief functions of the native facets is to stabilize the spinal segment and prevent excessive motion in the different directions. Each vertebra has two bilateral superior processes that create two bilateral joints with the two bilateral inferior processes of the vertebra above and two bilateral inferior processes that create two joints with the bilateral superior processes of the vertebra bellow. The two bilateral inferior processes of each vertebra are supported by the lamina and the pars to have the proper mechanical strength. 
     After a decompression procedure, a significant amount of the facet&#39;s bony support may be removed and thus its ability to stabilize the spine is compromised. The present invention seeks to provide the needed support for the facets so that they can properly stabilize the segment even after a wide decompression. 
     There is thus provided in accordance with a non-limiting embodiment of the present invention a facet support assembly including at least one rod including an upper portion rigidly fixed to a spinal fastener, and a lower portion configured to support an inferior articular process, wherein when the spinal fastener is secured to a pedicle of a lumbar vertebra, the lower portion of the at least one rod abuts against and supports the inferior articular process of the same lumbar vertebra. 
     In one embodiment, the spinal fastener includes a head of a polyaxial screw. 
     In a preferred embodiment, the facet support assembly includes left and right rods whose upper portions are rigidly fixed to left and right spinal fasteners, respectively, wherein when the left and right spinal fasteners are respectively secured to left and right pedicles of a lumbar vertebra, the lower portions of the left and right rods abut against and support the left and right inferior articular processes of the same lumbar vertebra. In one embodiment, the upper portion of the at least one rod is curved. In another embodiment, a cross bar connects the left and right facet support assemblies. 
     In yet another embodiment, a cross bar is attached to the left and right spinal fasteners, and the upper portions of the left and right rods are rigidly secured to the cross bar by mechanical fasteners. 
     There is also provided in accordance with a non-limiting embodiment of the present invention a facet support assembly including at least one rod including an upper portion rigidly fixed to a spinal fastener, and a lower portion formed with a depression, and a lower supporting element including a head shaped to mate with the depression, wherein when the spinal fastener is secured to a pedicle of a lumbar vertebra, the lower supporting element is positioned to support and abut against an inferior articular process of the same lumbar vertebra, and the head of the lower supporting element abuts against the depression of the lower portion of the at least one rod. 
     In one embodiment, a mechanical fastener secures the head of the lower supporting element with the depression of the lower portion of the at least one rod. In one embodiment, the depression is concave and generally spherical and the head is convex and generally spherical. 
     In another embodiment, left and right rods abut against left and right lower supporting elements. 
     In yet another embodiment, the spinal fastener includes a cross bar attached to left and right polyaxial screws, and the upper portions of the left and right rods are rigidly secured to the cross bar by mechanical fasteners. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be understood and appreciated more fully from the following detailed description, taken in conjunction with the drawings in which: 
         FIGS. 1A and 1B  are simplified posterior-view and lateral-view illustrations of a posterior-medial facet support assembly, respectively, constructed and operative in accordance with an embodiment of the present invention; and 
         FIGS. 2A and 2B  are simplified posterior-view and lateral-view illustrations of a posterior-medial facet support assembly, respectively, constructed and operative in accordance with another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       FIG. 1A  illustrates the area of two adjacent lumbar vertebrae, showing the body  10  of the vertebra, the transverse process  11 , superior articular process  12 , and inferior articular process  13  of the superior vertebra, and the superior articular process  14  and spinous process  15  of the inferior vertebra.  FIG. 1B  illustrates the area of the L1-L5 vertebrae, showing the L1 superior articular process  16 , L1 inferior articular process  17 , a facet joint  18  between L2 and L3, and the auricular surface  19  for the iliac bone. 
     As seen in  FIG. 1B , a laminectomy decompression has been performed on L4, wherein the spinous process and the lamina have been removed. Two polyaxial pedicle screws  9  have been screwed into the pedicles of L4. 
     In accordance with an embodiment of the present invention, as illustrated in  FIGS. 1A-1B , a posterior-medial facet support assembly  20  is provided for helping support the facets. The facet support assembly  20  includes at least one rod  22 , whose upper portion  24  is rigidly fixed to the head of the polyaxial screw  9 . It is noted that the term “rod” throughout the specification and claims is not limited to a round slender element, but also encompasses any slender element of any geometrical shape, such as but not limited to, a bar, wire, etc. of square, round, elliptical, hexagonal and other shapes. 
     Although for certain situations, it is possible to carry out the invention with just one rod  22  on either the left or right side pedicle, for most situations, two rods  22 , one on the left pedicle and the other on the right pedicle are employed. The upper portion  24  of rod  22  may be curved or bent to suit the geometry of the inferior articulating process and nearby structure. 
     The lower portion of rod  22  by itself may be used to support the inferior articular process  13 , by abutting against the inferior articular process  13 . Note that the upper portion of rod  22  is fixed (e.g., by means of polyaxial screw  9 ) to the pedicle of the same vertebra as the inferior articular process  13 . 
     In accordance with an embodiment of the present invention, the lower portion of rod  22  is not used by itself to support the inferior articular process  13 . Instead, the lower portion of rod  22  is formed with a concave, generally spherical depression  26 , which may be secured to a lower supporting element  28  with a mechanical fastener  30  (e.g., screw). The head of the lower supporting element  28  is convex and generally spherical to match (mate with) and abut against the generally spherical depression  26 . (Other shapes than convex and concave may also be used to carry out the invention.) Lower supporting element  28  is positioned to support and abut against the inferior articular process  13  of the same lumbar vertebra. Optionally, a cross bar  32  may be used to connect the left and right sides of the facet support assembly  20 . 
     The facet support assembly  20  is highly adaptable to the native morphology and geometry of the patient. The polyaxial screw head of polyaxial screw  9  may be oriented to fix rod  22  at the required rotational and translational position. The interface of lower supporting element  28  with the depression  26  of the lower portion of rod  22  may also be adjusted to any spatial orientation before fixing with mechanical fastener  30  and optionally cross bar  32 . 
     Reference is now made to  FIGS. 2A and 2B , which illustrate a posterior-medial facet support assembly  40 , constructed and operative in accordance with another embodiment of the present invention. The facet support assembly  40  is constructed similarly to the facet support assembly  20 , and like elements are designated by like numerals. 
     The facet support assembly  40  differs from facet support assembly  20  in that rods  42  of facet support assembly  40  are not fixed at their upper portions  44  to the pedicle screws  9 . Instead, a cross bar  46  is attached to and connects the two pedicle screws  9 . Cross bar  46  is held rigidly by the heads of the polyaxial screws  9 . The upper portions  44  of rods  42  are rigidly secured to cross bar  46  by mechanical fasteners (e.g., set screws)  48 . Because of the different attachment points, the rods  42  are shaped somewhat differently from rods  22  of facet support assembly  20 . 
     The facet support assembly  40  is also highly adaptable to the native morphology and geometry of the patient. The polyaxial screw head of polyaxial screw  9  may be oriented to fix cross bar  46 , and subsequently rod or rods  42  fixed to cross bar  46  with mechanical fastener  48 , at the required rotational and translational position. The interface of lower supporting element  28  with the depression  26  of the lower portion of rod  42  may also be adjusted to any spatial orientation before fixing with mechanical fastener  30  (and optionally a lower cross bar  32 ). 
     It will be appreciated by persons skilled in the art that the present invention is not limited by what has been particularly shown and described hereinabove. Rather the scope of the present invention includes both combinations and subcombinations of the features described hereinabove as well as modifications and variations thereof which would occur to a person of skill in the art upon reading the foregoing description and which are not in the prior art.