Selectively expanding spine cage with enhanced bone graft infusion

#The present invention generally relates to medical devices for stabilizing the vertebral motion segment. More particularly, the field of the invention relates to a remotely activated, hydraulically controllable, selectively expanding cage (SEC) and method of insertion for providing controlled spinal correction in three dimensions for improved spinal intervertebral body distraction and fusion.

#Conventional spine cages or implants are typically characterized by a kidney bean-shaped body comprising a hydroxyapatite-coated surface provided on the exterior surface for contact with adjacent vertebral segments or endplates which are shown in FIG. 1. A conventional spine cage is typically inserted in tandem posteriorly through the neuroforamen of the distracted spine after a trial implant creates a pathway.

#Such existing devices for interbody stabilization have important and significant limitations. These limitations include an inability to expand and distract the endplates. Current devices for interbody stabilization include static spacers composed of titanium, PEEK, and high performance thermoplastic polymer produced by VICTREX, (Victrex USA Inc, 3A Caledon Court, Greenville, S.C. 29615), carbon fiber, or resorbable polymers. Current interbody spacers do not maintain interbody lordosis and can contribute to the formation of a straight or even kyphotic segment and the clinical problem of “flatback syndrome.” Separation of the endplates increases space available for the neural elements, specifically the neural foramen. Existing static cages do not reliably improve space for the neural elements. Therefore, what is needed is an expanding cage that will increase space for the neural elements posteriorly between the vertebral bodies, or at least maintain the natural bone contours to avoid neuropraxia (nerve stretch) or encroachment.

#For the purpose of illustrating the invention, the drawings show aspects of one or more embodiments of the invention. However, it should be understood that the present invention is not limited to the precise arrangements and instrumentalities shown in the drawings, wherein:

#FIG. 1 is a representation of the vertebral column showing posterior insertion and placement of the SEC between the number 4 and 5 lumbar vertebrae according to an aspect of the invention. Whereas this diagram shows the implant anteriorly in the vertebral interspace between lumbar bones 4 and 5, the majority of lumbar fusions are performed between L5 and S1, into which implants are secured. The SEC can be used at any spinal level the surgeon deems in need of fusion;

#FIG. 2 is a side view of a vertebral body showing the placement of the SEC according to an aspect of the invention;

#Referring to FIG. 1, vertebral segments or end plates are shown with an average 8 mm gap representing an average intervertebral space. A complete discectomy is performed prior to the insertion of the SEC 100. The intervertebral disc occupying space 102 is removed using standard techniques including rongeur, curettage, and endplate preparation to bleeding subcondral bone. The posterior longitudinal ligament is divided to permit expansion of the intervertebral space.

#The intervertebral space 102 is distracted to about 10 mm using a rotating spatula (Not shown. This is a well-known device that looks like a wide screw driver that can be placed into the disc space horizontally and turned 90 degrees to separate the endplates).

#The SEC is inserted posteriorly (in the direction of arrow 102 between the no. 4 and 5 lumbar vertebrae as shown in FIG. 1 (lateral view) or into any selected intervertebral space. In accordance with an aspect of the invention, the SEC is reduced to small size in its unexpanded state to enable it to be inserted posteriorly through space 102 as shown in FIG. 1. In one exemplary embodiment, dimensions of an SEC are: 12 mm wide, 10 mm high and 28 mm long to facilitate posterior insertion and thereby minimize trauma to the patient and risk of injury to nerve roots. Once in place this exemplary SEC can expand to 16 mm, or 160 percent of its unexpanded size, enabling 20 degrees or more of spinal correction medial and lateral. FIGS. 2 and 3 are a side view and top view, respectively, showing the placement of the SEC 100 on a vertebral body.