Intervertebral disc implant

Abstract

An intervertebral disc implant having a body with a greater height than width comprised of a resilient material and an elongate cavity for receiving a key to maintain the spacing between the vertebrae adjacent an intervertebral disc when implanted into the space from which a portion of the disc is removed. To distribute and cushion against compression loads, and to mimic the normal kinematics of the intact, healthy intervertebral disc, the key is removed after the body is implanted into the disc space and a frame that both provides resistance to compression and tension loads and translates the axis of rotation of the spinal column anteriorally and posteriorally as the patient bends and rotates is inserted into the cavity in the implant body. The frame does not extend all the way into the cavity in the body and the portion of the cavity into which the frame does not extend is filled with a hydrogel.

1 . An intervertebral disc implant comprising an elongate body comprised of a resilient material having a cavity extending longitudinally into said body and a frame received within the cavity in said body comprised of two spaced apart arms with a bridge connecting the arms at one end, said frame being comprised of a material that tends to return to its original shape after said frame is subjected to either a compression or tension load, said frame extending only part way into the cavity of said body in which it is received.  
   
   
       2 . The intervertebral disc implant of  claim 1  wherein said frame is provided with a port for receiving an injection of hydrogel therein.  
   
   
       3 . The intervertebral disc implant of  claim 2  wherein said port is positioned so that the hydrogel injected into said port fills the portion of the cavity into which said frame does not extend.  
   
   
       4 . The intervertebral disc implant of  claim 1  additionally comprising a metal strip attached to at least a portion of the surfaces of said body that bear against adjacent vertebrae when implanted into the intervertebral disc space, said metal strip being provided with structure for contacting the adjacent vertebrae to resist movement of said body relative to the adjacent vertebrae.  
   
   
       5 . The intervertebral disc implant of  claim 4  wherein at least a portion of said metal strip is provided with a coating of or comprises porous or roughened titanium, calcium phosphate, titanium wire mesh, plasma-sprayed titanium, porous cobalt-chromium, or hydroxyapatite.  
   
   
       6 . The intervertebral disc implant of  claim 1  additionally comprising a key positioned in the cavity in said body and extending substantially all the way into the cavity, said key being withdrawn from the cavity after said body is implanted into the space between two adjacent vertebrae and before said frame is inserted into the cavity in place of said key.  
   
   
       7 . The intervertebral disc implant of  claim 1  additionally comprising a “U”-shaped ear extending at approximately a right angle from the end of one of the arms opposite the bridge and having a hole formed therein for receiving a screw for attaching said frame to a first adjacent vertebra and a “Y”-shaped ear extending at approximately a right angle from the end of the other arm opposite the bridge having holes formed in both forks of the Y-shaped ear for receiving screws for attaching said frame to a second adjacent vertebra.  
   
   
       8 . The intervertebral disc implant of  claim 1  additionally comprising a projection extending from the bridge between the arms of said frame.  
   
   
       9 . The intervertebral disc implant of  claim 1  wherein the arms of said frame are angled apart from each other.  
   
   
       10 . A method of mimicking the function of the intervertebral disc of the intact spinal column after removal of some or all of the intervertebral disc from between two adjacent vertebrae comprising the steps of: 
 inserting a first resilient body having a cavity formed therein and a key received in the cavity into the intervertebral disc space with the height of the body oriented substantially parallel to the longitudinal axis of the spinal column;    removing the key from the cavity after the body is inserted into the intervertebral disc space;    inserting a frame part way into the cavity in the body, the frame comprising first and second arms spaced apart arms connected by a bridge at one end for providing resistance to flexion and/or extension of the spinal column; and    filling the portion of the cavity in the body into which the frame does not extend with a hydrogel.    
   
   
       11 . The method of  claim 10  additionally comprising attaching the frame to the adjacent first and second vertebrae.  
   
   
       12 . The method of  claim 10  additionally comprising resisting anterior or posterior movement of the body in the intervertebral disc space.  
   
   
       13 . The method of  claim 10  additionally comprising limiting the movement of the arms of the frame as the spinal column flexes.  
   
   
       14 . The method of  claim 10  additionally comprising resisting relative movement between the frame and the implant body.