Effects of mal-placement of intervertebral disc allograft transplant on the kinematics of the spine

Abstract

In a recent clinical trial of intervertebral disc (IVD) allograft transplantation by Ruan etal. (2007), remodelling of the transplanted allograft with reasonable preservation of segmental motion was observed. It is hypothesized that remodelling of a mal-positioned IVD allograft can restore the function and stability of the grafted functional spinal unit. 18male goats(6-12months,25-30kg) were randomly assigned into 3groups: non-operated control group (n=6), centrally-placed allograft treatment group (n=6) and mal-positioned allograft treatment group (n=6). Transplantation of cryopreserved IVD allografts were performed in the lumbar region (L4-L5). In the centrally-placed treatment group, the IVD allografts were placed centred and flush with the vertebral margin. In the mal-positioned group, the allografts were placed anteriorly by 25% of the anterior-posterior length of the allograft. Lateral and flexion/extension radiographs were taken at 4, 12 and 24weeks post-operatively. Measurement of disc height index (%DHI), range of motion (ROM) and centre of rotation (COR) were made using an image analysis program developed in MATLAB. The results were compared to the non-operated control group using student t-test with P<0.05 being considered as significant. The %DHI of both groups showed an initial decrease at 4wks(80%) but stabilised at 12wks (79%) and 24wks (80%). No significant differences in the ROM was observed, both the centrally placed and the mal-positioned allograft were able to preserve segmental motion. No significant differences were found in the COR among the groups at different time points with the quality of the motion also preserved. Mal-positioned allograft transplantation was compatible with good functional outcome. In contrast to artificial disc replacements, precise positioning of allograft during transplantation is not essential for functional success.