The kinematics of the mal-placement of the intervertebral disc allograft transplant on the segmental mobility

Abstract

In a recent clinical trial of the Intervertebral disc (IVD) allograft transplantation, Ruan et al. (2007) observed remodelling of the transplanted allograft with reasonable preservation of segmental motion. We hypothesized that remodelling of a mal-positioned allograft implant can restore the function and stability of the grafted functional spinal unit (FSU). 18 male goats (age 6-12 months, weight 25-30 kg) were used in this study. The goats were randomly assigned into a control group (n=5), a centrally placed allograft group (n=5) and a mal-positioned allograft group (in=5). IVD were obtained from sacrificed goats (n=3) and were cryopreserved in liquid nitrogen. Transplantation of a size matching fresh-frozen IVD allograft was performed in the lumbar region (L4-L5) after disc excision. In the centrally placed allograft group, the IVD allografts were placed centered and flush with the vertebral margin. In the al-positioned allograft group, the allografts were placed anteriorly by 25% of the anterior-posterior length of the allograft. Post-operational lateral, flexion-extension x-rays were taken at 4 and 12 weeks for analysis. No significant differences in the range of motion were found among the groups at different time points. The disc height of the grafted segment showed an initial decrease at 4 wks (80%) but this decrease was stabilised at 12 wks (79%). Both the centrally placed and the mal-positioned allograft were able to preserve segmental motion. Mal-positioned allograft transplantation is compatible with good functional outcome through remodelling. In contrast to artificial disc replacement, precise positioning of allograft is not essential for functional success.