The effects of mal-placement on the kinematics of the intervertebral disc allograft transplanation

Abstract

Remodelling in the intervertebral disc (IVD) allograft was observed in a clinical study on IVD allograft transplantation. We hypothesize that through remodelling, kinematics of a mal-aligned IVD allograft will be restored to normal. 15 male goats were randomly assigned into a control group A (n=5), centred allograft group B (n=5) and mal-positioned allograft group C (n=5). Transplantation of a size-matched cryopreserved IVD allograft was performed in the lumbar region (L4-L5) following disc excision. In group B the IVD allografts were placed centred and flush with the vertebral margin. In group C the allografts were placed proud anteriorly by 25% of the anterior-posterior diameter of the allograft. The whole lumbar spine from L1-L6 was harvested at 6 months after transplantation. 3D kinematics assessments of the lumbar spines in the flexion-extension direction were then performed using a MTS testing machine and an optoeletronic camera system. The range of motion (ROM), neutral zone (NZ), and instantaneous axis of rotation (IAR) were calculated for the L4-L5 segment. When compared to the control intact spine, no significant difference in the ROM, NZ and IAR was found in the flexion-extension motion between the mal-positioned group and the centred group. Key kinematic parameters of both the centrally placed and the mal-positioned allograft were similar to the intact spine. Mal-placement of the allograft during surgery is compatible with good functional outcome through remodelling. In contrast to artificial disc replacement, precise positioning of allograft may not be essential for functional success of the IVD allograft transplantation.