In-vivo kinematics of the intervertebral disc allograft transplantation

Abstract

Summary: Kinematics of the intervertebral disc allograft transplantation was investigated. Introduction: In a recent clinical trial of the Intervertebral disc (IVD) allograft transplantation, Ruan et al.(2007) observed remodelling of the allograft and concluded that the transplanted allograft disc can preserve motion and stability of the spinal segment. It is hypothesized that remodelling of the allograft implant can restore the kinematics of the functional spinal unit. This study aims at studying the in-vivo kinematics of the patients that underwent IVD allograft transplantation in the clinical study. Methods: Five patients, average age 47 years, with cervical disc herniation underwent transplantation of fresh-frozen composite disc allografts after disc excision as described in Ruan et al.(2007). Dynamic active flexion-extension radiographs were taken 2 months after surgery, and every 3 months thereafter to a minimum followup of 5 years. Measurement of the Center of Rotation (COR) was analyzed using an image analysis program developed in MATLAB as described in Penning et al.(2005). The position of the COR between full flexion/extension was calculated and reported as a pair of coordinates offset from the posterior superior corner of the lower vertebral body. The COR coordinates were normalized as values based on the length and height of the lower vertebral body. The results were compared to the data found in the literature. Results: The COR positions are presented in Fig1. Studies of the position of the COR following the operation showed that the COR position have initially deviated to the very posterior position in the early stages following surgery. However, at the final follow up all patients showed that the COR position have been restored close to the normal position. Conclusion: Changes in the position of the COR were observed at different stages following the transplantation as opposed to the results of some of the artificial disc implants studies in which the position of the COR had deviated from the physiological position of a normal disc permanently. These changes in the position of the COR may suggest that the remodelling of the allograft may play a part in restoring the natural kinematics of the spine. Study of the allograft implantation demonstrated that the kinematics of the spinal segment may be restored in the long term.