The effect of remodeling on the kinematics of the malpositioned disc allograft transplantation

Abstract

STUDY DESIGN: A postoperative biomechanical study. OBJECTIVE: This study aimed to assess whether the mal-alignment of the intervertebral disc (IVD) allograft during transplantation would negatively affect the biomechanics of the spinal segment. SUMMARY OF BACKGROUND DATA: Studies of human IVD allograft transplantation have observed remodeling of the allograft implant, suggesting that the remodeling of the allograft may be able to restore the natural mechanics of the IVD. METHODS: Eighteen male goats (age: 6-12 months; weight: 25-30 kg) were randomly assigned into control (n = 5), aligned (n = 5), or malpositioned (n = 5) groups. Transplantation of a size-matched cryopreserved IVD allograft was performed in the lumbar region (L4-L5) after disc excision. In the aligned group, the IVD allografts were placed aligned and flush with the anterior vertebral margin. In the malpositioned group, the allografts were placed proud anteriorly by 25% of the anterior-posterior diameter of the allograft. The lumbar spines were harvested at 6 months after transplantation. Three-dimensional kinematic assessment of the lumbar spines was performed using an MTS testing machine and an optoelectronic camera system. The range of motion, neutral zone, and instantaneous axis of rotation were calculated. RESULTS: No significant difference in range of motion was noted between the groups in flexion, axial rotation, and lateral bending. Significance was noted with extension range of motion as detected in both the aligned (17.51 +/- 1.97 degrees; P = 0.019) and malpositioned groups (16.61 +/- 2.35 degrees; P = 0.027) compared with the control (10.11 +/- 1.03 degrees). No significant difference was detected in the neutral zone between the groups. Significant difference in the instantaneous axis of rotation orientation between the malpositioned and control groups was detected in the sagittal plane during lateral bending motion (P = 0.036). CONCLUSION: Kinematic parameters in both the aligned and malpositioned allograft were similar to those of the intact spine. This suggests that precise positioning of the IVD allograft may not be an essential factor affecting the biomechanics of the spinal segment after transplantation.