In vivo study of the kinematics in axial rotation of the lumbar spine after total intervertebral disc replacement: long-term results: a 10-14 years follow up evaluation.

INTRODUCTION: We did not find any in vivo study of spinal segment kinematics after disc replacement, especially over the long term. In vitro studies did show that it restores almost normal kinematics except for axial rotation. The goal of this study is to develop a new technique in order to analyse axial rotation of a spinal segment, in vivo, after total disc replacement. MATERIALS AND METHODS: A comparative retrospective study of motion in axial rotation at L4L5 level was carried out on 17 patients with artificial discs versus six healthy volunteers. Five patients carried one prostheses at L4L5 level and 12 carried two prosthesis at L4L5 and L5S1 levels. The follow up ranged from 10.8 to 14.3 years (average 12.4+/-1, median 12.6). Dynamic radiographs in axial rotation were made using a special protocol. A new technique associating a stereographic method and image processing software was developed in order to evaluate the range of motion in axial rotation as well as the mechanical coupling. RESULTS: The standard deviation of angular measurements was 1.8 degrees . Eleven (65%) patients had a normal mobility in torsion, identical to those of the volunteers and of the literature, whereas six (35%) had an abnormal increased mobility. If only one disc was replaced, mobility in torsion was identical to that of the volunteers, in the case of two replaced discs, 50% (6/12) of the patients had an abnormal increased mobility. In the sub-group of normal mobility, the coupling was identical to that of the volunteers. In the sub-group of increased mobility, the coupling was different with a strong flexion (10 degrees ), increased by about 7 degrees (P<0.001). CONCLUSION: The implementation of only one discal prosthesis SB Charité seems to restore kinematics close to that of the healthy volunteers and comparable to the literature. The implementation of two adjacent prostheses does not restore normal kinematics in 50% of the cases. It is probable that the existence of active stabilizing elements explains the difference with the in vitro studies carried out beforehand.

Clinical and radiological outcomes with the Charité artificial disc: a 10-year minimum follow-up.

This is the first report of clinical and radiologic outcomes for the CHARITE artificial disc with a minimum follow-up of 10 years. A total of 107 patients indicated for total lumbar disc replacement were implanted with the CHARITE prosthesis. Of these 107, 100 were followed for a minimum of 10 years (range 10-13.4 years). A total of 147 prostheses were implanted with 54 one-level and 45 two-level procedures and 1 three-level procedure. The prostheses were placed through a standard anterior retroperitoneal approach. Clinically, 62% had an excellent outcome, 28% had a good outcome, and 10% had a poor outcome. Of the 95 eligible to return to work, 88 (91.5%) either returned to the same job as prior to surgery or a different job. These included 63.2% (12) of those working in heavy labor employment returning to the same job. Mean flexion/extension motion was 10.3 degrees for all levels (12.0 degrees at L3-L4, 9.6 degrees at L4-L5, 9.2 degrees at L5-S1). Mean lateral motion was 5.4 degrees . In the sagittal plane, 9 (6.1%) were anterior of geometric center, 50 (34.0%) were centered, and 88 (59.9%) were posterior of center. In the frontal plane, 110 (75%) were centered, and 37 (25%) were noted to be lateral to center. Slight subsidence was observed in two patients, but they did not require further surgery. No subluxation of the prostheses and no cases of spontaneous arthrodesis were identified. There was one case of disc height loss of 1 mm. Five patients required a secondary posterior arthrodesis. A good or excellent clinical outcome rate of 90% and a return to work rate of 91.5% compare favorably with results described in the literature for fusion for the treatment of lumbar degenerative disc disease. With a minimum follow-up of 10 years, the CHARITE artificial disc demonstrated excellent flexion/extension and lateral range of motion with no significant complications.