The Biomechanical And Clinical Study Of Preserving Posterior Ligament Complex To The Adjacent Segment After Lumbar Fusion

The method of spinal fusion now has been the standard technique in the treatment of lumbar disease. The occurrence of further adjacent segment degeneration(ASDeg) and adjacent segment disease(ASDis) after lumbar fusion were the main complication, and also was the controversial topic. The biomechanical study of finite element confirmed the function of preserving the intact of posterior ligament complex(PLC), but it was not clear in human cadaver model and clinical study.Objective: To comparing the lumbar intervertebral range of motion(ROM) in the different situation of fixation length, curvature and preserving PLC with the load-control and displacement-control load. And further to identify the long-term radiologic and clinical outcomes of adjacent segment after fusion with the laminotomy decompression which can preserve the intact of PLC.Materials and Methods: 1. Biomechanical study part. Six fresh cadaver lumbar specimens were tested in the sequence of intact, L4-5 straight fixation, L4-5 physiological curvature fixation, L4-5 laminotomy with fixation and L4-5 laminectomy with fixation. With non-contact photographic recording system, both displacement-control and load-control load were applied. ROM of adjacent segments was measured. 2. Systematic review. Literature from 1966 to 2012 on fusion for lumbar degenerative pathology reporting adjacent segment degeneration or disease as an outcome measurement were searched. And method of Meta regression was applied to estimate pooled incidence of ASDeg and ASDis. 3. Clinical follow-up. The retrospective study included 158 patients who underwent surgery of lumbar posterolateral fusion(PLF) for degenerative lumbar pathology for the first time. Radiographic grading scale was used to evaluate the fate the adjacent segment, and the clinical outcome was evaluated.Results:1. Biomechanical study. 1) The flexion ROM of non-direct neighbor disc to fusion area was significantly increased in the displacement-control mode, and no difference in load-control mode. 2) The three-dimensional ROM was not found significant difference between local straight and physiological curvature fixation. 3) The flexion ROM of cranial and caudal adjacent segments were significantly increased in the displacement-control mode, but no difference in other type of motion and load-control mode.4) In the displacement-control mode, three-dimensional ROM was found significant difference between single and two-level fusion. 5) The method of laminectomy without preserving the PLC was found higher flexion ROM than laminotomy. 2. Systematic review. Thirteen articles were selected and the overall pooled incidence of ASDeg was 5.9% per year, and the incidence of ASDis was 1.8%. 3. Clinical follow-up study. Finally there were 102 patients with completely follow-up records enrolled into the retrospective study, and the follow-up rate was 64.6%. The average age was 62.2 years, and the average follow-up time was 65.2 months. 1) The cranial disc height and motion were found increased significantly than pre-operation. 2) The overall incidence of radiological ASDeg was 25.5%, equal to 4.72% per year, which is lower than the systematic review of 5.9%. 3) The ASDeg incidence for the cranial and caudal levels was not different(P=0.461), and the incidence of ASDeg with one, two and three levels fusion were significantly different(P=0.008).4) For the cranial level, the preexisted degenerative cranial discs were found higher incidence of ASDeg than non-preexisted degenerative group(P=0.012). For the caudal level, there was no significant difference. At the final clinical functional follow-up, the ASDeg group showed worse outcome than non-ASDeg group and the non-preexisted degenerative group showed better outcomes than the preexisted degenerative group.Conclusion: 1. The different load method brought different biomechanical outcome, and the motion change of adjacent segment post-fusion only occurred in the situation of displacement-control load. 2. In the displacement-control mode, the fusion length and fixation curvature could bring more effect to the motion. 3. The damage of PLC was the injuring to the intact of spinal unit and preserving PLC could decrease the risk of further degeneration. 4. The clinical follow-up study showed that preserving the intact of PLC could decrease the incidence of ASDeg. 5. The pre-existed degenerative neighbor disc had more opportunity of advancing to ASDeg. The pre-existed disc of UCLA C grade should be involved into the fusion area. 6. The degeneration of aging might be as the main risk factor to promote the formation of ASDeg compared with biomechanical factor.