Surgery-related Risk Factor Analysis And Early Clinical Observation Of Adjacent Segment Degeneration Following Lumbar Spinal Fusion

Background:Adjacent segment degeneration (ASD) is one of the most common complications following lumbar fusion surgery. The radiolographic and symptomatic ASD is reportedly to range from8%to100%and from5.2%to18.5%. In many cases. ASD could destroy the surgery effectiveness and lead to recurrent low back pain and dysfunction. Some cases may require further surgical interventions, while the results for the surgery are often unsatisfying. Therefore. it is necessary to study the etiology and mechanism of ASD, which could serve to preventing or retarding the progression of ASD. Avoiding the risk factors of ASD is a potential way to reduce the risk of postfusion ASD. Multifidus muscle and posterior ligament complex are often damaged during the conventional lumbar fusion surgery, and the literature suggests that the damage of these structures may correlate with ASD. However, there are some shortcomings in the current studies:1) the conventional fusion surgery usually involves multiple factors, including fusion, multifidus injury and posterior ligament complex injury, which prevents us from evaluating the contributions of the multifidus injury and posterior ligament complex injury to ASD independently;2) the possible role of multifidus injury on ASD still remains theoretically, lacking experimental support;3) although there are some data suggesting the possible role of posterior ligament complex injury on ASD, the involvement of confounding factors prevents us from drawing a definite conclusion.Objective:1. On the basis of studying the anatomical structure of the lumbar spine of the New Zealand rabbit, to analyze the contributions of multifidus muscle damage and posterior ligament damage to the disc degeneration by animal model experiment, using radiographic and histologic evaluation.2. To evaluate the interaction of multifidus muscle damage and posterior ligament damage respectively with fusion, to see the effects of combined factors on the progression of ASD, by using radiographic, histologyc and biochemical methods.3. Using quantitative MRI analysis to detect early ASD following lumbar spinal fusion, in comparison with those following conservative treatment, to determine the role of fusion in the progression of ASD and to identify possible risk factors for early ASD.Methods:1. On the basis of studying the anatomical structures of the rabbit lumbar spines,80rabbits are divided into four groups randomly:control group (Group A), anterior interbody fusion group (Group B), multifidus muscle damage group (Group C) and posterior ligament complex damage group (Group D). Evaluate the degeneration conditions of relevant discs at6,12,24,36weeks postoperatively by using radiographic, histologic and molecular biological methods.2.80rabbits are divided into four groups randomly:control group (Group A), posterolateral fusion group (Group B), posterolateral fusion+multifidus muscle damage group (Group C) and posterolateral fusion+posterior ligament complex damage group (Group D). Evaluate the degeneration conditions of relevant discs at6,12,24,36weeks postoperatively by using radiographic, histologic and biochemical methods.3.108included patients are divided into two groups:one-level L4-5instrumented posterior lumbar interbody fusion group (n=55) and conservative treatment group (n=53). The lumbar spines of all patients are examined by X-ray and MRI pre-and post-treatment. These two radiographic data are compared to determine the progression of ASD and to identify possible risk factors for ASD.Results:1. In the multifidus muscle damage group, the MRI grading scale and histologic grading scale of the relevant discs significantly increase since12weeks postoperatively (P<0.05), and the disc height significantly decrease since24weeks postoperatively (P<0.01). These changes are more severe at36weeks postoperatively and the changes are more severe at the caudal than the cranial segments. In the posterior ligament damage group, relevant disc remain relatively normal. In the fusion group, the histologic grading scale increases since6weeks postoperatively (P<0.05), and the disc height decreases (P<0.05) and the MRI grading scale increases (P<0.05) since12weeks postoperatively. These changes are more severe longer follow-up and are more severe at the caudal than the cranial segments.2. In the posterolateral fusion group, the water content, the GAG content of the nucleus pulposus and the MRI grading scale of the adjacent discs decrease since6weeks postoperatively (P<0.05), and the disc height decreases (P<0.05), MRI grading scale increases (P<0.05) and histologic grading scale increases (P<0.05) since12weeks postoperatively. These changes are more severe with longer follow-up time and are more severe at the caudal than the cranial segments. The degeneration of the caudal adjacent discs is more severe in the fusion+muscle damage group than in the fusion group. Differences lie in the MRI index, GAG content and water content (P<0.05) since12weeks postoperatively, and these differences are more severe with longer follow-up. The degeneration of cranial adjacent discs is more severe in the fusion+posterior ligament complex damage group than in the fusion group. Differences lie in the MRI index, histologic grading scale, GAG content and water content (P<0.05) since12weeks postoperatively, and these differences are more severe with longer follow-up.3. Evaluation of disc height and Pfirrmann grading scale can not detect the adjacent disc degeneration in any of the two groups (P>0.05). Quantitative MRI analysis effectively identifies the progression of disc degeneration in both surgical and nonsurgical groups by using surface area, signal intensity and MRI index (P<0.05). The degeneration is more severe at the first than the second adjacent segment (P<0.05), and such differences are not observed in the nonsurgical group. Further, the degeneration of the corresponding discs is more severe in the surgical group than the nonsurgical group (P<0.05). Those with smaller preoperative sacral inclination are apt to undergo more severe adjacent disc degeneration (P<0.01).Conclusion:1. Multifidus damage could lead to disc degeneration at relevant segments, and the degeneration is more severe at the caudal segment. Posterior ligament complex damage alone does not contribute to the disc degeneration of relevant segments. Anterior lumbar interbody fusion can lead to adjacent disc degeneration, which is more severe at the caudal segments. Adjacent disc degeneration caused by anterior interbody fusion is a ideal model for studying disc degeneration.2. The added multifidus muscle damage could accelerate adjacent disc degeneration in particular at the caudal adjacent segment. And the posterior ligament complex damage could accelerate the superior adjacent disc degeneration.3. Quantitative MRI analysis could detect early ASD by using surface area, signal intensity and MRI index; The significant changes of these quantitative MRI parameters indicate early biochemical degeneration, and further follow-up is required to determine whether these changes lead to pathological changes; Comparison between the surgical and nonsurgical group indicates lumbar fusion surgery is an independent factors that could accelerate ASD. Those with smaller preoperative sacral inclination are apt to undergo more severe adjacent disc degeneration...