How to prevent preoperative adjacent segment degeneration L5/S1 segment occuring postoperative adjacent segment disease? A retrospective study of risk factor analysis.

Objective: L5/S1 segment is one of the most common lumbar degenerative segments with high clinical failure rate. When the clinically responsible segment consists of one or more segments including L4/L5 segment, whether to merge the severely degraded L5/S1 segment together is a common problem plaguing clinicians. Therefore, the purpose of this study was to explore the risk factors for preoperative adjacent segment degeneration L5/S1 segment occuring Postoperative adjacent segment disease(ASDis), analyze the correlation between the high risk factors and the occurrence of adjacent segment disease, clarify the preventive measures and direction, and provide references for clinical selection of personalized treatment.

Methods: The data of 119 patients with L5/S1 segment degeneration who underwent fixed to L4/5 posterior lumbar fusion surgery and were followed up in the orthopedic ward of Shandong Hospital of Traditional Chinese Medicine from January 2016 to January 2018 were retrospectively analyzed. According to the occurrence of ASDis at the last follow-up, all patients were divided into ASDis group (17 cases) and asymptomatic group (102 cases). The age, gender, BMI, bone mineral density and underlying diseases of the two groups were analyzed and compared. Perioperative time, intraoperative blood loss, incision length, number of surgical fusion segments, postoperative time on the ground, and hospital stay were recorded and compared. The improvement of VAS score and ODI index before and after operation were recorded and compared. X-ray and CT measurements were used to compare preoperative L5/S1 intervertebral space height, endplate Modic changes, gas in articular process, disc herniation calcification, sacral vertebrae lumbalization of patients, intraoperative L4/5 immediately corrected intervertebral space height, and sagittal position parameters of L5/S1 segment Segmental lordosis (SL), Pelvic incidence (PI), sacral slope (SS),lumbar lordosis (LL), pelvic tilt (PT), PI-LL and so on. Pfirmann grade, paravertebral muscle CSA, fat infiltration FI, paravertebral muscle rFCSA, psoas major CSA, and vertebral body area were measured and compared by MRI before surgery. The relative paravertebral cross-sectional area (rCSA), relative psoas major cross-sectional area (rCSA) and relative functional paravertebral cross-sectional area (rFCSA) were calculated. logistic regression analysis was used to determine the risk factors for preoperative adjacent segment degeneration L5/S1 segment occuring Postoperative ASDis, and the receiver operating characteristic (ROC) curve was described and the area under the curve was calculated.

Results: All patients successfully completed the operation. Proportion of patients with osteoporosis combined with ASDis [yes/no, (9/8) vs. (21/81), P = 0.004], BMI [(27.55 ± 3.99) vs. (25.18 ± 3.83), P = 0.021], the number of fusion segments [(1.76 ± 0.75) vs. (1.28 ± 0.52), P = 0.020], the correction height of L4/5 intervertebral space [(2.71 ± 1.21) mm vs. (2.10 ± 1.10) mm, P = 0.037] were significantly higher than those in asymptomatic group. Bone mineral density T value in ASDis group [(-1.54 ± 1.68) g/cm² vs. (-0.01 ± 2.02) g/cm², P = 0.004] was significantly lower than that in asymptomatic group. There were no significant differences in operation time, incision length, intraoperative blood loss and walking time between the two groups (P > 0.05). Preoperative imaging: In ASDis group, paravertebral muscle CSA [(4478.37.3 ± 727.54) mm vs. (4989.47 ± 915.98) mm, P = 0.031], paravertebral muscle rCSA [(3.14 ± 0.82) vs. (3.87 ± 0.89), P = 0.002], paravertebral muscle rFCSA [(2.37 ± 0.68) vs. (2.96 ± 0.77), P = 0.003] were significantly lower than those in non-sedimentation group. Endplate Modic changes (I/II/III/ no, (3/5/4/7) vs (23/16/5/56), P = 0.048) and vertebral canal morphological classification (0/1/2 grade, (7/5/5) vs (69/25/8), P = 0.019) in ASDis group were significantly different from those in asymptomatic group. The proportion of patients with gas in L5/S1 segment in ASDis group [yes/no, (6/11) vs. (13/89), P = 0.019] was significantly higher than that in asymptomatic group. ASDis group of preoperative LL Angle [(34.10 + 13.83)° vs. (41.75 + 13.38) °, P = 0.032) and SL Angle [(15.83 + 5.07) vs. (22.77 + 4.68) °, P = 0.022],2 days after surgery LL Angle [(38.11 + 11.73) vs. (43.70 + 10.02) °, P = 0.038) and SL Angle [(15.75 + 3.92) vs. (19.82 + 5.46) °, P = 0.004), at the time of the last follow-up LL Angle [(37.19 + 11.99) vs. (43.70 + 11.34) °, P = 0.032) and SL Angle [(13.50 + 3.27) vs. (16.00 + 4.78) °, P = 0.041) were significantly less than the asymptomatic group. Postoperative imaging: There were no significant differences in the time of intervertebral bone fusion and the number of patients with failed internal fixation between the two groups (P > 0.05). At the last follow-up, VAS score [(3.24 ± 1.39) vs. (1.63 ± 0.84), P < 0.001] and ODI score [(21.00 ± 9.90) vs. (15.79 ± 4.44), P = 0.048] in ASDis group were significantly higher than those in asymptomatic group. Bivariate logistic regression showed that BMI value (OR = 1.715, P = 0.001) and number of surgically fused segments (OR = 4.245, P = 0.030) were risk factors for preoperative adjacent segment degeneration L5/S1 segment occuring Postoperative ASDis. The degree of spinal stenosis grade 0 (OR = 0.028, P = 0.003), the paraverteal muscle rFCSA (OR = 0.346, P = 0.036), and the Angle of Postoperative L5/S1 segment SL (OR = 0.746, P = 0.007) were protective factors for preoperative adjacent segment degeneration L5/S1 segment occuring Postoperative ASDis. Under ROC curve, the area of Postoperative L5/S1 segment SL Angle was 0.703, the area of paravertebral muscle rFCSA was 0.716, the area of BMI was 0.721, and the area of number of fusion segments was 0.518.

Conclusion: Excessive number of surgical fusion segments, spinal canal stenosis greater than grade 0, excessive BMI, too small Postoperative L5/S1 segment SL Angle, and too small paravertal muscle rFCSA are risk factors for preoperative adjacent segment degeneration L5/S1 segment occuring Postoperative ASDis. Prevention should be focused on the above aspects to reduce the incidence of L5/S1 segment ASDis.