Risk factors of adjacent segment disease after posterior L4/5 fusion

English Keywords:Lumbar fusion surgery  Adjacent segment disease  Segmental lordosis  Relative height of intervertebral space

English Abstract:

  【Abstract】 Objectives: To explore the risk factors of adjacent segment disease(ASD) after posterior L4/5 fusion. Methods: A total of 26 patients who underwent revision surgery for ASD after posterior L4/5 fusion in our hospital between September 2012 and September 2021 were retrospectively analyzed and included in the ASD group. Another 52 patients were matched in 1∶2 as the control group by gender, age at surgery, surgical segment, and follow-up time from those patients who underwent posterior lumbar fusion during the same period and without ASD at the final follow-up. The imaging data before operation, at postoperative 3d and final follow-up were collected of both groups of patients, and parameters were measured on lateral lumbar X-ray films such as lumbar lordosis(LL), segmental lordosis(SL), sacral slope(SS), and the relative height of the intervertebral space at L3/4, L4/5, and L5/S1. Disc degeneration in the adjacent segments of the fused one was assessed using the Pfirrmann classification on the first preoperative MRI images. Preoperative baseline data, lumbar sagittal alignment parameters at preoperation, postoperative 3d and final follow-up, and relative correction values of initial postoperative/preoperative lumbar sagittal parameters were compared between the two groups, and parameters with significant difference were incorporated in multivariate logistic regression analysis. The optimal predictive thresholds for ASD of the independent risk factors were determined by receiver operating characteristic(ROC) curves. Results: There was no significant difference between the ASD group and the control group in the first preoperative diagnosis, preoperative Pfirrmann grading of adjacent segmental discs, or comorbidities(P>0.05). The patients in the ASD group received a second surgery 5.4±2.3 years after the initial operation, and the fusion segments of the second surgery were L3/4 in 16 patients and L5/S1 in 10 patients. The preoperative SL, SS, and relative height of L3/4, L4/5 and L5/S1 intervertebral space between the two groups were of no significant difference, respectively(P>0.05). The patients in the ASD group had significantly smaller preoperative LL than those in the control group(P=0.031). After the initial fusion, both SL and LL were significantly smaller in the ASD group than those in the control group(P<0.05). At the final follow-up, both SL and LL were significantly smaller in the ASD group than those in the control group(P<0.001); also, the relative height of L3/4 intervertebral space was significantly smaller in the ASD group(P=0.002). When comparing the relative correction values of the parameters of the initial surgery between the two groups, the relative difference in SL(r△SL) was significantly smaller in the ASD group than in the control group(P<0.001), while the relative difference in LL(r△LL), L4/5 relative difference in disc height(r△DH), L3/4 r△DH, and L5/S1 r△DH were not significantly different between the two groups(P>0.05). In the multiple regression analysis of the occurrence of ASD, a smaller initial postoperative/preoperative r△SL was an independent risk factor(OR=0.031, 95%CI 0.005-0.209). The ROC curve suggested an area under curve(AUC) of 0.731 (95%CI 0.615-0.848) for r△SL. The best predictor of the occurrence of ASD for r△SL threshold was -10.5%. Conclusions: Inadequate local curvature correction during posterior L4/5 fusion may lead to long-term loss of adjacent segment height, which is an independent risk factor for the development of ASD after fusion.