Infra-adjacent Segment Disease After Lumbar Fusion An Analysis of Pelvic Parameters

Study Design. Cross-sectional observational cohort study. Objective. The aim of this study was to determine the incidence and risk factors associated with the development of sacroiliac joint (SIJ) dysfunction following lumbosacral fusion. Summary of Background Data. Adjacent segment degeneration to both proximal and distal areas of spinal fusion is a postoperative complication of lumbar fusion. Various studies examined supra-adjacent degeneration following lumbar fusion, but few focused on infra-adjacent degeneration. In lumbosacral fusion, fusion extends to the sacrum, placing increased stress on the SIJ. Methods. A total of 2069 sequential patients who underwent lumbosacral fusion surgery from 2008 to 2018 at a single academic medical center were retrospectively reviewed. Patients who subsequently developed SIJ dysfunction were identified. SIJ dysfunction was defined as patients who met the diagnostic criteria with physical examination and received an SIJ injection with clinical evidence of improvement. Controls, without subsequent SIJ dysfunction, were matched with cases based on levels of fusion, age, sex, and body mass index. Pre-and postoperative pelvic parameters were measured, including pelvic incidence, pelvic tilt (PT), sacral slope, lumbar lordosis, lumbosacral angle, L4 incidence and L5 incidence Results. Of 2069 patients who underwent lumbosacral fusion, 81 patients (3.9%) met criteria for SIJ dysfunction. Measurements were made for 47 of 81 patients who had SIJ dysfunction, that had both pre- and post-operative imaging. Measurements for 44 matched controls were taken. Postoperative PT was significantly lower in SIJ dysfunction patients compared to controls (20.82 degrees +/- 2.19 degrees vs. 27.28 degrees +/- 2.30 degrees; P< 0.05), as was L5 incidence (28.64 degrees +/- 3.38 degrees vs. 37.11 degrees +/- 3.50 degrees; P< 0.05). Conclusion. Incidence of the SIJ dysfunction after lumbosacral fusion surgery was 3.9% and these patients had a significantly lower PT and L5 incidence compared to the control group. Significantly low PT may be derived from weak hamstring muscles, predisposing a patient to SIJ dysfunction. Therefore, hamstring muscle strengthening exercise for patients with decreased PT after lumbosacral fusion may decrease the incidence of SIJ dysfunction.