Abstract: BACKGROUND: The correlation between sacroiliac joint degeneration and lumbar degenerative disease has been analyzed in the literature in the past, but the clinical efficacy and imaging changes after interbody fusion with sacroiliac joint ankylosis in patients with lumbar degenerative disease have not been reported in the literature. 
OBJECTIVE: To investigate the effect of sacroiliac joint ankylosis on the clinical efficacy and lumbar sagittal regression after L5/S1 single-segment transforminal lumbar interbody fusion in patients with lumbar degenerative disease.
METHODS: Thirty-seven patients who underwent L5/S1 segmental transforminal lumbar interbody fusion for lumbar degenerative disease with sacroiliac joint ankylosis between June 2020 and September 2023 in Affiliated Hospital of Xuzhou Medical University were retrospectively analyzed as group A. Thirty-seven patients with lumbar degenerative disease without sacroiliac joint ankylosis who were matched for general information during the same period were selected as controls in group B. Clinical efficacy was assessed using the Oswestry disability index and visual analog scale for lumbar and lower limb pain. The lumbar sagittal parameters included lumbar anterior convexity angle, lumbar partial anterior convexity angle, and lower lumbar anterior convexity angle. Pfirrmann grading was used to assess the degree of preoperative disc degeneration, postoperative endplate damage and screw loosening, and to record the fusion of the operated segments at the final postoperative follow-up visit.
RESULTS AND CONCLUSION: (1) There was no statistically significant difference in age, body mass index, bone mineral density, operation time, intraoperative bleeding, preoperative primary diagnosis and postoperative follow-up time between the two groups (P > 0.05). (2) The preoperative Pfirrmann grading of lumbar disc degeneration in group A patients (3.4±0.9) was significantly higher than that of group B (3.1±0.6), and the difference was statistically significant (t=2.059, P=0.044). (3) All patients showed significant improvement in postoperative lumbar sagittal parameters compared with preoperative ones (all P < 0.05). During the follow-up period, there was a loss of correction in patients in group A. There was no statistical difference in the lumbar anterior convexity angle, lower lumbar anterior convexity angle, and local anterior convexity angle at the last follow-up compared with the preoperative period (P > 0.05). The lumbar anterior convexity angle, lower lumbar anterior convexity angle, and local anterior convexity angle in group A were significantly lower than those of group B patients at both preoperative and final follow-up, and the differences were statistically significant (all P < 0.05). (4) There was no statistically significant difference in postoperative endplate injury between the two groups (χ²=0.181, P=0.670), and screw loosening was significantly higher in group A than in group B, with a statistically significant difference (χ²=4.163, P=0.041). (5) At the last follow-up, the incidence of grade 3 fusion and grade 4 fusion was significantly higher in group A than in group B. The difference in the distribution of fusion grades between the two groups was statistically significant (χ²=7.848, P=0.031). (6) The Oswestry disability index and lower limb visual analog scale scores at the last follow-up of both groups were significantly improved compared with the preoperative period (P < 0.05).The visual analog scale scores for low back pain at 3 months after surgery and at the last follow-up of group A were significantly higher than those of group B (t=2.010, P=0.048; t=2.133, P=0.036). (7) It is concluded that regardless of whether it is accompanied by sacroiliac joint ankylosis or not, lumbar degenerative disease patients who undergo interbody fusion with foramen magnum can achieve good therapeutic effects, but lumbar degenerative disease patients with sacroiliac joint ankylosis who undergo interbody fusion with foramen magnum at the L5/S1 segments have a poorer improvement of low back pain than patients without sacroiliac joint ankylosis after the operation. Furthermore, patients with preoperative sacroiliac ankylosis who underwent L5/S1 segmental transforminal lumbar interbody fusion had a low fusion rate and were prone to loss of correction of the lumbar sagittal position.

Key words: lumbar degeneration, sacroiliac joint ankylosis, lumbar fusion, clinical efficacy, fusion rate, fracture implant