Degeneration of sacroiliac joint after instrumented lumbar or lumbosacral fusion: a prospective cohort study over five-year follow-up.

STUDY DESIGN A prospective cohort study. OBJECTIVE To determine the cause-effect relationship between fusion and sacroiliac joint (SIJ) degeneration after instrumented posterolateral lumbar or lumbosacral fusion. SUMMARY OF BACKGROUND DATA Adjacent segment degeneration following spinal fusion has attracted considerable attention. However, little attention has been paid to the SIJ, which is one of the adjacent joints. METHODS This study prospectively examined 37 patients, who underwent instrumented posterolateral lumbar/lumbosacral fusion from July 1997 to October 1998. Among them, 32 patients were included in this study and defined as the fusion group (male/female: 10/22, mean age: 64 years). The fusion group was divided into 2 subgroups according to the range of fusion. Group 1 had floating fusion (fusion to L5) and included 22 patients (male/female: 7/15, mean age: 65.6 years). Group 2 had fixed fusion (fusion to S1) and included 10 patients (male/female: 3/7, mean age: 60.5 years). Thirty-four age-matched normal individuals (male/female: 18/16, mean age: 64.5 years) were recruited as a control group. SIJ degeneration was assessed by confirming the absence of degeneration in the SIJ by computed tomography scans before surgery and 2 weeks after surgery. The SIJ was evaluated again by taking computed tomography scans at 1 year and 5 years after surgery. The incidence of SIJ degeneration was evaluated and compared (fusion group vs. control group; group 1 vs. group 2). The clinical outcomes were evaluated using the Visual Analog Scales (VAS) and Oswestry Disability Index (ODI) before surgery and at the final follow-up. RESULTS The incidence of SIJ degeneration in the fusion group was 75% (24/32), which was significantly higher than that of the control Group 38.2% (13/34) (P < 0.05). The incidence of SIJ degeneration (bilateral and unilateral) and bilateral SIJ degeneration was higher in group 2 than in group 1 (P = 0.028 and 0.04, respectively). The incidence of SIJ degeneration was not associated with the number of fusion segments. At the 5-year follow-up, the patients in groups 1 and 2 reported significant improvements in the VAS and ODI scores compared with the preoperative scores. However, there was no significant difference in the decrease in VAS and ODI scores between the 2 groups (P = 0.145 and 0.278, respectively). CONCLUSION Instrumented posterolateral lumbar/lumbosacral fusion can be a cause of SIJ degeneration. SIJ degeneration develops more often in patients undergoing lumbosacral fusion regardless of the number of fusion segments.