Risk factor analysis of adjacent segment disease requiring surgery after short lumbar fusion: the influence of rheumatoid arthritis.

BACKGROUND CONTEXT: The influence of rheumatoid arthritis (RA) on the lumbar spine has received relatively little attention compared with cervical spine, and few studies have been conducted for adjacent segment disease (ASD) after lumbar fusion in patients with RA.

PURPOSE: The present study aims to determine the incidence of ASD requiring surgery (ASDrS) after short lumbar fusion and to evaluate risk factors for ASDrS, including RA.

STUDY DESIGN: This is a retrospective cohort study.

PATIENT SAMPLE: The present study included 479 patients who underwent lumbar spinal fusion of three or fewer levels, with the mean follow-up period of 51.2 (12-132) months.

OUTCOME MEASURES: The development of ASD and consequent revision surgery were reviewed using follow-up data.

METHODS: The ASDrS-free survival rate of adjacent segments was calculated through Kaplan-Meier method. The log-rank test and Cox regression analysis were used to evaluate risk factors comprising RA, age, gender, obesity, osteoporosis, diabetes, smoking, surgical method, and the number of fusion segments.

RESULTS: After short lumbar fusion, revision surgery for ASD was performed in 37 patients (7.7%). Kaplan-Meier analysis predicted that the ASDrS-free survival rate of adjacent segments was 97.8% at 3 years, 92.7% at 5 years, and 86.8% at 7 years. In risk factor analysis, patients with RA showed a 4.5 times higher risk of ASDrS than patients without RA (p<.001), and patients with three-segment fusion showed a 2.7 times higher risk than patients with one- or two-segment fusion (p=.005).

CONCLUSIONS: Adjacent segment disease requiring surgery was predicted in 13.2% of patients at 7 years after short lumbar fusion. Rheumatoid arthritis and the number of fusion segments were confirmed as risk factors.