Long-Term Risk of Adjacent-Segment Disease in Isthmic Spondylolisthesis Treated with Posterior Interbody Fusion

OBJECTIVE: Posterior interbody fusion can be associated with adjacent-segment disease (ASD) some years after surgery. The aim of this study is to confirm the rate of ASD in isthmic spondylolisthesis treated by posterior fusion. METHODS: The records of patients treated by posterior lumbar fusion between January 2014 and June 2022 were collected. Inclusion criteria encompassed adults diagnosed with isthmic spondylolisthesis and available preoperative, postoperative, and follow-up radiologic images. RESULTS: Of the 140 patients included in the study, the majority were female (53.6%) with a mean age of 48.5 years. In 111 (79.3%) patients the spondylolisthesis was located at L5-S1; in 20 (14.3%) patients at L4-L5; 5 (3.6%) cases presented the defect at L4-L5-S1, and in 4 (2.8%) cases at L3-L4. In 75 (53.6%) patients, the listhesis was classified as grade I (Meyerding); in 50 (35.7%) cases as grade II; in 12 (8.6%) cases as grade III; and in 3 (2.1%) cases as grade IV. The average follow-up of this study was 67 (10-111) months. Two cases (1.43%, 95% confidence interval 0.17%-5.07%) of ASD were observed. Evaluations of clinical symptoms revealed a notable reduction in the average Numeric Rating Scale score from 8 to 1.9 at the last follow-up. Postoperative pelvic incidence-lumbar lordosis mismatch <10 correlating with a favorable outcome (Numerical Rating Scale <= 3). CONCLUSIONS: This study confirms data already present in the literature regarding the low incidence of ASD in patients who underwent surgery for isthmic spondylolisthesis. The posterior approach seems to remain a safe and effective technique in these patients.