Incidence and risk factors of adjacent segment degeneration in lumbosacral or lumbo-iliac fusion with L2 as the uppermost instrumented vertebra

Abstract

Objective: Lumbosacral or lumbo-iliac fusion may be warranted in patients with symptomatic diffuse lumbar spondylosis or mild to moderate lumbar spinal deformity. Depending on the extent of pathology, the L2 vertebra may be chosen as the uppermost instrumented vertebra (UIV) to avoid fusion crossing the thoracolumbar junction. However, the incidence of adjacent segment degeneration (ASD) following L2 to sacrum or ilium fusion has not been well studied. The authors aimed to determine the incidence of ASD following instrumented fusion in adult patients undergoing L2 to sacrum or ilium fusion and to identify the risk factors for this complication.

Methods: The medical records of adult patients who underwent decompression and lumbosacral or lumbo-iliac instrumented fusion for diffuse lumbar spondylosis, degenerative scoliosis, or sagittal malalignment with L2 as the UIV between January 2016 and December 2023 were retrospectively reviewed. ASD is defined as the progression of disc degeneration, worsening of spinal stenosis, junctional kyphosis, UIV or UIV+1 compression fracture, and screw pullout or loosening that caused pain or neurological deficits. The incidence of ASD was analyzed. Kaplan-Meier analysis was used to evaluate symptomatic ASD-free survival. Univariate and multivariate logistic regression were used to assess potential risk factors, including patient-related factors, surgery-related factors, and pre- and postoperative spinopelvic parameters.

Results: Eighty-nine patients (57 males, 32 females; mean age 68.5 years) were included. The mean duration of follow-up was 38.6 months. Thirty-six (40%) patients developed symptomatic ASD, and 21 (23.6%) required reoperation. Simultaneous decompression at L2-3, preexisting L1-2 disc degeneration, greater postoperative pelvic incidence-lumbar lordosis (PI-LL) mismatch, and higher lordosis distribution index were risk factors for the development of ASD. Twelve (13.5%) patients developed distal failure, including 9 pseudarthroses at L5-S1, 2 sacral fractures, and 1 rod fracture between S1 and the iliac screw. Male sex, young age, and lack of iliac screws were risk factors for distal failure.

Conclusions: These findings suggest that the overall incidence of ASD is high in adult patients with lumbar degeneration or spinal deformity who undergo instrumented fusion from L2 to the sacrum or ilium. Significant risk factors for developing ASD include simultaneous decompression at L2-3, preexisting advanced disc degeneration at L1-2, greater postoperative PI-LL mismatch, and higher lordosis distribution index.

Keywords: adjacent segment degeneration; deformity; degenerative; fusion; instrumentation; lumbar; proximal junctional kyphosis; pseudarthrosis.