Risk Factors for Adjacent Segment Degeneration Following Lumbar/Thoracolumbar Fusion with Pedicle Screw Instrumentation: A Minimum 5-Year Follow-Up

Methods: 181 patients with minimum 5 year follow-up who had single or multilevel lumbar/thoracolumbar fusion with pedicle screw instrumentation for degenerative disorders (one institution 1985 to 2000) were included. Radiographs were analyzed with regard to degeneration at the adjacent levels. Radiographic ASD was defined either by: 1) development of spondylolisthesis >4mm; 2) segmental kyphosis >10 ; 3) complete collapse of disc space, or 4) more than 2 grade worsening in Weiner classification. Symptomatic ASD was defined as 1) symptomatic spinal stenosis, 2) intractable back pain; or 3) sagittal or coronal imbalance.

Results: Average age of patients was 55 (range 26-81). Average follow-up was 7.9 years (range 5-16). Number of levels fused were; 1-2 levels (n=133), 3-4 levels (n=29), and 5-8 levels (n=19). Radiographic ASD occurred in 44%(79/181) of patients, 56% (44/79) were symptomatic. Patients with radiographic ASD had worse Oswestry scores (20.3 vs.12.5) (p=0.001). Symptomatic ASD manifested as spinal stenosis (n=43), instability-type back pain (n=5), and sagittal or coronal imbalance (n=4). 8 of them didn't show radiographic ASD. There was no significant difference in age, follow-up period and postoperative lumbar lordosis between the patients who had symptomatic ASD and who didn't. Length of fusion, circumferential fusion vs. posterior-only and location of proximal instrumented vertebra (PIV) were not significant factors in the development of ASD (Table).

Hibbs Award Nominee for Best Clinical Paper