Clinical and radiological evaluation of lumbosacral motion below fusion levels in idiopathic scoliosis.

The purpose of this study was to evaluate the unfused segments of the lumbar spine in patients who had Harrington instrumentation and fusion for idiopathic scoliosis. Forty-eight patients, with an average follow-up of 11 years, were evaluated. The translational motion in the unfused segments below the instrumented levels was measured, using lateral flexion and extension radiographs of the lumbar spine. This motion was compared with values obtained from an earlier study of asymptomatic nonscoliotic individuals. The amount of disc space narrowing, retrolisthesis, length and level of the fusion, and the presence of traction spurs also were recorded. The incidence of low-back pain was highest in those patients fused to L4 (62%). Individuals instrumented and fused to L3 or L4 had significantly more translational motion in the adjacent lower interspace when compared with the control group (P = 0.05 and P = 0.001, respectively). Increased translational motion correlated with the presence of low-back pain in patients fused to L4. Retrolisthesis occurred in 81% of patients instrumented to L4, in 40% of those fused to L3, and was not found in patients fused to high levels. Its presence was strongly associated with low-back pain. There was no relationship between low-back pain and traction spurs, length of the fusion mass, lumbar lordosis, or width of the disc space in the unfused lower levels. The authors conclude that retrolisthesis and increased translational motion are important factors in determining low-back pain following surgery for idiopathic scoliosis. Instrumentation to L4 should be avoided if possible.