Lumbar Disc Degeneration Below a Long Arthrodesis (Performed for Scoliosis in Adults) to L4 or L5

Summary: This study evaluates the long term effects of arthrodesis for scoliosis in adults on the disc of the distal 1 or 2 mobile segments. Clinical and radiological outcome was measured. There was a significant increase in disc degeneration at a mean follow up of 9.3 years. Clinically however, only 11 patients had a poor clinical outcome and 10 of these underwent extended fusion distally: 5 solely secondary to pain, 3 with stenosis and 2 pseudarthroses.

Study Design: A retrospective analysis of adults treated with long instrumented fusion for scoliosis from the thoracic spine proximally to L4 or L5 distally.

Objective: To evaluate long term clinical outcomes as well as radiological changes in distal unfused mobile segments and to evaluate aetiological factors that may predispose to distal disc degeneration and/or poor outcome.

Method: 151 mobile segments in 85 patients (65 female), mean age 43.2 (range 21-68), were studied. Curve type, number of fused levels and pelvic incidence were recorded. Clinical outcome was measured using the Whitecloud function scale and disc degeneration measured using the UCLA disc degeneration score. All MRI and discography findings were recorded. Overall spinal balance, local segmental angulation and lumbar lordosis were measured pre- and post-operatively as well as at the most recent follow up - mean 9.3 years (7-19).

Results: 62 % of patients had good or excellent outcome. 11 patients had poor outcome of which 10 underwent extension of fusion - 5 for pain alone, 3 pain and stenosis and 2 pseudarthroses. Pre-operative disc degeneration was often asymmetric and was slightly greater in older patients. There was no difference in the rate of degeneration between patients less than 40 and those older than 40. Overall, there was a significant deterioration in distal disc degeneration score (p<0 .0001, paired t-test), but this did not correlate with clinical outcome. There was no correlation between pre-operative grade and subsequent disc degeneration.

Conclusion: Disc degeneration occurs below an arthrodesis for scoliosis. As in the normal population, this does not always correlate with clinical outcome. Disc degeneration below a scoliotic curve is often assymetric and does not preclude leaving the segment unfused. Whether primary discal degeneration or mechanical factors are responsible for this degeneration (or a combination of both) is not known and more research is needed.