Decompensation And Imbalance Problems In Idiopathic Scoliosis Treated With Cotrel-Dubousset Instrumentation

Abstract

Current principles of idiopathic scoliosis treatment are three dimensional correction and rigid fixation. Although it is accepted that the Cotrel-Dubousset Instrumentation (CDI) meets these goals, there is concern about the potential risk of trunk imbalance and spinal decompensation during the derotation manouvre. The results of 5 patients with idiopathic scoliosis treated with CDI between December 1988 and August 1992 were prospectively analyzed. Mean age was 14.3 years and mean follow up was 48.6 months. A mean correction of 49.6% was achieved in the Cobb angles of major curves. The best results were obtained in King Tip III curves with a 69.4% correction. Spinal imbalance was evaluated by measuring Lateral Trunk Shift (LT). Shift of Head (SH) and Shift of Stable Vertebra (SS). Decompensation was measured by the increases in secondary curves. When all curve types were included, the average preoperative LT value of 1.96 Vertebral Units (VU) was brought down to 0.91 VU postoperatively achieving a 55.9% correction. Fourteen patients had a SH of zero preoperatively and remained balanced after instrumentation. Of the 41 remaining cases, 21 became zero postoperatively. When all cases were included the average preoperative SH was 1.0 VU and was corrected to 0.42 VU with CDI (69% correction). An average of 75.5% correction was obtained in SS, and the mean preoperative value of 0.73 VU was corrected to 0.19 VU. At the last follow-up visit a secondary curve had formed above the major curve in one case and three patients had a junctional kyphosis. Loss of correction in the frontal plane was correlated with loss in the correction of LT. The rigid and semi-flexible lumbal curves had a tendency to progress when they were not instrumented, especially in Type II curves. Junctional kyphosis could be prevented when concave laminar claws were used in the thoraco-lumbal region. It was concluded that spinal decompensation and imbalance could be minimized with careful preoperative planning, avoidance of over-correction and a long instrumentation in double major curves.