Classification of coronal trunk imbalance in degenerative lumbar scoliosis and its influence on osteotomy strategy.

Objective To propose a classification system of degenerative lumbar scoliosis based on frontal trunk imbalance and to investigate the correction outcomes following the osteotomy strategy according to this system. Methods From October 2000 to October 2006, thirty-six patients with degenerative lumbar scoliosis were treated in our hospital. It included 13 males and 23 females with a mean age of 60.1 years (ranged 49-73 years). Based on the pre-operative posteroanterior standing X-ray films, all patients were classified according to frontal truncal balance (the distance between C7 plumb line to center sacral vertical line): Type A, the distance between C7 plumb line and central sacral vertical line is less than 3 era; Type B, C7 plumb line shifts more than 3 cm to the concave side of the lumbar curve; and Type C, C7 plumb line shifts more than 3 cm to the convex side. Results All patients received posterior 3-D instrumentation correction with osteotomy and were followed up for 28 months (ranged 12-60 months). According to the classification system, there were 10 cases with Type A, 20 cases with Type B, 6 cases with Type C. For patients with Type A and Type B, the osteotomies were performed from convex side and the post-operative average angle were 22° (correction rate of 58%). For patients with Type C curve, the osteotomies were performed from distal end area of concave side and the post-operative average angle were 26° (correction rate of 40%). The average distance between C7 plumb line and center vertical sacral line was 0.6 cm, 1.0 cm and i.2 cm, respectively. There was no significant loss of correction in all types and no death and infection occurred during the followups. Conclusion This classification system for degenerative lumbar scoliosis was established on the basis of frontal trunk imbalance. According to this system, options of the osteotomy level and the osteotomy approach could be decided with satisfactory outcomes. Key words: Scoliosis; Osteotomy; Treatment outcome