Changes in surface and radiographic deformity after Universal Spine System for right thoracic adolescent idiopathic scoliosis: is rib-hump reassertion a mechanical problem of the thoracic cage rather than an effect of relative anterior spinal overgrowth?

Abstract

Analysis of preoperative, 8-week, 1-year, and 2-year data from patients with right thoracic adolescent idiopathic scoliosis treated by posterior Universal Spine System (Stratec Medical, Oberdorf, Switzerland). Report 2-year results and the association between back surface and radiographic assessments. Few longitudinal studies have related surface and radiographic data in the follow-up of surgical patients. Of 34 patients with right thoracic adolescent idiopathic scoliosis having posterior Universal Spine System instrumentation, 27 had complete prospective back surface and radiographic appraisal. Cobb angle corrected from 58 degrees to 34 degrees (41%), apical vertebral rotation from 26 degrees to 20 degrees (23%), apical vertebral translation from 4.5 to 2.4 cm (47%), and maximum angle of trunk inclination from 17 degrees to 13 degrees (22%) (preoperative to 2 years). Rib-hump reassertion occurred between 8 weeks and 1 year, regardless of age, and correlated with changes in vertebral translation (for 10 vertebral levels corresponding to 10 back surface levels between C7 and S1, P = 0.001 MANOVA). Preoperative frontal tilt of L1 with concave fifth rib-spinal angle predicted the percentage correction of maximum angle of trunk inclination, and the concave ninth rib-spinal angle predicted reassertion of maximum angle of trunk inclination. Almost half of initial back surface correction is lost by 2 years. Segmental vertebral translation measurements most strongly correlate with segmental angle of trunk inclination measurements during follow-up. Rib-hump reassertion is best explained by unwinding of the thoracic cage tensioned by surgery rather than through relative anterior spinal overgrowth. Spine and thoracic cage factors determine rib-hump correction, so surgical disruption of the latter by costoplasty may prevent rib-hump reassertion. Results of scoliosis surgery should include surface data.