[Prognostic factors of the crankshaft phenomenon in patients with scoliosis and open triradiate cartilage. Is the double approach the solution?].

OBJECTIVE To study young patients after scoliosis surgery in order to determine risk and prevention factors for developing a crankshaft phenomenon (CP). MATERIAL AND METHODS Retrospective study of a cohort of 26 skeletally immature patients. Six were excluded due to progression of various conditions. Crankshaft was defined as an increase in the Cobb angle >10°, or an increase in the Mehta angle (DAVC) >10°, or any decrease in the apex-rib thoracic distance, or increase in the apical vertebral translation (AVT). Patients with and without CP development were compared in order to analyse preoperative, surgical and postoperative risk factors, as well as the influence of different surgical techniques. RESULTS The mean follow-up was 83.9 months. Nine patients (45%) developed the crankshaft phenomenon. Only immaturity parameters were associated with development of CP. No preoperative or postoperative radiographic parameters appeared to influence its development. The amount of correction may be a protective factor (41.4 vs. 61.4%; P=.06). The double approach was able to prevent the development of CP (0%) compared with single posterior instrumentation (44%), P=.02. DISCUSSION None of these preoperative factors seemed to predispose to CP: gender or aetiology, T5-T12 kyphosis or apical hypokyphosis, coronal Cobb, vertebral rotation, or DAVC. The residual postoperative Cobb, achieved kyphosis, or wired instrumentation versus hooks, also seemed to have no influence. CONCLUSION In patients with open triradiate cartilage under 11 years of age, it seems advisable to correct by double approach to avoid the appearance of the crankshaft phenomenon.