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Biomechanical assessment of variable instrumentation strategies in adolescent idiopathic scoliosis: preliminary analysis of 3 patients and 6 scenarios.

Since the introduction of modern multi-segmental instrumentation systems, disagreement exists about the appropriate instrumentation strategies for the "optimal" correction of scoliotic deformities, and the difference between alternative scenarios is difficult to predict a priori. The purpose of this study is to evaluate the effect of different instrumentation strategies using a computer assisted surgery simulator (S3). We obtained from 32 experienced Fellows of the Scoliosis Research Society and members of the Spinal Deformities Study Group the detailed preoperative planning for three AIS patients with Lenke curve types 1A, 3A and 5C. Their scenarios were individually simulated using a computer model implemented in a spine surgery simulator (S3). The resulting Cobb angles varied for the 3 cases (e.g.: main thoracic: 6-17 degrees; 16-29 degrees; 16-30 degrees). The variability of correction remained important when sub-classifying the results according to the instrumentation strategies: A- "Pedicle Screws Constructs"; B- "Hooks Constructs"; C- "Hybrid Constructs". But overall, the average correction was better in group A (71%) than in groups B (55%) and C (54%). For the first time the effect of various instrumentation strategies can be assessed preoperatively thanks to S3. A large variability of instrumentation strategies exist within experienced surgeons and these produce rather different results. This study also questions the criteria for optimal configuration and standards to objectively design the best surgical construct.