Effects of alternative instrumentation strategies in adolescent idiopathic scoliosis: a biomechanical analysis.

The recent advent of modern instrumentation systems has improved the correction of scoliosis, but complicated the surgical decision-making process, especially with the introduction of diverse spinal fixation devices, new preoperative corrective maneuvers, and the reevaluation of many rules concerning the selection of fusion levels and other guidelines for surgical correction. Our objective was to assess the biomechanical effects of different instrumentation strategies for the same scoliotic cases. Several instrumentation strategies suggested by a group of 32 experienced senior surgeons for five cases were individually simulated using a validated computer model implemented in a spine surgery simulator. The resulting geometric indices varied among the five cases (e.g., range of main thoracic Cobb angles: 5-17 degrees , 16-29 degrees , 25-44 degrees , 15-34 degrees , 16-32 degrees ; kyphosis: 22-33 degrees , 20-54 degrees , 33-55 degrees , 24-49 degrees , 29-46 degrees ; and lordosis: 10-52 degrees , 24-38 degrees , 26-54 degrees , 8-28 degrees , 34-53 degrees ). The average correction was better with pedicle screws (71%) than with hooks (51%) and hybrid constructs (67%). For the first time, to our knowledge, the effect of different instrumentation strategies was compared on the same patients, which is possible only with a surgery simulator. A large variability of instrumentation strategies existed among experienced surgeons and produced rather different results. This study questions the criteria for optimal configuration and standards to design the best surgical construct.