Effects of Alternative Instrumentation Strategies in Adolescent Idiopathic Scoliosis (AIS)

Purpose: Surgical instrumentation planning for the correction of scoliosis involves many decisions, especially since the advent of modern instrumentation systems. Although several clinical publications have attempted to assess the effects of surgical strategies, no clear consensus exists on an appropriate treatment for optimal clinical outcome in AIS. The purpose of this study is to evaluate the effects of different instrumentation constructs and fusion levels for the same scoliotic cases.

Methods: We obtained from 32 experienced Fellows of the SRS and members of the Spinal Deformities Study Group the detailed preoperative planning (e.g.: selection and location of the implants, rod shape, reduction maneuvers, etc) for 3 AIS patients with Lenke type 1A, 3B and 5C curves. Different scenarios were individually simulated using a validated computer model implemented in a "spine surgery simulator" (S3). A cost function that included six 3D descriptors of the scoliotic deformities was used to quantify the global spinal correction for each specific strategy.

Results: The resulting Cobb angles varied significantly for the 3 cases (main thoracic: 6-17; 7-30; 16-23; proximal thoracic: 14-28; 0-37; 6-30 ). The resulting implant-vertebra loading also varied significantly. The variability of correction remained important (up to 11 of standard deviation) when sub-classifying the results according to the instrumentation strategies: A- "Pedicle Screws Constructs" [n=21]; B- "Hooks Constructs" [n=2]; C- "Hybrid Constructs", [n=7]. But overall, the average correction was better in group A (74%) than in groups B (55%) and C (68%).

Discussion: This is the first study that compares the effect of instrumentation strategies on the same patients, which is possible only with such a surgery simulator. A large variability of instrumentation strategies exist within experienced surgeons and these produce considerably different results. This questions the criteria for optimal configuration and standards to objectively design the best surgical construct.