Does a Correlation Exist Between Instrumentation Type, Number of Fixation Points, and Cost in the Surgical Correction of Adolescent Idiopathic Scoliosis?

• a - DePuy Acromed

Purpose: During posterior correction of Adolescent Idiopathic Scoliosis, controversy exists regarding the optimal type of instrumentation (hooks, wires, pedicle screws) and required number of fixation points. Recent reports claim improved correction with constructs utilizing a larger percentage of thoracic pedicle screws. Similarly, many authors have demonstrated superior correction with segmental fixation. However, pedicle screws and segmental fixation typically increase the overall cost of the instrumentation. The purpose of this study is to determine if immediate coronal plane correction is dependent on: type of instrumentation, number of points of fixation, and cost of instrumentation. Do more expensive constructs result in greater scoliosis correction?

Methods: 325 patients with Adolescent Idiopathic Scoliosis treated with instrumented posterior spinal fusion between 1995-2001 were included. All patients obtained pre-operative upright and bending films and postoperative upright films. Only the implants utilized within the thoracic curve were evaluated. Using vertebrae included in the thoracic Cobb angle, data was collected regarding: the number of possible fixation points (assumed to be 2 times the number of vertebrae in the Cobb angle), actual number of fixation points utilized in the construct, type of fixation at each site (hook, wire, screw), and estimated cost of the instrumentation. Pearson’s correlation test was performed to determine the relationship of these variables to the percentage of curve correction achieved.

Results: Preoperative thoracic curves averaged 57o and achieved average correction to 17o at immediate post-op (69 % correction). The average number of levels included in the Cobb angle was eight. Pearson’s correlation revealed a significant relationship between curve correction and: increasing number of fixation sites utilized (r= 0.37, p<0 .001), increased number of pedicle screws (r="" p<0.001), and overall cost the construct p<0.001). There was no significant correlation found comparing hooks alone percent curve correction -0.052, p<0.36). Of variables, strongest identified between total implants (greater segmental fixation) correction.

Discussion: Optimal surgical correction of thoracic idiopathic scoliosis is gained by maximizing the number of fixation points within the vertebrae of the Cobb angle. Of the implants evaluated, pedicle screws provided the greatest correction. Consistent with these findings were data to indicate that increased total implant cost (more implants and more costly implants, e.g. screws) did result in greater scoliosis correction. Debate will likely continue with regards to whether the incremental increase in correction warrants the increase in implant cost.

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