Three Dimensional Analysis of Two Fusionless Scoliosis Treatments: A Flexible Ligament Tether Versus a Rigid Shape Memory Alloy Staple

• (a, b - Medtronic Sofamor Danek)

Purpose: To analyze the three dimensional effect of two different fusionless scoliosis treatment techniques on an experimental idiopathic-type scoliosis using plain radiographs and computerized tomography.

Methods: Scoliosis was created in 24 Spanish Cross X female goats (age 6-8 weeks, weight 8-12 kg.) using a flexible left posterior asymmetric tether from the T4-6 to L1-2 laminae. Convex rib resection and concave rib tethering from T8-13 were performed prior to tensioning of the posterior braided synthetic ligament (3.5 mm polyethylene core/polyester sleeve). After 8 weeks of posterior tethering, goats were randomized into 3 treatment groups: Group I, no treatment; Group II, anterior SMA (shape memory alloy) staple; Group III, anterior ligament tether with bone anchor. The 6 levels of maximal curvature were instrumented in Groups II and III. All goats were observed for an additional 12 to 16 weeks. Serial radiographs and CT scans were used to document progression/ correction of coronal, sagittal and transverse plane deformities throughout the study. A deformity score was created to compare the three dimensional effect of both treatments.

Results: Twenty goats achieved progressive, structural, idiopathic-type, lordoscoliotic curves convex to the right in the thoracic spine over the 8 week tethering period. The table demonstrates the initial deformity at the time of randomization, the deformity immediately following treatment (staple or bone anchor/ligament), and the final deformity at the end of 12-16 weeks observation. Scoliosis (S), lordosis (L), and axial rotation (R) measurements are provided as well as the overall deformity score (D) where S+L+R=D.

Conclusion: The data in this study demonstrate the ability of a bone anchor/ligament tether to modestly correct scoliosis in the coronal plane, but not in the sagittal or axial plane. And although a significant decrease in the deformity score was demonstrated initially in this group (p<0 .001), the effect was lost over time. The final deformity in bone anchor/ligament tether group significantly less than either stapled or untreated groups (p<0.03). Further study is warranted to provide a better understanding of three-dimensional effects fusionless scoliosis treatments.

• If noted, the author indicates something of value received. The codes are identified as: a-research or institutional support; b-miscellaneous funding; c-stock or stock options; d-royalties; e-other financial or material support.