Mechanical modulation of vertebral growth in the fusionless treatment of progressive scoliosis in an experimental model.

STUDY
DESIGN: Wedging of apical spinal segments was measured during creation and correction of an experimental scoliosis in a goat model.
OBJECTIVES: To create and correct apical vertebral wedge deformities in a progressive experimental scoliosis model by purely mechanical means. SUMMARY OF BACKGROUND DATA: The creation and correction of vertebral wedge deformities has been previously described in a rat tail model using external fixation.
METHODS: Experimental scoliosis was created in 14 goats using a posterior asymmetric tether with convex rib resection and concave rib tethering. After a period of up to 13 weeks, all tethers were removed and goats were randomized into treated (n = 8) and untreated (n = 6) groups. Treated goats underwent anterior thoracic stapling with four shape memory alloy staples along the convexity of the maximal curvature. Goats were followed for an additional 7 to 13 weeks during treatment. Serial radiographs were used to document progression or correction of the maximal scoliotic deformity as well as to measure the wedging of the apical spinal segment (two adjacent vertebrae and the intervening disc).
RESULTS: During the tethering period, all goats achieved a progressive, structural, lordoscoliotic curve of significant magnitude (mean: 61 degrees, range: 49 to 73 degrees). Wedging of the apical spinal segment measured 11.1 degrees at the beginning and 22.4 degrees at the end of the tethering period. The increase in apical spinal segment wedging of +11.3 degrees (10.7 degrees vertebral/0.6-degree disc) was significant (P = 0.001). During the treatment period, the scoliosis in the stapled goats measured 56.8 degrees at the beginning and 43.4 degrees at the end for an average correction of -13.4 degrees (range: 0 to-22 degrees) (P = 0.001), whereas the untreated goats measured 67.0 degrees at the beginning and 59.8 degrees at the end for an average correction of -7.2 degrees (range: +7 to -21 degrees) (P = 0.19). Additionally, wedging of the apical spinal segment in the stapled goats measured 22.5 degrees at the beginning and 20.3 degrees at the end for an average correction of -2.2 degrees (-0.6 degrees vertebral/-1.6-degree disc); wedging of the apical vertebral segment in the untreated goats measured 22.3 degrees at the beginning and 25.8 degrees at the end of the treatment period for an average progression of +3.5 degrees (3.5 degrees vertebral/0.0-degree disc). The difference in apical spinal segment correction versus progression in the stapled (-2.2 degrees) versus control (+3.5 degrees) goats was significant (P < 0.05).
CONCLUSIONS: This study demonstrates the ability to create wedge deformities at the apex of an experimental scoliosis in a large animal model and to control the progression of these deformities using anterior thoracic staples.