Unilateral pedicle screws asymmetric tethering: an innovative method to create idiopathic deformity

To evaluate the feasibility of the method that unilateral pedicle screws asymmetric tethering in concave side in combination with convex rib resection for creating idiopathic deformity.

Various methods are performed to create idiopathic deformity. Among these methods, posterior asmmetric tethering of the spine shows satisfying result, but some drawbacks related to the current posterior asymmetric tether were still evident.

Unilateral pedicle screws asymmetric tethering was performed to 14 female goats (age: 5-8 week-old, weight: 6-8 kg) in concave side in combination with convex rib resection. Dorsoventral and lateral plain radiographs were taken of each thoracic spine in the frontal and sagittal planes right after the surgery and later every 4 weeks.

All animals ambulated freely after surgery. For technical reasons, 2 goats were excluded (one animal died for anesthetic during the surgery, and one animal was lost for instrumental fail due to postoperative infection). Radiography showed that 11 goats exhibited scoliosis with convex toward to the right side, and as the curve increased with time, only 1 goat showed nonprogressive. The initial scoliosis generated in the progressors after the procedures measured 29.0 degrees on average (range 23.0 degrees -38.5 degrees ) and increased to 43.0 degrees on average (range 36.0 degrees -58.0 degrees ) over 8 to 10 weeks. The average progression of 14.0 degrees was measured. The curvature immediately after tethering surgery (the initial Cobb angle) did have a highly significant correlation with the final curvature (p < 0.001). The progressive goats showed an idiopathic-like deformity not only by radiography, but in general appearance.

Unilateral pedicle screws asymmetric tethering is a practical method to create experimental scoliosis, especially for those who would like to study the correction of this deformity.