Creation of an Experimental Idiopathic-Type Scoliosis in an Immature Goat Model Using a Flexible Posterior Asymmetric Tether

· (a – Medtronic Sofamor Danek)

PURPOSE: The purpose of this study is two-fold. First, to create a progressive, structural, idiopathic-type, lordoscoliotic curve in the right thoracic spine of the immature goat using a flexible posterior asymmetric tether. Second, to maintain the anterior and posterior elements of the spine along the maximal curve in a pristine state to allow for subsequent study of the deformity.

METHODS: Scoliosis was created in 20 Spanish Cross X female goats (age 6-8 weeks, weight 8-12 kg) using a left posterior asymmetric tether from the T4-6 to L1-2 laminae. Convex rib resection and concave rib tethering from T8-T13 were performed prior to tethering with a braided synthetic ligament (3.5mm polyethylene core/polyester sleeve). Goats were followed for an 8-10 week period with serial radiographs to document progression of deformity. After 8-10 weeks of tethering, goats were randomized into treatment and control groups for additional study.

RESULTS: Of the 20 goats that underwent tethering, 17 (85%) developed progressive, structural, idiopathic-type, lordoscoliotic curves in the right thoracic spine. Three (15%) encountered neurologic complications and were eliminated from the study. Initial scoliosis after tethering measured 55.4o on average (range 37-74 o) and progressed to 74.8 o on average (range 42-93 o) over 8-10 weeks. The average progression of +19.4 o (range 5-33 o) was statistically significant (P<0.001). All 17 curves demonstrated characteristic radiographic features of idiopathic scoliosis including significant displacement of the apical vertebra from the midline, wedging of both the vertebral body and disc space, rotation (average Nash-Moe II) and decreased flexibility.

DISCUSSION: Though our previous experimental scoliosis model created progressive, structural, idiopathic-type, lordoscoliotic curves in the thoracic spine of the immature goat, the current study demonstrates the effectiveness of a flexible posterior asymmetric tether in creating idiopathic-type deformities. This method also avoids violation of the spinal elements along the maximal portion of the curve providing an ideal opportunity for the study of various 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-royalties; d-stock options.