Creation of an ovine model of progressive structural lordo-scoliosis using a unilateral laminar tether

Purpose: To characterise changes in vertebral dimension in an ovine model of scoliosis and determine whether a reproducible curvature could be created that would be suitable for future testing of curve modifying surgical implants.

Methods: At a mean age of 5 weeks, 28 Scottish blackface sheep were anaesthetised. A 4 mm braided synthetic tape was laid under the left lamina of T5 and L1 and tightened to ‘hand’ tension. A scoliosis was then created by binding the six lowest ribs on the same side just distal to their rib angles and resecting a segment from each of the opposite ribs. Radiographs were taken at 4 weekly intervals, and CT images at 2, 5 and 7 months post tethering, to determine multi-planar curve progression. 20 animals were assessed at age 3 months, 12 at 41 weeks and 10 at 1 year with comparisons to five control animals.

Results: A significant bi-planar deformity was produced in all animals (scoliosis 32 ± 13º and lordosis 53 ± 21º 2 months post tethering; mean ± SD, n = 22). During the next 5 months the scoliosis decreased slightly (p = 0.08) but the sagittal deformity remained static: 21 ± 18° and 53 ± 19°, respectively (n = 12). The values at 7 months were associated with a mean 6 ± 4º rotational deformity. There was approximately twice as much growth in the right anterior aspects of the apical vertebrae as in the left posterior.

Conclusions: With appropriate care it was possible to obtain a reproducible curvature in immature sheep. The methods described are suitable for use in studies of growth modulation and other spinal devices.