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

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.

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.

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.

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.