Mechanical modulation of calf tail vertebral growth: implications for scoliosis progression.

The purpose of this study was to determine whether compression and distraction applied to adjacent vertebrae in the calf tail could modulate vertebral growth. Seven 6-week-old calves had two pairs of adjacent tail vertebrae instrumented with an Ilizarov external fixator with calibrated springs designed to apply a 30-50-N axial load to the vertebrae. Data were obtained from 17 vertebrae loaded in compression and 4 vertebrae loaded in distraction. Vertebrae adjacent (cranial and caudal) to the instrumented vertebrae served as controls. The length of each vertebra on the postoperative radiograph was subtracted from the length of the same vertebra on the radiograph taken 6 months after the operation to calculate vertebral growth. The vertebrae loaded in compression had a growth rate of 68 +/- 42% of that of the controls. In contrast, the vertebrae loaded in distraction had a growth rate of 123 +/- 78% of that of the controls.