PROGRESSION OF VERTEBRAL WEDGING IN AN ASYMMETRICALLY LOADED RAT TAILMODEL

Study Design. A rat tail model was used to test the hypothesis that an gulation and asymmetric axial compressive loading would lead to verteb ral wedging because of asymmetric longitudinal growth in the physes. O bjectives. To study the effect of angulation and asymmetric loading on the progression of spinal curvature in a rat tail model. Summary of B ackground Data. Large idiopathic scoliotic curves in children with sig nificant growth remaining are the curves most likely to progress, The mechanism of progression of skeletal deformities is thought to be cont rolled by the Hueter-Volkmann law, whereby additional axial compressio n decelerates growth, and reduced axial compression accelerates growth . It has been hypothesized that spinal curvature leads to asymmetric l oading transversely along the vertebral growth plate, causing progress ive vertebral wedging by means of a vicious cycle. Methods. Two 32-mm diameter external ring fixators were glued to 0.7-mm pins that had bee n inserted percutaneously through the eighth and 10th caudal vertebra of 10 6-week-old Sprague-Dawley rats, Calibrated springs and 15 degree s wedges, mounted on stainless steel threaded rods passing through hol es distributed around the rings, imposed a 30 degrees Cobb angle and a xially compressed the instrumented vertebrae. Fluorochrome labels and radiographs were used to document the progression of vertebral wedging . Results. The wedging initially was entirely in the intervertebral di scs, but by 6 weeks the wedging of the discs and vertebrae were approx imately equal. Fluorochrome labeling confirmed that the vertebral wedg ing resulted from asymmetric growth in the physes. Conclusions. This s tudy shows that vertebrae, when asymmetrically loaded, become wedged. This is consistent with the concept of mechanically provoked progressi on of scoliotic deformities according to the Hueter-Volkmann law.