Mechanical modulation of growth for the correction of vertebral wedge deformities

This study tested the following hypotheses: (a) a vertebral wedge deformity created by chronic static asymmetrical loading will be corrected by revers al of the load asymmetry; (b) a vertebral wedge deformity created by chroni c static asymmetrical loading will remain if the load is simply removed; an d (c) vertebral longitudinal growth rates, altered by chronic static loadin g, will return to normal after removal of the load. An external fixator was used to impose an angular deformity (Cobb angle of 30 degrees) and an axia l compression force (60% body weight) on the ninth caudal (apical) vertebra in two groups of 12 5-week-old Sprague-Dawley rats. This asymmetrical load ing was applied to all rats for 4 weeks to create an initial wedge deformit y in the apical vertebra. The rats from group I (load reversal) then underw ent 1 week of distraction loading followed by 4 weeks of asymmetrical compr essive loading with the imposed 30 degrees Cobb angle reversed. The rats fr om group II (load removal) had the apparatus removed and were followed for 5 weeks with no external loading. Weekly radiographs were obtained and seri al fluorochrome labels were administered to follow vertebral wedging. After the initial 4-week loading period, the combined average wedge deformity th at developed in the apical vertebra of the animals in both groups was 10.7 +/- 4.4 degrees. The group that underwent load reversal showed significant correction of the deformity with the wedging of the apical vertebra decreas ing to, on average, 0.1 +/- 1.4 degrees during the 4 weeks of load reversal . Wedging of the apical vertebra in the group that underwent load removal s ignificantly decreased to 7.3 +/- 3.9 degrees during the first week after r emoval of the load, but no significant changes in wedging occurred after th at week. This indicated a return to a normal growth pattern following the r emoval of the asymmetrically applied loading. The longitudinal growth rate of the apical vertebra also returned to normal following removal of the loa d. Vertebrae maintained under a load of 60% body weight grew at a rate that was 59.4 +/-: 17.0% lower than that of the control vertebrae, whereas afte r vertebrae were unloaded their growth averaged 102.4 +/- 31.8%. These find ings show that a vertebral wedge deformity can be corrected by reversing th e load used to create it and that vertebral growth is not permanently affec ted by applied loading.