STUDY DESIGN: The authors developed a rat-tail model to investigate the hypothesis that vertebral wedging during growth in progressive spinal deformities results from asymmetric loading in a "vicious cycle." OBJECTIVES: To document growth curves with axial compression or distraction applied to tail vertebrae to determine whether compression load slows growth and distraction accelerates it. SUMMARY OF BACKGROUND DATA: Progression of skeletal deformity during growth is believed to be governed by the Hueter-Volkmann law, but there is conflicting evidence to support this idea. METHODS: Twenty-eight 6-week-old Sprague-Dawley rats were assigned to one of three groups: compression loading, distraction loading, or sham (apparatus applied without loading). Under general anesthesia, two 0.7-mm diameter stainless steel percutaneous pins were used to transfix each of two vertebrae. The pins were glued to 25-mm diameter external ring fixators. Springs (load rate, 35 g/mm) were installed on three stainless steel threaded rods that were passed through holes in each ring and compressed with nuts to apply compression or distraction forces between 25-75% of bodyweight. Vertebral growth rates in microns/day were measured by digitizing the length of the vertebrae images in radiographs taken 0, 1, 3, 5, 7, and 9 weeks later. RESULTS: The loaded vertebrae grew at 68% of control rate for compressed vertebrae and at 114% for distracted vertebrae. (Differences statistically significant, P < 0.01 by analysis of variance.) For the compressed vertebrae, the pinned vertebrae, which were loaded at one of their two growth cartilages, grew at a reduced rate (85%), although this effect was not apparent for the distraction animals. CONCLUSIONS: The findings confirm that vertebral growth is modulated by loading, according to the Hueter-Volkmann principle. The quantification of this relationship will permit more rational design of conservative treatment of spinal deformity during the adolescent growth spurt.
STUDY DESIGN: The authors developed a rat-tail model to investigate the hypothesis that vertebral wedging during growth in progressive spinal deformities results from asymmetric loading in a "vicious cycle." OBJECTIVES: To document growth curves with axial compression or distraction applied to tail vertebrae to determine whether compression load slows growth and distraction accelerates it. SUMMARY OF BACKGROUND DATA: Progression of skeletal deformity during growth is believed to be governed by the Hueter-Volkmann law, but there is conflicting evidence to support this idea. METHODS: Twenty-eight 6-week-old Sprague-Dawley rats were assigned to one of three groups: compression loading, distraction loading, or sham (apparatus applied without loading). Under general anesthesia, two 0.7-mm diameter stainless steel percutaneous pins were used to transfix each of two vertebrae. The pins were glued to 25-mm diameter external ring fixators. Springs (load rate, 35 g/mm) were installed on three stainless steel threaded rods that were passed through holes in each ring and compressed with nuts to apply compression or distraction forces between 25-75% of bodyweight. Vertebral growth rates in microns/day were measured by digitizing the length of the vertebrae images in radiographs taken 0, 1, 3, 5, 7, and 9 weeks later. RESULTS: The loaded vertebrae grew at 68% of control rate for compressed vertebrae and at 114% for distracted vertebrae. (Differences statistically significant, P < 0.01 by analysis of variance.) For the compressed vertebrae, the pinned vertebrae, which were loaded at one of their two growth cartilages, grew at a reduced rate (85%), although this effect was not apparent for the distraction animals. CONCLUSIONS: The findings confirm that vertebral growth is modulated by loading, according to the Hueter-Volkmann principle. The quantification of this relationship will permit more rational design of conservative treatment of spinal deformity during the adolescent growth spurt.
Authors: Behrooz A Akbarnia; Robert M Campbell; Alain Dimeglio; Jack M Flynn; Gregory J Redding; Paul D Sponseller; Michael G Vitale; Muharrem Yazici Journal: J Child Orthop Date: 2011-04-27 Impact factor: 1.548