Biomechanical and densitometric bone properties after callus distraction in sheep

Assessment of biomechanical stability of diaphyseal bone lengthened by call us distraction is an unsolved problem. A middiaphyseal corticotomy was perf ormed in the left tibia of 24 sheep. After 7 days, callus distraction was b egun at a rate of 0.5 mm every 12 hours for 30 days using a standard unilat eral fixator system, Animals were euthanized 4, 8, or 12 weeks after the en d of distraction. The lengthened tibia and the contralateral control tibia from each animal were evaluated by radiographic, densitometric (dual energy xray absorptiometry, quantitative computed tomography), and biomechanical (axial compression testing, torsion testing to failure) methods. The bone m ineral density and maximum torque for the lengthened tibia were significant ly greater in the 8-week group than in the 4-week group. However, the value s in the 12-week group were significantly smaller than in the 8-week group, In the lengthened tibias, there was a correlation between the maximum torq ue and the bone mineral density, and between the maximum torque and the bon e density. Bone density measurements are useful prognosticators for the saf e removal of external fixators after leg lengthening procedures. By using t hese methods, clinical fractures after leg lengthening could be avoided in the future.