Loss of bone strength after intramedullary nailing. Torsion tests of tibial osteotomies in rabbits.

Rigid intramedullary nailing was used in 75 rabbits to stabilize a transverse osteotomy of the midshaft of the tibia. In 36 additional rabbits intramedullary nailing was performed without osteotomy. No additional external immobilization was used postoperatively. After removal of the nail the mechanical strength of the tibiofibular bones was tested torsiometrically in 30 osteotomized and 18 non-osteotomized animals from 3 to 24 weeks after the operation. At 3 weeks the torsional load fractured all osteotomized bones through the osteotomy line. At later stages a spiral fracture occurred either crossing or close to the osteotomy area, usually distal to the tibiofibular junction. The increase in mechanical strength of the osteotomized bones reached a maximum at 6 weeks and then decreased. The strength of the non-osteotomized nailed bones also decreased slightly. The results suggest that rigid intramedullary nailing, although providing good conditions for early consolidation of experimental osteotomy, leads secondarily to deterioration of the mechanical properties of tubular bone.