Mechanical effects of function on bone healing. Nonweight bearing and exercise in osteotomized rats.

The effects of different degrees of function and weight bearing on the healing of femoral osteotomies were studied in rats. A transverse osteotomy of the left femur was stabilized by intramedullary pinning. The rats were allocated to three groups: (1) tenotomy of the left achilles tendon to avoid weight bearing, (2) unrestricted weight bearing, and (3) a 4-week training programme 4 weeks after the osteotomy. After 8 weeks, the rats were killed; and callus production, bending moment, bending rigidity, and fracture energy at the osteotomy site were evaluated. There were no differences in the area of external callus. The bending moment was less in the nonweight-bearing rats. Bending rigidity and fracture energy were marginally less in the nonweight-bearing rats. There were no significant differences between the weight bearing and exercised rats. The results indicate that normal weight bearing stimulates bone healing, whereas activity above normal neither accelerates nor impairs this process.