Muscle contraction increases the strength of healing tibial fracture in the rat.

Tibial fractures in 7-week-old rats were fixed with intramedullary nails. After 25 days of healing the nails were removed and the tibiae loaded in vivo with intact soft tissues until refracture. The animals were tested in three-point anterior cantilever bending either during muscle contraction (n 8) or with relaxed muscles (n 8). Muscle contraction increased the ultimate bending moment by 84 percent, energy absorption by 108 percent, bending stiffness by 21 percent, and ultimate deflection by 49 percent.