It has been generally accepted that mechanical stimulation is an
important factor in the promotion of formation of bone. Fracture-healing
consists of periosteal bridging of the fracture, which achieves stability,
and proliferation of endosteal bone to fill the defects between the ends of
the bone. To evaluate the effect of weight-bearing on bone-healing, an
operatively created defect in the tibial cortex was chosen as an
experimental model. In one set of dogs (Group 1), a bilateral defect in the
tibial cortex was created and weight-bearing was permitted on one tibia but
not on the opposite one. In Group 2, a bilateral defect in the tibial
cortex was made and weight-bearing was allowed on both tibiae. A third
group of dogs of similar age (Group 3) had no tibial defects. Quantitative
histomorphometry was used to measure formation and porosity of bone.
Weight-bearing was measured with both static and dynamic techniques.
Significantly less woven bone formed in the defects in the
non-weight-bearing tibiae than in the weight-bearing tibiae. This appeared
to be due to a disuse response in the underloaded tibiae, in which less
bone formed, rather than to the formation of more bone in the
weight-bearing tibiae. The data suggest that weight-bearing is a permissive
factor, not a stimulus, for formation of woven bone in a tibial defect.
Clinical Relevance: This animal model supports the concept that lack of
weight-bearing decreases the amount of woven bone that is formed in a
healing tibial defect. The results of this study indicate that
weight-bearing increases the formation of bone in
fracture-healing.(ABSTRACT TRUNCATED AT 250 WORDS)