Exercise History and Remodelling Stress Fracture are Related to Cortical Bone Ultimate Strength (P264)

Abstract

Mechanical load deforms bone tissue first elastically then plastically. The tissue adapts to the load through internal remodelling and external modelling. Large or repetitive loads can induce significant damage and cause large changes in bone shape and density. Remodelling initially causes transient osteoporosis during damage removal. Intense exercise can damage bone material, we hypothesised that exercise history reduces bone ultimate strength and that ultimate strength is reduced in bones with evidence of stress fracture syndrome. Equine humeri from 18 Thoroughbred racehorses were categorised on the basis of periosteal callus (none, mild, moderate, severe). The location of the callus was consistent with stress related modelling at the proximocaudal stress fracture site. Cortical cores from the humeral diaphysis distal to the callus site were monotonically compressed to failure (strain rate: 0.01s(-1)). The effect of stress fracture callus severity on ultimate strength was assessed using non-parametric tests. The relationships between ultimate strength and exercise history variables were examined with univariate and stepwise linear regression (p<0.05). Cores with mild and moderate callus had 5.0% and 6.6% lower ultimate strength than cores without callus. High speed exercise distances (race, work, and total event distances in the 2-4 months before death) had positive, linear, univariate relationships with ultimate strength (r(2)>0.213). Average total high speed distance was the only parameter retained in the stepwise model (r(2)=0.42). Degradation of material properties occurred in cortical diaphyseal bone material of bones with early evidence of stress fracture syndrome at a distant site, and was related to intense exercise. Thus, remodelling events likely associated with stress fracture syndrome are not isolated to the site of stress fracture. PU - SPRINGER VERLAG PARIS PI - PARIS PA - 1 RUE P CEZANNE, 75008 PARIS, FRANCE