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  Discussion on Research: Exercise and Bone Remodeling
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DrO

Posted on Thursday, Jul 29, 2010 - 8:56 pm:

This is a rather complicated reaffirmation of the common sense notion that hard training horses experiencing increasing levels of exercise need rest time for the skeleton to recover following intense training.

Recovery time allows for replacement of minerals in the bone and remodeling of the organic portion of the bone to better support the newly experienced stresses as training progresses. However the amount of time for any level of stress is still speculative. We give suggestions in the article on Physiology and Conditioning but more scientific work on this would be nice.
DrO

2. Bone. 2010 Jul 23.
Third metacarpal condyle fatigue fractures in equine athletes occur within previously modelled subchondral bone.

Whitton RC, Trope GD, Ghasem-Zadeh A, Anderson GA, Parkin TD, Mackie EJ, Seeman E.
Faculty of Veterinary Science, University of Melbourne.

Abstract
Bone modelling and remodelling reduce the risk of fatigue fractures; the former by adapting bone to its loading circumstances, the latter by replacing fatigued bone. Remodelling transiently increases porosity because of the normal delay in onset of the formation phase of the remodelling sequence. Protracted intense loading suppresses remodelling leaving modelling as the only means of maintaining bone strength. We therefore hypothesized that race horses with fatigue fractures of the distal third metacarpal bone (MC3) will have reduced porosity associated with suppressed remodelling while continued adaptive modelling will result in higher volume fraction (BV/TV) at this site. Using high resolution peripheral quantitative computed tomography (HR-pQCT), we measured the distal aspect of the MC3 obtained at postmortem from 13 thoroughbred race horses with condylar fractures of the MC3 (cases), 8 horses without fractures (training controls), 14 horses with a fracture at another site (fractured controls) and 9 horses resting from training (resting controls). Porosity of the subchondral bone of MC3 was lower in cases than resting controls (12+/-1.4% vs. 18+/-1.6%, P=0.017) although areas of focal porosity were observed adjacent to fractures in 6/13 horses. BV/TV of the distal metacarpal epiphysis was higher in horses with condylar fractures (0.79+/-0.015) than training controls (0.74+/-0.019, P=0.070), but also higher in controls with a fracture elsewhere (0.79+/-0.014) than the training controls (0.74+/-0.019, P=0.040). BV/TV was higher in horses over three years of age than those aged two or three years (0.79+/-0.01 vs. 0.74+/-0.01, P=0.016). All metacarpal condylar fractures occurred within focal areas of high BV/TV. We infer that intense training in equine athletes suppresses remodelling of third metacarpal subchondral bone limiting damage repair while modelling increases regional bone volume in an attempt to minimise local stresses but may fail to offset bone fragility.
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