The effect of exogenous somatotropin (eST) on bone changes were evaluated in twenty-nine juvenile horses in race training using radiographs of the third metacarpal obtained over the course of a 128 day research project. A biodensitometer was used to measure bone density, and a micrometer was used to measure cortical bone width and medullary cavity width. Fifteen horses were given daily intramuscular injections of eST and fourteen horses were given daily intramuscular injections of sterile saline and served as the control group. By day 128, the increase in total radiographic bone aluminum equivalence (RBAE) was significantly greater in the eST horses than in the control horses. The increases in RBAE in the dorsal and the medial cortices were greater in the eST horses than in the control horses, but these differences were not significant. There was a trend for changes in the ratio of RBAE in the dorsal to palmar and in the medial to lateral cortices to be greater in the eST than in the control horses. By day 128, the increases in both the dorsal and the medial cortical bone width were significantly greater in the eST than in the control group of horses. The eST horses had a significantly greater decrease in dorsal to palmar medullary cavity width, and increase in dorsal to palmar bone diameter than the control group. A computed index of dorsal cortical bone increased significantly more in the eST than in the control group. The stresses applied to bone are greater in the dorso-medial direction in racehorses. To decrease the strain, bone must either increase in bone mineral density, cortical width, and/or bone diameter. Both the eST group and the control group did make these changes in bone over time, but the eST group more effectively remodeled and modeled bone to increase the strength of the third metacarpal than did the control group of horses. In this research project, exogenous somatotropin treatment had a positive effect on the density and geometry of the third metacarpal. These changes are believed to result in a decreased risk of bone injury to the eST treated horses.

Stress fractures are common in the limb bones of human and equine athletes alike. Repetitive skeletal loading can lead to remodeling and the accumulation of microdamage in bone, which only becomes grossly evident during catastrophic fracture of the bone due to the accumulated microdamage. Though various metrics attempting to quantify bone health exist, none have distinguished themselves as early predictors of the susceptibility of bone to fracture. In this exploratory study, we examine the ability of several evaluation methods to distinguish between third metacarpal (MC3) bones from racehorses that have experienced a limb-bone fracture and from those that have not. Third metacarpal bones were harvested from deceased Thoroughbred racehorses and categorized into four groups: MC3 bones from horses whose cause of death was not related to skeletal fracture (Control group, n = 20), MC3 bones form horses that were euthanized after fracturing proximal sesamoid bones (Sesamoid group, n = 20), MC3 bones from horses that were euthanized after fracturing a non-MC3 long bone (Long Bone group, n = 19), and MC3 bones from horses that were euthanized after fracturing an MC3 (MC3 group, n = 5). Each MC3 bone underwent testing using a variety of tools and methods at the proximal, midshaft, and distal levels of the lateral, dorsal, and medial surfaces. All tools and methods (OsteoProbe reference point indentation, BioDent reference point indentation, x-ray, micro-CT, and pQCT) exhibited some capability in differentiating between control and fracture groups. The long-term objective of this project is to create a model that will utilize data from a set of evaluations and output the susceptibility of the horse to fracture a bone, a long bone, or the MC3, specifically. Although the sample size in this study is not sufficient to create a reliably predictive logistic regression model, promising results from preliminary models provide incentive to further explore the possibility of creating one. While clinical practicality will be a vital consideration for a model in the future, establishing this basis for the capability of each evaluation at hand is a necessary first step in predicting and preventing fracture in bone.

A fundamentação de métodos diagnósticos precoces na ortopedia de eqüinos é de extrema importância clínica, cirúrgica e econômica. O presente estudo teve como objetivo estudar a correlação da densidade mineral óssea do terceiro metacarpiano de eqüinos, obtida pelo método de absorciometria radiográfica, com a resistência dos mesmos quando submetidos a ensaios biomecânicos de compressão e flexão. Utilizaram-se trinta pares de osso terceiro metacarpiano de eqüinos adultos, os quais foram dissecados, radiografados, analisados pelo método de absorciometria radiográfica, submetidos ao estudo tomográfico e a ensaios biomecânicos. Através dos dados obtidos não se observou correlação significativa entre os valores de densidade óptica radiográfica e as propriedades biomecânicas do osso terceiro metacarpiano. Concluiu-se que não se pode inferir que os valores de densidade óssea obtidos pela absorciometria radiográfica do osso terceiro metacarpiano de um eqüino tenha correlação com a capacidade deste osso de absorver cargas de compressão e flexão. / The complete knowledge about non-invasive methods for early disgnostics in equine orthopedy is economicaly important. This experiment has studied the correlation between bone mineral density determined by radiographic absorptiometry and bone resistance of equine third metacarpal bone submitted to both compression and flexion testings. Thirty pairs of third metacarpal bone of adult horses were collected, dissected, radiographed, analysed by the radiographic absorptiometry technique, and submitted to tomographic study and biomechanical testings. The results have shown there is no significant correlation between radiographic bone density values and biomechanical properties of the third metacarpal bone. Therefore, it has been concluded bone mineral density of the third metacarpal bone determined by radiographic absorptiometry do not predict bone capacity to resist compression and flexion loads.

A fundamentação de métodos diagnósticos precoces na ortopedia de eqüinos é de extrema importância clínica, cirúrgica e econômica. O presente estudo teve como objetivo estudar a correlação da densidade mineral óssea do terceiro metacarpiano de eqüinos, obtida pelo método de absorciometria radiográfica, com a resistência dos mesmos quando submetidos a ensaios biomecânicos de compressão e flexão. Utilizaram-se trinta pares de osso terceiro metacarpiano de eqüinos adultos, os quais foram dissecados, radiografados, analisados pelo método de absorciometria radiográfica, submetidos ao estudo tomográfico e a ensaios biomecânicos. Através dos dados obtidos não se observou correlação significativa entre os valores de densidade óptica radiográfica e as propriedades biomecânicas do osso terceiro metacarpiano. Concluiu-se que não se pode inferir que os valores de densidade óssea obtidos pela absorciometria radiográfica do osso terceiro metacarpiano de um eqüino tenha correlação com a capacidade deste osso de absorver cargas de compressão e flexão. / The complete knowledge about non-invasive methods for early disgnostics in equine orthopedy is economicaly important. This experiment has studied the correlation between bone mineral density determined by radiographic absorptiometry and bone resistance of equine third metacarpal bone submitted to both compression and flexion testings. Thirty pairs of third metacarpal bone of adult horses were collected, dissected, radiographed, analysed by the radiographic absorptiometry technique, and submitted to tomographic study and biomechanical testings. The results have shown there is no significant correlation between radiographic bone density values and biomechanical properties of the third metacarpal bone. Therefore, it has been concluded bone mineral density of the third metacarpal bone determined by radiographic absorptiometry do not predict bone capacity to resist compression and flexion loads.