Abstract
The metacarpophalangeal joint is one of the most common regions to sustain injury in the equine forelimb. Pathological conditions of the third metacarpal, proximal phalangeal and the proximal sesamoid bones are very common amongst both Standardbred and Thoroughbred racehorses. These conditions are of a great economic cost to the horse industry as well as being detrimental to the welfare of the horses themselves. A recent study (0HAlrtib et al., 2012) has shown some significant differences in morphology in the bones contributing to the fetlock joint between the equine breeds. These variations might be due to both genetic and mechanical effects which are likely to be associated with the different performance requirements and other selection pressures that have produced the different breeds. The aims of the proposed study were to: 1. develop reliable and repeatable radiological measurements of the fetlock joint bones in Thoroughbreds; 2. investigate possible relationships between bone morphometry and the pathological incidences in this breed; and 3. identify any correlations between these measurements and specific performance requirements in the breed. A circle circumference was best fit onto latero-medial radiographs of the most dorsal region of the lateral condyle of three fetlock joints with radio-opaque markers fixed on the bony prominences. The circle centre was assumed to approximate the centre of fetlock joint motion. Fetlock joint angles of ten vertically-fixed cadaver forelimbs were measured with a goniometer five times by rater A, and once by rater B. Fourteen horses were measured before and after lifting the contralateral limb. Five (standing) and eight (limb lifted) horses were measured six and five times in random order respectively. Marked fetlocks of five horses were filmed in five different head positions (forward, right, left, raised, and lowered). Duplicate front fetlock angles of 6 control and 6 exercised horses were measured before and after treadmill exercise. iii Six (three right and three left) distal forelimbs of six different adult horses were used in the study. Each forelimb was set in the load cell to apply specific loads to get seven different fetlock joint angles. Standard dorso-palmar and latero-medial radiographs were taken for each limb at each fetlock joint angle. All selected parameters were measured on each radiograph and the effect of fetlock angle on those parameters was calculated. Another seven right distal forelimbs with no history of any orthopaedic lesions were used. Each specimen was scanned using a CT machine (Siemens Somatom Emotion 16 Excel Editor- Germany). All morphometric measurements were taken on the images obtained from 3D modules, converted from CT scan images. The standard view was chosen as a zero view. Once the zero view was determined, the effect of the orientation angle and the fetlock joint angle on the measurement values was also calculated. A number of radiographs, which were taken for horses with fetlock problems, were collected from clinics along with their radiological reports and also sets of DP and LM radiographs were taken from 18 experienced racehorses with no fetlock problems. These radiographs were measured and the difference between the two groups was studied. The study identified specific measures of the equine fetlock joint bones that may be made using radiological methods. In addition, it identified some basic morphological measures to assist in selecting horses that are at greater risk of specific pathology in the fetlock joint and that are more suitable for different activities especially high speed racing.