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 58,342 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The elongated, distally tapered limbs of horses are adapted for high-speed locomotion. Because these traits are artificially selected for in modern racehorses, they operate at a morphological extreme with a high risk of fracture. Racehorses are subject to different training and racing regimes depending on their breed and gait, and are therefore an interesting model to examine bone functional adaptation under variable biomechanically intense conditions. This study compares bone structural properties in the third metacarpal (MCIII) of Thoroughbred (n = 9) and Quarter Horse (n = 11) racehorses, using feral Assateague Island ponies (n = 6) as an untrained/unraced outgroup, to determine whether structural properties reflect variable racing and training regimes. Geometric section properties and bone mineral densities were determined using peripheral quantitative CT at two diaphyseal sites and through the distal epiphysis. Diaphyseal strength of the MCIII in all three breeds does not differ relative to body size, but in the mid-diaphyseal region Thoroughbreds have higher antero-posterior relative to medio-lateral bending strength than Quarter Horses, as well as higher bone mineral densities in left MCIII epiphyses (particularly in the lateral condyle). Interestingly, all breeds have lower bone mineral densities in the lateral versus medial condyle, an inherent structural feature that may influence predisposition to fracture when running around turns. Our results suggest that despite subtle differences in bone structure between different racehorse breeds, basic morphology of the third metacarpus is relatively similar among racing and non-racing horses, possibly reflecting intense selection (natural and artificial) across domestic equids for similar structural features within distal limb elements.
Anat Rec (Hoboken) 2020 Aug 17
PMID:Locomotion on the edge: Structural properties of the third metacarpal in Thoroughbred and Quarter Horse racehorses and feral Assateague Island ponies. 3280 66

Polydactyly is a congenital malformation resulting from an autosomal dominant mutation manifesting as supernumerary digits of the hands or feet. It is most commonly reported in humans and domestic mammals, though there have also been isolated examples across a range of wild vertebrate species. Here we report a case of extremely unusual bilateral preaxial polydactyly on the pectoral limbs of a male western grey kangaroo (Macropus fuliginosus) from the South West region of Western Australia, in which two supernumerary digits were present on each manus. A supernumerary digit I on each manus was rudimentary in morphology without extrinsic muscular connections. However, supernumerary digit II present on each manus had fully developed extrinsic and intrinsic muscular connections, suggesting that these digits possessed normal function in flexion and extension. An alternative hypothesis is that the two supernumerary digits are both representatives of the most radial digit I, though this would then require the true digit I to have taken on the appearance of digit II by acquiring an additional phalanx and modified muscular attachments. The carpal bones exhibited a number of subtle differences in morphology when compared to normal pentadactyl individuals. The presence of a distal, rather than proximal, epiphysis on the first metacarpal was unexpected but further investigation suggested that this characteristic is perhaps more variable (in this species at least) than has been previously recognized. This case provides an unusual example to be considered within the broader context of limb development.
Anat Rec (Hoboken) 2020 Oct 09
PMID:Extreme bilateral polydactyly in a wild-caught western grey kangaroo. 3303 15


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