Extensive ossification of the ungular cartilages and other osseous abnormalities of the proximal and distal phalanges

Abstract

SummaryOssification of the ungular cartilages of the equine foot has been well documented. There is growing evidence to suggest that extensively ossified cartilages (≥grade 4) can be associated with injury, pain and lameness. The objectives of this study were to describe the locations and extent of new bone on the proximal and distal phalanges and to determine the frequency of occurrence related to the ossification grade of the ungular cartilages. It was hypothesised that new bone formation would be seen more commonly in horses with grades ≥4 ossification than those with ossification of grade ≤3. Data were collected from 929 sets of images from individual limbs of 589 horses. Logistic regression modelling was used to indicate predictor variables that were significant. In 15.4% of limbs, there was grade 4 or 5 ossification of one or both ungular cartilages. New bone formation was seen on the palmaromedial and palmarolateral aspects of the diaphyseal and distal metaphyseal regions of the proximal phalanx in 28.7% of limbs. New bone formation was seen on the dorsal, dorsomedial and dorsolateral aspects of the distal phalanx, midway between proximal and distal in 7.2% of limbs. New bone formation was seen more commonly on the proximal phalanx (P≤0.002) and the distal phalanx (P≤0.042) in feet with grade ≥4 ossification of the ungular cartilages than in feet with ossification grade ≤3. Thoroughbred (odds ratio [OR] 0.398) and Warmblood (OR 0.522) breeds had a lower risk of new bone formation on the proximal phalanx compared with other breeds. Increasing age was a risk factor for new bone formation on the proximal phalanx (OR 1.092) but was associated with reduced risk of new bone on the distal phalanx. New bone formation on the proximal and distal phalanges may contribute to pain and lameness.