Tropical joint syndrome: Exostosis on the dorsal aspect of the proximal phalanx in racing Thoroughbreds in Asia

Tropical joint syndrome (TJS) is poorly documented in the published literature but appears to be associated with horses undergoing intensive training in tropical areas: South East Asia and Northern Australia. Tropical joint syndrome is characterised by a firm, often nonpainful swelling at the front of the fetlock, which has a slow and insidious onset. Swelling associated with TJS can reach an alarming size, with a marked loss of fetlock flexion. Radiographs reveal varying degrees of exostosis, initially on the dorsolateral aspect of proximal phalanx (P1) but, as the condition progresses, onto the dorsomedial P1 and distal dorsal third metacarpal bone. A survey of equine veterinarians employed in racing practices in Southeast Asia and Australia (n = 10) was undertaken to estimate the prevalence of this condition and treatment methods. Additionally, a retrospective study of clinical records was undertaken at the Singapore Turf Club to identify horses with TJS, with racing performance post-diagnosis compared with matched controls. All 10 racing veterinarians responded to the survey. All respondents recognised TJS in horses in their practice as ‘new bone deposits of unknown origin’, with most estimating prevalence between 1 and 10% in their population of horses. The most common treatment for TJS was intra-articular medication (n = 9) and/or shockwave therapy. In total, 79 horses had TJS diagnosed by equine veterinarians at the Singapore Turf Club between 2008 and 2015, 64 of which had complete race records. There was no significant difference in racing performance between horses with and without TJS. However, 29 cases that were retired from racing were retired with chronic, severe and irreversible fetlock pain. The high number of horses retired with fetlock pain due to TJS is a welfare concern. More research is required to identify management and treatment strategies to aid in dealing with this condition.