ALTHOUGH there is some variability in the pattern of musculoskeletal injuries sustained by thoroughbred horses at racecourses in different countries, fractures of the distal limb are common in racing thoroughbreds worldwide. Many thoroughbred racehorses are euthanased due to musculoskeletal injury. Fractures of the distal limb are a particularly common reason for euthanasia (McKee 1995). A recent study by Reardon and others (2014), summarised on p 477 of this issue of Veterinary Record , describes the distribution of fatal distal limb fractures affecting thoroughbred horses racing in Great Britain over a six-year period from 1999 to 2005, according to postmortem examination. Over a similar period, there has been growing recognition that cyclic fatigue injury to bone is an important explanatory mechanism for distal limb fracture in racing thoroughbreds (Boyde and others 1999, Riggs and others 1999, Muir and others 2006, 2008, Turley and others 2014). Advances in our understanding of the causative mechanisms for common fatal limb fractures in racing thoroughbreds suggest that early diagnosis of fatigue injury to bone before development of a distal limb stress fracture should be a focus for future work (Muir and others 2008, Anthenill and others 2010). This approach promises better overall management of racehorses and a reduction in the prevalence of stress fracture and associated fatal distal limb fracture. Accumulation of fatigue damage in the subchondral plate of the distal end of the third metacarpal or metatarsal bone is an important component of the mechanism that leads to condylar fracture and palmar osteochondral disease, two common stress fractures in racing thoroughbreds (Riggs and others 1999, Muir and others 2006, 2008). Past ex vivo studies suggest that damage accumulation in adapted bone is an important prodromal marker for condylar fracture …