A postmortem grading system for articular cartilage loss of the dorsoproximal aspect of the proximal phalanx of Thoroughbred racehorses

The metacarpophalangeal and metatarsophalangeal joints in Thoroughbred racehorses are common injury sites, given their high range of motion and compression during galloping. In New Zealand, the proximal phalanx (P1) is a common site for race-day fracture, but the lesions of this bone have not been described. Therefore, we created a scoring system to describe cartilage on the dorsoproximal aspect of P1 in New Zealand Thoroughbred racehorses. We collected 102 P1s from racehorses submitted for postmortem examination. Horses were categorized into 2 cohorts: 1) fracture (18 horses euthanized because of catastrophic fracture) or 2) control (16 racehorses euthanized for reasons unrelated to musculoskeletal injury). We used a modified 3-point scoring system to grade the dorsoproximal surface of P1 (from no damage [0] to severe damage [3]). The articular cartilage score did not differ between fracture and control cohorts ( p > 0.05). Cartilage scores were higher in the medial aspect of the left forelimb and right hindlimb ( p < 0.05), as expected given that those limbs experience greater strain when traveling in the counterclockwise race direction common in New Zealand. The articular cartilage score increased with increasing horse age and career starts ( p < 0.05). Our results reflect the greater load on the medial aspect of the limb and reduced capacity of articular cartilage to repair as horses age.