Pathological and clinical features associated with palmar/plantar osteochondral disease of the metacarpo/metatarsophalangeal joint in Thoroughbred racehorses.

REASONS FOR PERFORMING STUDY: Palmar/plantar osteochondral disease (POD) of the metacarpo/metatarsophalangeal (Mc/MtPh) joints is common in Thoroughbred racehorses, but there is little information on predilection sites, associated pathologies and clinical signs.

OBJECTIVES

To describe the distribution of POD at post mortem examination and to examine the association of POD with other pathologies and clinical histories.

METHODS

The Mc/MtPh joints of 102 Thoroughbred racehorses were examined post mortem. Gross pathology of associated osteochondral elements, suspensory ligament and flexor tendons was recorded. Clinical data were extracted from computerised records. Relationships between all Mc/MtPh joint pathologies, clinical data and grade of POD in each condyle were determined using multilevel, ordinal logistic regression models.

RESULTS

Palmar/plantar osteochondral disease was recorded (grade 1-3 in at least one condyle) in 80.4% (95% confidence interval 71-88) of horses. The grade of POD was significantly higher in the forelimb, where the medial condyle had higher grades, than in the hindlimb, where the POD grade was higher in the lateral condyle. There was a significant positive relationship between POD grade and multiple other joint pathologies, whereas grades of linear fissures had a negative relationship with grade of POD. There was no relationship between grade of POD and tendon and suspensory ligament gross pathology, although horses with a history of tendon injury had significantly lower POD grades. Horses that had a clinical history of a Mc/MtPh joint problem had higher POD grades. In addition, horses that had been retired from racing for more than 2 months at the date of death had significantly lower POD grades.

CONCLUSIONS AND POTENTIAL RELEVANCE: Palmar/plantar osteochondral disease has specific predilection sites. Horses with a clinical history of Mc/MtPh-associated lameness had higher POD grades, whereas those with a history of superficial digital flexor tendon injury and retired horses had lower grades. The progression of POD and its ability to heal requires further evaluation.