Plantar osteochondral fragments in the metatarsophalangeal joints in Standardbred trotters; result of osteochondrosis or trauma?

Abstract

Summary Hindlimb fetlock joints with plantar osteochondral fragments (POF) were collected from 21 horses (17 Standardbred trotters, 4 Swedish Warmblood riding horses; 8 stallions, 5 geldings, and 8 mares; ages 5 months‐21 years) and from 28 horses with no metatarsophalangeal joint pathology. The morphology of the osteochondral fragments and adjacent tissues was studied by dissection, high‐resolution radiography, and histology. There were 22 joints affected, and 20 out of 25 POF found were located medially. In 3 joints there were fragments both laterally and medially. The fragments were attached to the short sesamoidean ligaments and facing the joint cavity they had a smooth cartilage covered surface which measured between 4 times 2 mm and 12 times 6 mm. A small central trabecular osseous core was seen radiographically in the young horses (<1 year of age), and the proportion of the bony component increased during the first years of life. In 18 out of 25 POF sites, a defect was seen in the adjacent bone of the proximal phalanx. Histology did not show any findings indicative of osteochondrosis. It is suggested that plantar osteochondral fragments are the result of outwardly rotated hindlimb axes and subsequent point loading in the medial fetlock area. Repeated high tension loads in the short sesamoidean ligaments may cause fragments of tissue with osteogenic properties to come off the proximal phalanx into the ligament, later forming osteochondral fragments.