CHARACTERIZATION OF OSSEOUS BODIES OF THE DISTAL PHALANX OF FOALS

The distal phalanx and metacarpal physis of both forelimbs of 32 Thoro ughbred foals 3-32 weeks of age were radiographed to identify those li mbs with osseous bodies at a palmar process (PP) Of the distal phalanx . Osseous bodies (ossicles) were identified radiographically in 19% of the foals. Sixteen of the 32 foals were selected for microradiographi c and histological evaluation: 6 foals with radiographic evidence of o ssicles and 10 foals without. Fourteen ossicles of the PP were observe d radiographically. Ossicles were either a triangular bone fragment at the palmar aspect of the distal angle of the PP, or an oblong bone fr agment separated from P3 by a radiolucent line extending 1-3 cm from t he incisure of the PP to the solar margin. One foal had radiographic e vidence of bilateral distal metacarpal physitis. Seventeen of 35 PPs e xamined microradiographically were considered normal, in that the dors al and solar cortices were thin with trabecular bone orientated parall el to the cortical surfaces, and there was a depression in the dorsal cortical surface (i.e. parietal sulcus). Abnormal microradiographic fi ndings in the other 18 PPs included a fracture line extending from the dorsal cortical surfaces and trabecular bridging of the fracture gap. The fracture line was often continuous with the parietal sulcus. Micr oradiographic evidence of a fracture was found in 75% of foals evaluat ed. Normal histological findings in 16 PPs included thin dorsal and so lar cortices with trabeculae orientated parallel to the cortical surfa ces, parallel-fibred dense connective tissue attachments of the deep d igital flexor tendon to the solar cortical surface, and a neurovascula r bundle associated with the parietal sulcus. Abnormal histological fi ndings of the other 20 PPs included: a fracture line extending from th e dorsal to solar cortical surfaces, trabecular bridging of the fractu re gap, and fibrocartilage which was within the fracture gap and orien tated parallel to the longitudinal axis of the gap. Histological findi ngs consistent with a fracture were found in 69% of foals evaluated. I t was concluded that ossicles of the PP in foals 3-32 weeks of age are fractures, not all of which are visible radiographically.