RADIOGRAPHIC CHARACTERISTICS OF THE FORELIMB DISTAL PHALANX AND MICROSCOPIC MORPHOLOGY OF THE LATERAL PALMAR PROCESS IN FOALS 3-32 WEEKS OLD

Developmental morphology of the forelimb distal phalanges and lateral palmar processes of 9 Thoroughbred foals aged 3-32 weeks was assessed using radiography, microradiography and histology. For inclusion in th e study, all distal phalanges had no pathologic radiographic abnormali ties. Vascular channels that are characteristically found in the dorsa l region of the distal phalanx were not evident radiographically in th e palmar process, The proximal and distal angles of the palmar process es were separated by a lucent line continuous with the inclsure in foa ls only through 12 weeks of age. The distal phalanges were triangular- shaped in foals 3-12 weeks of age, and were oval-shaped in older foals . The palmar aspect of the distal phalanx was the major contributor to growth of the distal phalanx in the sagittal plane, especially betwee n 3 and 12 weeks of age, Growth of the lateral palmar process occurred through the means of endochondral ossification. The body and cortices of the lateral palmer process were composed of coarse cancellous bone . Porosity within the lateral palmer process was greater in regions sa mpled axial, compared to abaxial, to the parietal sulcus and did not c hange with age. A fracture was identified microradiographically and/or histologically in 9 of 18 (50%) and 10 of 17 (59%), respectively, of the lateral palmar processes examined. The fracture line was consisten tly associated with the parietal sulcus on the dorsal cortical surface and was always immediately abaxial to the deep digital flexor tendon attachment, No age-related morphological changes of the lateral palmar processes were identified with microradiography or histological exami nations.