Radiographic Appearance of the Fore Digit and Carpal Joint in the Mule Foal from Birth to 3 Months of Age

SIMPLE SUMMARY: Radiography is important for the diagnosis of prematurity and musculoskeletal abnormalities in foals. Given that no data on the normal radiographic anatomical development of the mule foal are available, we evaluated the radiographic development of the mule fore digit and carpal joint from 0 to 3 months of age. The radiographs highlighted that growth plate closure times differed depending on the fore digit bones, and on whether the carpal bones were immature at birth. Distal phalanx was triangular at birth, palmar processes had developed by one month, and proximal sesamoid bones were trapezoidal by three months. No distal phalanx remodeling was evident within the hoof capsule or variations in the hoof axis with growth, and hoof capsule thickness increased. We identified a baseline for the interpretation of radiological features of the forelimb in the mule foal, and we highlighted specific radiographic parameters that were intermediate between those found in horses and donkeys. ABSTRACT: Few studies have established the normal radiographic anatomical development of the donkey foal and, to date, no data are available for mules. Our aim was thus to evaluate the radiographic development of the fore digit and carpal joint in the mule foal from 0 to 3 months of age. Ten forelimbs of five healthy full-term mule foals were included. Radiographs of the fore digit lateromedial and dorsopalmar and the carpus dorsopalmar were performed weekly for the first month of age, and bi-monthly during the following two months. Fore digit growth plate closure times, morphological, angular, and linear radiographic parameters, and also carpal cuboidal bone mineralization were evaluated. Growth plates were graded as open, closing, and closed. Carpal bone appearance was graded as mature, slightly immature, or immature. Growth plate closure times showed the following: middle phalangeal distal physis (DP) closed at birth, and proximal physis (PP) started to close at around two months; first phalanx DP closed at seven days, and PP started to close at three months; and third metacarpal bone DP started to close at two months. Carpal bones were immature at birth. Distal phalanx (PD) was triangular at birth, palmar processes had developed by one month, and proximal sesamoid bones were trapezoidal by three months. The hoof wall, PD dorsal wall, and palmar angles values changed in parallel, and hoof capsule thickness increased. No PD remodeling evidence within the hoof capsule or variations in the hoof axis with growth were found. We identified a baseline for the interpretation of forelimb radiological features in mule foals. The specific features found were intermediate between those found in horses and donkeys.