Lameness in the Young Horse

During fetal development, equine long bones have two main centers of ossification. The primary ossification center develops first and forms the diaphysis and metaphysis of the bone, while the secondary ossification center will form the epiphysis. The epiphysis forms early in life at one or both ends of long bones between the growth plate and the articular cartilage. These articular-epiphyseal complexes form in a manner similar to ossification of the cartilage models of the small cuboidal bones. This ossification mostly increases the size of the epiphyses but contributes very little to the length of the bone. The cartilage cells of the growth plate can be divided into a number of zones, which vary in height and cell number, histological appearance, and cellular function. These include the resting/reserve, proliferative, hypertrophy, provisional calcification, and ossification zones. The most widely accepted classification of growth plate injuries is based on the Salter-Harris system.