Some of you might recognize this syndrome as the disease formerly known as epiphysitis. This disease–or more correctly disturbance of growth–is most commonly recognized as that problem when foals get the enlarged, often painful areas just above their knees (carpi) or hocks. But as my clients have been asking me: What is it, and what does it mean for my foal?

Physitis is simply defined as inflammation of the growth plate (physis = growth plate, itis = inflammation). Growth plates are the areas within the bones of young horses from which the bones grow or lengthen. (In adults, the plates have "closed" and are no longer present.) Technically, the growth plate is referred to as the metaphyseal growth plate. Each region of a bone has a different name, with the middle of the bone called the diaphysis, the slightly flared portions of the bone before the growth plate called the metaphysis, and the ends of the bones, where the articular cartilage is located, is called the epiphysis (see "Long Bone Anatomy" on page 63).

In young horses (where growth plates are present), the growth plate occurs within the metaphysis and becomes the line that separates the metaphysis and the epiphysis.

What Does it Mean to My Horse?

Physitis is often considered to be a developmental orthopedic disease (DOD), and as a result, it does not affect adult horses. Physitis only affects young, growing horses–more specifically, those young horses with active growth plates.

Growth plates are specialized areas within the bones of horses (and all mammals for that matter), that can be located either at one end–or in some cases b