Page 54 - July 2020

EQUINE HEALTH
DEVELOPMENTAL
PROBLEMS IN
YOUNG HORSES
Part One: OCD, Bone Cysts and Physitis
Part 2 will appear in our August 2020 issue by Heather Smith Thomas
Developmental orthopedic disease (DOD) is a catch-all term that covers several abnormal skeletal develop-
ments due to improper bone growth in young growing horses. These problems include angular and flexural limb deformi- ties, osteochondrosis (improper calcification of bone directly under the cartilage layer), and wobbler syndrome. Michael Schramme, DVM, MRCVS, PhD at the University
of Lyon in France, deals with many of these problems.
Schramme says that osteochondrosis includes OCD (osteochondritis dissicans, or dissecting lesions in joints) and subchondral bone cysts (cystic lesions in joints). Both of these problems are due to abnormal ossifi- cation of growing cartilage. “The ends of bones in foals have a thick layer of cartilage over them. During normal growth, the thick
cartilage progressively turns into bone, pro- ducing bone growth. At maturity, the result is a thin cartilage layer, with a thick, strong bone layer directly underneath it,” he says. In osteochondrosis, things go wrong and the cartilage doesn’t turn to bone.
“Another common problem is physitis, where the abnormal ossification process occurs in growth plates at the ends of the long bones rather than in joints. One form of phy- sitis is angular limb deformity, which usually affects foals very early in life. Another form is cervical vertebral malformation (wobbler dis- ease), in which growth plates of vertebrae in the neck become misshapen because the grow- ing cartilage does not progress into normal bone formation. Another form of improper skeletal development includes various flexural deformities (often called contracted tendons),” says Schramme.
OCD
The most common developmental problem Schramme deals with is OCD, or osteochon- dritis dissicans. “This is a condition in which cartilage or cartilage/bone fragments separate out in joints. During the ossification process when cartilage should be turning into bone, there are shearing, dissecting lesions develop- ing in the cartilage. It tends to occur at specific sites in specific joints. Most affected is the hock, second most common is the stifle, third is the fetlock joint and fourth is the shoulder,” says Schramme. OCD shows up more often in the hind limb than the front.
“There are two types of presentations with OCD. One would be a foal with large defects
in the articular surfaces of the joint, containing large cartilage fragments or bone fragments. These horses tend to have marked joint effusions (distension) early on in life, from weanling
Although some claim they are close to identifying the genetic marker for OCD, it must be remembered that the condition is multi-factorial and therefore may not be dependent on one gene.
Physitis is the abnormal ossification process that occurs in growth plates at the ends of the long bones rather than in joints.
52 SPEEDHORSE July 2020