DEVELOPMENTAL ORTHOPAEDIC DISEASE - PHYSITIS

By Sharon May-Davis
B.App.Sc.,Cert. Hon.(USA), M.App.Sc. ACHM, EBW, EMR

long bone

"Known species, through the process of natural selection, have evolved many unique and versatile structures in the struggle for existence." Charles Darwin 1859.
One could think that Darwin had Equus in mind when he wrote this statement. Its athletic prowess, versatility and adaptability to domestication inspired many an individual to breed for selected traits. However, many of those selected traits have now proven to be both taxing and arduous to its anatomical structure. Furthermore, in an attempt to meet specific demands, load-bearing structures have faltered and suffered accordingly.
Hence, we are now presented with an array of anatomical problems that require investigation. At present, Developmental Orthopaedic Disease or DOD is one such structural issue that requires specific attention. The American Quarter Horse Association first coined this umbrella term in 1986 and it encompasses all orthopaedic problems seen in the growing foal. These structural abnormalities can either individually or collectively render the athletic horse a statistical wastage within any industry. And furthermore, 67% of Thoroughbred foals exhibit DOD and 18.7% were not commercially viable. Thoroughbreds are not the only breed of horse that renders a high statistical percentage of DOD. Quarter horses, Standardbreds and Warmbloods experience this disease worldwide and at an alarming rate. This would explain why known contributory factors have come under considerable scrutiny over the last two decades. And particularly, the role that nutrition has played with its involvement in DOD.
Therefore, for the purpose of this exposé those known factors that influence the incidence of DOD and especially Physitis will be evaluated and reported. But perhaps more relevantly, those factors that can be influenced through managerial procedures to reduce the incidence of DOD will be dealt with extensively.

What is DOD ?
"Any disturbance of the skeletal growth in horses can be classified as Developmental Orthopaedic Disease."
Avery 1996.
As the term Developmental Orthopaedic Disease implies, a range of skeletal problems associated with the growth and development in foals has been reported and documented. However, controversy exists over which diseases should be classified as DOD under this umbrella term. But to generalise, those diseases / disorders listed below are generally accepted as being part of the DOD complex:
- Osteochondrosis dissecans (OCD), Dyschondroplasia (DCP) or Osteochondrosis (OC) - are similar conditions that occur in the articulating cartilage or underlying bone.
- Physitis - changes in the growth plates. Also know as epiphysitis and physeal dysplasia.
- Angular limb deformities (ALD) - outward or inward deviation of the lower legs.
- Flexural deformities (FLD) - tightening or shortening of the flexor tendons in the lower leg.
- Subchondral cystic lesions (SCL) - fluid filled cysts occurring within the bone.
- Cervical vertebral malformation (CVM) - compression of the spinal cord in the neck.
- Cuboidal bone malformation - malformation of the small bones in the hock or knee.
In addition, it should be noted that each condition primarily involves a different region of the musculoskeletal system and accordingly, observations in the growth rate of young horses will exhibit different preliminary patterns. For example; a potential wobbler foal tends to eat with its legs wide apart and pace with its head held forward as early as 2 - 3 weeks of age. Physitis can be seen in foals as early as 1 month with noted enlargement of one or several growth plates in the distal (lower) limbs.

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