Friday, March 12, 2010

3/12/2010 - Anatomy and OCD

Vet tip of the Day: Significance of OCD based on anatomic location
Key Words: Osteochondrosis, lameness, joint, anatomy

This cute foal picture is here to remind you that OCD is a developmental orthopedice disease.  In other words, it develops as a foal grows, although it may not manifest itself clinically until later in life when joints are subjected to the rigors of training and controlled exercise.  When we consider the prognosis of various OCD lesions, then, there is one common sense rule to keep in mind: foals that develop significant lameness early in life due to OCD are likely to have more severe lesions than animals that do not show any clinical signs until they are older and in training. 

Regardless of the anatomic location, the larger and deeper the OCD lesion is in a given animal, the less likely it is that surgical treatment will be successful.  In general, the degree of lameness and age at onset correlate with the severity of the lesion.  Consider our mare Classy, a five year old just completing 60 days of fairly rigorous training and only demonstrating a grade 1 lameness and mild joint swelling.  Even before examining her radiographs, one can be hopeful that her prognosis for full function would be favorable.  And this is in fact the case.  Classy has an excellent prognosis for a full athletic career following surgical debridement of her stifle lesions.  On the other hand, a 6 month old weanling with grade 3 lameness and severe swelling of the stifle joint undoubtedly has a more conservative prognosis for an athletic career, even with appropriate treatment.

OCD can occur in any joint in the body. The most commonly affected joints are the stifle, hock and fetlock, and less commonly the shoulder and cervical spine (neck).  Within each of these joints there are several locations where lesions can occur.  In addition, lesions may occur as mineralized cartilage fragments that have separated from the underlying bone (see Classy's x-ray's for a beautiful example) or they may appear as cyst-like lesions, where the cartilage lining the bone is still intact, but is no longer attached in one region, with fluid and tissue debris filling the area between the detached cartilage and underlying bone. Remember our jump painting analogy?  The detached lesions are like paint chips, leaving the wood of the jump exposed, the cyst-like lesions are like bubbles in the paint, detached from the wood, but with the paint surface still intact. 

The prognosis for full athletic function for OCD of the lateral trochlear ridge in the stifle and most locations in the hock is excellent in the majority of cases, particularly when lameness is not severe, and does not become apparent until the horse enters training.  OCD of the fetlock is often treated successfully, but caries a more conservative prognosis in general than lesions of the hock or stifle.  OCD of the shoulder and cervical spine in general carry a guarded prognosis. There are certain anatomic locations where OCD lesions may be detected radiographically in a sound horse during a pre-purchase examination, for example, and be considered clinically insignificant, depending on their severity, and the horse's level of performance.

While surgical debridement (scraping the lesion just as you would scrape the paint on your jumps before correctly applying fresh paint) remains the gold standard for treatment of OCD, there are many emerging treatments under investigation which may alter our approach to this complex disease.  Intra-articular stem cell therapy is one of the most promising of these.  And still, many foals and weanlings with early diagnosis of less severe forms of OCD respond well to simple rest and careful rehabilatation with intra-articular chondoprotective therapy, allowing mother nature to do her own magic in healing lesions.

I've barely scratched the surface of the subject of OCD in these past few posts, but hopefully you will take away the message that in most horses this diagnosis does not mean the end of an athletic career.

I'm off to dinner after a long, cold day of work in windy, 45 degree rain spitting Reno today.

Enjoy.

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