Sep 222017

By Patty Wilber

That is not Obsessive Compulsive Disorder.

It is Osteochondritis Dessicans and is a bone and cartilage problem in horse joints that is multifactorial in origin and can affect any breed. According to The American College of Veterinary Surgeons the causes could be:

  • “Rapid growth and large body size
  • Nutrition: Diets very high in energy or have an imbalance in trace minerals (low copper diets)
  • Genetics: Risk of OCD may be partially inherited
  • Hormonal imbalances:  Insulin and thyroid hormones
  • Trauma and exercise: Trauma (including routine exercise) is often involved in the formation and loosening of the OCD flap”

Indy had some swelling in her hock and since I didn’t know of any particular injury nor had she been working super hard, it seemed odd. Also, she wasn’t lame, but she was a bit reluctant to pick up her left lead, which had heretofore been preferred.

Indy ponying LT back in January

So, we went to the vet and it turned out she had the classic presentation of OCD in the hock, with less swelling than shown in the picture I got off this site on the Internet. The swelling with lack of lameness is also common.  The only thing off was that she was kind of old, at three, to just now be showing signs.  This apparently indicates that I don’t over work my equines.

Osteochondritis Dissecans (OCD) classical swelling.

This kind of swelling is called a “bog spavin”, which describes the appearance of the hock, not the cause.

“Bog spavin” sounds very old timey to me, so I Googled the etymology and this is what I found:

1400-50; late Middle English spaveyne < Old French (e)spavain, esparvain swelling < ? This bunch differs from bog spavin in that it is hard, while bog spavin is soft. … Distension of the capsular ligament of the tibial tarsal (tibioastragular) joint with synovia is commonly known as bog spavin.

Bog spavin | Define Bog spavin at

We did x-rays and this confirmed that she had the OCD “bone chip”.  I had heard of bone chips before, and I thought they were sharp shards poking around in the joint.

From the same site I got the photo of the leg, I got this graphic.

“Figure 1. Normal development results in a bone (shown in blue) with a subchondral bone plate to which a smooth cartilage cap is attached (shown in yellow).

Figure 2. Abnormal development due to a defect in endochondral ossification results in an area of thickened and/or weakened abnormal bone and cartilage (shown in green).

Figure 3. Trauma or exercise can further damage the abnormal area as the horse flexes and extends the joint.

Figure 4. Separation of the abnormal bone and cartilage from the underlying and surrounding tissue results in an OCD fragment, which can form a flap or can detach and float as a free body within the joint.”

The recommended treatment is arthroscopic surgery to remove the offending piece.

Indy’s fragment was not sharp at all.  It was more like a bone bean and had not detached.

That is it to the right.

And that is it with my finger for scale.

She is recovering well.  She has a little residual swelling in her hock which may be permanent (but will only be cosmetic) and some slight swelling in her fetlock (which better not be another bone bean, but according to the CSU college of Veterinary Medicine it is UNusual for a hock and a fetlock in the same horse to be affected. Also, affected fetlocks fail the flexion test* and she passed.).

It will be a few more weeks until she goes back to real work. To aid recovery, she is being hand walked…or ponied.

In the meantime, LT is getting some action both on cows and as the pony horse.

Photo by Ed Armstrong

*Flexion tests.