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> Can someone give me more details on what epiphysitis
> is? Saw this mentioned in the post on joint disease
> and young horses (great post by the way, Susan G).
Thanks.

Epiphysitis is kind of a misnomer, since there is no actual active
inflammation in the affected bones.  "Physeal dysplasia" is what they taught
us in vet school, and refers to a disruption of the physeal growth
cartilages.  In the previous post, there was a description of how bones
normally form from endochondral 'plates' to mature, ossified bone, right?
If something disrupts this process, then you get the classic symptoms of
heat, pain, swelling and lameness and what has traditionally been called
epiphysitis.

So what can disrupt this ossification process---if the problem is in more
than one limb, then a nutritional problem is mostly likely involved.  If
only one limb is involved, then trauma or some other abnormal biomechanical
stressor moves higher on the list, though nutrition-related problems might
still be a contributing factor.  Genetics is also a big contributor, since
there's much higher incidence in breeds that have been selected for rapid,
early growth and large mature weights---but it *can* occur in any breed.
It's absolutely untrue that DOD doesn't occur in Arabs.  Incidence of DOD
has also been traced to some specific (warmblood and standardbred)
stallions, even though the stallion himself may not have ever had DOD
problems.

Due to my older horse's
> joint problems I began reading a whole lot on DJD and
> OCD. Don't know much about epiphysitis though. Is it
> hard swellings on the fetlock area? And is it caused
> by same things as DJD?
Okay, let's straighten out the definitions.  Sorry, this can get confusing,
because there's a lot of overlap in terms and syndromes.  In young horses,
anything affecting normal bone development is very generally classified as
DOD syndrome---developmental orthopedic disease.  As commented on above,
there are lots of different things that can cause DOD, including nutrition,
genetics, premature birth, fracture, trauma, abnormal stressors from poor to
grossly abnormal conformation, overwork, etc etc.  DOD can affect any
developing bone prior to 'closure' of the growth centers.  You often see it
along the long bones of the legs and causing problems at the joints of those
long bones---stifle, hock, elbow, knees, etc.  You can also see defects in
the fetlock, but because those growth centers normally close at 2-3 months
of age, there's less time for poor management to cause problems there (and
the flip side of that is if the problem was present at birth, you have a
much tighter window of opportunity for therapy to fix the problem).  The
take-home message here is that you can get DOD lesions at any growth center,
and from a whole slew of causes, but lesions are more likely to occur at the
ends of long bones, and where abnormal stress is likely to occur.

As long as a growth center remains open, there's potential for lesions to
develop there and cause problems.  Remember that growth centers close from
the bottom up---some of the most distal parts of the legs are closed at or
soon after birth, moving up over months and years---some of the last areas
to close are along the spinal vertebrae as late as 6-7 years.  Yup, you can
develop lesions here as well, causing either "wobbler's syndrome", various
neurological syndromes or later DJD.

Moving on to OCD, osteochondrosis and/or osteochondritis dissecans.  OCD is
a sub-type of DOD, but the two are NOT synonymous conditions.
Osteochondrosis is a defect in the cartilagenous ossification center
secondary to some event that disrupted blood supply to the area---again,
trauma, abnormal stress, whatever.  Without blood supply, there is an area
of cartilage tissue that not only ceases to grow, but dies and becomes
necrotic.  This creates not only a cyst where bone should be, but can also
affect the quality of bone that develops over and beyond that cyst.
Example, if the cyst is underlying an area where a ridge of bone is supposed
to develop, then the ridge may not completely or adequately form.  Or, it
may form abnormally, creating more abnormal stress on the joint when the
horse is later put to work.

Osteochrondritis dissecans is a type of osteochondrosis in which a bone or
cartilage flap or fragment develops in the affected joint.  Sometimes these
fragments can break loose within the joint capsule and because the fragment
is still deriving its nutrition from the synovial fluid, it continues to
grow and thus becomes a "joint mouse" which must be removed surgically.

Okay, so let's assume you have an adult horse that had some amount of a DOD
problem during growth and has some area of abnormal bone development in a
joint---let's say a hock.  The horse starts a conditioning program for
whatever discipline he's going to do.  Whenever there's an area of
instability in a joint, the body tries to stabilize by depositing calcium.
Unfortunately, not always appropriately and if the calcium deposits cause a
roughening of surfaces over which tendons, ligaments or joints are supposed
to slide smoothly---voila, you have degenerative changes or DJD.  Problems
during growth aren't exclusively the reason for DJD later as an adult, just
one scenario.  Anything that creates abnormal stress and instability in a
joint is also going to contribute to the same cascade of events.  So DJD can
be either the ultimate outcome of DOD problems as a youngster; or, can be
the outcome of inappropriate exercise, poor shoeing, overriding, riding
before the horse is ready for that level of stress, etc etc etc.  You get
the picture.


> Now I am so careful about what I am feeding my filly
> (Equine Junior Development by Purina and lots of grass
> hay) and making sure she has plenty of exercise, I
> just hope she will be fine :)
Just remember there's a fine line between plenty of exercise and too much.
Not enough exercise can also contribute to DOD, but so does too much forced
exercise.  Just one more argument for babies raised in pastures.

Hope this helps.  :-)

Susan G



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