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Here is another reply to the question Tom Ivers and I have been asking. This
one is from Dr. Hanneman.
Jim, safely ensconced in Massachusetts now and taking a break from getting my
talk at Tufts ready.
Here is what I see. This is okay to post.
Biomechanically, all joints in the horse have a small amount of rotation
medial-lateral due to the off-centeredness of the center of gravity....even
the hinged joints. So when the leg flexes, the joints are designed to rotate
slightly medial to lateral and when it extends slightly lateral to medial.
The fixations I see depend on what bone(s) in the knee are subluxating and
what the other joints are doing. When there is a posterior subluxation, it
usually involves the the accessory carpal bone (which in turn will change
tension in the flexor tendons and proximal suspensory ligament) and involves
a medial-posterior rotation. It is more common than an anterior subluxation
which usually involves the radial and intermediate carpal bones and they tend
to rotate lateral-anterior. I think that the posterior luxation occurs more
often due to the horse compensating for weight shifts by putting the front
legs more behind the vertical and thus will usually rotate the legs slightly
lateral. This in turn changes the direction of pull of the forearm muscles
that go on to make up the flexor tendon which in turn changes the forces of
rotation, flexion and extension of the knee joint. Of course this is
speculation, but it is what I see clinically and what I am extrapolating from
an applied biomechanics point of view. Does that help? Let me know if I can
help anymore. I don't get on endurance.net much due to lack of time, so let
me know what the thread is.
Kim Henneman, DVM
Certified Veterinary Chiropractor
Certified Veterinary Acupuncturist
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