Probably the most important joint/bone in the horse's hind leg, hip and hoof is the hock. The hock is the center of flexibly, bending, and motion. When a horse is going to jump, he flexes his knee (the bone at the stifle) and his hock and then releases the tension in those joints in muscles, pushing off the ground in the desired direction. Everything is connected.
Before we go any further, you have to understand how the horse's stifle is built. That is the most crucial part to my research - since Zan's problem lies in his stifle joint, muscle, and cartilage, our research and focus is on the stifle (or knee) and the muscle surrounding it.
The left side of this diagram shows the stifle joint and the cartilage/muscle (it's not a very clear diagram) in between the joint and the skin. There's supposed to be ligaments and muscles there, and then cartilage to cushion the muscles and bone from the skin - or rather, to protect the bone and muscle from being deteriorated by rubbing against the skin, which is exactly what's happening to Zan.
Do you see how the stifle bone creates a sort of bulge on the leg? Well, imagine that on Zan's back right, just 10x bigger. Yup, that's what's going on right now. Apparently, Zan doesn't have that cartilage that's supposed to cushion that bone and muscle tissue; the skin and bone and muscle just rub together and are slowly all deteriorating. It breaks my heart. Anyways, continuing on...
See the diagram above? This shows how the hoof, hocks, hip, and stifle are all connected. When the bones, muscles, and cartilage are all arranged this delicately, if one thing goes wrong, the leg fails. Hence the easy lameness, especially in thin or light-boned horses. Since the stifle is directly connected to the muscles/bones in the upper leg and hock (the flexion center for the back legs), when the stifle cramps or fails, the leg might cramp up and if the bone actually deteriorates, that is bad stuff there folks.
The middle part of the diagram above shows the view of the legs and rump from the back. Look at the top of the horse's rump - see how each side of the spine has a nice, rounded, full shape? Well the left side of Zan's rump is like that, but the right side doesn't have all that muscle development and all that you see is a large slope downwards, his hip bone, and then his stifle poking out, making a bump on his leg.
See the hind legs, how when the horse's leg is flexed (this is showing a trot, FYI), the patella (knee/stifle) doesn't stick out, but rather simply bends in a smooth, flowing motion? Well, when Zan trots (for example), his patella pokes out because the cartilage that is supposed to be there to separate his skin and bone is nonexistent. In his left leg, it's there. Apparently, though, his right leg just never fully developed.
I've read up and talked to Erica and Whitesell (the vet) and apparently this is a genetic disorder. Good thing Zan isn't a stud! That would be bad bad bad - that would mean more horses that could have this handicap, which would mean more horses put down in the end. But, for now, we're safe. For now. Though, I'm going to read up a bit on Zan's pedigree to try and find out which of his parents - if either of them - had this condition or if it just appeared in Zan and developed. Whitesell said that this is genetic, and that if it appears in a generation it could more than likely be passed to the next, even if the sire or dam didn't have this problem.
So complicated!
Guess this was more a rant than research, right? Well, I sort of had to get all of my thoughts and conclusions out of me. It's all just been contained for so long. Thanks for listening, guys.
Go hug a horse.
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