Speaking of Rehab...

This is the horse I've been working with, Falcor. We took this video in late October to see if we could document his "knuckling", which I believe(d) to be attributed to a sticky stifle. We have since discovered that this is not JUST a sticky stifle, but also likely due to nerve impingement/damage in his back from being stuck lying on his side all pretzeled up for 2 hours when he had his accident. He does this much more rarely now, but you can see how bad this must hurt!

(Oh, ignore me...I'm the one trotting him and being a goon)

http://www.youtube.com/watch?v=gCh6liG91z8

I can't show the video here because it's private...but I CAN show this video of him in 2011 when J was in FL trying him...watch the right hind at the trot, and if you fast forward to about 1:40 you will see why I maintain he has stifle issues. It's subtle, so watch closely.

The art of watching movement is all about subtlety and rhythm. If you watch his trot, the rhythm behind is off by just a hair: it looks OK, but there is something just not right...around 1:40 you can see a very small "stick" of his stifle. Doesn't look like much, but it's a big deal.

Why does this happen? Let's see if I can put it somewhat eloquently *teacher hat on*:

The stifle is the equivalent of the human knee. It's movement is governed by the hip joint, and it governs the movement of the hock joint. Whatever the stifle does the hock must do, so the degree to which the hock flexes is directly controlled by the degree to which the stifle flexes. To put it in very simplified terms, these three joints are thus controlled by a reciprocating system of tension-ized ligaments and tendons which parallel the leg all the way from the lower back to the toe. From this, you could surmise this law: "whatever the stifle does, the hock must do."

However, there is much more going on here than just the stifle and hock. This whole system is governed not just by long tendons and ligaments, but by the entire hip and the long muscles of the back and lumbo-sacral area. Essentially, this reciprocating system is just a sub-system of a much larger biomechanical system. Thus, a much better and more accurate "law" is as follows:

Whatever the lumbo-sacral joint (hip) does, the stifle really wants to do.

The stifle gets some leeway here because when stuff's broken, i.e. not working right, you get funky kinks in movement. So the stifle really WANTS to follow the hip, and in a functionally correctly moving horse, it does, but when things aren't quite right, it doesn't. Case and point: a slipping/sticking/catching stifle (all of these terms mean the same thing, but you'll hear them all used...)

Now we can go into specifically what stifle catching is: very, very simply, the horse has that lovely stay mechanism in place so he can stand and snooze. It's great when he's not moving, but not so awesome when he is. This system involves the patella (knee-cap) and the femur. In normal movement, the patella slides back and forth over the articulating surfaces of the femur, controlled by patellar ligaments and a very specific muscle called the tensor fasciae latae (TFL). With each stride, the TFL pulls the patella UP to allow the femur and it's bumpy parts to slide underneath. Then it's allowed back down, and the process starts over. This is supposed to work to keep the patella up and out during the point in movement at which the horse's stifle is widest open (i.e. when the horse's hind leg is extended out behind him). 

If the TFL fails for whatever reason, it will thus fail to contract and lift the patella up and out at the exact correct time, making it so it catches as the horse starts to move to return the leg underneath his body. The result is that appearance of the the leg getting stuck, as if it just dropped out from underneath the horse. 

The horse can feel is coming, and often compensates by dropping his hip dramatically to lessen the discomfort and weight placed on the compromised limb.

Why does this occur in the first place? Muscle tightness, unevenness and tension. Anything the rider does to create tension over the horse's topline can cause stifle catching. In Falcor's case, he's had this issue, albeit not on as grand a scale, for a long time. Now that he has serious muscle death, tightness over the topline and nerve damage from the accident, it's coming back tenfold. 

*teacher hat off*