A client found a large, hard, golf-ball sized lump on her horse`s stifle a couple of weeks ago. He didn`t seem to be in any pain, wasn`t lame in anyway; the only symptom seemed to be a reluctance to pick up right canter and a few days after the lump appeared he seemed slightly weaker on the hind when being ridden.
Personally, I`d never seen a lump quite like it – it was similar to a the lumps on Sylvester`s head when Tweety fights back.
Doing some research, my client wondered if it was locking stifle, as the lump was right over the patella. However, the movement of the limb wasn`t actually inhibited, or particularly affected, so we wondered if it was where he was having a growth spurt his tendons and ligaments were a bit stretchy (like those beanpole kids who start dislocating limbs on a daily basis) and his patella was moving a bit. His owner backed off his work load and a week later it still hadn`t markedly improved so she got it checked and was told it was an injury – God knows how he did that! Anyway, he was given field rest for a week and it was cold hosed for a couple of days.
Today he was ridden again for the first time, and the lump is barely noticeable, albeit still there, and he seemed happier in himself and worked really, really well. We kept it to walk and trot though, and will bring him back into work slowly.
The suggestion of his having a locking stifle made me realise that, although I have heard of it and know the process of backing them up to release it, I know very little about the condition.
Locking stifle occurs when the medial patella ligament gets hung up over the end of the femur, as it is supposed to to stabilise the leg when the horse is standing and dozing, otherwise he`d fall over. When a normal horse walks forwards this ligament unhooks so that the hind leg can be flexed forwards. Usually pushing a horse backwards, or up a hill (should you be lucky enough that he has locked his stifle at the bottom of the hill) will release the ligament and allow him to walk freely.
I`ve only known a large 16.2hh Irish and a 13.2hh New Forest have locking stifle, so it isn`t linked closely to breeds, but rather to those horses with an upright hind leg, with an over straight hock and stifle.
If a horse is prone to locking stifles it can be overcome, or the incident rate reduced, by building up the muscle strength around the stifle slowly, so that the tendons and ligaments are stronger and less likely to malfunction. I also read that young horses who gain weight, and a subsequent fat pad behind the patella, have a reduced incidence rate, but weight gain should be monitored closely and done over a long period of time.
Corrective shoeing can encourage hoof rotation by trimming the inside wall or applying a lateral heel wedge. Together with improving the medial breakover point can also help eliminate locking stifles.
If nothing else works sufficiently I know vets can inject the area with a steroid, but I think this is more commonly used when there is trauma which causes the locking stifle. Vets can also mildly damage the ligament to decrease it`s elasticity and making it harder to become locked in place. I guess that mild anti-inflammatories are also useful in the maintenance of a horse with sticky stifles.
All in all, locking stifles is not always a serious problem, as long as the rider is aware that they shouldn`t leap off into canter, or any other athletic movement, from halt. Mildly affected horses often show signs of shortened hind leg strides, difficulty picking up the foot over poles, difficulty on one canter lead, and scrambling up or down hills. At the other end of the scale, riders should consider their safety when riding a horse who regularly locks his stifles and doesn`t regain his normal gait after a few strides.