My lovely and beautiful Hobo has been roughed off since March with subtle forelimb lameness. I thought I might as well use him to demonstrate gait analysis with a mobile phone (any phone will do, I happened to take this vid with an iPhone).
First here’s the video at normal speed, taken at a funny angle during a poorly executed trot up. Obviously a side-on and front-on video of a horse trotting freely in a straight line on a loose rein, filmed in high speed and high resolution with a tripod is ideal. This video was taken with no real care or attention to show that it is not always necessary. I’ve included the video here so that you can familiarize yourself with the level of soundness – would you have spotted this horse as unsound?
Once the video was recorded I could scan through it on my phone and choose the frames I wanted to look at. Here are some example frames for the near and off fore. If you are very unlucky your horse is lame on both sides. Let’s worry about that at the end. The majority of lameness’ happen in one leg so first let’s compare the same limb positions for both forelimbs and see if the horse is even on both sides.
Some people get very excited about high speed video and seeing how the hoof lands, and that’s fair enough, because that really is exciting. Catching a proper hoof impact reliably and accurately takes a very high frame rate and well prepared ground so let’s not fool ourselves that we’re doing that. Instead let’s look at the forelimb just before it hits the ground, maximum extension if you will, but bearing in mind that we may not be catching exactly maximum. Here we don’t look at how forward the leg has swung, because that’s too unreliable (and we’re not trying to sell anything). Let’s just look at where the other foreleg is.
When the off fore (nearest you) is swinging through and near full extension the near fore is also swinging and flexed, when the near fore is swinging through, the off fore is still very much on the ground. So with our naff video, we’ve already spotted the asymmetry.We can check a few different strides to see if it’s a consistent thing, and it is.
So what’s going on? Essentially he’s keeping one leg on the ground for longer – so he’s trying to take more of his weight with this leg. This is the most common indicator of lameness. He’s basically saving the leg he doesn’t want to use (the near fore), and trying to hop along on the other leg. There are plenty of others indicators in this horse, and these more specific ones tell us why he’s sparing that leg, but that’s probably enough to start with!
If the horse was equally lame on both sides we’d actually need to compare this horse with himself (a previous video) or know enough to spot that this crouch gait was happening on both sides. If you look at the last frame you might instinctively already see that this Groucho Marx trot is not normal. You see the same gait in elephants (they don’t like to spring their full weight onto their legs either) and it’s not technically a run. So many future blog posts yet to write…