Does a horse have two knees or four? This is a question I love debating. Strictly speaking, a horse has knees in front and stifles behind – but it’s the stifle that’s the equivalent of the human knee. It’s the hinge between the femur and the tibia, and the fibro-cartilaginous pads within the ligaments act as shock absorbers. In turn, the cruciate and collateral ligaments prevent the stifle from opening past the optimal extension.
The patella (kneecap), which is the small bone in front of the knee, adds strength to the surrounding tendons. When the stifle locks, the kneecap locks. In the wild, horses are vulnerable when sleeping on the ground, as they struggle to get back up again. As a result, they’ve evolved an ingenious lock-and-stay mechanism that enables them to sleep standing upright – and get moving rapidly if a threat materialises.
Problems arise when the stifle (or knee) fails to unlock. This causes the leg to point either forward or backward, making it almost impossible for the horse to move forward. Needless to say, it’s distressing to see one’s horse in this state.
Which horses are affected?
In some cases, after a few strides, the stifle (or kneecap) will ‘unlock’ with a loud click and the leg will shoot forward. Inexperienced horse owners can sometimes confuse this behaviour with stringhalt. ‘Locking’ can affect any horse, but there are a few common denominators. Locked stifles is an inherited ailment, and is more common in over- or under-weight horses.
In addition, horses recovering from illness should be monitored closely for locked stifles due to the uneven weight distribution across all four legs. Between your farrier, vet, trainer and nutritionist, your horse can be helped if it has locked stifles. Surgery is usually successful, but you will probably be encouraged to first try rehabilitation. This involves rein back, trotting poles, massage, supplements, corrective trimming or shoeing, and work.
Working the muscles correctly and reducing spasms can lead to a permanent solution. Remember, though, to avoid soft deep sand during rehabilitation. Manual manipulation of the patella should be followed by rein back, then lunging if it’s safe to do so. The horse will need to work for 30 minutes until the ligaments are warmed up and loose.
In addition, ensure that your horse’s workload and diet are increased – in moderation – and its feet are trimmed every six weeks.