Lameness is common in horses.A lameness examination is one of the most common exams performed by equine veterinarians. In some cases, determining the leg that is lame is really easy if the lameness is moderate to severe. However, if the lameness is mild, especially in a hind leg, it can be difficult and sometimes dangerous to determine which leg is lame. If the horse is lame in more than one leg, it can be very difficult to make a diagnosis, especially if the lameness is in one hind and one foreleg. Some horses will appear to be lame on one leg when the horse is actually compensating for lameness in another leg.
A group in Scotland found that lameness diagnosis of the foreleg is much easier than the hind leg and they did a three-year study of 37 horses with lameness in rear legs. About half of the 37 had lameness in the hind legs only, one-third had lameness in both limbs on the same side, and a few had lameness in a hind leg and foreleg of opposite sides. They found that some horses with a hind limb lameness can appear to also be lame on the forelimb of the same side. It is not a true lameness, however, as the horse is trying to get off the rear leg and off load the lame hind leg. And when the lame rear limb was blocked or numbed with a local anesthetic, the altered gait of the foreleg was gone. However, if the lameness was in the opposite hind limb and forelimb, blocking or numbing the lame rear leg did not stop the appearance of lameness in the foreleg. To make matters even more complicated, if the front leg is lame, the opposite hind limb will show a false lameness but a lame rear leg does not show false lameness in the opposite foreleg. I know this is confusing and this is the reason some lameness cases are not easy and why it can take your veterinarian some time to correctly diagnose these lameness cases.