Differentiating between hock and stifle lameness is difficult. Flexion tests won’t do it, and local nerve blocks often give equivocal results. Palpation of the joints helps but may be hampered by many horses being “touchy” in these areas anyway, making it difficult to distinguish from sensitivity caused by pain.
There are subtle clues. A horse with hock pain will usually point the leg and place it under the body more, especially if the pain is toward the inside of the hock. A horse with stifle problems will also rest the more painful leg but may be more comfortable standing with the stifle joint rotated to the outside.
Shoes are also a good indicator. Horses with stifle pain usually show more toe wear, as they tend to drag the toe when the walk. They may also wing the whole leg to the outside when moving.
It’s not easy to tell when you’re riding, but there are hints. In general, the horse with stifle pain feels “weak” behind and lacks impulsion. Going downhill is particularly painful with resistance. He may feel like he is collapsing behind when he comes to a stop and you may see the stifles “give way” when the horse is playing in the field and comes to a stop. The horse with hock pain gives you more of a feeling of jarring. He also lacks impulsion but feels more short and stiff than weak.
Telling which side hurts can be tough though. You may get the most notable “jolt” when the sore leg comes down or from the “good” side if he is taking a much greater proportion of his weight on that side. With both conditions, the horse will feel twisted away from the painful side and toward the good side.
Finally, a diagnostic acupuncture exam can be extremely useful. The two points at the bottom of the muscular groove are painful with hock problems, the upper three if the stifle is involved. Running a capped ballpoint pen down the muscular groove will result in well-localized and unmistakable point tenderness in these areas. There are other sensitive points that can be found through acupuncture.
You will only have to see for yourself once or twice how specific the tenderness is at these points to be convinced. In fact, many otherwise “traditional” veterinarians rely on hind-end acupuncture points to assist in diagnosis and treatment.