There is not much that will sink a rider's spirit faster than a lame horse. It can be subtle: a hitch in the stride, a bob of the head, a drag of a toe, or more blatant signs like an unwillingness, inability to put a hoof to the ground, or a grossly swollen limb. The causes of any of those signs are tenfold.
Any person that has ever owned, or looked at, a horse will have an opinion and solution for the lameness. Those remedies and ideas about a course of action can range from insane to lackadaisical. I have faith that anyone reading this would fall nicely between the two at reasonable.
Diagnosing lameness can be done very quickly, if a horse owner has wads of hundred dollar bills falling out of her pockets. It merely takes a quick trip to an equine clinic filled with radiograph machines, ultrasound devices, MRI and CAT and other acronymical (pretty sure I just made that word up) contraptions, lasers, digital images, arthroscope thingies, and so on. It just takes loads, or wads, of cash to be able to access that type of equipment and the people trained to use it.
Even a vet with a lowly x-ray machine is going to require a fistful (technically: 1/2 of a wad) of dough to examine a horse. However, most horse people I know will call the vet for a lame horse, but will wrap their own broken hand with some Vetrap and swallow a half-dozen Advil calling it good. Calling the vet is necessary when the horse is non-weight-bearing on one limb or has a swollen joint because those can be quite serious. But with the more subtle lameness, it's hard to know if a little rest, Bute, cold hosing, wrapping and/or poultice will solve the issue. How long should we give that lame horse before calling in a vet? A week? A day? 2 days? Whether or not the lameness is discovered on the weekend can be a factor in deciding when to call due to the cost of a farm visit from the vet on a weekend jumping from a fistful, to a chunk of cash.
Not that any one of our horses isn't worth many chunks of cash to us, but horsepeople operate on strict budgets. If the vet visit isn't necessary, that money can be used for board, feed, a blanket or something else more essential. It can be a tough call. The horses don't help. They can be so stoic and so willing to work that they will carry on with a significant problem which can lead an owner to believe that it's not that bad. My own horse gamely tried to trot with a fractured pelvis while the vet and I tried several different treatments before discovering the problem. In fact, the only reason I knew he wasn't right was that he couldn't canter. He tried, because that's how amazing horses are, but he couldn't physically do it. Thankfully, after stall rest, anti-inflammatories and eventually, chiropractic work, he returned to full soundness.
Often, as in the previous example, a source of lameness is determined only by process of elimination. Meanwhile the horse carries on, jogging a hundred times for examinations, trying his best to comply even with pain. A horse will still race, compete, trot around the ring when asked - even if he is in pain. That doesn't mean it doesn't hurt that much, it means the horse is an animal that needs to move to live and aims to please so much, that he carries on.
Lameness in a horse does not just crush our dreams of riding, but it is agonizing to watch a horse move with pain. They can not speak to tell us where it hurts and what is making them hurt. We have to guess. We have to be sleuths. We have to be interpreters and clairvoyant. And we have to be patient.
It can take a long time for some causes of lameness to be resolved and even then, if the horse returns to soundness, care must be taken to ease the horse back into work. Putting a horse back into the same schedule it had pre-lameness, after time off can cause a new lameness, or re-injure the newly healed one. One of my horses has tendon sheaths that look like shredded wheat because of being put back to work too quickly after an injury. That was before I got him, so don't accuse me.
Along with deciding when to call the vet comes the decision about medicating the horse so that he can still be ridden. As a person who often requires NSAIDs to function, I can empathize with a horse that needs a little something to ease discomfort in order to move around. IF (capitalized on purpose) a horse enjoys his work and is eager to do it and can be lightly assisted by non-harmful means, then there is no reason not to medicate. An example would be an older horse with signs of arthritis that finds freedom of movement after treatment with Adequan, oral supplements or an occasional dose of Bute. Masking an injury with drugs, or asking a horse to perform with an lameness that will be made worse through work, is shameful.
Lameness is inevitable at some point in a horse's life. The only ways to ward off a lameness are to keep our horses fit, keep their hooves in good condition with regular trimming, be mindful of footing, and pay attention to changes in performance in order to catch a problem early. There is no way to completely protect a horse from becoming lame so go ahead and enjoy riding your horse and let him live outdoors, as a horse should and continue to walk the line between lackadaisical and insane.