The most common injuries for a hind leg include:
1. A partial or complete tear of the cruciate ligament in the knee (stifle).
2. Exacerbation of degenerative joint disease (arthritis) in the knee or hips
Note: Hip dysplasia is early age arthritis due to genetics, whereas, many older pets can have age-related arthritis changes in their joints due to age.
3. Any other soft tissue injury (tendon, muscle, ligament)
4. A fracture
5. A paw trauma, fractured nail, or a foreign body in the paw.
Especially, the cruciate ligament tears, you must be very careful. If really not putting a lot of weight on the leg, it is clearly painful, even if not showing it. In that case, I do not recommend any over-the-counter treatment. I'll mention aspirin below, but strongly recommend you get in to a vet much sooner. Aspirin is not very strong.
The only over-the-counter non-steroidal anti-inflammatory I recommend in dogs (NOT CATS) is aspirin. Due to potential toxicity issues if not dosed correctly, many veterinarians do not consider Tylenol, Ibuprofen (Advil), and Aleve safe.
You can give 10mg per pound of body weight up to every 12 hours. Just remember, there are different pill sizes for aspirin, so look to see if it is regular strength or maximum strength.
Aspirin can be upsetting to the stomach, so discontinue if any digestive upset and definitely consult a vet if not helpful. If available, buffered aspirin, with the enteric coating, can help as well. Sometimes giving some Pepcid A.C. antacid 1 hour beforehand can be helpful.
Pepcid A.C. (famotidine) comes in 10mg, 20mg, or 40mg tablets.
You can give it every 12 hours. You can give 0.5mg per pound of body weight. So, a 20 pound dog would get 10mg.
***Do not give aspirin or any other non-steroidal anti-inflammatory medication if your pet is already on prednisone or any other anti-inflammatory medication***
Severe stomach and intestinal ulcers can result from giving a pet aspirin, tylenol or ibuprofen when they are also on medications like Rimadyl, Deramaxx, Prednisone, Metecam, Zubrin, and Previcox***