Ask a Dog Vet and Get Answers to Your Dog Veterinary Questions
Hello, my name is***** and I'm happy to help answer your question about your dog. I'm sorry to hear that he hurt his right hind limb. What is his name?
The most common cause of sudden onset lameness in the hind limb of a dog is rupture of the ACL (also called CCL in veterinary medicine), which is a ligament that stabilizes the knee. Without this ligament in place the knee becomes unstable and the thigh and shin bone move abnormally relative to each other with every step, causing pain and inflammation. This inflammation eventually leads to degenerative joint disease (osteoarthritis) of the knee, which can cause chronic lameness or decreased function of the limb. ACL injury is diagnosed on physical exam, so I recommend taking your dog in for evaluation by his primary care veterinarian on Monday.
Other possible causes of non-weight bearing lameness in the hind leg include broken bones (fracture) at any point along the limb, hip or ankle luxation, foreign body (such as a thorn, as you mentioned), and cancer of the bone or muscles in that limb. These possibilities can be sorted through when you take him in for an exam on Monday.
Please DO NOT give any over the counter pain medication such as aspirin or ibuprofen, as this can interfere with the drugs your vet may want to prescribe. I wish you both the best!