Good Morning and welcome! I am Dr. Loretta, a licensed veterinarian and I am happy to answer your question.
Because of Topaz's age, I worry that she is suffering from arthritis either in this leg or the disc in the cervical region that would affect this area. It is best to have your vet examine Topaz and xray this area to know for sure. Your vet will have medications ot help prevent this and decrease the inflammation that is probably causing this in your old friend.
Does that make sense to you?
Please let me know if you have ANY other questions. My goal is to give you 100% satisfaction and if you are not yet satisfied, please REPLY so I can clarify for you.
Sincerely, Dr. Loretta