Aspirin is not commonly suggested for use in dogs by veterinarians because of the higher risk of GI bleeding and ulceration from it in dogs. It is okay for occasional use, but long term use in dogs can be dangerous because of the GI side effects.
Please research TRAMADOL. This drug does not...
I managed similar pain in one of my older dogs with a drug called Tramadol. It does not have the scary side effect of the family of drugs that include Rimadyl.
This dog did pretty well on Tramadol with occasionally a schedule of prednisone.