Could it be arthritis?
Marley started limping off and on and I thought maybe a torn cruciate ligament.
The vets also thought this but after xrays, arthritis was diagnosed which had been there for a long time judging by the degeneration in her joints

. She is only 5.
Instead of a very invasive operation, I have opted for more natural help - a magnetic collar, Yumove supplement, fish oil and hydrotherapy once a week which is really helping her.
Now that I am aware of her condition, I control her weight/exercise and make sure she doesn't stay damp and keep her warm.
I hope that Troy is not suffering but if he is, there is a lot you can do to help him.
