It's just age-related stiffness in a hock. He shows signs of stiffness when the weather turns chilly and has been on Boswellia since the end of September.
I use it - my mare has spavin, and arthritis of the fetlock in her hind legs. She appears to be sound at the moment. I did try Devil's Claw first of all, but that made no difference whatsoever (yet it works for my back ache!!)