Prepurchase exam on a lame horse?

Your vet would be able to do the exam but, no offense intended here, it'd be pretty stupid to do it knowing the horse is lame. Because the horse won't pass if she's lame and the entire point of your PPE is to make sure that the horse is healthy and not lame. And I'll be honest, I'd be extremely wary of any horse who needs hock injections at six years old.