Our Staffordshire Bull Terrier who has had a history of problems in his hind legs, having to have multiple operations to repair his cruciate ligements, began to limp about two weeks ago and this progressed to him not even being able to put any pressure on his foot. We took him to the vets and they did not see anything wrong and gave us some painkillers, but as he did not get any better, he was booked in for an X-ray, which had to be sent off to a specialist to be looked at. It has been about a week since and we have not yet heard back.
With more painkillers he is able to walk on his foot but without these we can see no improvement.
Does anyone have any ideas as to what may be wrong, Thanks.

Luxating Patella maybe?  My staffie had this and she couldn't put her foot to the ground for a few days and she then needed surgery a couple weeks later.