old english bulldog- limp leg

Question
I have a 2 year old, old english bulldog.  About 3 months ago she began limping on one of her rear legs after playing fetch in the cold weather, but for no other apparent reason and has been limping ever since.  Two different vets can not find a reason for the limp in her leg.  X-rays were done, blood tests were done and still no answer.  I have also recently noticed a large hard lump on the inside of her knee.  The most recent vet put her on a pain med last week, the limp has not gone away, and now she has severe diarrhea and the limp is worse now than ever.  What is going on?  Are the diarrhea and limp related?  Is this a common issue with old english bulldogs?

Answer
You really at a loss for a good vet it seems.

First of all, I don't understand why a vet would put a dog on pain meds if he can't figure out what the cause is. Has anyone xrayed the dogs knees? This seems like an ACL stain more than anything. This is common in Oldies because they play hard and make sudden, sharp turns while playing.  This is what either strains or tears the AC/Ligament.

The diarrhea should have nothing to do with the limp. I would get that checked out asap. Take in a stool sample and have them do a smear as well as a float.