[header] How to diagnose patellar luxation in shih tzus [title] Look for skipping on the back leg. [step] A typical sign of patellar luxation is when the dog skips on a back leg. He may be perfectly mobile and not in pain, but every now and again he skips a step. 
He may also carry a back leg for several steps before putting it back down again. [substeps] This is due to the mechanical locking of the knee joint due to the faulty anatomy.