Normal kneecaps cannot be luxated even with force, so luxating patella is something that can be diagnosed on a physical exam without x-rays. Especially with low grades, as positioning for the x-ray is likely to stabilize the kneecap in a normal position and make it look normal.
Having said that, it's not that uncommon dogs with LP to tear their ACL as well, and often in a dog with a history of LP without any symptoms who suddenly starts having problems that's the cause. If you choose to do surgery for the LP, that's something the orthopedist should be able to see and repair at the same time one s/he's in there surgically.
Having said that, it's not that uncommon dogs with LP to tear their ACL as well, and often in a dog with a history of LP without any symptoms who suddenly starts having problems that's the cause. If you choose to do surgery for the LP, that's something the orthopedist should be able to see and repair at the same time one s/he's in there surgically.