Lateral patella. On the sunrise view, the patella should be laterally tilted and subluxated overhanging laterally with narrowing of the joint space. Usually it would be bone on bone with large osteophytes dripping off the lateral patella. On exam the patella will be tight and tilted off laterally, and unable to tilt it to neutral if you can tilt the patella beyond neutral, a lateral release will make the knee worse it should never be down for lateral patellar instability only for severe arthritis at the lateral patella. I might do 1 every 2-3 years if that

For me, it is generally reserved for an older lady with severe anterior knee pain worse going from sitting to standing and going up and down stairs with severe lateral tilt, subluxation and arthritis. If they are old, then a patella femoral or total knee replacement younger sometimes will do tibial tubercle osteotomy to elevate rotate patella. They generally get a couple years relief, and then do the knee replacement.