Here is a picture of the knee under the skin. You can see that the patella is surrounded by a number of ligaments whose job it is to keep the patella in place. The one concerned here is that sneaky little tendon peaking out called the Lateral retinaculum. In the second image, it shows how, when the lateral retinaculum becomes tight or the medial one gets slack, it can cause the patella to be out of alignment to where it should be. The surgeon will approach this via arthroscopy which will just leave you with a couple of little 'stab' wounds. He looks inside the knee using the camera and an instrument. Water is used to inflate the joint so he can see what he's doing! He then approaches the retinaculum from inside and makes a small cut in the centre to make it slack off. Pain after this is minimal but there will be some, mostly from the knee being inflated, some from the cut in the retiniculum and a little from the skin incisions. This should all be well controlled with paracetamol/Tylenol but you should take adequate doses, being 1,000mgs 4 times a day at 6hrly intervals. Also, weight bearing and activity should be pretty normal though you might find a couple of crutches helpful for the first few days. Hope this is explains it all.