Basti wrote:Wearing casts has no effects on your knees if you have Arthritis. His knees are lacking cartilage which in turn causes the kneecaps to grind on the bones causing tons of pain. .
Small correction here. I do not think it is kneecaps which are causing it. Kneecap or patella itself is a bone and it is sliding in patellofemoral groove of femoral bone during flexion and extension of the knee. Problem is he lacks cartilage ( meniscus) which helps absorb shock during impact exercise like running and jumping. So it is way more likely that it is femoral condyles rubbing on tibial plateau causing pain. Still bone on bone at the end of the day.
Here is a little knee anatomy picture to understand better. Menisci are cartilaginous discs sitting between femur and tibia and providing shock absorbtion, take them out and you have bone on bone whenever you jump or run.