Quick Check: is your pain from Chondromalacia Patella? caused by weakening of the tissue (cartilage) on the underside of the kneecap (patella). Pain results when the knee and the thigh bone (femur) rub together. You may feel a dull, aching pain and/or a feeling of grinding when the knee is flexed. Need help picking the right knee brace? ask our kinesiology team.