What is chondromalacia patella? Chondromalacia patella (knee pain) is the softening and breakdown of the tissue (cartilage) on the underside of the kneecap (patella). Pain results when the knee and the thigh bone (femur) rub together. Dull, aching pain and/or a feeling of grinding when the knee is flexed may occur. The most common way to treat symptoms of chondromalacia patella is to rest the knee.