Etiology of Knee Pain There are many causes of pain in or around the knee in athletes, particularly runners, including Subluxation of the patella when bending the knee Chondromalacia of the undersurface of the patella (runner's knee, which is softening of the knee cap cartilage) Intra-articular pathology, such as meniscal tears and plicae (infolding of the normal synovial lining of the knee) Fat pad inflammation Stress fractures of the tibia Malalignment of the lower extremities Patellar (or infrapatellar) tendinitis (jumper's knee, which is an overuse injury to the patellar tendon at the attachment to the lower pole of the patella) Knee pain may be referred from the lumbar spine or hip or result from foot problems (eg, excessive pronation or rolling inward of the foot during walking or running).