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—see Chondromalacia Patellae)
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—see Infrapatellar Tendinitis)
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).
Diagnosis requires a thorough review of the injured athlete’s training program, including a history of symptom onset and aggravating factors, and a complete lower-extremity examination (for knee examination, see Evaluation of the Patient With Joint Symptoms : Physical Examination and see Knee Sprains and Meniscal Injuries).
Mechanical symptoms, such as locking or catching, suggest an internal derangement of the knee such as a meniscal tear. Instability symptoms, such as giving way and loss of confidence in the extremity when twisting or turning on the knee, suggest ligamentous injury or subluxation of the patella.
Chondromalacia is suggested by anterior knee pain after running, especially on hills, as well as pain and stiffness after sitting for any length of time (positive movie sign). On examination, pain is typically reproduced by compression of the patella against the femur.
Pain that becomes worse with weight-bearing suggests a stress fracture.
Treatment is tailored to the specific cause of the pain.
Treatment of chondromalacia includes quadriceps strengthening exercises with balanced strengthening exercises for the hamstrings, use of arch supports if excessive pronation is a possible contributor, and use of NSAIDs.
For patellar subluxation, use of patella-stabilizing pads or braces may be necessary, especially in sports that require rapid, agile movements in various planes (eg, basketball, tennis).
If there is excessive pronation of the foot, and all other possible causes of knee pain have been excluded, use of an orthotic insert is sometimes useful.
Stress fractures require rest and cessation of weight-bearing activity.
Intra-articular pathology often requires surgery.