A 22-year-old female distance runner presents to the clinic with a 4-month history of aching pain in the front of her right knee. She reports that the pain is most noticeable when she is running downhill, squatting to perform strength training, or sitting for prolonged periods during her university lectures. She denies any history of trauma, locking, of the knee, or sensation of the knee giving way. On physical examination, there is no joint effusion or ligamentous laxity. There is no joint line tenderness. Extension of the knee while the clinician applies downward pressure on the superior aspect of the patella reproduces the patient's pain. Strength testing of the hip abductors and quadriceps reveals mild bilateral weakness.
Which of the following is the most likely diagnosis?
The correct answer is:
D) Patellofemoral pain syndrome
The patient is presenting with patellofemoral pain syndrome (PFPS), one of the most common causes of anterior knee pain in young, active individuals, particularly females. The pathophysiology is often related to maltracking of the patella within the trochlear groove, leading to increased pressure on the retropatellar cartilage. The clinical hallmark is moviegoer’s sign, which is aching pain after prolonged sitting with the knees flexed, and pain exacerbated by activities that increase the patellofemoral compressive force, such as stair climbing or squatting. The physical exam maneuver described in the vignette is the patellar compression test (or Clarke’s sign), which is used to provoke pain by compressing the patella against the femur. Another common finding in PFPS is weakness of the hip abductors and quadriceps, which can contribute to poor lower extremity alignment (increased valgus) and subsequent patellar maltracking.
Answer choice A: Iliotibial (IT) band syndrome, is incorrect. IT band syndrome typically causes pain on the lateral aspect of the knee rather than the anterior aspect. The pain is usually localized over the lateral femoral epicondyle and is often seen in runners and cyclists.
Answer choice B: Osgood-Schlatter disease, is incorrect. This is a traction apophysitis of the tibial tubercle seen in adolescents during growth spurts. It presents with exquisite tenderness and a visible prominence specifically over the tibial tubercle, rather than retro-patellar pain.
Answer choice C: Patellar tendonitis, is incorrect. Also known as "jumper's knee," this condition causes localized tenderness at the inferior pole of the patella and the patellar tendon itself. It is common in athletes involved in jumping sports such as volleyball and basketball.
Answer choice E: Prepatellar bursitis, is incorrect. Prepatellar bursitis involves inflammation of the bursa located between the skin and the patella. It presents with localized swelling and fluctuance over the kneecap, which is absent in this patient.
Key Learning Point
Patellofemoral pain syndrome is a clinical diagnosis characterized by anterior knee pain that is worse with weight-bearing on a flexed knee or prolonged sitting. Management is primarily conservative, emphasizing strengthening of the hip abductors and quadriceps to improve patellar tracking. Imaging is usually unnecessary unless symptoms are atypical or fail to respond to physical therapy.
