CLINCIAL PRESENTATION
ACUTE DISLOCATION
Patients with acute PTFJ dislocation present with pain, tenderness, swelling, and asymmetry of the lateral side of the knee, while the knee joint is not swollen and range of knee motion is not limited.17 A bony prominence might be felt, and the biceps femoris tendon can often appear to be tense.13 Active or passive ankle movements often exacerbate the lateral knee pain.11 It is also important to examine the peroneal nerve, as transient peroneal palsy has been described in all types of PTFJ dislocations but most often with posteromedial dislocations. Sensory disturbance in the peroneal nerve distribution is more common than motor loss, but foot drop is also a potential presenting sign.11 On examination, palpation of the fibular head illustrates tenderness and aggravates the pain.
SUBLUXATION/CHRONIC INSTABILITY
Subluxation of the PTFJ can be difficult to recognize because the history, signs, and symptoms of lateral knee pain can be subtle and sometimes misleading. In addition, current literature provides little information on specific tests, measurements, signs, or subjective information regarding subluxation. Patients rarely reveal a history of trauma or mechanism of injury. Subluxations are often associated with patients participating in repetitive sports requiring running, jumping, or twisting movements, and can be present bilateral. Instability has also been described in patients with osteomyelitis, rheumatoid arthritis, septic arthritis, pigmented villonodular synovitis, below-knee amputations, osteochondroma, and in runners who recently increased mileage (especially during the first 2-3 miles and during downhill running).11,13 Patients normally do not have difficulty with activities of daily living, but symptoms may arise when making movements with a sudden change of direction.11
These patients usually complain of instability of the knee and pain along the lateral aspect of the knee. Pain radiating proximally into the region of the iliotibial band and medially into the patellofemoral joint can be seen.13 Patients may also report clicking, popping, or catching of the lateral knee; while others will report a sense of giving way of the knee joint.11,13 Progressive peroneal nerve symptoms are usually seen in older patients; however, they are more common with acute PTFJ dislocations as discussed.13
A clinical method for examining a PTFJ with possible subluxation or chronic instability has been described by Sijbrandij.18 With the patient in the supine position, the knee is flexed to 90° to relax the LCL and biceps femoris tendon. The fibular head is then held between the thumb and index finger, and moved anteriorly and laterally. Dislocation or subluxation will be felt and visualized as the fibular head translates, and should be compared with the uninjured PTFJ. On release, the fibular head will return to its normal position, often with a click. Asking the patient if this subluxation/reduction maneuver reproduces the symptoms or causes apprehension or pain may also be helpful.18 Another method for examination is eliciting the Radulescu sign.11,13 While the patient lies prone, the examiner stabilizes the thigh with 1 hand while the knee is flexed to 90°. The examiner then applies an internal rotation force on the lower leg. Observing an abnormal excursion of the fibular head in an anterior and lateral direction represents a positive test.11,13
OSTEOARTHRITIS
Clinical evaluation for osteoarthritis in the PTFJ is not well described in the literature. A single report describes applying manual pressure over the fibular head during active ankle motion.16 A test known as the grinding test is used as a sign to detect the involvement of the PTFJ as a component of osteoarthritis of the knee. A positive test will elicit pain and/or tenderness of the joint.16
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