by Nathan Wei, MD, FACP, FACR
Nathan Wei is a nationally known board-certified rheumatologist and author of the Second Opinion Arthritis Treatment Kit. It's available exclusively at this website... not available in stores.
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Patellofemoral osteoarthritis (PFO) is a result of osteoarthritis (OA) affecting the joint between the patella (knee cap) and the femur (lower leg bone).
Risk factors for PFO include: advancing age, obesity, overuse, chronic joint instability, prior fractures occurring within the joint, high intensity running or weight-lifting, and systemic inflammatory conditions. PFA can also occur in younger patients as a result of misalignment of the patella and the femur. Trauma is also a risk factor.
PFO occurs because the layer of cartilage lining the underside of the kneecap and the cartilage covering the surface of the femur starts to wear away. The term "chondromalacia" is used to describe early changes in the cartilage of the patella that eventually leads to patellofemoral arthritis.
Osteoarthritis of the patellofemoral joint should be considered as a separate condition from OA in the medial and lateral tibiofemoral compartments of the knee. Not all patients with patellofemoral arthritis have osteoarthritis in the other compartments; arthritis may develop at different times and with different causes in the different compartments of the knee.
Articular cartilage in the patella differs from that of other joints in that this cartilage is less stiff and, thus, more compressible than that of other joints.
Isolated patellofemoral arthritis may cause anterior knee pain that worsens with stair climbing or when rising from a seated position and is not present with other activities, such as walking or running on level surfaces.
Patellar instability is associated with intermittent sharp pain at the kneecap. A feeling of "giving way" may be related to muscle weakness or to instability.
Recurrent patellar subluxation or dislocation may lead to an osteochondral fracture (fracture of the cartilage and underlying bone) or chronic cartilage damage as a result of repeated microtrauma.
The patella normally enters the trochlea (groove in the femur where the patella sits) from a lateral (outside) position and becomes centralized with increasing bending of the knee. Abnormalities can occur if the patella stays too far lateral as it enters the trochlea.
The Q angle is the angle between the anterior superior iliac spine (outer front of the pelvis) to the patella and the patella through the midpoint of the shaft of the tibia. Normal values are less than 20°. Women tend to have larger Q angles than men because of the wider position of their hips. Some feel the Q angle, if abnormal, may predispose to PFO.
The compression test is done by pressing down on the patella as the patient flexes (bends) his knee. Pain often accompanies this maneuver if arthritis is present. Resisted knee extension (straightening) also may reproduce the patient's symptoms in arthritic conditions.
If the physician pushes the patella laterally with the knee in extension, patients may complain of pain. Patients with instability contract their quadriceps muscles or complain of pain because of the feeling that their kneecap is going to dislocate.
Non-surgical treatment involves the use of non-steroidal anti-inflammatory drugs (NSAIDs), activity modification, and muscle-strengthening activities. Strengthening of the quadriceps muscle group can be beneficial, especially in patients with abnormal tracking and weakness of these muscles. Activities should be modified so that prolonged knee flexion (as with squatting) and stair climbing are avoided. A knee sleeve may also relieve symptoms.
Viscosupplementation also is an option. This involves the injection of hyaluronic acid derivatives using ultrasound needle guidance. These lubricants are sometimes effective in reducing pain and improving function.
Taping of the patella to pull it medially, followed by quadriceps exercises, has recently been recommended for the treatment of young people with anterior knee pain arising from the patellofemoral joint (chondromalacia patellae).
The data indicate that tape applied with a force pulling the patella medially reduced knee pain and was preferred to taping in the lateral or neutral positions. The differences for all observations except pain at one hour or one day were statistically significant, and all favored the medial taping. The degree of pain relief was clinically as well as statistically significant, many patients spontaneously reporting great relief as well as improved function. (J Cushnaghan, C McCarthy, P Dieppe BMJ 1994;308:753-755)
Indications for surgical management include persistent pain with no response to conservative measures, loss of functional ability, arthritis that is correlated with the symptoms, and symptoms that do not respond to physical therapy.
In patients with patellofemoral arthritis, the goal of surgical procedures should be to improve patellar biomechanics and to correct articular damage.
For patients with anterior knee pain directly associated with poor patellar positioning, surgical procedures that attempt to correct the malalignment may be beneficial. A lateral retinacular release changes the tilt of the patella, decreasing pressure on the lateral patella by releasing the lateral constraints of the patella.
Other more aggressive types of surgery have also been attempted. Results are mixed.
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