Patellofemoral arthritis
PFO occurs because the layer of cartilage lining the underside of the kneecap and the cartilage covering the surface of the femur that the patella interacts with begins to wear away. This form of arthritis may be asymptomatic or it may cause only vague knee pain at the front of the knee. It may result in difficulties with stair climbing and walking. The term chondromalacia is used to describe early changes in the cartilage of the patella that may eventually lead 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 (the inner and outer joints between the femur and the tibia). 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. Some studies have indicated that risk factors for the development of PFO include increasing body weight, high-intensity running or weight lifting, prior knee injury, and prior patellar dislocation or partial dislocation (subluxation). 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. Patella 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 cause an osteochondral fracture (fracture of the cartilage and underlying bone) or chronic cartilage damage as a result of repeated microtrauma. The angle of force of the quadriceps muscle group (ie, the Q angle) is thought to be a factor in the development of knee injuries and arthritis. However, no findings conclusively support this assertion. Careful observation of how a patient walks and whether there are any misalignments in their legs is important. Leg-length differences and deformities of the femur, tibia, and feet should be noted. How a patient walks without shoes. Excessive pronation of the feet (flattening of the arch), patella tracking (how the knee cap moves in the groove of the femur), and rotation of the leg should be observed. Muscle tone and atrophy of the quadriceps and hamstrings should be assessed. Patella tracking with bending and straightening of the leg and with squatting should be determined. The physician should determine the presence of ligament laxity, instability, and abnormal tracking of the patella to determine the source of pain. 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. Imagine the patella traveling in a J pattern. 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. Tests of stability and motion: A through knee examination of both the affected and nonaffected sides should be performed. The presence of crepitus (“crunching”) is nonspecific. A standard knee examination should be performed. Passive and active range of motion should be recorded. Strength and tightness of hamstring and quadriceps muscle groups should be determined. Knee stability should be assessed. Ligamentous stability of the The stability of the patella to medial and lateral stress should be determined, as should evidence of abnormal tilting of the patella.
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 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. 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). However, data from controlled clinical trials to support such recommendations have not been published. The aims of this study were, firstly, to evaluate the symptomatic benefit of knee taping designed to realign the patella in older subjects with knee osteoarthritis and, secondly, to apply rigorous clinical trial methodology to a physical form of treatment. 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)
Patients typically present with anterior knee pain. Indications for surgical management include pain, 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 is performed to change 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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