What is the Patellofemoral Joint?

The knee is one of the most complex joints in the human body, and is actually made up of two joints. The main joint, called the tibiofemoral, is formed by the tibia, or large shin bone, and the femur, or thigh bone, and has two compartments. A third compartment is formed by the second knee joint, the patellofemoral joint, also named after the bones which form it: the patella, or knee cap, and the femur. A pad of cartilage called the meniscus is placed between the joints, providing a smooth sliding surface which helps to evenly distribute the weight load.

The knee is a weight-bearing joint, and can become irritated or damaged by injury, excessive use, foot problems, and chronic wear and tear. One of the most common causes of knee pain is a condition referred to as chondromalacia (CMP) which involves the patellofemoral joint. This can be identified through X-ray or magnetic resonance imaging (MRI), and is characterized by fraying or damage to the patellar cartilage. The patella is normally pulled over the femur in a straight line by the front thigh muscles, called the quadriceps. In patients with CMP, the patella tracks toward the outside, causing the bottom surface of the knee cap to grate. This weakens and damages the cartilage.

Symptoms of CMP include pain in the inner knee, which increases when walking down stairs or when sitting with the knees bent for an extended period of time. There may also be a clicking or grinding sound when the knee is straightened. Treatment usually involves anti-inflammatory medications and physical therapy to strengthen the quadriceps and the hamstring, or back thigh muscle. In many cases, strengthening these two muscle groups can correct the tracking of the patella and relieve the symptoms of CMP.

Another common knee complaint is patellofemoral pain syndrome (PFPS), which is identified by pain in the front of the knee. Like CMP, the pain increases with activities such as running and bending and going down steps or slopes. PFPS does not involve damage to the cartilage, however, and may or may not be caused by improper tracking of the knee. There are diverse opinions about the cause of PFPS, probably because there may be several causes, such as injury, overuse from excessive running or similar activities, weakness in the quadriceps and issues with the feet.

The initial treatment for CMP and PFPS is similar; reduce or replace activities which cause undue stress to the patellofemoral joint, use ice and anti-inflammatory medication if there is swelling, and assess the possible causes of the condition. One thing the physician will look at is the condition of the feet. The knee is balanced between the hips and the feet, and if a person has either no medial arch, flat feet, or too high of an arch, the balance is thrown off and the knee has to function at an improper angle. If the feet do have arch problems, the patient may find relief simply by getting orthotic inserts or shoes with proper arch support.

Permanent relief from patellofemoral joint pain usually involves specific changes in exercise. Aerobic activities such as jogging and running are replaced with non-impact exercises like swimming, elliptical machines and stationary bikes set at low resistance. If the knee is tracking incorrectly, then a daily exercise routine is designed to strengthen the quadriceps, which extends the knee, and the hamstring, which flexes the knee. If therapy does not work, then surgical options are available to either remove the damaged cartilage or to replace the patellofemoral joint completely.