Patellofemoral Instability

An Overview Of Patellofemoral Instability

What Is Patellofemoral Instability?

The knee can be divided into three compartments: patellofemoral, medial and lateral compartment. The patellofemoral compartment is the compartment in the front of the knee between the kneecap and thighbone. The medial compartment is the area on the inside portion of the knee, and the lateral compartment is the area on the outside portion of the knee joint. Patellofemoral instability means that the patella (kneecap) moves out of its normal pattern of alignment. This malalignment can damage the underlying soft structures such as muscles and ligaments that hold the knee in place.

Causes Of Patellofemoral Instability?

A combination of factors can cause this abnormal tracking and include the following:

  • Anatomical defect: Flat feet or fallen arches and congenital abnormalities in the shape of the patella bone can cause misalignment of the knee joint.
  • Abnormal Q angle: The high Q angle (angle between the hips and knees) often results in mal tracking of the patella such as in patients with knock knees.
  • Patellofemoral arthritis: Patellofemoral arthritis occurs when there is a loss of the articular cartilage on the back of the kneecap. This can eventually lead to abnormal tracking of the patella.
  • Improper muscle balance: Weak quadriceps (anterior thigh muscles) can lead to abnormal tracking of the patella, causing it to subluxate or dislocate.

Young, active individuals involved in sports activities are more prone to patellofemoral instability.

Symptoms Of Patellofemoral Instability?

Patellofemoral instability causes pain when standing up from a sitting position and a feeling that the knee may buckle or give way. When the kneecap slips partially or completely you may have severe pain, swelling, bruising, visible deformity and loss of function of the knee. You may also have changes in sensation such as numbness or even partial paralysis below the dislocation because of pressure on the nerves and blood vessels.

Diagnosis Of Patellofemoral Instability?

Your doctor evaluates the source of patellofemoral instability based on your medical history and a physical examination. Other diagnostic tests such as X-rays, MRI and CT scan may be done to determine the cause of your knee pain and to rule out other conditions.

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