Patellofemoral instability

The patella (kneecap) attaches to the femur (thigh bone) and tibia (shin bone) by tendons. The patella fits into a groove at the end of the femur (trochlear groove) and slides up and down as the knee bends and straightens. Patellar instability occurs when the kneecap moves outside of this groove.

There are two types of patellar instability. The first is known as a traumatic patellar dislocation. This is most often the result of an injury to the knee. In a patellar dislocation, the patella gets pushed completely out of the groove. The other type of instability is known as chronic patellar instability. In this type, the kneecap usually only slides partly out of the groove. This is known as a subluxation.

What causes patella instability?

There are several factors implicated in the cause of patellar subluxation. Possible factors include:

• A wider pelvis
• A shallow groove for the kneecap
• Abnormalities in gait
• A misaligned patella
• Patella instability or subluxation of the patella may be caused by either a traumatic event or an atraumatic event.
• A traumatic event is when an accident has happened to cause a sudden twisting of the knee.
• An atraumatic event means that no specific injury has occurred, but there are abnormalities in the gait. The groove for the patella may be too shallow or the patella is misaligned.

What are the symptoms?

• Sensation that the kneecap has shifted or moved out of place
• Buckling/catching, locking sensation 
• Swelling and pain behind the kneecap. 
• Pain when you bend or straighten your leg.

What are the treatment options?

Treatment of the unstable patella is first to ensure that the patella is not dislocated. In patients with a kneecap dislocation, the kneecap may need to be repositioned, or “reduced.”

General treatment of patellar subluxation includes:

• Physiotherapy 
• Bracing – Taping, or the use of a brace on the patella
• Better Footwear – Choosing the correct footwear may help to control your gait while running and decrease the pressure on the kneecap.

If conservative treatment has failed, a knee arthroscopy can be considered. The surgeon will make a small incision in the knee to allow a camera to be inserted. This camera is no wider than a pencil and allows the surgeon to see the structures of the knee and any damage that is present.

How can physiotherapy help?

Based on the assessment, your physiotherapist will prescribe an exercise program, which promotes the strengthening of the quadriceps muscle to realign the pull on the patella. Also strengthening of the hip abductors and flexors may offer better control of the patella.

While you are recovering from your injury you will need to change your sport or activity to one that will not make your condition worse. For example, you may need to bicycle instead of run.