Patellar Instability

The patella (kneecap) is a bone in the font of the knee that is part of the extensor mechanism, connecting the quadriceps and patellar tendons.  The patella articulates with the femur to form a patellofemoral joint.  The patella is protected by  ligaments which secure the kneecap from sliding out of place.  One of the most important ligaments prevents lateral translation is the medial patellofemoral ligament (MPFL).

Dislocation of the patella occurs when the patella moves completely out of the patellofemoral groove (trochlea).  If the patella partially comes out of the trochlea and slides back in, it is called a subluxation.  Patellar instability is commonly observed in young athletes between 15 and 20 years old and can more commonly affect women.

Some causes of patellar dislocation include direct blow or trauma, twisting of the knee while changing direction, and patellofemoral dysplasia.  It is common to experience lateral patellar subluxation or dislocation when the MPFL is torn. The common symptoms include pain, tenderness, swelling around the knee joint, restricted movement of the knee, numbness below the knee, and discoloration of the area where the injury has occurred.

Dr. Fischer will examine your knee and may recommend diagnostic imaging such as X-ray, CT, and MRI to further evaluate the injury and guide treatment. There are non-surgical and surgical ways of treating patellofemoral instability.

Non-surgical treatment includes:

  • RICE (rest, ice, compression, and elevation)
  • Non-steroidal anti-inflammatory drugs and analgesics to treat pain and swelling
  • Bracing or splinting which will immobilize the knee and allows the soft tissues to heal and maintain a more stable position of the patella
  • Physical therapy is often recommended to helps to treat pain and swelling, prevent scarring, restore range of motion, and strengthen supportive muscles.

Surgical treatment is recommended for those individuals who have recurrent patella dislocationinstability. Some of the surgical options include:

  • Lateral-release - Arthroscopic release of the tight lateral ligaments that pull the kneecap to the outside of the knee.
  • Medial patellofemoral ligament reconstruction - The torn MPF ligament is reconstructed using auto or allograft.  Grafts are usually harvested from the hamstring tendons, located at the back of the knee and are fixed to the patella tendon using screws.
  • Tibial tubercle realignment or transfer - The tibial tubercle is a bony prominence that the patellar tendon attaches to just below the knee joint.  In this procedure, the tibial tubercle is moved toward midline to improve the tracking of the patella within the trochlea.  Screws hold the bone in place until it reattaches.