Dislocated kneecap: When is surgery recommended?

Photo of a teenager and doctor in the hospital (PantherMedia / Monkeybusiness Images) Surgery can stabilize the knee and lower the risk of the kneecap becoming dislocated again. It is considered after a second kneecap dislocation or if the knee is very unstable.

The doctor will first push the kneecap back into place. Then there are two treatment options:

  • Conservative treatment: The kneecap is stabilized for a few weeks using a brace or bandage. Physical therapy is started at the same time, with the goal of strengthening the muscles that support the kneecap.
  • Surgery: Doctors operate on the knee to stabilize the kneecap. During the surgery, cartilage or bone injuries may be treated or misalignments might be corrected as well. Physical therapy is started after surgery too.

What is currently recommended?

Experts often disagree on the issue of whether surgery should be done. Conservative treatment is typically used if it's the first time you have dislocated your kneecap. If it happens a second time or if it keeps happening, surgery is usually considered. Other factors that also play a role include:

  • Which conservative treatments have already been tried
  • Whether cartilage or bone have been damaged
  • Whether you have misalignments or other risk factors
  • Age and sports-related goals

It’s a good idea to discuss the advantages and disadvantages of surgery with your orthopedist and then consider them on your own.

What are the different types of surgery?

There are many different kinds of surgery to treat an unstable kneecap. The basic types are:

  • Surgery on the joint capsule and the ligaments: This involves tightening or replacing parts of the capsule and ligaments that stabilize the kneecap on the inner side of the knee, particularly including the medial patellofemoral ligament (MPFL, see illustration). This ligament is usually torn the first time the kneecap is dislocated. Then it can be replaced by part of a tendon taken from the back part of the thigh muscles. This procedure is supposed to ensure that the kneecap doesn’t slip out of place so easily outwards (in the lateral direction).
  • Surgery on the bones to correct anatomical misalignments: These procedures can deepen the trochlear groove that the kneecap fits into. It is also possible to move the patellar tendon on the shinbone to the side. The aim of doing this is to keep the kneecap in the middle of the groove when force is put on it. Sometimes the axis (alignment) of the leg is also corrected by straightening the thigh and lower leg and stabilizing them with a plate.

The techniques that are considered depend on the anatomical form of the knee and leg.


Illustration: Front view of right knee, with supportive bands of tissue and thigh musclesFront view of right knee, with ligaments and thigh muscles

How effective is surgery?

Researchers from the Cochrane Collaboration analyzed six studies comparing surgery with conservative treatments. Nearly 350 teenagers and young adults participated in these studies.

Each of them had either conservative treatment or surgery. The surgery in these studies involved stitching and tightening the torn MPFL or replacing it with a tendon. There are currently no comparative studies on any of the other types of surgery.

The studies showed that the procedure can lower the risk of dislocating your kneecap again:

  • Without surgery, 21 out of 100 participants dislocated their kneecap again in the following years.
  • With surgery, 12 out of 100 participants dislocated their kneecap again.

It's not clear whether the surgery led to a greater improvement in symptoms and knee function than conservative treatment did. Previous studies have not shown that surgery has any advantages here. Because only a few studies looked into these aspects, further research is needed.

Only one study provided information on the frequency of complications. A few of the people in this study had complications after surgery, such as an infection or a poorly healing wound.