Kneecap Dislocation

A Dislocated Patella Damages Ligaments

A dislocation of the kneecap occurs when the patella comes completely out of its groove on the end of the thigh bone (femur), and comes to rest on the outside of the knee joint. Kneecap dislocations can occur with or without significant injury the first time the injury occurs, and the kneecap may dislocate much more easily thereafter.

Woman getting a knee exam
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Kneecap Dislocation Symptoms

A kneecap dislocation causes significant pain and deformity of the knee joint. The kneecap almost always dislocates to the outside of the joint. Pain and swelling are common symptoms of kneecap dislocation. Over time, bruising may also develop around and below the knee joint.

The typical signs of a kneecap dislocation include:

  • A painful pop in the knee
  • Inability to straighten the leg (held with the knee bent)
  • Swelling and deformity of the front of the knee

A kneecap dislocation should not be confused with a knee dislocation. A knee dislocation occurs when the thigh bone (femur) and shin bone (tibia) lose contact, as if the knee is bending in the wrong direction.

Kneecap dislocation occurs with the kneecap dislodges from its groove on the thigh bone. Sometimes people use the words knee dislocation to describe a kneecap dislocation; this is incorrect.

Instability of the kneecap may result in a complete dislocation of the kneecap outside of its normal groove, or it may result in sensations that the kneecap is unstable within its groove. The sensations of instability may be called a subluxation, rather than a dislocation.

A subluxation implies that the kneecap shifting, but not coming completely out of place. Subluxations may result in discomfort, but generally, do not require immediate intervention as is the case when a dislocation of the kneecap occurs.

Recurrent Kneecap Dislocations

When the kneecap comes out of joint the first time, ligaments that were holding the kneecap in position are torn. The most important torn structure is called the medial patellofemoral ligament, or MPFL. This ligament secures the patella to the inside (medial) part of the knee. When a kneecap dislocation occurs, the MPFL can be torn or stretched.

Once the MPFL is torn, it often does not heal with proper tension, and the kneecap can subsequently dislocate more easily. That is why recurrent dislocations of the kneecap can continue to occur in some patients who have this injury.


Most kneecap dislocations will go back into place on their own, but if not, they are treated with prompt reduction (repositioning) of the kneecap.

Most patients will go to the emergency room, and while repositioning the kneecap is relatively straightforward, pain and muscle spasm can prevent this from being easily accomplished. Therefore, anesthesia (either local or general) may be administered to help reposition the kneecap.

Most kneecap dislocations can be repositioned by simply straightening the knee once control of the pain and spasm allows.

After repositioning the kneecap, treatment usually begins with R.I.C.E. treatment (rest, ice, compression, elevation) to control pain and help with swelling. Crutches and a knee brace are usually offered to help control pain.

While preventing weight on the leg may help with pain, it is not necessary to keep all weight off of the leg. Once the acute swelling has subsided, treatment may progress.

The next phase of treatment usually consists of physical therapy and bracing the kneecap. As discussed earlier, kneecap dislocations can become a recurrent problem. By strengthening the muscles around the joint, and with the use of specialized knee braces, the hope is to stabilize the knee to help prevent recurrent injury.

In patients who have recurrent (repeat) dislocations, there are surgical options. The usual treatment is to reconstruct the ligament that pulls from the inside of the kneecap to keep in place. In some circumstances, a realignment of the extremity, involving cutting and repositioning bone, may be recommended.

Surgery After First Dislocation?

Recent interest has developed in preventing these recurrent dislocations. Each time the kneecap dislocates, the cartilage can be injured, and the ligaments can become more stretched out.

Concerns about increasing the likelihood of arthritis development from repeated trauma have made some doctors more aggressive in trying to prevent repeat dislocations. Some surgeons are trying to restore the normal anatomy by repairing the MPFL after a first-time dislocation.

Surgery after the first dislocation is controversial because not all patients who dislocate their kneecap will have another dislocation. In addition, early surgery has not been shown through scientific study to be helpful in preventing arthritis.

If your surgeon is recommending surgery, and you are unsure to proceed, it never hurts to seek out another opinion. Just remember: there is not always a right and a wrong answer. While some surgeons and patients may have strong opinions, there is not always a clear answer as to how to best proceed.

It never hurts to seek out some other advice. That said, it is also important to remember that too much advice can clutter thinking. If you find a surgeon you trust, and you are confident they are looking out for your best interest, then sticking with them may be your best bet!

6 Sources
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By Jonathan Cluett, MD
Jonathan Cluett, MD, is board-certified in orthopedic surgery. He served as assistant team physician to Chivas USA (Major League Soccer) and the United States men's and women's national soccer teams.