Patellar Subluxation: What to Do About an Unstable Kneecap

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A little bit of anatomy helps in understanding what exactly patellar subluxation is. The patella, or kneecap, is one of three bones that forms the knee joint. Each of these bones has a protective layer of cartilage where their surfaces come into contact. The patella is also enveloped by a tendon. This tendon connects the quadriceps muscle of the thigh to the shinbone (tibia) below the knee.

The kneecap slides up and down a groove on the end of the thigh bone as the knee bends.

This groove is called the trochlea. The kneecap is designed to fit in the center of the trochlear groove and slide evenly within the groove. In some people, the kneecap is pulled towards the outside of the trochlear groove. As this happens, the kneecap does not slide centrally within its groove—we call this patellar subluxation.

Symptoms

Depending on the severity of the patellar subluxation, the improper tracking may not cause the individual any symptoms, or it could lead to dislocation of the patella (where the kneecap fully comes out of the groove). Most commonly, patellar subluxations cause discomfort with activity and pain around the sides of the kneecap, called patellofemoral pain syndrome, or PFPS.

Many people with symptoms of kneecap pain are diagnosed with patella subluxation or maltracking of the patella. These issues, with the mechanics of how the knee joint bends, are thought to be a common cause of symptoms that range from knee pain to dislocation of the kneecap.

Causes

There are dozens of factors implicated in the cause of patellar subluxation. The bottom line is that several factors lead to instability of the kneecap. Possible factors include a wider pelvis, a shallow groove for the kneecap, and abnormalities in a person's gait.

There has been tremendous interest in recent years of the way our muscles help guide the kneecap as it bends in the knee joint.

In particular, the muscles around the hip are thought to be the most important muscles in controlling the mechanics of the joint and how the kneecap moves as the joint bends.

Typically, the pain associated with patellar subluxation is attributed to PFPS. Other causes of kneecap pain include knee arthritis, patellar tendonitis (Jumper's knee), and plica syndrome. It is important to know that not every cause of kneecap pain is simply the result of patellar subluxation, and other factors may also be important to determine the cause of pain and the treatments that should be recommended.

Treatment

There are several treatment options to correct a patellar subluxation, and the most appropriate option depends on the severity of the condition and the cause of the abnormal positioning of the kneecap. 

Treatment should first ensure that the patella is not dislocated. Your doctor can determine by examining your knee and obtaining x-rays to see if the kneecap is outside of its groove. In people with a kneecap dislocation, the kneecap may need to be repositioned, also known as "reduced."

The kneecap position depends not only on the the muscles directly around the knee joint, but also the muscles that control the position of the entire extremity.

For example, when the thigh bone internally rotates, the kneecap will tend to pull to the outside of the trochlea. This is precisely why improving the stability of the core and the hips is so critical to improving the mechanics of the knee joint and relieving patellar subluxation.

Physical Therapy

Treatment includes traditional physical therapy, which is used to strengthen the muscles that surround not only the knee but also the entire lower extremity.

Some research has shown that isolated quadriceps strengthening is not the critical factor in eliminating kneecap problems. Focusing instead on strengthening the hip abductors and hip flexors (so-called pelvic stabilization exercises) offers better control of the kneecap by stabilizing the function of the entire extremity.

Braces and Tape

Bracing and taping of the kneecap is also a controversial topic in the rehabilitation of kneecap problems. These often provide symptomatic relief, but are certainly not a long-term solution. However, if a patient has symptomatic relief with a brace or tape, it is certainly appropriate to continue with this as a treatment.

Shoe Choice

Footwear contributes to the gait cycle. Motion control running shoes may help control your gait while running and decrease the pressure on the kneecap.

Surgery

Some patients are not cured by simple treatments and surgery may be needed, especially in patients who have significant pain or recurrent dislocation. By looking into the knee with an arthroscope, the surgeon can assess the mechanics of the knee joint to ascertain if there is an issue that can be corrected.

Some of these options for surgical treatment include:

  1. Lateral Release: A lateral release is a surgical procedure performed to loosen the pull of the tight ligaments and joint capsule on the outer side of the knee. While often the easiest surgical approach, it does the least to improve patellar alignment.
  2. Medial Ligament Reconstruction: Repairing or reconstructing the ligaments on the inner side of the knee that pull the kneecap inwards have become a more common treatment. This surgery is typically done to repair the medial patellofemoral ligament (MPFL) on the inner side of the knee.
  3. Bone Realignment: In more severe situations a bone realignment may be necessary. There are many types of bone realignment, commonly they shift the position of the tibial tubercle, which determines the direction of pull on the kneecap.

While surgery can be a useful tool to help manage kneecap problems, it is important to clearly understand what the goal of surgery is and how the procedure will help to correct the underlying problem. For a number of years, arthroscopic surgery was performed, as well as a procedure called a lateral release, for vague kneecap problems.

While some patients improved, others didn't get better with surgery. Simply performing a surgery, without understanding the specific problem being targeted for correction, can lead to unsatisfactory results. Discuss this option if it's what your doctor recommends and make sure it's the best option for your situation.

A Word From Verywell

Kneecap function is critical to normal knee mechanics, and when the kneecap is not held in proper position, people can feel significant pain and disability. Correction of patellar subluxation and dislocations can typically be accomplished with nonsurgical treatment, and the mainstay of treatment is physical therapy aimed at improving the mechanics of the lower extremity.

However, there are situations where surgery may be necessary. In these situations, choosing the right surgery is critical to finding success with treatment.

Sources:

Smith, T. Donell, S. Song, F., Hing, C. National Institutes of Health National Library of Medicine. "Surgical versus non‐surgical treatment after kneecap dislocation." Oct 2014.

Koh JL, Stewart C. "Patellar instability." Orthop Clin North Am. 2015 Jan;46(1):147-57.

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