Kneecap dislocations are a common type of knee injury that can occur in young female athletes. The kneecap (patella) is a small protective bone that attaches near the bottom of the thigh bone (femur). As the leg straightens or bends, the kneecap moves up and down in a groove called the trochlea. Patellar instability is when you have an unstable kneecap. It can lead to dislocation when the kneecap dislodges from the groove.
“Kneecap dislocations can be a very limiting condition, particularly for athletes,” says Miho J. Tanaka, MD, a Mass General Brigham Sports Medicine orthopaedic surgeon and director of the Women's Sports Medicine Program at Massachusetts General Hospital. Dr. Tanaka is a researcher with an expertise in kneecap injuries and gender-based differences in orthopaedic injuries. “Not only is a dislocation a very painful event in which the kneecap goes out of place, patients can be left with continued instability even after the initial injury has healed.”
Dislocation Causes and Risk Factors
Dislocations can be caused by events such as a sudden twist of the leg during a basketball game or through a blow to the knee on the soccer field. This type of injury can be commonly seen in dancers as well.
There are certain risk factors that increase the likelihood of dislocating a kneecap. These include having bony abnormalities (such as a shallow trochlea or abnormal lower extremity alignment) that make the kneecap less likely to be stable, or having loose ligaments, which are the tissues that connect bone to bone as part of the kneecap’s support system. Kneecap dislocation is most common among females between ages 10 and 17.
A Dislocation. Now What?
What should you do if you have a patellar dislocation? Dr. Tanaka recommends getting off your feet and applying the RICE method — rest, ice, compression (wrapping it with a bandage) and elevation. And then it’s important to see your health care provider, who can and assess the extent of injury and safely realign the kneecap if it remains out of place.
For some people, a dislocation may be a one-time event with no long-term effects. But for others, the concern is that there may be a related injury, or that dislocations will become a chronic problem.
“Even though some patients may be willing to deal with the pain or the functional limitations associated with patellar instability, there are also long-term implications for the health of your knee with continued dislocations,” says Dr. Tanaka. “Young patients who repeatedly dislocate their kneecaps are at an increased risk for developing arthritis at a younger age.”
Conservative Management and Physical Therapy
An important focus of treatment is the prevention of future dislocations. Once your sports medicine physician confirms that there aren’t any injuries to other parts of your knee, they may recommend conservative management. This typically means using a specially designed knee brace to help support your kneecap and physical therapy (PT). PT often involves strengthening the leg muscles near the kneecap, but it doesn’t end there.
“Physical therapy also focuses on strengthening the hip muscles and the core, because those can affect the dynamic alignment and stability of the knee” says Dr. Tanaka. “And the focus is not just on strength, it is also on improving functional movement and coordination that allows a patient to resume sports and activities.”
When surgery is required, it can involve a combination of procedures that is tailored to each individual’s anatomy:
- Reconstructing the primary ligament that supports the kneecap
- Improving the alignment of the knee to increase patellar stability
- Deepening the groove that the kneecap fits into
The good news is that clinician-researchers, like those at the Mass General Brigham Women’s Sports Medicine Program, are investigating ways to better predict who is at risk for chronic kneecap dislocations and the optimal treatments to avoid this fate.
“Patellar disorders used to be called the ‘black box’ of orthopaedics,” says Dr. Tanaka. “But even in the last decade, technological advances and new imaging techniques have allowed us to quantify patellar motion, allowing us to better predict an individual’s risk for future dislocations while improving our understanding of how to tailor treatments to optimize their recovery and the long term health of the knee.”