What is patellar instability, and how is it related to patellar dislocation? In the front of the knee, the kneecap slides up and down in a groove in the thigh bone, and patellar instability describes a spectrum from partial slipping (subluxation) to full patellar dislocation (also referred to as kneecap dislocation). When the kneecap fully comes out of the groove, this is called a patellar dislocation; when it partially comes out and goes back, it is called a subluxation or partial dislocation, and both are part of the spectrum of patellar instability.
Sometimes, these slips cause pain, swelling, and cartilage injury, which is especially common after a true patellar dislocation event. Some people notice a popping sensation when the kneecap moves out of place, followed by immediate pain and difficulty walking. Over time, repeated episodes of patellar instability or patellar dislocation can wear down the cartilage and contribute to early arthritis in the knee.
It can feel unstable and in severe cases it can be difficult to fully extend the knee. Sometimes patients have to go to the ER to get the patella back into the groove after a kneecap dislocation. Often, these injuries are accompanied by swelling and it can take weeks to months to feel normal again. Daily activities like going up and down stairs, squatting, or getting out of a chair may feel painful or unsteady. Some patients describe a sense of ‘giving way’ or feeling like they cannot trust the knee during sports or even routine movements. Because of this, people may avoid activities they enjoy, which can lead to muscle weakness and even more instability over time.
In some patients it happens without any trauma and at a young age. In others, unfortunately, it can occur playing sports with or without a contact injury. It can recur, especially when the first episode of patellar dislocation or kneecap dislocation happens before the age of 25. In many patients, a combination of anatomy (such as a shallow groove or high-riding kneecap) and ligament injury sets the stage for repeated dislocations. Strength and alignment of the hip and thigh muscles can also affect how well the kneecap tracks in the groove.
Both young women who are loose jointed and female athletes who experience a traumatic dislocation while playing their sport are at risk for recurrent subluxation and patellar dislocation. Additionally, although subluxation and dislocations do occur in men and boys, it happens much less frequently. Common risk factors include:
In most cases, patellar instability due to patellar dislocation can be fixed by reconstructing the MPFL (Medial Patellofemoral Ligament), which is a minimally invasive surgery with a 4-6 month recovery. In patients who have suffered cartilage damage the surgery may be more complicated with the addition of a bone re-aligning surgery such as a tibial tubercle osteotomy and/or a cartilage replacement surgery.
Non-surgical treatment often includes physical therapy focused on strengthening the quadriceps and hip muscles, improving balance, and training the kneecap to track properly. Bracing or taping can sometimes provide extra support during sports or higher-risk activities. The decision between continued non-surgical care and surgery depends on factors like your age, activity level, anatomy, and how many dislocations you’ve had.
If you have had a patellar dislocation or kneecap dislocation, it is important to be evaluated for cartilage injury and ligament damage, especially to the MPFL, because these injuries can increase the risk of future instability.
Even after a first-time patellar or kneecap dislocation, many patients benefit from a treatment plan that may include bracing, physical therapy, and, in some cases, surgery to help prevent recurrent dislocations and protect the cartilage in the knee.
Early evaluation after a first-time patellar dislocation helps identify patients at higher risk for recurrence and allows a more tailored treatment plan. The goal is not only to stop the kneecap from dislocating again, but also to protect the cartilage and keep you as active and comfortable as possible.
For more information about patellofemoral instability (also known as patellar instability or kneecap instability), check out this article on the Hospital for Special Surgery website. You can also download this information about patellofemoral instability.