Patellar Instability

Patellar instability occurs when your kneecap (patella) moves out of its normal position, either partially (subluxation) or completely (dislocation). This can cause pain, swelling, and a feeling that your knee is giving way. It often results from an injury or underlying anatomical factors, and treatment aims to stabilize the kneecap and prevent future episodes.

What is Patellar Instability?

Patellar instability is a condition where your kneecap, also known as the patella, moves out of its normal groove at the front of your knee joint. This can be a partial shift, called a subluxation, or a complete displacement, known as a dislocation. It often causes pain, swelling, and a feeling of the knee giving way.

Your kneecap (patella) normally sits in a shallow groove at the end of your thigh bone (femur), called the trochlear groove. It slides smoothly up and down this groove as you bend and straighten your knee. Patellar instability happens when the kneecap moves too far to one side, usually the outside of the knee, causing it to slip out of this groove. When the kneecap partially slips out of its groove and then returns to place, it's called a patellar subluxation. If the kneecap fully comes out of its groove and stays out, it's a patellar dislocation. Both subluxation and dislocation can damage the ligaments and cartilage that support the kneecap, leading to pain and a feeling of looseness in the knee joint.

Symptoms

When your kneecap becomes unstable, you might experience sudden pain, swelling, and a popping sensation in your knee. Other common symptoms include a feeling that your knee is giving way, difficulty bending or straightening it, and sometimes a visible deformity if the kneecap is fully dislocated.

The symptoms of patellar instability can vary depending on whether the kneecap partially or completely moves out of place. A sudden, sharp pain is common, especially during a dislocation. You might hear or feel a "pop" as the kneecap shifts. After the event, your knee will likely swell rapidly due to bleeding inside the joint. You may also feel tenderness around the kneecap. It can become difficult or impossible to bend or straighten your knee. If the kneecap is fully dislocated, you might see a noticeable bump on the side of your knee where the kneecap has moved, and the front of your knee may look flat.

Causes & risk factors

Patellar instability can be caused by a direct injury to the knee, such as a sudden twist or a blow, or by underlying anatomical issues that make the kneecap prone to slipping. Risk factors include certain sports, being young and female, having loose ligaments, or a kneecap that sits too high or a shallow groove in the thigh bone.

One common cause of patellar instability is an acute injury, such as a direct blow to the knee or a sudden twisting motion of the leg. This can happen during sports activities like basketball, soccer, or gymnastics, which involve pivoting and quick changes in direction. Many cases of patellar instability are also linked to anatomical factors that make the kneecap naturally less stable. These can include a shallow trochlear groove in the thigh bone, which normally holds the kneecap in place, or a kneecap that sits too high (called patella alta). Loose ligaments around the knee, muscle imbalances (such as weak quadriceps or hip abductor muscles), or a previous patellar dislocation also increase the risk. Certain individuals are more prone to patellar instability. Young people, especially females, have a higher risk. Conditions that cause general joint looseness, like Ehlers-Danlos syndrome, can also contribute. A family history of patellar instability may also indicate a genetic predisposition.

How it's diagnosed

Diagnosing patellar instability usually begins with a physical examination of your knee, where a doctor checks for tenderness, swelling, and range of motion. Imaging tests like X-rays are used to assess bone alignment and rule out fractures, while an MRI can provide detailed views of soft tissues, including ligaments and cartilage.

When you see a doctor for suspected patellar instability, they will first ask about your symptoms and how the injury occurred. They will then perform a physical examination of your knee. This involves gently feeling around the kneecap for tenderness and swelling, checking your knee's range of motion, and assessing the stability of your kneecap. To get a clearer picture, imaging tests are often used. An X-ray can show the alignment of your kneecap and thigh bone, help identify if your kneecap sits too high (patella alta), and rule out any fractures that might have occurred during the injury. An MRI (magnetic resonance imaging) provides more detailed images of the soft tissues, allowing the doctor to see if there's damage to the ligaments (like the medial patellofemoral ligament, or MPFL), cartilage, or other structures within the knee joint.

Treatment options

Treatment for patellar instability often starts with non-surgical methods like rest, ice, pain relief, and physical therapy to strengthen supporting muscles. If these approaches are not effective, or if instability is recurrent or severe, surgery may be recommended to repair or reconstruct damaged ligaments or correct anatomical issues.

Initial treatment for a dislocated kneecap often involves reducing the dislocation, which means gently moving the kneecap back into its proper position. This is usually followed by conservative measures such as rest, applying ice, compression, and elevation (RICE), along with pain relievers to manage discomfort and swelling. Non-surgical treatment focuses heavily on physical therapy. A physical therapist will guide you through exercises designed to strengthen the muscles around your knee and hip, particularly the quadriceps and hip abductors. These exercises help improve knee stability and control. Bracing or taping the kneecap may also be used to provide support during recovery. If non-surgical treatments do not prevent recurrent instability, or if there is significant damage to the knee structures, surgery may be considered. Common surgical procedures include medial patellofemoral ligament (MPFL) reconstruction, which repairs or replaces the main ligament that holds the kneecap in place. Another option is a tibial tubercle osteotomy, which involves moving the attachment point of the patellar tendon to improve kneecap alignment. While surgery may reduce the risk of future dislocations compared to non-surgical treatment, the effectiveness can vary depending on the specific procedure and individual factors.

Recovery & outlook

Recovery from patellar instability varies depending on the severity and type of treatment, often taking weeks to several months. Physical therapy is a crucial part of recovery, helping to restore strength and stability. While many people recover well, there is a possibility of the kneecap becoming unstable again, especially after an initial dislocation.

The recovery period for patellar instability can range from several weeks for mild cases treated non-surgically to several months following surgery. Physical therapy is a cornerstone of recovery, regardless of the treatment approach. It helps restore strength, flexibility, and balance to the knee and surrounding muscles, which is vital for preventing future instability. After a first-time dislocation, there is a risk of the kneecap dislocating again. While surgery may reduce this risk compared to non-surgical treatment, it does not eliminate it entirely. Your doctor will discuss the likelihood of recurrence based on your specific situation. Long-term, repeated episodes of instability or significant cartilage damage can increase the risk of developing knee arthritis later in life. Most individuals can return to their normal activities, including sports, after completing their rehabilitation program. Following your physical therapist's instructions and gradually increasing your activity level are key to a successful recovery and a positive outlook.

When to see a doctor

You should see a doctor immediately if you experience sudden, severe knee pain, significant swelling, or if your kneecap appears visibly out of place. Seek medical attention if you cannot move your knee or put weight on it, as these could be signs of a serious injury requiring prompt evaluation.

If you suspect your kneecap has dislocated or if you experience any of the following symptoms, it's important to seek medical attention promptly: * Sudden, severe pain in your knee. * Rapid swelling around the kneecap. * A visible deformity, such as your kneecap appearing to be on the side of your knee. * Inability to straighten or bend your knee. * Difficulty putting weight on the affected leg or walking. Even if your kneecap seems to pop back into place on its own, it's still crucial to see a doctor. A medical professional can assess for any underlying damage to ligaments or cartilage and recommend appropriate treatment to prevent future episodes and potential long-term complications.

Frequently asked questions

Can patellar instability heal on its own?

A dislocated kneecap may sometimes pop back into place on its own, but it's crucial to see a doctor afterward. While some mild cases of instability might improve with rest and physical therapy, professional evaluation is needed to prevent recurrence and address any underlying causes or damage to the knee structures.

What exercises are bad for patellar instability?

Exercises that involve deep knee bending, twisting, or sudden pivoting movements can put excessive stress on an unstable kneecap and should generally be avoided, especially during recovery. Your physical therapist can guide you on safe exercises and those to avoid based on your specific condition and recovery stage.

How long does it take to recover from patellar dislocation?

Recovery time varies significantly. For a first-time dislocation treated non-surgically, it might take 6-8 weeks or more to return to normal activities, with physical therapy continuing longer. Surgical recovery can take several months, often 4-6 months or longer, before returning to sports, depending on the procedure and individual progress.

Is patellar instability a disability?

For most people, patellar instability is a temporary condition that can be managed with treatment and rehabilitation. However, severe or recurrent instability that significantly limits daily activities or work, even after treatment, could potentially be considered a disability. This is best discussed with a healthcare provider and relevant authorities.

Can I prevent patellar instability?

While not all cases are preventable, especially those due to anatomical factors, you can reduce your risk. Strengthening the muscles around your knee and hip, particularly the quadriceps and hip abductors, maintaining good balance, and using proper technique during sports can help improve knee stability.

What is the difference between patellar subluxation and dislocation?

Patellar subluxation is a partial displacement where the kneecap moves out of its normal groove but then returns to place on its own. A patellar dislocation is a complete displacement where the kneecap fully comes out of its groove and stays out until it's manually put back or reduces spontaneously. Both cause pain and instability.

Sources

• MedlinePlus — Patellar Instability
• Mayo Clinic — Patellar Instability
• Cochrane Library — Patellar Instability