Patellar Subluxation

Patellar subluxation is when your kneecap (patella) partially slips out of its normal groove at the front of your knee. This can cause pain, swelling, and a feeling of instability. It often happens due to a sudden twist or a direct blow to the knee, or sometimes because of underlying structural issues.

What is Patellar Subluxation?

Patellar subluxation is a condition where your kneecap (patella) partially moves out of its normal position in the groove at the end of your thigh bone (femur). Unlike a full dislocation, the kneecap doesn't completely leave the groove, but it can still cause significant pain, swelling, and a feeling that your knee is unstable or "giving way."

Your kneecap, or patella, normally sits in a shallow groove called the trochlear groove on your thigh bone. It acts like a pulley, helping your leg muscles straighten your knee. When subluxation occurs, the kneecap usually shifts towards the outside of the knee. This partial slipping can stretch or tear the ligaments that hold the kneecap in place, particularly the medial patellofemoral ligament (MPFL). Even though it's not a full dislocation, the movement can damage the cartilage on the underside of the kneecap or within the knee joint. Patellar subluxation is often a temporary event, with the kneecap returning to its proper place on its own. However, it can sometimes lead to ongoing instability and a higher risk of future subluxations or full dislocations if not properly managed.

Symptoms

The main symptoms of patellar subluxation include sudden knee pain, especially when moving or bending your knee, and swelling around the kneecap. You might also feel a sensation that your kneecap is shifting or "giving way," and it can be difficult to straighten your leg fully.

When a patellar subluxation happens, you might feel a pop or a sudden shift in your knee. The pain can range from mild to severe, and it often gets worse when you try to bend or straighten your knee, or put weight on it. Swelling usually develops quickly around the kneecap due to inflammation and sometimes bleeding within the joint. You may also notice tenderness to the touch around the kneecap. Some people describe a feeling of instability, as if the knee is going to buckle or give out. In some cases, you might even be able to see that your kneecap looks slightly out of place, although it typically returns to its normal position on its own.

Causes & risk factors

Patellar subluxation can be caused by a direct blow to the knee or a sudden twisting motion of the leg. Certain structural issues in the knee, such as a shallow groove for the kneecap or loose ligaments, can also increase your risk. Weak thigh muscles and previous subluxations are common risk factors.

**Causes**: A common cause is a direct impact to the knee, such as during a fall or a sports injury. Another frequent cause is a sudden, forceful twisting motion of the knee, especially when the foot is planted on the ground. This can happen during activities like basketball, soccer, or dancing. **Risk Factors**: Several factors can make you more likely to experience patellar subluxation. These include having a shallow trochlear groove (the groove where the kneecap sits) or having ligaments that are naturally looser than average. Muscle imbalances, particularly weak quadriceps muscles (the muscles at the front of your thigh), can also contribute. Other risk factors include being female, being young and active, and having a history of previous patellar subluxations or dislocations. Certain genetic conditions that affect connective tissue, such as Ehlers-Danlos syndrome, can also increase the risk due to joint laxity.

How it's diagnosed

Patellar subluxation is diagnosed through a physical examination of your knee, where a doctor will check for tenderness, swelling, and how your kneecap moves. Imaging tests like X-rays are often used to rule out fractures, and an MRI scan can provide detailed views of soft tissues and cartilage damage.

During the physical exam, your doctor will gently feel your knee, looking for signs of swelling, tenderness, and any unusual movement of your kneecap. They will also assess your range of motion and the stability of your knee joint. They may perform specific tests to see if the kneecap can be easily moved out of its groove. An X-ray is typically performed to check for any broken bones (fractures) and to evaluate the alignment of your kneecap and the shape of the trochlear groove. While X-rays show bones well, they do not show soft tissues like ligaments or cartilage. To get a more detailed view of the ligaments, tendons, and cartilage around your knee, your doctor may order a magnetic resonance imaging (MRI) scan. An MRI can help identify any damage to the medial patellofemoral ligament (MPFL), cartilage injuries, or other soft tissue problems that might contribute to the subluxation or result from it.

Treatment options

Treatment for patellar subluxation usually begins with conservative methods, including rest, ice, compression, and elevation (RICE) to manage pain and swelling. Physical therapy is crucial to strengthen the muscles around the knee and improve stability. In some cases, a brace or tape may be used, and surgery might be considered for recurrent instability.

**Conservative Treatment**: Initial treatment focuses on reducing pain and swelling. This often involves the RICE method: **R**est your knee, apply **I**ce packs, use a compression **C**wrap, and **E**levate your leg. Over-the-counter pain relievers, such as ibuprofen or naproxen, can help manage discomfort. **Physical Therapy**: A cornerstone of treatment is physical therapy. A physical therapist will guide you through exercises designed to strengthen the quadriceps muscles (especially the vastus medialis obliquus), hamstrings, and hip muscles. These exercises help improve knee stability and alignment, reducing the risk of future subluxations. **Bracing or Taping**: Sometimes, a knee brace or athletic tape can be used to help keep the kneecap in its proper position during activity, providing support and a sense of security. Your doctor or physical therapist can advise on the most appropriate type of brace or taping technique for your specific situation. **Surgery**: If conservative treatments are not effective, or if you experience recurrent subluxations, your doctor might recommend surgery. Surgical options can include repairing or reconstructing the medial patellofemoral ligament (MPFL), which is often torn during subluxation, or procedures to realign the kneecap or deepen the trochlear groove. The goal of surgery is to stabilize the kneecap and prevent future episodes.

Recovery & outlook

Recovery from patellar subluxation varies but typically involves several weeks to months of rehabilitation, with physical therapy being essential for regaining strength and stability. Many people recover well with conservative treatment, but recurrence is common, especially in young, active individuals.

The recovery timeline depends on the severity of the subluxation, any associated damage, and your adherence to the treatment plan. For most people, initial pain and swelling subside within a few days to weeks. However, regaining full strength and stability through physical therapy can take several months. A significant number of individuals recover fully with non-surgical treatment and can return to their normal activities, including sports. However, it's important to understand that patellar subluxation has a relatively high chance of happening again, particularly in younger individuals and those who participate in sports that involve twisting or jumping. Even after surgery, a dedicated rehabilitation program is crucial for a successful outcome. While surgery aims to reduce recurrence, it does not eliminate the risk entirely. Long-term outlook is generally good with appropriate management, but ongoing muscle strengthening and proper body mechanics are important for preventing future episodes.

When to see a doctor

You should see a doctor immediately if you experience sudden, severe knee pain, especially if your kneecap looks visibly out of place or you cannot straighten or bear weight on your leg. Prompt medical attention is important to assess the injury and rule out more serious damage like a fracture or complete dislocation.

If your kneecap has completely dislocated and remains out of place, or if you notice a significant deformity in your knee, seek emergency medical care. This requires immediate reduction (putting the kneecap back into place) by a medical professional. Even if the kneecap seems to have returned to its normal position, it's wise to see a doctor if you have persistent pain, swelling, or a feeling of instability after an injury. They can properly diagnose the extent of the injury, check for any associated damage to cartilage or ligaments, and recommend the best course of treatment. Ignoring symptoms or delaying treatment can potentially lead to chronic knee pain, recurrent instability, or further damage to the knee joint over time. A medical professional can provide an accurate diagnosis and a tailored treatment plan to help you recover safely and effectively.

Frequently asked questions

Can I walk on a subluxated kneecap?

It's generally not recommended to put full weight on a subluxated kneecap, especially immediately after the injury. Walking can increase pain, swelling, and potentially worsen the injury or cause the kneecap to slip further. It's best to rest, apply ice, and seek medical advice.

How long does it take for a patellar subluxation to heal?

The healing time for patellar subluxation varies depending on the severity and whether there's associated damage. Mild cases might improve in a few weeks with rest and physical therapy, while more severe cases or those requiring surgery can take several months for full recovery and rehabilitation.

Is patellar subluxation the same as a dislocated kneecap?

No, patellar subluxation is a partial dislocation, meaning the kneecap only partially slips out of its groove and often returns on its own. A dislocated kneecap (patellar dislocation) means the kneecap completely leaves its groove and usually requires medical help to put it back into place.

What exercises should I avoid with patellar subluxation?

Initially, you should avoid exercises that involve deep knee bends, twisting motions, or high-impact activities that put stress on your kneecap. Your physical therapist will guide you on safe exercises and when to gradually reintroduce more challenging movements as your knee heals and strengthens.

Can patellar subluxation be prevented?

While not all cases can be prevented, you can reduce your risk by strengthening the muscles around your knee and hips, especially your quadriceps. Maintaining good flexibility, using proper technique during sports, and wearing appropriate footwear can also help. If you have anatomical risk factors, discuss them with your doctor.

Will I need surgery for patellar subluxation?

Most cases of patellar subluxation are treated successfully with conservative methods like physical therapy and bracing. Surgery is typically considered for individuals who experience recurrent subluxations, have significant damage to ligaments or cartilage, or have specific anatomical issues that contribute to instability.

Sources

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