Kneecap Dislocation: Why the Patella Slips and How to Prevent It Again

A kneecap dislocation occurs when the patella (kneecap) slips out of its normal position, usually towards the outer side of the knee. It can happen due to a sudden twist, a sports injury, a fall or an awkward landing. The injury can cause severe knee pain, swelling and difficulty walking. While the kneecap may sometimes return to its normal position on its own, proper medical evaluation and rehabilitation are important to prevent another dislocation.

If your kneecap keeps slipping or you have experienced a displaced kneecap before, understanding why it happens and how to protect your knee can help you avoid repeated injuries.

What Is a Kneecap Dislocation and How Does the Patella Slip Out of Place?

The patella is a small, triangular bone located at the front of your knee. It protects the knee joint and helps the thigh muscles straighten your leg. It normally moves up and down within a groove at the lower end of the thigh bone (femur) when you bend or straighten your knee.

A patella dislocation occurs when the kneecap moves completely out of this groove. In most cases, it slips towards the outer side of the knee. This is also known as a lateral patellar dislocation.

A partial movement, where the kneecap moves out of its normal position but does not completely leave the groove, is called patellar subluxation.

A displaced patella can sometimes return to its normal position without medical assistance. However, this does not mean the injury has healed completely. The ligaments and cartilage around the kneecap may still be damaged.

It is also important to understand that a dislocated kneecap is different from a dislocated knee joint. A knee joint dislocation involves the thigh bone and shin bone losing their normal alignment. It is a more serious injury that can damage blood vessels  and nerves and requires emergency medical attention.

What Causes Kneecap Dislocation and Who Is at Risk?

A kneecap dislocation usually happens when the knee twists or turns suddenly while the foot remains firmly on the ground. However, some people are more likely to experience this injury because of their knee structure or ligament strength.

Common causes and risk factors include:

• Sudden twisting movements: Quickly changing direction while running, jumping or playing sports can force the kneecap out of its groove.
• Direct impact: A fall, collision or blow to the knee can push the patella out of position.
• Sports injuries: Activities such as football, basketball and gymnastics involve sudden movements that increase the risk of patellar dislocation.
• Loose ligaments: Ligaments help keep the kneecap stable. If they are naturally loose or stretched due to an earlier injury, the kneecap may slip more easily.
• Muscle weakness: Weakness in the thigh and hip muscles can affect knee alignment and stability.
• Knee structure: A shallow groove in the thigh bone or an unusually high kneecap can make it easier for the patella to move out of position.
• Previous dislocation: Once the kneecap has dislocated, the supporting ligaments may become stretched or damaged, increasing the risk of another episode.

Some people also have congenital patellar dislocation, a condition in which the kneecap is displaced from birth due to differences in the development or structure of the knee. This is different from an injury-related dislocation and may require specialised treatment.

What Are the Symptoms of a Dislocated Kneecap?

The symptoms of a dislocated kneecap usually appear immediately after the injury. Their severity depends on how far the patella has moved and whether the surrounding ligaments or cartilage are damaged.

Common dislocated knee symptoms include:

• Sudden and severe knee pain: You may feel sharp pain around the front or outer side of the knee.
• Visible displacement: The kneecap may appear out of place or shifted towards the outer side.
• Swelling: The knee may swell quickly due to inflammation or bleeding inside the joint.
• Difficulty bending or straightening the knee: Movement may become painful or restricted.
• Feeling of instability: You may feel that your knee is giving way or cannot support your body weight.
• Bruising and tenderness: The area around the kneecap may become painful to touch.
• Difficulty walking: Standing or putting weight on the affected leg may become difficult.

Sometimes, a slipped patella returns to its normal position before you reach a doctor. Even then, pain, swelling and a feeling of instability may continue.

Do not try to force a displaced kneecap back into place yourself. Seek medical attention, particularly if you cannot move your knee, have severe pain or notice significant swelling.

How Is Kneecap Dislocation Diagnosed and Treated?

Doctors diagnose a kneecap dislocation through a physical examination and imaging tests. Treatment depends on whether it is the first dislocation, whether the kneecap has returned to its normal position and whether there is damage to the surrounding structures.

Diagnosis

Your doctor will examine the knee to check its position, swelling, tenderness and movement. They may also assess the stability of the kneecap and compare the affected knee with the other one.

Imaging tests may include:

• X-rays: Help confirm the position of the kneecap and identify fractures or bone injuries.
• MRI scan: Helps detect damage to the ligaments, cartilage and other soft tissues around the knee.

These tests help doctors decide whether non-surgical treatment is sufficient or whether surgery may be needed.

Treatment

Most first-time kneecap dislocations without major associated injuries can be managed without surgery.

Treatment options may include:

• Reduction: If the kneecap is still displaced, a doctor carefully moves it back into its normal position. This procedure is called reduction.
• Rest and ice: Resting the knee and applying ice wrapped in a towel can help reduce pain and swelling.
• Knee brace: A brace may be recommended for a short period to support the kneecap while the injured tissues recover.
• Pain relief: Doctors may recommend suitable pain-relieving medicines to manage discomfort.
• Physiotherapy: Guided exercises help strengthen the thigh and hip muscles, improve knee stability and restore movement.

When Is Surgery Needed?

Surgery may be recommended if the kneecap dislocates repeatedly, there is significant cartilage or bone damage, or the knee remains unstable despite appropriate rehabilitation.

Depending on the injury, surgical options may include medial patellofemoral ligament (MPFL) reconstruction to restore the ligament that helps prevent the kneecap from slipping towards the outer side. In some patients, doctors may also recommend procedures to correct underlying bone alignment or structural problems.

The choice of surgery depends on the patient's age, knee anatomy, injury severity and history of previous dislocations.

How Can You Prevent Recurrent Kneecap Dislocation?

If your kneecap has dislocated once, you may have a higher risk of experiencing it again. This is because the ligaments that support the patella may have been stretched or damaged during the first injury.

Recurrent subluxation of patella can also occur when the kneecap repeatedly moves partially out of its normal position. The good news is that appropriate rehabilitation and changes in physical activity can help improve knee stability.

Here are some ways to reduce the risk of another dislocation:

• Strengthen your thigh muscles:Exercises that target the quadriceps help support the kneecap and improve knee control.
• Improve hip strength: Strong hip muscles help maintain proper leg alignment during walking, running and other activities.
• Follow a physiotherapy plan: A physiotherapist can recommend exercises based on your injury and recovery progress.
• Improve balance and coordination: Guided balance exercises help your body control knee movements during physical activity.
• Avoid sudden movements during recovery: Do not return to running, jumping or sports until your doctor or physiotherapist confirms that your knee is ready.
• Wear appropriate footwear: Supportive shoes can help maintain stability during walking and exercise.
• Use protective support when advised: A knee brace may be recommended during certain activities, depending on your injury.

If your knee cap keeps slipping despite physiotherapy, consult an orthopaedic specialist. Repeated dislocations may indicate an underlying structural problem that needs further evaluation.

Conclusion

A kneecap dislocation can cause sudden pain, swelling and difficulty moving your knee. Although many first-time injuries can be treated without surgery, ignoring the injury or returning to physical activities too soon can increase the risk of another episode.

Early diagnosis, appropriate treatment and a guided physiotherapy programme can help restore knee stability. If your kneecap keeps slipping or you experience repeated dislocations, consult an orthopaedic specialist to identify the cause and discuss suitable treatment options.

Frequently Asked Questions