Dislocated Kneecap (Dislocated Patella) (for Parents)

en español: Rótula dislocada

Reviewed by: Melanie L. Pitone, MD

What Is a Dislocated Kneecap?

A dislocated kneecap is when the bone in the front of the knee — called the kneecap or patella — slides out of place.

What Are the Signs & Symptoms of a Dislocated Kneecap?

Common symptoms of a dislocated kneecap or dislocated patella (peh-TELL-uh) include:

• feeling like the knee buckled or “gave out” 
• sudden, severe pain and swelling
• a bump noticed on the outside of the knee. This is the kneecap that is out of place. 
• the knee is held in a bent position
• bruising around the knee

How Does a Dislocated Kneecap Happen?

The kneecap sits on the front of the knee joint. When the knee is bent and straightened, the kneecap slides up and down in a groove in the front of the knee. A direct blow to the knee, such as in a fall or an accident, can push the kneecap out of the groove, or dislocate it. The kneecap also can dislocate when the knee gets twisted during sports or play.

A dislocated kneecap can happen to any child or teen who has a blow or twist to the knee. Some kids have conditions that make them more likely to dislocate the kneecap. These include things like some leg muscles being stronger than others or loose ligaments (bands of tissue that hold bones together at joints).

How Is a Dislocated Kneecap Diagnosed?

Often, doctors can tell there is a dislocated kneecap by asking questions and looking at the knee. X-rays aren’t needed for a diagnosis, but are done after the kneecap is back in place to check for small fractures in the bone. These can happen as the kneecap slides out of its groove and then back into place.

How Is a Dislocated Kneecap Treated?

A person with a dislocated kneecap needs care at the hospital right away. After giving pain medicine, the doctor or another health care provider will gently slide the kneecap back into place while straightening the leg. This quick maneuver is called a reduction. Then, they’ll order an X-ray to check for fractures.

Sometimes a dislocated kneecap may move back into place on its own if the child straightens the leg before getting to the hospital. If this happens, the doctor will still get an X-ray to check the knee for fractures.

After a kneecap is back in place, a child will need to wear a knee immobilizer (a brace that keeps the knee straight) on the knee for a few weeks and avoid activities that cause pain, such as walking, standing, and repetitive bending. Kids and teens may need crutches to help with walking. Physical therapy and strengthening exercises help to heal the knee. Often, a person will go see an orthopedic provider (bone specialist) to make sure the knee is healing well.

What Else Should I Know?

After dislocating a kneecap, kids and teens must stay out of sports and other physical activities for a few weeks. Most kids can return to these in about 4–6 weeks with therapy and exercises to build strength. Some kids might need to also use a supportive knee wrap or athletic brace during sports for a while. Your care team will let you know when your child is ready.

To help your child heal as quickly as possible, follow the doctor’s advice about:

• which activities to avoid
• which activities are OK (for example, swimming may be fine while your child heals)
• strengthening exercises
• going to all follow-up doctor visits

Talk to your health care provider about ways to prevent a future dislocation, such as:

• stretching before and after sports
• working to strengthen the leg muscles

These steps also can help protect against other injuries.

Reviewed by: Melanie L. Pitone, MD

Date reviewed: February 2022

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Dislocate Your Knee? What to Know About Patellofemoral Instability

For most people, the kneecap, or patella, glides nicely within a V-shaped groove at the end of the thigh bone called the trochlea. As you bend and straighten the knee, the patella moves up and down and is stable within the trochlea, allowing you to stand, sit, walk and run without a problem.

Unfortunately, for others, things can go awry. “Sometimes we think of the patella as the train, and the notch it sits in, called the trochlear groove, as the track,” says Theresa Chiaia, PT, DPT, a physical therapist at HSS. “The issue for patients who dislocate their patella is that the train comes off the track, leading to the knee giving way, as well as pain and swelling.”

In a complete dislocation, the patella comes out of the track completely. Some people may experience more subtle issues with instability, which is known as subluxation, or partial dislocation. A partial dislocation also results in pain, swelling, popping or cracking sensations or stiffness, but these are much less severe, and the recovery is usually days instead of weeks or months.

Whether a person has a partial or a complete dislocation, the soft tissues of the knee, including the ligaments and cartilage, are often injured. If the ligament that keeps the patella in place, called the medial patellofemoral ligament (MFPL), is stretched or torn, it increases the chance that dislocation will continue to happen.

How do you know you if have dislocated your patella?

If you have a partial dislocation, the signs may be subtle. You may have pain around the kneecap, or it may feel like the knee is popping out and popping back in.

A dislocation is usually more obvious. The affected knee will buckle and be unable to support your weight, and you may have significant swelling, pain and stiffness. The kneecap may pop itself back in, or you may need help from someone else to get it back in place. Even if the kneecap shifts back into place on its own, pain and swelling can remain.

Who is at risk for a dislocated patella?

While these issues can happen in men and women, young and old, they happen most frequently to young women in their teens or early 20s. People who have patella dislocations usually have some physical risk factors, such as a notch (trochlea) that is not shaped correctly; significant laxity, or looseness, in their soft tissues; or a kneecap that sits too high on the thighbone, all of which can be hard for someone to know without being told by a doctor.

How is a dislocated patella diagnosed?

After listening to the story of how the injury happened, your doctor will perform a physical exam. The exam will begin with you seated and moving your knee. Then you’ll probably lie down and your doctor will bend your knee slightly and guide your kneecap outward. This feels uncomfortable and potentially painful for people with patellar instability. Your doctor may take measurements to see how the bones are aligned, and he or she may watch you walk as well.

Patients typically will have an X-ray to see how the kneecap fits in the groove, though if the kneecap has already returned to the correct position, the X-ray may look normal. This is why the physical exam is so important. You may also need an MRI to look at the ligaments and cartilage to check for damage, which to some degree is always seen after a dislocation. However, if that damage is minimal and it is the first time it has happened, then you may be treated without surgery.

Is it possible to dislocate your patella more than once?

People over the age of 25 who dislocate their patella for the first time have a fairly low chance of it happening again if they are treated appropriately with a brace, crutches and physical therapy. These people often don’t need surgery. People who are under 25 and who have a shallow groove have a much higher chance of the problem continuing to happen. These patients may need surgery. “That’s why it’s so important to manage these issues right away,” says Chiaia. “If you stop the kneecap from dislocating, you can stop further damage from happening.”

How do you treat a dislocated patella?

If the kneecap is dislocated and hasn’t returned to its proper place on its own, it needs to be put back where it belongs. Your doctor will apply gentle pressure to push it back, a process called reduction. Afterwards, rest, a knee brace and crutches will help the swelling to go down and allow the knee to heal. If the knee is very swollen, draining the knee of fluid can help reduce the discomfort. After a week or two of rest, physical therapy can help strengthen the muscles around the kneecap to help keep it aligned in the trochlear groove, and help the knee get back to a normal range of motion.

If an MRI shows that bone or cartilage has been damaged on the thigh bone or on the underside of the kneecap, arthroscopic surgery may be necessary. Both of these issues can cause locking, buckling or additional pain in the knee. In people who have had more than one dislocation, surgery can recreate the ligament that was torn. Sometimes in addition to ligament surgery, the doctor will recommend realigning the bone in a procedure called a tibial tubercle osteotomy to help keep the kneecap on track. The success rate of surgery for patellar instability is very high. More than 95% of patients have no more dislocations, and more than 85% return to sports they played before their injury at the same or a higher level.

About the Expert

Beth E. Shubin Stein, MD

Dr. Shubin Stein is Co-Director of the Women’s Sports Medicine Center at HSS specializing in arthroscopic and reconstructive surgery of the shoulder and knee.

Sabrina M. Strickland, MD

Dr. Strickland is a sports medicine surgeon at HSS specializing in patellofemoral surgery, cartilage disease and arthritis, ACL and shoulder surgery.

Theresa Chiaia, PT, DPT

Theresa Chiaia is the Clinical Manager of the Sports Rehabilitation Center and physical therapist at Hospital for Special Surgery.

Health

What Does a Pop in Your Knee Mean?

Knee injury: consequences and rehabilitation

Knee injury is one of the most common reasons people seek medical attention. First of all, professional athletes are at risk, as well as rollerbladers and cyclists, skiers, and snowboarders. Sometimes people get a knee injury as a result of a car accident.

For mild knee injuries, it is recommended to reduce physical activity and apply ice compresses. Severe injuries will require surgery and rehabilitation with the participation of a physical therapist. The most common types of knee injuries are: bruise, dislocation, knee fracture, sprain, meniscus tear.

Let’s talk about common injuries and rehabilitation methods.

Patient in physical therapy session

Fracture of the knee

Any bone in and around the knee can be broken, but the most common fracture is the patella, for example as a result of a fall or car accident. People with osteoporosis are at risk of fracture due to reduced bone density.

A displaced fracture may require surgery, but if the bone is in the correct position, it is enough to wear an orthopedic immobilizer (fixator) to keep the knee in the desired position, and also not to load the leg and patiently wait for recovery.

If the injury was caused by jumping and landing on a straight knee, then it is important to take not only an x-ray of the patella, but also a CT scan to make sure that the bones are not displaced, the fracture will not cause complications to the femur and will not lead to arthritis in the future and chronic pain.

Knee dislocation

Falls, contact sports and car accidents are the most common causes of knee dislocation. With it, one or more bones can be displaced from their natural position. A dislocation can damage the blood vessels and nerves around the knee and may require surgery. Displacement of the patella can be very painful, but easily reversible injury – you need to see a doctor to set the patella in place and apply a splint. Subsequently, a set of physiotherapeutic exercises developed by a specialist in a hospital or rehabilitation center is recommended.

Tendon rupture

Tendons are soft tissues that connect muscles to bones. In the event of a knee injury, the tendon of the kneecap is damaged. This injury can be obtained during sports and as a result of accidental falls. The elderly are also at risk.

If a person cannot lift their leg due to a torn tendon, they should see a doctor as soon as possible. You may need to do an x-ray and an MRI. If they confirm the rupture, then surgery will be required, after which a plaster is installed. Recovery can be lengthy and should be supervised by an orthopedic surgeon and a physical therapist.

Injury to the meniscus

The meniscus is a small piece of cartilage that acts as a shock absorber in the joint, so if it is damaged, the knee loses stability. A meniscus injury is characterized by inability to flex and straighten the leg, difficulty going up and down stairs, and a characteristic click can be heard when the knee moves. Athletes and dancers know a lot about meniscus damage – this is one of the most common injuries.

A meniscal tear can be identified using X-ray and MRI. Damage may require arthroscopy or surgery. A torn meniscus may require surgery to remove it. When displaced, the orthopedic doctor sets the meniscus in place and puts a plaster or splint, after which physiotherapy is necessary.

There are also degenerative lesions of the meniscus caused by the aging process. Then the injury can be obtained when performing simple exercises: squats, getting up from your haunches, or even in a dream. Treatment and rehabilitation for degenerative lesions should be discussed with an orthopedic and physical therapist.

Tendinitis

This is an inflammation of the tendon that connects the lower leg and the kneecap. Athletes, especially runners, are most at risk, as the cause of tendinitis is constant overexertion and microtrauma. Tendinitis is characterized by pain when pressing on the ligaments and sharp pain during peak exercise during sports. For treatment, you will first need to give up sports, then relieve inflammation with the help of medications, take a course of therapeutic exercises. In special cases, surgery may be needed to remove diseased tissue.

General symptoms

Pain characteristics and intensity may depend on the type of knee injury. But there are symptoms that you should pay attention to in all cases of injury:

• Swelling of the knee,
• Inability to bend or straighten the knee,
• Cracking in the knee,
• Visible bone deformity,
• Increased temperature in the knee area,
• Difficulty in carrying weights,
• Constant aching and non-recurring sharp pain,
• Loss of sensation in the knee area.

When to see a doctor

If your symptoms are as described above and first aid and home care do not help, you should see a doctor.
Emergency care is needed immediately after an injury to prevent complications, and in situations of severe swelling and fever in the knee area, which may be an indicator of infection. This is especially important for people with weak immune systems, children, and people who have had previous knee surgery.

An initial examination can be performed by a general practitioner. To make an accurate diagnosis, it is worth contacting a surgeon and an orthopedist. To determine the nature of the injury, the doctor examines the knee and palpates, revealing pathologies. An x-ray may be needed to assess the nature of the injury. An MRI is needed if there is a suspicion of ligament and meniscal injury. Physiotherapists will ensure an effective rehabilitation process.

Risk factors

Factors that increase the risk of knee injury:

• Overweight. Increases stress on the knee joints even during normal activities such as walking or going up and down stairs. It also increases the risk of developing osteoarthritis by destroying articular cartilage.

• Lack of muscle flexibility. Strong and toned muscles help stabilize and protect joints, while muscle flexibility allows for greater range of motion and thus less risk of meniscus injury.

• Some sports. Alpine skiing, basketball, jogging require more stress on the knees than other sports. If you play these sports, it is worth checking regularly with your doctor.

• Previous injury. Having a previous knee injury increases the chance of getting a new one.

The recovery process

The goal of knee treatment and recovery is to return the person to their level of activity and quality of life as they were before the injury. The prognosis for recovery is always individual and depends on the type of injury, as well as the amount of exercise performed.