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The kneecap (patella) is the bone that covers the knee joint. Abnormalities in the support structure of the knee and unusual forces can cause a dislocated kneecap.
What is a dislocated kneecap?
A dislocated kneecap is when the bone that covers the knee joint, the kneecap or patella, is moved out of place. The kneecap is normally held in place by tendons that connect it to muscles around the knee joint. Dislocation can be caused by planting the foot and twisting a flexed knee, direct trauma to the knee, or hyperextending the knee.
Symptoms include a feeling of the knee "giving way," severe knee pain, a limited range of motion of the knee, as well as swelling or a dislocation that is a noticeable bulge in the leg.
Treatments include pain medication, manual or surgical reduction of the knee, rest and at-home remedies, and physical therapy and rehabilitation.
You should visit your primary care physician within the next 24 hours. The first step is to return the kneecap to its proper place, a process called reduction.
Symptoms of a dislocated kneecap
There are a few main symptoms of a dislocated kneecap that most people will experience as well as a few others experienced by some people with this condition.
The main symptoms experienced by people with a dislocated kneecap include:
- A feeling of the knee "giving way": Most people who develop a dislocated kneecap will experience a feeling of the knee "giving way" at the time of the dislocation. They may feel or hear a pop or tear at the time of the dislocation.
- Severe knee pain: Shortly after the dislocation, most people will experience severe knee pain. The pain may prevent the affected leg from bearing any weight. The knee may also be tender when pushed on, especially along the edges of the kneecap.
- Limited range of motion of the knee: The position of the kneecap keeps the knee from bending normally if it is dislocated. The knee is usually stuck in a position that is bent at 20 to 30 degrees.
Some people can also experience the following with a dislocated kneecap:
- Swelling of the knee: This swelling is usually caused by fluid that accumulates in the knee joint due to inflammation after the dislocation, but in some cases, it may be due to blood collecting in the knee joint.
- Noticeable abnormal location of the kneecap: This is most common when the kneecap is dislocated to the outside of the leg, as it will look like a bulge on the outer side of the knee.
Causes of a dislocated kneecap
Abnormalities in the support structures surrounding the kneecap or unusual forces to the knee can cause dislocation. The kneecap can dislocate in several different directions; most commonly, to the outside of the leg. Specific causes of a dislocated kneecap include planting the foot and rotating a flexed knee, direct trauma to the knee, and hyperextension.
Planting the foot and rotating the leg while the knee is flexed
Planting the foot and rotating the leg while the knee is flexed is the most common cause of a dislocated kneecap. When the knee is bent, the kneecap is usually pushed toward the outside of the leg. Suddenly twisting the leg while the leg is in this position may cause the kneecap to dislocate to the outside of the leg. This may be seen in sports such as gymnastics, running, ice skating, basketball, tennis, baseball, or softball.
Direct trauma to the knee
The direction of the trauma to the knee and the position that the leg is in when the knee is hit will determine which way the kneecap dislocates.
- From the inside or outside: Direct trauma to the inside of the knee will usually cause the kneecap to dislocate outward, while direct trauma to the outside of the knee may cause the kneecap to dislocate inward.
- From above or below: Trauma to the knee from above or below while the knee is bent can cause the kneecap to dislocate into the knee joint, which is a more serious form of a dislocated kneecap.
Hyperextension of the knee
Hyperextension of the knee — straightening the knee more than it normally should move — can cause a dislocated knee in rare cases. This is more common in older people who may have a degenerative joint disease.
Who is most likely to be affected
Kneecap dislocations occur more frequently in:
- Teenagers and young adults who engage in sports activities
- Overweight individuals
- Older people with a degenerative joint disease
Treatment options and prevention for a dislocated kneecap
Several treatment options exist for a dislocated kneecap, depending on the type and severity of the dislocation. In some cases, the dislocated kneecap may spontaneously reduce (return to its normal position) from straightening the leg. In other cases, a physician may need to use certain maneuvers or even surgery to reduce the dislocated kneecap. Other treatments may include pain medication, at-home remedies, and physical therapy and rehab, described below.
Because dislocated kneecaps tend to cause a lot of pain, most people with dislocated kneecaps will need pain medications to control the pain and allow for the kneecap to be put back in place. Pain medications may be given through an IV and may include morphine or fentanyl, among others.
Manual reduction of the kneecap
People with dislocated kneecaps that do not spontaneously return to the proper position may need a maneuver to manually reposition the kneecap.
- Timing: This can be done immediately following the dislocation if it is witnessed, or later after administration of pain medications.
- Details: The individual is placed on his or her back with the hips bent and the physician slowly straightens the leg while pushing inward on the kneecap to return it to its normal position.
Surgery to reduce the kneecap and repair tendon damage
Surgery to reduce the kneecap and repair any damaged tendons or ligaments may be required — especially in people whose kneecaps cannot be manually reduced or whose kneecaps were dislocated into the joint space.
Rest and at-home treatments
After the dislocated kneecap has been successfully reduced, the physician may recommend the following. The main methods can be remembered by the mnemonic RICE:
- Rest: This can be achieved by limiting standing, walking, or repeated bending.
- Ice: Apply ice to the knee to reduce swelling.
- Compression: Try wrapping the knee with bandages.
- Elevation: Try to elevate the knee above the level of the heart.
- Additional bracing: The knee may be placed in an immobilizer or a brace while it recovers.
Physical therapy and rehabilitation
Following treatment of the dislocated kneecap, most people will benefit from a course of physical therapy and rehabilitation to help strengthen the muscles around the knee and improve the outcome.
When to seek further consultation for a dislocated kneecap
If you experience any symptoms of a dislocated kneecap, such as feeling the knee give way, severe knee pain, an inability to bend the knee, or an abnormal location of the kneecap, you should go to your physician or emergency department. A physician can examine your knee to see if you have a dislocated kneecap and help return the kneecap to its proper position.
Questions your doctor may ask to determine dislocated kneecap
- Is your knee pain constant or come-and-go?
- Is the knee pain affecting one or both knees?
- How severe is your knee pain?
- Which of these if any make your knee hurt worse?
- How long has your knee pain been going on?
Self-diagnose with our free Buoy Assistant if you answer yes on any of these questions.
Dr. Liu received his medical degree from the University of Pennsylvania Perelman School of Medicine and is pursuing a career in ophthalmology. He graduated Phi Beta Kappa from Swarthmore College with a BA in biology. He has published research in multiple ophthalmology and healthcare journals and has received awards from Research to Prevent Blindness. In his free time, he enjoys running, biking, and spending time with his friends and family.
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