The patella, or kneecap, is one of three bones, along with the tibia (shin bone) and femur (thigh bone), that make up the knee joint. All of these bones are covered with a layer of cartilage at points where their surfaces come into contact. Furthermore, the patella is wrapped within a tendon. This tendon connects the quadriceps muscle of the thigh to the shin bone (tibia) below the knee joint.
The patella is important functionally because it increases the leverage of the knee joint. From a mechanical perspective, the patella allows for an increase of about 30 percent in the strength of extension of the leg at the knee joint.
Problems with the kneecap typically cause pain in the area around the kneecap. Often these symptoms are noticed doing specific activities, including walking stairs (particularly down), prolonged sitting, or kneeling.
Kneecap problems can be diagnosed on physical examination by a skilled clinician. Sometimes kneecap pain can be difficult for an individual to describe. Often the symptoms occur around the kneecap, but often people will feel it "deep" inside the knee or even in the back of the knee.
There are several common problems associated with the kneecap that can cause problems and pain in the knee:
Chondromalacia patellae (runner's knee): The most common disorder is known as chondromalacia, often called runner's knee. Chondromalacia occurs because of irritation of the cartilage on the undersurface of the kneecap.1
Prepatellar bursitis: Prepatellar bursitis is a condition of swelling and inflammation over the front of the knee. This is commonly seen in patients who kneel for extended periods, such as carpet layers and gardeners.2
Patellar subluxation: Also called an unstable kneecap, patients who experience this painful knee condition have a patella that does not track evenly within its groove on the femur.3
Kneecap dislocation: When the kneecap comes completely out of its groove, the condition is called a patella dislocation. When the kneecap dislocates, it must be put back into its groove.4
Patellar tendon tear: Patellar tendon tears are serious injuries when the tendon connecting the kneecap to the shin is ruptured. Recovery takes at least four to six months, possibly longer for a return to sports.5
When to See a Doctor
If knee pain is severe or lasts for more than 48 hours.
In the swelling is sudden or lasts for more than 48 hours.
If there was a loud popping noise at the time of an injury.
The knee is unstable or cannot bear weight.
If the knee is physically deformed.
If the knee locks with movement.6
Your physical examination may include specific tests and maneuvers that cause compression to the cartilage on the back of the kneecap to help determine if those provoke your symptoms of pain.
Tests commonly performed to diagnose kneecap problems include X-ray, ultrasound, computed tomography (CT), and magnetic resonance imaging (MRI).
If your doctor suspects a knee infection, blood tests may be used to detect inflammation while arthrocentesis can be used to extract fluid from the knee for evaluation in the lab.
Treatment of these various kneecap conditions depends on the diagnosis, however there are some general guidelines that can be followed.7 For more information, and for a diagnosis of your knee pain, it is important to see your doctor.
Rest: Resting the injured knee to allow time for inflammation to subside is very important. Cross-training will allow you to keep in shape. When you do return to activity, do so gradually.
Ice application: Apply ice to the knee to reduce inflammation in the knee. Ensure there is a cloth barrier between the ice pack and the skin, and do not ice the injury for more than 15 minutes.
Anti-inflammatory drugs: Nonsteroidal anti-inflammatory drugs like Advil (ibuprofen) and Aleve (naproxen) may help with inflammation and will also help alleviate some of the pain associated with patella conditions.
Kneecap stabilization: When the problem with the kneecap is an issue with dislocation or instability, there are several surgical options to stabilize the kneecap.
Physical therapy: Physical therapy is very important to balance the strength of the muscles around the knee joint. Most importantly, the quad and hamstring muscle groups should be flexible and balanced.
Arthroscopic surgery: While surgery is seldom needed because of a kneecap problem, arthroscopy is a treatment option if the problem is not getting any better with conservative treatment.
Patellar resurfacing: There are surgical options to replace the kneecap. Much like people have a full knee replacement, just the kneecap portion of the joint can be replaced.