Acute Patellar (Kneecap) Injuries: Types, Treatment and More

An acute injury to the patella (kneecap) can happen from a blow to the knee or a fall. There may be damage to the soft tissues, such as a patellar tendon tear, or a fracture to the bone.

Symptoms may include pain, swelling, or a feeling of instability or that the joint is locked. Some types of injuries can be treated with bracing and rehabilitation exercises, but others may need surgery.

The patella is part of the knee joint, along with the tibia (shin bone) and femur (thigh bone). It is wrapped in the patellar tendon, which connects the quadriceps muscle of the thigh to the tibia below the knee joint.

Sitting at the front of the knee joint, the patella tracks in a groove at the end of the femur (the patellofemoral joint) and enhances the extension of the knee.

The most common types of acute patellar injuries include the folllowing.

Acute injuries of the kneecap will produce symptoms common to other soft tissue and bone injuries, such as pain, swelling, and deformity. You often will have functional symptoms as well.

Common symptoms include the following.

Injuries to the patella usually result in difficulties in moving the knee, walking, or running. The patella is important functionally because it increases the leverage of the knee joint and the strength of extension of the leg.

A dislocated kneecap may spontaneously pop back into place. This can produce bruising and damage to the soft tissues. You should see your healthcare provider as soon as possible for further assessment even if there doesn't seem to be damage.

Prepatellar bursitis (inflammation and swelling of the sac around the knee) can be a complication of traumatic injuries to the patella, either due to the injury itself or infection following an injury. In addition to swelling at the front of the kneecap, the area may be tender and warm. If bursitis is due to infection, there may be fever and chills as well.

Acute patellar injuries can occur as a result of trauma, sports activities, or anatomical problems within the knee joint.

The location of the patella at the front of the knee makes it vulnerable to fracture, dislocation, or tendon tears during falls, blows to the knee, or sharp impacts such as with the dashboard in a car accident.

Traffic accidents are the cause of 78.3% of patella fractures. Work-related accidents and accidents in the home account for 13.7% and 11.4%, respectively.

If a person has osteoporosis, the weakness of the bone may increase the risk of a patella fracture from a minor fall or blow to the knee. Pathologic patella fractures may also be seen in cases of bone infection or a bone tumor.

Acute patellar injuries can also happen during sudden movements, such as those that may be made during sports activities—for example, when the foot is planted and the torso rotates swiftly during a swing of a baseball bat.

You can also tear your patellar tendon when landing from a jump with the knee bent and foot planted. You may be predisposed to a patellar tendon tear if you already have patellar tendonitis (jumper's knee), which is inflammation caused by overuse of the knee joint. It is seen in people who jump on hard surfaces, such as basketball or volleyball players.

A sudden contraction of the quadriceps can result in a patella fracture. This can happen when you land a jump from a height, although it is uncommon.

Variations in the anatomy of the knee can contribute to risk of injury, especially when it comes to instability or dislocation.

Some people are born with an uneven or shallow femoral groove. This compromises the stability of the patellofemoral joint and can result in the kneecap being displaced due to seemingly normal activities—not just a blow or a fall.

Some people may be more prone to kneecap dislocations because they have looser ligaments. Kneecap dislocations are most commonly reported in adolescent females.

Depending on the circumstances, you may see your primary healthcare provider or seek emergency treatment. Urgent assessment is best if the knee injury was sustained during a fall or accident, or if a kneecap dislocation has not popped back into place.

The healthcare provider will take your history and report of what led to the knee pain, symptoms at the time (such as hearing a pop), and your current symptoms.

During the physical examination, the healthcare provider will observe whether you are able to walk and bend or unbend your knee. They will palpate the knee to see if there are areas that show defects, displacement, or localized pain. A visual exam of the knee assesses whether there is swelling, deformity, or obvious displacement.

Manual tests and maneuvers are used to assess damage to the kneecap or tendons, including trying to extend your knee against gravity. The straight leg raise test can reveal disruption of the extensor mechanism, which includes the quadriceps tendon, patella, and patellar tendon.

An X-ray is often the first imaging test used, as it can show whether there is a fracture, which is important to find or exclude early.

It may be the only imaging done, or the provider may order magnetic resonance imaging (MRI) to further assess damage to the ligaments, tendons, or cartilage.

Blood tests are not commonly performed for knee injuries, but can be ordered specifically to look for signs of inflammation if an infection is suspected. If there is significant swelling, in some cases arthrocentesis can be performed to extract fluid from the knee for evaluation in the lab to look for infection or blood from an injury.

Differential diagnoses may include arthritis and chondromalacia patellae (runner's knee). These can be the source of knee pain without a traumatic incident, or they may be present in addition to other patellar injuries.

Treatment of these various acute kneecap conditions depends on the diagnosis. However, there are some general guidelines that can be followed. Your healthcare provider will advise you based on your diagnosis.

Acute kneecap injuries require self-care, which you can do until you get medical treatment and afterward as recommended by your healthcare provider:

A kneecap dislocation needs to be reduced (a procedure in which the kneecap is returned to the femoral goove). If this didn't happen spontaneously, the healthcare provider will do the reduction as soon as possible.

A reduction might require pain medication so the provider can extend the leg and manipulate the kneecap. Often, it will snap back into place with gentle pressure when the leg is extended.

Any of the acute patellar injuries may need to be immobilized with a cast, splint, or brace to allow healing of the bone, tendon, or other soft tissues. Your healthcare provider will recommend which of these is appropriate, if any.

Your healthcare provider may recommend you not bear weight on the affected leg during the immobilization period. You may need to use crutches or other mobility aids until this period is complete.

A fractured kneecap may require surgery if any pieces of bone are out of place. This often means installing wires, screws, plates, or pins to unite the bone pieces and keep them in place while you are healing.

Complete patellar tendon tears often require surgical repair. Sutures are placed in the tendon and anchored to holes or surgical anchors on the patella. This can be performed as an outpatient surgery.

There are several surgical kneecap stabilization procedures that can be done for recurring patella dislocations or subluxations. Recurring partial and full dislocations are associated with damage to the medial patellofemoral ligament, which holds the kneecap in place. Surgery can be performed to repair or reconstruct the ligament.

For any acute patellar injury, physical therapy is likely to be recommended after the initial inflammation has subsided and immobilization is no longer needed. Immobilization itself will result in stiffness and loss of muscle strength. Your physical therapist will work to restore the knee's range of motion and muscle strength.

If weight bearing was not allowed, you will gradually progress to being able to support weight on the injured leg. This starts with toe-touch weight bearing for a couple of weeks, then progresses to 50% weight bearing, and finally full weight bearing after four to six weeks, depending on your type of injury.

The function of the knee joint requires balancing the strength of the muscles around the knee joint. Most importantly, the quadriceps and hamstring muscle groups should be flexible and balanced. Your physical therapist will recommend specific exercises depending on your condition.

An acute kneecap injury is often not only painful, but frustrating, as it will mean restrictions in your activities while you heal. Talk to your healthcare provider and physical therapist so you understand what you can do to ensure a full recovery. Most people are often able to return to their previous activities following treatment for a fracture, tendon tear, or dislocation.

The biggest clue would be having severe symptoms, such as pain in or around the knee, swelling, inability to walk, instability, and difficulty moving the knee. Any of these symptoms would warrant a visit with a healthcare provider to assess the damage.

Recovery time depends on the type of knee injury. For example, recovery for a patella fracture is usually three to six months and a tendon tear would require four to six months of recovery time. Dislocating the knee only takes approximately four to six weeks of recovery.