Brief overview
- First aid: Calm the affected person, immobilize the leg, remove tight-fitting clothing, cool if necessary, take the affected person to a doctor or call the emergency services
- Healing time: Depends on possible concomitant injuries, generally a few days immobilization of the knee joint after dislocation, then wearing an orthosis for six weeks
- Diagnosis: Physical examination, imaging procedures, in the case of an effusion, possibly removal of the fluid (puncture)
- Therapy: Manual adjustment by a doctor, surgical measures for concomitant injuries
- Risk factors: Previous patellar dislocation, female gender (young and slim), knock-knees, congenital malformation or high position of the kneecap, weakened extensor muscles in the thigh, diseases with weak connective tissue
- Prevention: training to build up the muscles that stabilize the knee, coordination exercises, warming up the muscles, wearing optimal equipment for sports
Attention!
- Never try to put a popped-out kneecap back in place yourself. You would most likely make the injury worse.
- Never place ice cubes or cool packs directly on the skin to cool the knee, but always with at least one layer of fabric in between. Otherwise there is a risk of local frostbite.
- Even with optimal treatment, recurrent patellar luxations cannot be ruled out. This is especially true if surgery is performed late.
What is a patellar dislocation?
A patellar dislocation is a displacement of the kneecap, usually to the side, often caused by external force such as a fall (traumatic dislocation). It occurs less frequently as a concomitant injury when there is a capsular ligament injury to the knee joint. Doctors speak of a habitual dislocation if the joint instability is congenital or acquired (such as due to very loose ligaments) and occurs even with minor movements without external force.
A patellar dislocation is very painful. The affected person is unable to move the lower leg. If a bruise also forms in the joint, the pressure inside the joint increases, which intensifies the pain. Occasionally, small pieces of bone break off the kneecap or femur in the course of a patellar dislocation. The bone fragments then float loosely in the joint. The retaining ligaments around the kneecap also sometimes tear.
If the kneecap has slipped out of place, it should be reset by a doctor as soon as possible. A visit to the doctor is necessary even if the kneecap has repositioned itself: he or she will check whether surrounding structures have been damaged by the dislocation.
A patellar dislocation is often a shock for the person affected: When your own kneecap suddenly sticks out of the side of your leg like a “lump”, it is frightening – and very painful. This makes it all the more important for you as a first aider to act decisively if someone’s kneecap has popped out. Here’s what you should do:
- Reassure the person affected and explain everything you are doing. This builds confidence.
- Remove any tight-fitting clothing in the joint area (trousers), as the area around the joint usually swells considerably in the event of a dislocation.
- Take the weight off the knee: sit the affected person down if they are not already sitting. People with a dislocation often instinctively adopt a relieving posture in which the pain subsides somewhat. Do not force the affected person into a different position.
- Very important: do not move the knee if possible! Otherwise you may damage the surrounding ligaments, muscles and nerves.
- If possible, cool the swollen area (e.g. with a cool pack). This will relieve the bruising, swelling and pain somewhat.
- Take the affected person to a doctor or call an ambulance as soon as possible. This also applies if the kneecap has slipped back into the joint on its own.
How long does it take to heal?
The healing time depends on possible accompanying injuries and the necessary treatment.
If there are major injuries and the knee is operated on, it can take considerably longer for the knee to be able to bear weight properly again. Physiotherapy exercises help to support the healing process.
How does the doctor examine a patellar dislocation?
The doctor can usually tell at first glance whether the kneecap is dislocated. Sometimes, as soon as the doctor examines the patient, it has already slipped back into its original position on its own (“spontaneous reduction”). The doctor then diagnoses a patellar dislocation based on the information provided by the patient.
Physical examination
The doctor uses certain examinations to check whether the knee joint is actually dislocated. One example is the so-called apprehension test. In this test, the doctor exerts lateral pressure on the kneecap in an outward direction. If the patient shows a defensive posture or if the thigh muscle (quadriceps) reacts more strongly, this is a sign of a dislocation.
Imaging procedures
These show whether there are possible concomitant injuries to the patellofemoral joint and surrounding structures. First and foremost, an X-ray examination is used. In some cases, magnetic resonance imaging (MRI) or arthroscopy may also be necessary.
Joint puncture
What treatments are available?
Manual repositioning is usually sufficient treatment for a patellar dislocation when the kneecap has popped out for the first time as a result of force. The doctor slowly stretches the leg in the knee and carefully guides the kneecap into its correct position. The patient usually takes a painkiller and sedative beforehand.
As soon as the kneecap is back in place, the knee joint is splinted for a few days and then stabilized with a motion orthosis.
Surgical procedure for patellar dislocation
If the doctor is unable to manually realign the knee joint and/or there are accompanying injuries, surgery is necessary. The same applies if the kneecap has repeatedly popped out. This is because the more frequently a joint dislocates, the more unstable the supporting structures become. During an operation, the doctor tightens these again and thus stabilizes the joint.
Ultimately, there are a number of different surgical techniques for treating a patellar dislocation. They all aim to reduce the traction on the kneecap on the outer side of the knee and thus reduce the risk of dislocation.
Doctors operate more frequently on young, athletically active people with patellar luxation than on older patients.
Are there risk factors?
Possible risk factors for a knee joint dislocation are
- A history of patellar dislocation: If a kneecap has already popped out once, the likelihood of a new dislocation is increased. This is because every dislocation and associated stretching or injury to surrounding structures makes the joint more unstable.
- Female gender: Patellar dislocation is particularly common in young, slim female athletes.
- X-legs: Due to the axial misalignment, the lateral pull on the kneecap is stronger than normal.
- Congenital malformations of the kneecap or the patellar gliding bearing
- Congenital or accident-related elevation of the kneecap
- Weakness or imbalance of the extensor muscles of the thigh
- Systemic diseases with connective tissue weakness, such as the hereditary diseases Marfan syndrome and Ehlers-Danlos syndrome
