Patellar dislocation
A patellar dislocation is a knee injury in which the patella (kneecap) slips out of its normal position. Often the knee is partly bent, painful and swollen. The patella is also often felt and seen out of place. Complications may include a patella fracture or arthritis.
| Patellar dislocation | |
|---|---|
| Other names | Kneecap dislocation, dislocated kneecap |
| X-ray showing a patellar dislocation, with the patella out to the side. | |
| Specialty | Emergency medicine, orthopedics |
| Symptoms | Knee is partly bent, painful and swollen |
| Complications | Patella fracture, arthritis |
| Usual onset | 10 to 17 years old |
| Duration | Recovery within 6 weeks |
| Causes | Bending the lower leg outwards when the knee is straight, direct blow to the patella when the knee is bent |
| Risk factors | High riding patella, family history, loose ligaments |
| Diagnostic method | Based on symptoms, X-rays |
| Treatment | Reduction, splinting, physical therapy, surgery |
| Medication | Pain medication |
| Prognosis | ~30% risk of recurrence |
| Frequency | 6 per 100,000 per year |
A patellar dislocation typically occurs when the knee is straight and the lower leg is bent outwards when twisting. Occasionally, it occurs when the knee is bent and the patella is struck directly. Commonly associated sports include soccer, gymnastics, and ice hockey. Dislocations nearly always occur away from the midline. Diagnosis is typically based on symptoms and supported by X-rays.
Reduction is generally done by pushing the patella towards the midline while straightening the knee. After reduction, the leg is generally splinted in a straight position for a few weeks. This is then followed by physical therapy. Surgery after a first dislocation is generally of unclear benefit. Surgery may be indicated in those cases where a fracture occurs within the joint or where the patella has repeatedly dislocated.
Patellar dislocations occur in about 6 per 100,000 people per year. They make up about 2% of knee injuries. It is most common in those 10 to 17 years old. Rates in males and females are similar. Recurrence after an initial dislocation occurs in about 30% of people.