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Patellar (kneecap) dislocations are among the most common in the body. They usually occur in adolescents or young adults with contact or noncontact twisting injuries with the knee close to full extension. Almost always, the dislocation occurs with the patella dislocating to the outside (lateral aspect) of the knee. Putting the patella back in place (a reduction) usually happens with straightening the knee and gently pushing it back into place.
Most contact patellar dislocations can be treated without surgery and a period of 4-6 weeks of rehabilitation to regain one’s muscle strength. Noncontact patellar dislocations also are usually treated without surgery initially, but these may have a higher risk of redislocation.
Patients who require surgery initially are those who have a lateral patellar dislocation and who knock a piece of bone and cartilage or just cartilage off of the patella. In these cases, surgery usually recommended to treat the pathology.
The most important factor to assess in terms of one’s risk for a repeat lateral patellar dislocation is one’s bony geometry of the kneecap joint overall. Patients who have a deep end of the femur, called the trochlea, have better bony stability of the kneecap joint than those who have a flatter end of the femur. A flat end of the femur is called trochlear dysplasia. Many patients with trochlear dysplasia also have their patella sit up higher than normal (called patella alta), which also makes it not sit as well within the end of the femur and puts them at risk for a lateral patellar dislocation. These patients with less overall bony stability of their patellofemoral joint have higher rates of noncontact lateral patellar dislocations.
Patients with “normal” bony geometry with a first time patellar dislocation have a 5-10% chance of redislocation after a proper period of rehabilitation. However, those with trochlear dysplasia and patella alta have a 30-40% chance of a dislocation.
In general, the initial treatment of most patellar dislocations is nonoperative with a well-focused rehabilitation program. In those patients who have multiple dislocations, the recommended treatment is almost always surgery to prevent the kneecap from becoming arthritic and to better restore patient’s function. In these cases, a complete workup including a physical examination, x-rays, an MRI and often a CT scan are necessary to determine the best way to treat that particular patient’s pathology.