A patellar dislocation is a common knee injury in sports. Frequently I will hear an athlete complain that his or her “knee” popped out of place, but usually they are referring to their patella (kneecap). A true knee dislocation is much less common and involves tearing multiple ligaments of the knee, often including the anterior cruciate ligament (ACL) and the posterior cruciate ligament (PCL), where the tibia is pulled completely out from under the femur.
Mechanism of injury in a patellar dislocation
First-time patella dislocations, in my experience, typically involve youth or high school athletes. It can occur in college and professional athletes, but it seems to be a problem that affects younger athletes. Typically the mechanism involves some sort of twisting injury to the knee. The athlete will often plant his or her foot to change directions. At the same time, there is often a valgus force on the knee, which involves the foot moving toward the outside of the body while the knee moves toward the inside. Patella dislocations in young athletes.
If this is the first time an athlete has had a patella dislocation, he or she will usually be in a tremendous amount of pain, especially if the patella is still out of place. If an athletic trainer or physician is available at the game or practice, it is usually fairly easy to put the patella back in place. Usually all that is required, if you can get to these injuries quickly, is to straighten the knee. Sometimes adding gentle pressure to push the kneecap from where it is dislocated on the outside of the knee back into place on the center of the knee is necessary. If the athlete is in too much pain to try to put it back in place on the sidelines, sending the player to the emergency room to reduce the patella with medications for pain and sedation is necessary.
Should I worry about my kneecap popping out?
Diagnosis and tests
Often the athlete will say that the patella popped out of place and popped right back into place. A sports medicine physician can often make the diagnosis even though he or she did not see the actual event. Often trying to push the patella out of place, called the patellar apprehension test, will recreate the sensation that the patella will pop out of place. The knee is often very swollen, as there is often blood from a cartilage or bone injury when the patella popped out of place. X-rays are often negative, but they are often used to confirm that the patella is back in place and can show a small piece of bone pulled off. Sometimes an MRI is performed to see the full extent of the injury. An MRI will show if the soft tissue on the inside of the patella has been torn or if bone or cartilage has been injured from the undersurface of the patella or front of the femur.
Treatment of a patellar dislocation
Treatment is somewhat controversial, but generally with first-time dislocations, especially in younger athletes, nonsurgical treatment is attempted first. Short-term use of a brace can help alleviate the patient’s pain. I typically don’t leave the athlete in a brace for long, as I like to get the knee moving as soon as possible. I usually send the athlete to physical therapy to work on getting the swelling down, improving the knee range of motion, and improving the strength of the quadriceps muscles to help stabilize the patella. Sometimes I will add a patella stabilization brace as the athlete returns to more functional and sport-specific activities. Surgical treatment is an option, especially for recurrent patella dislocations that have failed trials of nonoperative treatment. Also, some sports medicine physicians advocate surgical repair for high-level athletes, even after a first-time dislocation. Return to sports, whether treated nonoperatively or with surgical repair, can take weeks or even months, so this can be an injury that threatens to end the athlete’s season.
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