Ask a Sports Medicine Doc: Dislocated knee cap

Q: My 16-year-old daughter was recently playing soccer when her knee cap popped out and then back in. How do we treat this?

A: It is not uncommon for young people, particularly females, to dislocate their knee cap (or patella) when doing cutting and pivoting sports like soccer. This is due to the fact that teenagers, particularly females, have generalized increased laxity in their ligaments. For instance, many teenagers can hyperextend their elbows or pull a thumb back and touch their forearm with it. This ability can be advantageous in certain sports, but it can also predispose them to joint dislocations such as in this case. Another predisposing risk factor is that women’s knees tend to be somewhat knock-kneed (or in valgus), whereas men tend to be bowlegged (or in varus). When a knee is knock-kneed or in valgus, there is an outwardly directed force vector on the patella predisposing it to dislocate laterally or to the outside.

Dr. Rick Cunningham

Sometimes, the patella will pop out and then pop back in spontaneously as was the case in your daughter. In other cases, the patella stays dislocated and the injured athlete has to go to the emergency room in order to have the patella popped back in place or reduced. Instead of a true dislocation, other young athletes see me in the office for a patella that slides partially out of place and then slides back in place on a more frequent basis. This is called a subluxation, not a dislocation.

When a young athlete dislocates their patella, they partially or fully tear the medial patellofemoral ligament (MPFL). In a patient with a first time patellar dislocation, I typically recommend non-surgical management consisting of RICE: rest and avoidance of pivoting sports, ice, elevation and compression. I also send these athletes to physical therapy in order to restore their range of motion and decrease the swelling. However, I may order an MRI based on the physical exam findings to determine if there is a loose piece of cartilage in the knee that was sheared off as a result of the dislocation. The MRI also shows the degree of injury to the MPFL and what sort of tear it sustained (i.e. where along the course of the ligament it tore and whether it was a full or partial tear).

I often prescribe a knee brace to stabilize the patella. When the athlete has restored full, painless knee range of motion, the knee swelling has resolved, and there is good return of strength, then they are ready to return to unrestricted sports. Recovering from a patellar dislocation and returning to unrestricted sports can take two to three months.

If a person has repeated patellar dislocations despite knee bracing and therapy, then surgery to reconstruct the MPFL is considered. In this surgery, a tendon graft (from a donor) is used to augment the torn and stretched out MPFL. This reconstructed MPFL acts as a “check rein” to prevent the patella from dislocating laterally. If a patient has a history of multiple patellar dislocations with a torn or incompetent MPFL and also has a mal aligned patella with a patella that naturally tracks laterall, then this patient may require an MPFL reconstruction in combination with a bone-cutting procedure in which the knee cap is realigned so it tracks centrally. This latter surgery takes longer to recover from but can effectively prevent future patellar dislocations and allow an athlete to resume all sports without further knee cap problems.

Dr. Rick Cunningham is a Knee and Shoulder Sports Medicine Specialist with Vail-Summit Orthopaedics. He is a Physician for the US Ski Team and Chief of Surgery at Vail Valley Medical Center. Do you have a sports medicine question you’d like him to answer in this column? Visit his website at www.vailknee.com to submit your topic idea. For more information about Vail-Summit Orthopaedics, visit www.vsortho.com.

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