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Treatment for Children with Dislocating Kneecaps

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Many people of all ages suffer from a condition known as recurrent patellar dislocation or patellar instability. In this condition, the patella or kneecap as it is more commonly referred to pops off to the side (usually to the lateral side away from the other knee). It may or may not pop back in place, a movement called reduction.

Early on in the acute phase, treatment is likely to be conservative care with taping or bracing, and exercises. But with repeated episodes causing pain and loss of knee function, surgery may be necessary. Children and teens with this problem must be treated carefully to avoid damaging the growth plate when full growth has not been reached yet.

In this study, the results of two surgical techniques for recurrent patellar dislocation in adolescents are compared. One method (medial retinaculum plication) or MRP is minimally invasive using an arthroscopic approach.

The second surgery (vastus medialis plasty) or VMP is done with an open incision. Both of these treatment approaches are physis-sparing (don't affect the growth plate) so don't cause leg length differences after surgery.

Medial retinaculum plication refers to a procedure in which the medial (side closest to the other knee) retinaculum (connective tissue that holds the knee cap in the middle) is tied back using three sutures. At the same time, the lateral retinaculum on the other side of the knee (outer edge) is cut or "released" so that it can no longer pull the knee cap off center.

The vastus medialis plasty is a more complex procedure. The surgeon still releases the lateral retinaculum. But instead of tying the medial retinaculum back and holding it firmly in place, the medial portion of the hamstrings and connecting joint capsule (also on the medial side) are cut, released, and moved over to the opposite side of the knee. The idea is to suture these structures in place so that they continue to exert a pull on the kneecap to keep it in the midline (middle of the knee joint).

The question these surgeons wanted an answer to was this: which one of these two surgical techniques work better? They usually use the open medial vastus medialis plasty (VMP) but if the less invasive medial retinaculum plication (MRP) would work just as well, then the cosmetic appeal (no scars) might tip the scales in favor of the arthroscopic MRP approach.

To compare results of these two procedures, one surgeon performed all 60 surgeries (30 teens in each treatment group). Then they followed each patient for two years at regular intervals. This type of multiple series of evaluations helps show any hidden factors that might help determine the best treatment approach for these children.

CT scans were used to look at the position of the patella. The International Knee Documentation Committee (IKDC) tool was used to measure knee function. Results showed that the more invasive open surgery (vastus medialis plasty or VMP) had the better results.

There were fewer re-dislocations in the group of patients who had the VMP procedure. The VMP group also had better clinical outcomes. And in the end, the VMP group had better overall results despite the fact that patients in both groups experienced deterioration of knee stability over time.

In conclusion, the more invasive procedure (VMP) is also a more reliable way to treat chronically recurrent patellar (knee cap) dislocations. The medial soft tissue structures just weren't strong enough to counteract the lateral pull on the knee cap. Even so, there was a high rate of recurrence in both groups.

The authors suggest future studies are needed to take a closer look at this finding. It's possible that with activity restriction after surgery, repeated episodes of patellar dislocation can be prevented. There may be other patient factors that could predict which surgical approach would work best for each individual patient. Number of previous dislocations, bony alignment or other anatomic differences from normal, and even the post-op rehab program may influence results and should be studied more closely.

Reference: Jinzhong Zhao, MD, et al. Recurrent Patellar Dislocation in Adolescents. In The American Journal of Sports Medicine. January 2012. Vol. 40. No. 1. Pp. 123-132.

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