Medical Professional Publications

Reducing the Risk of AVN With the Modified Dunn Procedure

Columbus, OH - July 2016

In the largest study of its kind, clinician-researchers at Nationwide Children's Hospital have found that the modified Dunn procedure substantially reduces the risk of avascular necrosis (AVN) compared to traditional surgery for an unstable slipped capital epiphysis in pediatric patients.

Historically, the rates of AVN have ranged from 20 to 60 percent or higher in these children. But a review of 31 consecutive modified Dunn surgeries performed by one orthopedic surgeon showed that only two patients, or 6 percent, suffered from the complication.

The study also showed that the window to successfully perform the surgery is larger than had previously been presumed — within 24 hours after the child is diagnosed rather than within 8 to 12 hours.

"This approach maintains blood supply but gives us access to the hip in a safe fashion and helps us restore anatomy. And now it's shown to reduce the risk for avascular necrosis in unstable slips," says Kevin Klingele, MD, chief of the Department of Orthopaedics at Nationwide Children’s and senior author of the study.

In so doing, the procedure lessens the risk of further complications, such as reduced mobility and hip arthritis, the authors say. Due to its success, the modified Dunn has become the procedure of choice at Nationwide Children's and a growing number of pediatric surgical centers.

An unstable slip is like a fractured femur: the epiphysis or ball of the hip joint has lost enough structural continuity with the femur that they no longer move as one unit.

Historical treatments, such as a closed reduction, manipulating the leg and inserting a screw percutaneously, and opening incisions to drain hematomas, still resulted in more than a 50 percent risk of AVN, Dr. Klingele says. "The child was often left with a deformity in the hip and AVN, which turns into a non-reconstructable hip."

And, he points out, studies suggest that the higher the degree of deformity left from the slip, the earlier the onset of arthritis in the hip.

This study, published in the Journal of Pediatric Orthopaedics, focused on 31 surgeries Dr. Klingele performed from 2006 to 2013 on 30 patients aged 10 to 14. Half were boys, half girls.

X-rays showed restoration of slip angle, alpha angle, femoral neck length and greater trochanter height. In 20 of 21 patients, antegrade drilling showed blood flow in the femoral head. None of the 21 developed AVN.  

The two patients who suffered from AVN underwent surgery more than 24 hours after being diagnosed but otherwise had no statistically significant differences from the rest of the children in the study. 

The researchers are continuing to follow the patients, some now in their 20s. "We don't know what they will look like in 50 years," Dr. Klingele says.

The research team is also reviewing the outcomes of the modified Dunn procedure on children who suffered from less acute chronic stable slips. 

Persinger F, Davis RL 2nd, Samora WP, Klingele KE. Treatment of unstable slipped capital epiphysis via the modified Dunn procedure.Journal of Pediatric Orthopaedics.2016 Feb 10. [Epub ahead of print]

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