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Patients with AVN not only had a higher rate of THA, they also had the procedure at a much younger age than patients in whom degenerative joint disease or femoroacetabular impingement (FAI) developed.“Any steps that we, as orthopaedists, can take to reduce the rate of AVN will benefit our patients and hopefully decrease the need for total joint replacement in this population,” she said.

AAOS Now

Published 6/1/2009
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Annie Hayashi

AVN drives need for THA in patients with SCF

By Annie Hayashi

Relatively low incidence of AVN, but condition leads to earlier arthroplasty

Avascular necrosis (AVN) was the leading cause for total hip arthroplasty (THA) in young adults with slipped capital femoral epiphysis (SCFE), according to a study presented by Amy L. McIntosh, MD, at the recent Annual Meeting of the Pediatric Orthopaedic Society of North America (POSNA).

Amy L. McIntosh, MD

Identifying patient groups
Using the computerized Mayo Clinic joint registry, the investigators searched for those patients with previously treated SCFE who had primary hip arthroplasty. They identified 33 patients (38 THAs). Researchers also recorded the time from surgical treatment for SCFE until arthroplasty, the reason for THA, the type of implant, and any additional surgeries or revision arthroplasty.

Once the patients had been selected, researchers used clinical histories to determine chronicity and stability of the slip. Two independent reviewers graded slip severity as mild, moderate, or severe based on frog-leg lateral radiographs. “This determination was made by subtracting the epiphyseal shaft angle of the affected hip from the angle of the unaffected side,” explained Dr. McIntosh.

Comparison reveals significant differences
The study group included 23 males and 10 females. The mean age of the males at the time of the SCFE diagnosis was 14.1 years (range: 10 to 18.3 years); mean age for females was 12.1 years (range: 10.2 to 15 years).

The hip arthroplasties were divided into the following groups based on these diagnoses:

  • Group 1—AVN or chondrolysis (n=25)
  • Group 2—degenerative changes and/or FAI (n=13)

In 21 hips, AVN was the primary diagnosis leading to THA; chondrolysis was found in 4 hips, degenerative changes in 11 hips, and impingement in 2 hips.

AVN was associated with 70 percent of the severe slips, 71 percent of the acute or acute-on-chronic slips, and 78 percent of the unstable slips (Fig. 1).

The mean time from slip diagnosis to THA was shorter in group 1 than in group 2—7.6 years versus 23.6 years (P<0.0001). patients in group 1 also had a younger mean age at arthroplasty when compared to group 2—20 years versus 38 years (p><0.0002).>

“This study can help us provide some important information to our patients,” Dr. McIntosh said. “Previously, we told patients that we would watch them over time. Now we have some actual data to share. The risk of needing a THA is probably less than 5 percent for all patients with SCFE. If AVN develops, however, the patient is more likely to require a total joint replacement and will need that procedure at a younger age.”

Preventing AVN in the SCFE patient
“Although AVN may develop in a small percentage of SCFE patients overall, it has been reported that 14 percent to 58 percent of acute or unstable slips may progress to AVN,” said Dr. McIntosh.

“Future continued research targeted at reducing the rate of AVN is likely to have the greatest impact on decreasing the need for hip arthroplasty in patients with acute, unstable SCFE,” she said.

A recent study of 15 patients with unstable SCFE who were treated with surgical dislocation, open reduction, and internal fixation found that AVN developed in only 1 patient.

Other investigations have found that routine capsulotomy may play a role in preventing AVN from developing in patients with acute, unstable SCFE. Combining a capsulotomy with an incidental reduction (achieved while positioning the patient on the fracture table) and screw fixation may be an alternative that most orthopaedic surgeons could perform.

Co-authors for “Avascular necrosis rather than femoroacetabular impingement is most common indication for hip arthroplasty in patients with slipped capital femoral epiphysis” include A. Noelle Larson, MD; Robert T. Trousdale, MD, and David G. Lewallen, MD.

The authors reported the following disclosures: Dr. Trousdale: Depuy, A Johnson & Johnson Company; Wright Medical Technology, Inc.; Stryker; and Zimmer. Dr. Lewallen: Zimmer; FIOS; and Orthosonics. Drs. McIntosh and Larson report no conflicts.

Annie Hayashi is the senior science writer for AAOS Now. She can be reached at hayashi@aaos.org