OTA 2012 Posters

Scientific Poster #30 Hip/Femur OTA-2012

Radiographic Identification of Atypical Subtrochanteric snd Femoral Shaft Fractures

Lise A. Leveille, MD1; Penny Brasher, PhD2; Pierre Guy, MD1; Peter J. O’Brien, MD1;
1Department of Orthopaedics, University of British Columbia, Vancouver,
British Columbia, Canada;
2Department of Statistics, University of British Columbia, Vancouver, British Columbia, Canada

Background/Purpose: Atypical subtrochanteric (ST) and femoral shaft (FS) fractures (OTA Fracture Compendium type 32-A3) have been increasingly reported in the literature. Their association with long-term bisphosphonate use has been debated. Smaller case series and case-control studies have suggested an association between atypical ST/FS fractures and long-term bisphosphonate use. Some larger, population-based studies have not supported this association. In the majority of these larger studies, no radiographic review was completed. The purpose of this study was to first, identify the proportion of atypical fractures in patients admitted to a Level I trauma center with a low-energy ST/FS fracture using the American Society for Bone and Mineral Research (ASBMR) radiographic criteria. Second, we sought to quantify the interobserver reliability of using this method for identification of atypical ST/FS fractures. Finally, we wanted to identify the proportion of atypical ST/FS fracture subjects with a history of bisphosphonate exposure.

Methods: A prospectively collected trauma database was used to identify patients greater than 55 years of age presenting to a Level I trauma center with a low-energy ST/FS fracture between January 2000 and February 2011. Exclusion criteria were clinical or radiographic evidence of active malignancy, periprosthetic fracture, history of metabolic bone disease, or fracture outside the defined region of interest. Digital radiographs were assessed by three blinded, independent reviewers and categorized as either atypical or nonatypical based on the ASBMR radiographic criteria for atypical ST/FS fractures. A chart review was completed on all atypical fractures.

Results: 358 ST/FS fractures were identified. Exclusion criteria were met in 195 fractures. 39 fractures were radiographically categorized as atypical, with an interrater reliability (concordance) of 96% and kappa of 0.92. Of the atypical ST/FS fractures, 10 were excluded after chart review for history of metastatic cancer, high-energy mechanism of injury, or Paget disease. Of the remaining 29 atypical fractures in 26 subjects, 86% were taking a bisphosphonate at the time of fracture. The average duration of bisphosphonate use was 8.2 years.

Conclusion: The majority of low-energy ST/FS fractures are not atypical fractures according to the ASBMR radiographic criteria. Use of database-identified cohorts, without radiographic review, results in overinclusion and masking of any association between atypical femoral fractures and long-term bisphosphonate use. Three independent reviewers using the ASBMR radiographic criteria is a reliable means of identifying atypical ST/FS fractures. In this series of atypical ST/FS fractures, the majority had a history of bisphosphonate exposure, which is consistent with previously reported case series.

• The FDA has not cleared this drug and/or medical device for the use described in this presentation   (i.e., the drug or medical device is being discussed for an “off label” use).  ◆FDA information not available at time of printing. Δ OTA Grant.