Identifying Atypical Femoral Fractures—A Retrospective Review

Abstract

Subtrochanteric atypical femoral fractures (AFFs) have been reported in patients on osteoporosis therapy (bisphosphonates and denosumab). In 2010, and again in 2013, the ASBMR AFF Task Force developed strict diagnostic criteria for AFFs. This is the first study using these criteria to define the prevalence of AFFs in Canada. This study is a retrospective review of all adult patients (April 2002-March 2013) with an ICD 10 code for hip, femoral or subtrochanteric fracture, from two referral hospitals in Alberta, Canada. All identified as isolated subtrochanteric fractures were further evaluated by chart review, prescription review and examination of radiographs. Of 349 subjects, 79 had isolated subtrochanteric fractures. Of the 70 cases of subtrochanteric fractures that were radiographically assessed (9 films unavailable), 41 fulfilled ASBMR 2013 AFF criteria. The remaining subjects had subtrochanteric fractures but did not meet the ASBMR criteria to qualify as AFFs. There were 11 AFFs in 2012/2013, giving a rate of AFFs of 1.42 per 100,000 50 + year adults, compared to a rate of 103.47 per 100,000 50+ year adults for typical hip fractures. Isolated subtrochanteric fractures are rare. They cannot reliably be identified by ICD coding alone. In this study, only 59 % of all isolated subtrochanteric/femoral shaft fractures fulfilled the ASBMR task force criteria for true AFFs. The rate of typical hip fractures was substantially higher than the rate of AFFs, defined by ASBMR diagnostic criteria.

Current Understanding of Epidemiology, Pathophysiology, and Management of Atypical Femur Fractures

“…The major differences between the original and revised definitions are as follows: (1) periosteal or endosteal thickening of lateral cortex at the fracture site (“beaking or flaring”) was changed from a minor to a major feature, (2) minimal comminution was permitted, and (3) the wording “transverse or short oblique configuration” was expanded to specify that the fracture line must originate at the lateral cortex and remain transverse across the cortex, but permitted the fracture line to become oblique as it progressed medially across the femur. Recent studies, using the 2013 case definition and a variety of designs, report a low incidence of AFFs [ 6 , 7 ••, 8 ••, 9 , 10 ].…”

Epidemiology and postoperative outcomes of atypical femoral fractures in older adults: A systematic review

“…Using the first ASBMR definition, the prevalence of AFFs accounted for only 0.2-0.8% of total hip fractures and 3.5-30.3% of subtrochanteric and femoral shaft fractures (13,(17)(18)(19)(20). Similarly, three studies using the revised ASBMR definition reported a low prevalence of AFFs, estimated to be 0.63% of total hip fractures and 3.5-5.7% of subtrochanteric and femoral shaft fractures (22,24,25).…”

“…In all studies except for one, the mean age of patients with AFFs were reported to be above 65 years (Table 1) (12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25). Amongst these studies, six retrospective case-control studies showed that patients with bisphosphonate-related AFFs were younger than patients with typical proximal femoral fractures (TPFFs) (mean age range of 66-75 years versus 75-89 years respectively), at the time of fracture (12-15, 19, 22).…”

Bilateral Incomplete Atypical Femoral Fracture due to Long-Term Bisphosphonate Use: A Case Report

“…When BPs are stopped, the risk of AFF declines (8). There have been reports of AFF with denosumab which is another antiresorptive agent (8,9). The pathogenesis of AFF can be related to long-term suppression of bone turnover.…”