Genetic Risk Factors for Atypical Femoral Fractures (AFFs): A Systematic Review

Atypical femoral fractures (AFFs) are uncommon and have been associated particularly with long-term antiresorptive therapy, including bisphosphonates. Although the pathogenesis of AFFs is unknown, their identification in bisphosphonate-naïve individuals and in monogenetic bone disorders has led to the hypothesis that genetic factors predispose to AFF. Our aim was to review and summarize the evidence for genetic factors in individuals with AFF. We conducted structured literature searches and hand-searching of conference abstracts/reference lists for key words relating to AFF and identified 2566 citations. Two individuals independently reviewed citations for (i) cases of AFF in monogenetic bone diseases and (ii) genetic studies in individuals with AFF. AFFs were reported in 23 individuals with the following 7 monogenetic bone disorders (gene): osteogenesis imperfecta (COL1A1/COL1A2), pycnodysostosis (CTSK), hypophosphatasia (ALPL), X-linked osteoporosis (PLS3), osteopetrosis, X-linked hypophosphatemia (PHEX), and osteoporosis pseudoglioma syndrome (LRP5). In 8 cases (35%), the monogenetic bone disorder was uncovered after the AFF occurred. Cases of bisphosphonate-naïve AFF were reported in pycnodysostosis, hypophosphatasia, osteopetrosis, X-linked hypophosphatemia, and osteoporosis pseudoglioma syndrome. A pilot study in 13 AFF patients and 268 controls identified a greater number of rare variants in AFF cases using exon array analysis. A whole-exome sequencing study in 3 sisters with AFFs showed, among 37 shared genetic variants, a p.Asp188Tyr mutation in the GGPS1 gene in the mevalonate pathway, critical to osteoclast function, which is also inhibited by bisphosphonates. Two studies completed targeted ALPL gene sequencing, an ALPL heterozygous mutation was found in 1 case of a cohort of 11 AFFs, whereas the second study comprising 10 AFF cases did not find mutations in ALPL. Targeted sequencing of ALPL, COL1A1, COL1A2, and SOX9 genes in 5 cases of AFF identified a variant in COL1A2 in 1 case. These findings suggest a genetic susceptibility for AFFs.

Medical management of patients after atypical femur fractures: a systematic review and recommendations from the European Calcified Tissue Society

Context Atypical femur fractures (AFFs) are serious adverse events associated with bisphosphonates and often show poor healing. Evidence acquisition We performed a systematic review to evaluate effects of teriparatide, raloxifene, and denosumab on healing and occurrence of AFF. Evidence synthesis We retrieved 910 references and reviewed 67 papers, including 31 case reports, 9 retrospective and 3 prospective studies on teriparatide. There were no RCTs. We pooled data on fracture union (n = 98 AFFs on teriparatide) and found that radiological healing occurred within 6 months of teriparatide in 13 of 30 (43%) conservatively managed incomplete AFFs, 9 of 10 (90%) incomplete AFFs with surgical intervention, and 44 of 58 (75%) complete AFFs. In 9 of 30 (30%) nonoperated incomplete AFFs, no union was achieved after 12 months and 4 (13%) fractures became complete on teriparatide. Eight patients had new AFFs during or after teriparatide. AFF on denosumab was reported in 22 patients, including 11 patients treated for bone metastases and 8 without bisphosphonate exposure. Denosumab after AFF was associated with recurrent incomplete AFFs in 1 patient and 2 patients of contralateral complete AFF. Eight patients had used raloxifene before AFF occurred, including 1 bisphosphonate-naïve patient. Conclusions There is no evidence-based indication in patients with AFF for teriparatide apart from reducing the risk of typical fragility fractures, although observational data suggest that teriparatide might result in faster healing of surgically treated AFFs. Awaiting further evidence, we formulate recommendations for treatment after an AFF based on expert opinion

"Atypical" atypical femur fractures and use of bisphosphonates

Background: Atypical femur fractures (AFFs) present a rare but serious condition associated with use of bisphosphonates. Underlying mechanisms and clinical risk factors remain unclear. According to the diagnostic criteria formulated by the ASBMR, a lateral localization of an AFF is required. Case history: We present a patient who developed bilateral leg pain while using an oral bisphosphonate and aromatase inhibitor in the course of adjuvant treatment for breast cancer. Initially she was diagnosed with bone metastases and received radiotherapy on the right femur. However, the bilateral periosteal reactions of the subtrochanteric femur are highly suggestive of AFFs. Our case meets all criteria for AFF except that she presented with lesions at the medial side of the femur. Therefore they could be best described as "atypical" atypical femur fractures. Discussion: Since the pathogenesis of AFFs is not fully understood, we cannot rule out that AFFs also occur in the medial femur or in other weight-baring bones. Hence we propose that medial stress reactions belong to a spectrum of atypical fractures associated with use of antiresorptive drugs. The localization may depend on yet unknown biome-chanical factors. Conclusion: We propose that these periosteal reactions of the subtrochanteric femur are in fact AFFs with uncommon medial localization and could hence be considered "atypical" AFFs. We recommend being alert of AFFs in patients with bone pain and medial subtrochanteric lesions. More epidemiological studies are needed to investigate the occurrence of both medial and lateral AFFs and to gain more insight into its frequency and pathogenesis