Background/Purpose: Atypical femoral fractures (AFF) are low energy femoral fractures and subtrochanteric/diaphyseal localization that have been related to long-term bisphosphonate therapy. Patients with AFF exhibit cortical thickening in femoral shaft, suggesting that AFF may occur due to cortical stress. Analysis of cortical bone microarchitecture, biomechanical properties of bone and bone remodeling in AFF are poorly explored in the literature. Our aim is to evaluate patients with AFF including: 1) cortical bone microarchitecture and bone stiffness by high resolution peripheral quantitative computed tomography (HR-pQCT) and 2) cortical microarchitecture and parameters of bone remodeling by bone histomorphometry of iliac crest.

Methods: Eighteen patients with AFF by the American Society of Bone Mineral Research. Cortical bone parameters (cortical volumetric bone mineral density: Ct.vBMD, mgHA/cm³; and cortical thickness: Ct.Th, mm) and bone stiffness (S, kN/mm) were studied at tibia and distal radius by HR-pQCT and compared to healthy controls matched for sex and age. Cortical thickness (Ct.Th, μm) and bone remodeling (bone formation rate: BFR/BS, μm³/μm²/day) were assessment (Osteomeasure software®) and compared with healthy individuals matched for sex and age.

Results: The mean age of the patients was 64.9±13.3 years old, 94.4% women and 72.2% Caucasian. Seventeen used bisphosphonates (5.8±2.7 years) and 83.3% alendronate at the time of fracture. One patient was on denosumab, but had received bisphosphonate for 6 years. Presence of rheumatic disease was observed in 50% of the patients, most of them with rheumatoid arthritis and 44.4% of the patients used oral glucocorticoid. All fractures were diaphyseal, of which 16 (88.8%) were complete and 4 (22.2%) were bilateral. HR-pQCT (n=12) at tibia showed decreased/normal Ct.vBMD in 83.3% and decreased/normal Ct.Th in 91.6% of the patients. Similar findings were observed at distal radius. Seventy-five percent of the patients had decreased S at tibia and 58.3% at radius. At tibia, S was positively correlated with Ct.Th (r = 0.783, p = 0.001) and Ct.vBMD (r = 0.573, p = 0.004). At radio, S was positively correlated with Ct.Th (r = 0.720, p = 0.007). Bone histomorphometry (n=6) exhibited Ct.Th decreased in 66.6% and normal in 33.3% of the cases. All patients had suppressed bone remodeling.

Conclusion: Our data suggest that AFF patients maintain bone fragility observed in peripheral sites (tibia and radius) and in the iliac crest. Impairment of cortical microarchitecture associated with decreased bone stiffness and suppression of bone remodeling would explain bone fragility in these patients. Our data warn that the cortical bone should be contemplated in the treatment of AFF.

« Back to 2018 ACR/ARHP Annual Meeting

ACR Meeting Abstracts - https://acrabstracts.org/abstract/evaluation-of-cortical-microarchitecture-bone-stiffness-and-bone-remodeling-in-patients-with-atypical-femoral-fracture/