Plenary Poster 30th Australian and New Zealand Bone and Mineral Society Annual Scientific Meeting 2020

Bone Compartment Characteristics in Patients with Atypical Femoral Fractures on 3D Dual X-Ray Absorptiometry (DXA) (#16)

Albert S Kim 1 2 , Jean Doyle 1 , Lillias Nairn 1 , Gareth Crouch 2 , Maria-Liza Nery 1 , Andrew Ellis 3 , Roderick Clifton-Bligh 1 2 , Christian Girgis 1 2 4
  1. Department of Endocrinology, Diabetes and Metabolism, Royal North Shore Hospital, St Leonards, NSW, Australia
  2. Faculty of Medicine & Health, University of Sydney, NSW 2600, Australia
  3. Department of Orthopedic and Trauma Surgery, Royal North Shore Hospital, St Leonards, NSW, Australia
  4. Department of Diabetes and Endocrinology, Westmead Hospital, Westmead, NSW, Australia

Introduction: Atypical femoral fractures(AFF) represent a rare but devastating complication related to long-term antiresorptive therapy for osteoporosis(1). While generalised increase in cortical thickness of the femoral diaphysis on X-ray has been associated with AFF(2), the underlying microarchitectural changes remain unclear. A three-dimensional(3D)-DXA software algorithm(3DSHAPER,GalgoMedical,Barcelona,Spain) was utilised to quantify cortical thickness and volumetric bone mineral density(BMD) of trabecular and cortical bone from DXA projections(3).

Methods: Retrospective review of areal BMD and 3Dassessment of trabecular and cortical parameters at the hip and femoral shaft in patients on long-term therapy(>5years) who sustained AFF and those who did not, in a case-control ratio of 1:2.

Results: 30 femoral models were obtained using the 3D-DXA algorithm from 10 patients with AFF and 20 patients without(example output in Figure 1). There were no significant differences in mean age (AFF 72.4±11.4 and Control 76.9±8.2 years,p=0.29) or duration of antiresorptive therapy (AFF 9.9±6.9and Control 11.4±4.6years,p=0.56). There were no significant differences in the areal BMD in the femoral neck, trochanter, shaft and total hip.

Femoral neck area was significantly smaller in patients with AFF compared to controls (4.64±0.25 and 5.05±0.26cm2,p<0.001). Cortical bone mineral content was significantly lower in the AFF group at the neck (1.77±0.26 and 2.23±0.34g,p<0.001) and the shaft (6.77±1.80 and 8.57±1.56g,p=0.16). This difference was not seen in the trabecular compartment. There was no significant difference in mean cortical thickness (1.67±0.26 and 1.80±0.13g,p=0.16).

Cortical thickness was not correlated with age or duration of therapy. There was significant correlation between duration of treatment and total cortical volume(r=0.467,r2=0.218,p=0.04) in the control group but this was not significant in the AFF group

Conclusion: Lower cortical bone mineral content but no significant cortical thickening was observed in AFF patients compared to those on a similar duration of antiresorptive agents. Reduced cortical bone mineralisation may increase the risk of developing AFF.

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