Oral Virtual Presentation (Virtual only) ESA-SRB-ANZBMS 2021

  Misalignment by producing Ineffective Load Conduction May be Responsible for Atypical Femoral Fractures (AFFs) (#224)

Roger Zebaze 1 , Hanh Nguyen 1 , Frances Milat 2 , Cherie Chiang 3 , Peter Ebeling 1
  1. Monash University, School of Clinical Sciences, Clayton, VIC, Australia
  2. Hudson Institute of Medical Research, Clayton, Vic, Australia
  3. Endocrinology and Medicine, Austin Health, Heidelberg, VIC

 

Introduction –The lack of a tool to identify individuals at risk for AFFs is an important unmet need in osteoporosis management. 

        Bone has two key different mechanical functions: (i) to bear loads, this requires high bone density and strength; (ii.)  to conduct (transmit) received forces (loads) until they reach a final structure. (e.g., sound conduction by the middle ear ossicles). To perform this second function effectively, bone does not need to be dense or strong. Instead, bone needs to be a good conductor to efficiently receive and transmit loads. To achieve this, an effective cohesion between components is required-i.e., good alignment.

 

        Impairment in either function may produce fracture. As AFFs are localized, associated with deformities (e.g. bowing) and occur in settings of relatively preserved bone density, we propose ineffective load transfer produced by misalignment is an important mechanism responsible for AFFs. Thus, comparing AFFs (n=4) and fracture-free controls (n=6), we tested the hypothesis that femoral misalignment is associated with AFFs.

 

Methods – Accordingly, we develop a Misalignment Detector (Alignogram1.0); Using Pelvic X-rays, this novel software quantifies and displays the degree of misalignment (expressed as percent) at each position along the femur as a curve. The Alignogram further separates the curve into zones, and highlights misaligned zones (outliers).

 

Results – AFFs patients had a 4-fold greater misalignment than controls (4.8±0.96 vs 19.18±2.25 %;p<0.001); and a more heterogeneous curve (1.61±0.23 vs 2.78±0.20;p=0.0007). In all patients with AFFs, the Alignogram showed at least one misaligned zone (see figure). None was found in controls.

 

Conclusion – AFFs are associated with ineffective load transfer rather than reduced bone density or strength. Measurement of misalignment from readily available X-ray images may hold the key in identifying patients at risk for AFFs. Thus, guiding appropriate therapeutic decisions.  Larger studies are needed to confirm our findings.

 

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