Poster Presentation ESA-SRB-ANZBMS 2024 in conjunction with ENSA

Bone disorganisation may contribute to atypical femoral fractures by reducing fatigue strength: A finite element analysis model (#391)

Simon Zhang 1 , Xuanchi Liu 2 , Catherine Martin 3 , Catherine Shore-Lorenti 1 , Tessa Makebeh 4 , Michael Thompson 5 6 , Frances Milat 1 7 8 , Peter Ebeling 1 8 , Roger Zebaze 1 8
  1. Department of Medicine, Monash University, Melbourne, Victoria, Australia
  2. Department of Infrastructure Engineering, The University of Melbourne, Melbourne, Victoria, Australia
  3. School of Public Health and Preventive Medicine, Monash University, Melbourne, Victoria, Australia
  4. ZEZE co, Yaoundé, Cameroon
  5. Menzies Institute for Medical Research, University of Tasmania, Hobart, Tasmania, Australia
  6. Department of Endocrinology, Royal Hobart Hospital, Hobart, Tasmania, Australia
  7. Hudson Institute of Medical Research, Melbourne, Victoria, Australia
  8. Department of Endocrinology, Monash Health, Melbourne, Victoria, Australia

The mechanism responsible for atypical femoral fractures (AFFs) in patients with normal bone mineral density (BMD) and bone microarchitecture remains unclear. Recently, we proposed that abnormal transfer of loads through disorganised (misaligned) bone elements may increase the propensity of developing fatigue-induced fractures, such as AFFs (1). Here, we tested the hypothesis that higher bone disorganisation is associated with lower fatigue strength.

 

We developed a fatigue-based finite element model in COMSOL Multiphysics using the stress-life method. An initial transverse microcrack (0 degrees), resembling an incomplete AFF, was simulated on a cortical bone model with normal BMD and structure. Further microcracks of angles 15, 30 and 45 degrees relative to the initial transverse microcrack were then simulated using the same model. At each microcrack orientation, mean disorganisation value (DV) was quantified using the ALIGNOGRAM software (2). Fatigue strength was estimated as the minimum number of loading cycles (n) required for the microcrack to propagate across one third of the cortex. This was measured under varying body weight.

 

Fatigue strength decreased with increasing mean disorganisation value (Figure 1). Highest disorganisation values and lowest fatigue strengths were observed when the microcrack was oriented transversely (0 degrees). A change in microcrack direction from 45 degrees to 0 degrees was associated with an 11.2-fold increase in the DV (0.48 vs 5.36 for 70 kg) and a 23.8% decrease in fatigue strength (n=133486 vs n=101745 for 70 kg). Moreover, the fatigue strength of cortical bone decreased with increasing body weight at each level of disorganisation.

 

Bone disorganisation markedly reduces fatigue strength independently of BMD and bone structure. Transverse microcracks produced the highest disorganisation and greatest reduction in fatigue strength, which may explain the unique horizontal configuration of AFFs. Thus, measurement of disorganisation and fatigue strength may play an important role in the assessment of bone diseases.   

66a8c1d866df4-Screenshot+2024-07-30+at+8.34.12%E2%80%AFPM.jpg

  1. Zebaze R, Ebeling PR. Disorganization and musculoskeletal diseases: novel insights into the enigma of unexplained bone abnormalities and fragility fractures. Current Osteoporosis Reports. 2023;21(2):154-66.
  2. Zebaze R, Shore Lorenti C, Nguyen HH, Chiang C, Milat F, Ebeling PR. A quantification method for disorganized bone components: Application to the femoral shaft. Journal of Bone and Mineral Research Plus. 2023;7(2):e10713.