PSI - Issue 42

N.S. Hennicke et al. / Procedia Structural Integrity 42 (2022) 404–411 Hennicke et al. / Structural Integrity Procedia 00 (2022) 000 – 000

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On the basis of the determined T-score and Z-score values from the QCT scans, scaling factors (see Appendix A) were identified for each femur to extrapolate the original BMD of the patient for different age groups and severity levels of osteoporosis. For this purpose, statistical data from the National Health and Nutrition Examination Survey III (Looker et al., 1998) on the BMD measured in the proximal femurs of 2930 Caucasian men was used. Afterwards, the overall density of the femurs was scaled with the determined factors while the subject specific density distribution remained unchanged. For the first simulations, the density was extrapolated along the patient’s percentile curve to simulate the femurs in different age groups from their twenties to over eighty under the assumption, that the Z-score stayed the same during their life time (see Fig. 2). For the other simulations, the density was scaled to simulate different severity levels of osteoporosis with T-scores ranging from 0 for healthy bone to -3 for bone with severe osteoporosis (see Fig. 2).

Fig. 2. Statistical data of BMD development in the proximal femur of Caucasian men during aging (Looker et al., 1998) with T-score values and data extrapolation for simulations of femurs 1L and 3L 3. Results and discussion The force-displacement curves, which were measured vertically at the implant head, are shown in Fig. 3 for simulations of the two femurs in different age groups. To eliminate contact noise as a result of element deletion, a two-pass, zero phase shift, second-order Butterworth filter (CFC 60, SAE J211) was applied to all force-displacement curves. The fracture load was defined at the first peak of the curve. It can be seen, that for both femurs fracture load and stiffness decreased with advancing age. The fracture load for femur 1L decreased by 0.685 kN over the life time of this donor. The fracture load for femur 3L decreased by 2.54 kN.

Fig.3. Force-displacement curves from simulations in different age groups; A : femur 1L, B: femur 3L