[home] [Personal Program] [Help]

---

Session: MSK & Sweat sensing
Session starts: Friday 27 January, 11:30
Presentation starts: 11:45
Room: Room 530

---

Thomas Gersie (Radboudumc)
Thom Bitter (Radboudumc)
David Wolfson (Depuy Synthes)
Robert Freeman (Depuy Synthes)
Nico Verdonschot (Radboudumc)
Dennis Janssen (Radboudumc)

Abstract:
INTRODUCTION The success of orthopaedic implants designs mainly depends on the initial fixation. The accurate modelling of this primary stability relies on accurate material properties. To our knowledge, nonlinear stress relaxation of trabecular bone has not been quantified in relation to bone mineral density and strain level. In this work, we present preliminary data of multiple stress relaxation experiments. METHODS 32 Trabecular femoral bovine bone cylinders were harvested. Stress relaxation experiments on 16 samples were conducted by applying a uniaxial compressive strain (0.2-0.8%) for 24 hours to determine the optimal test duration. The other samples, divided over four BMD groups, the samples were compressed with 0.2% strain for 30 minutes, after which they were stored to recover for 24 hours. This sequence was repeated for 0.4%, 0.6, and 0.8% strain. RESULTS After 24 hours, stress relaxation ranging from 41.0% to 68.7% was observed. Up to 52.9% of this stress relaxation occurred in the first 10 minutes . Moreover, stress relaxation did not level off after 24 hours. At last, it was shown that samples with a lower BMD displayed a lower peak force than samples with a higher BMD, with similar stress relaxation behavior. DISCUSSION Most of the stress relaxation occurs within 10 minutes, which in clinical practice is still during surgery. However, stress relaxation continued even after 24 hours of testing. It is therefore important to model the viscoelastic behavior up to 24 hours. Moreover, performing an experiment for 30 minutes provides an ideal tradeoff between fit accuracy and experimental testing time. Furthermore, it was shown that the BMD has an influence on the peak force, but no significant effect on the relative stress relaxation. Further testing will illuminate the relation between BMD and the viscoelastic response for both bovine and human trabecular bone. The next step is to incorporate the viscoelastic behavior in simulations of primary fixation in total knee arthroplasty components to demonstrate the influence of bone relaxation on primary fixation. SIGNIFICANCE This work contributes to improving analytical tools to study the initial fixation of orthopaedic implants to allow testing of new designs in a preclinical phase.