Computational simulation of bone grafts for impaction bone grafting

Author: Ashwin Jeyakar Dhanasekaran

Dhanasekaran, Ashwin Jeyakar, 2021 Computational simulation of bone grafts for impaction bone grafting, Flinders University, College of Science and Engineering

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Revision arthroplasty with impaction bone grafting is an attractive method with the potential to restore bone stock in the tibia/femur when there is bone loss caused by the removal of failed primary replacement implants. However, the surgery is complex and problematic implant subsidence is often reported as a root cause of failure in these procedures. The mechanism that causes this subsidence is not well understood due to a lack of knowledge on the material characteristics of the bone grafts or a universal standard procedure to achieve a stable impaction. As the bone loss pattern in each patient is unique, revision replacement systems consist of a variety of stems and sleeves that augment to fill bone defects, restore alignment, and ensure adequate fixation to the remaining bone. The array of components in a revision replacement system provides challenges for both the manufacturer and the surgeon.

The primary objective of this thesis was to understand the mechanical properties of bone grafts and capture them using numerical modelling. The secondary objective was to validate the numerical model and analyse the data captured from the numerical model to explain the characteristics of bone grafts that cannot be explained from experimental testing methods. The study demonstrated that mechanical properties of bone grafts are highly variable and can be captured by performing a repeatability test and performing statistical analysis on the results to estimate uncertainty. Finite element models can better understand the mechanical characteristics that cannot observe traditional experimental testing. The results from the model demonstrated that when bone grafts are impacted in a single layer, the impaction stresses were only concentrated in the proximal end of the impaction site and not evenly distributed across to the distal end of the graft bed. Single-layer impactions produced a lower graft stiffness and shear strength, with the bone grafts at the proximal side exhibiting a high magnitude of plastic deformation with high impaction stress levels. The model also demonstrated that most stress consolidation occurs in the first 20 impaction cycles with impact stresses 3.0MPa – 5.0 MPa. The study demonstrated that impacting bone grafts at stresses between 3.0 MPa – 5.0 MPa for 10 to 20 impactions cycles is adequate to achieve a stable impacted bone graft in revision tibias. Impacting the bone grafts in evenly distributed layers can help increase the graft stiffness by equally distributing the impaction forces across the bone grafts and achieving a densely packed bone graft.

Keywords: bone grafts, impaction bone grafting, computational simulation

Subject: Engineering thesis

Thesis type: Doctor of Philosophy
Completed: 2021
School: College of Science and Engineering
Supervisor: Mark Taylor