An Investigation on the Influence of Stumbling Loads on Femoral Fracture Risk, Using a Novel Gradient Enhanced Quasi-Brittle Finite Element Model

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Creator: 

Haider, Ifaz

Date: 

2017

Abstract: 

Stumbling is associated with large hip contact forces, but it remains unclear whether these events contribute to osteoporotic hip fracture risk. We hypothesized that stumbling may increase risk, either causing fracture directly, or damaging the femur leaving it susceptible to future loading. This hypothesis can be tested in-silico, but previously published finite element (FE) models are susceptible to large errors in predicted fracture load and pattern. We developed and validated a novel gradient enhanced quasi-brittle damage model, for improved fracture prediction, and used the model to assess the influence of stumbling on fracture risk. Preliminary FE models were used to explore relevant physics and boundary conditions (BC’s) needed to accurately model the femur in fall and stumbling configurations. The study investigated the influence of different BCs, viscoelasticity, inertial dynamics, and biphasic (pore fluid) effects; the potential importance of these phenomenon had been discussed, but not well-explored, in literature. After implementation, the gradient enhanced quasi-brittle damage model was validated through experimental testing. Average fracture load prediction error was 9.6%, compared to 10%-20% errors reported in previous models and fracture pattern was correctly predicted for all cases, compared to the 60-80% accuracy of previous models. This validated model predicted that four of six specimens had a moderate risk of fracture due to stumbling alone, and risk increased significantly with simulated advanced osteoporosis. The model also predicted compaction of the subcapital region, a pattern consistent with impacted fractures observed in clinical settings. Finally, we investigated if progressive damage accumulation from combinations of stumble and fall could increase fracture risk. Most specimens were resilient to accumulated damage and only one experienced reductions in strength (5-15%) from repeat loading. However, two specimens experienced moderate (20-30%) increase in fracture load, for some load cases; this was a novel finding. In these cases, initial damage accumulation caused the load to be more evenly distributed upon subsequent loading events. These results suggest that stumbling alone can result in hip fracture and therefore future preventative intervention strategies may be more effective if they target both fall and stumbling induced fractures.

Subject: 

Engineering - Biomedical

Language: 

English

Publisher: 

Carleton University

Thesis Degree Name: 

Doctor of Philosophy: 
Ph.D.

Thesis Degree Level: 

Doctoral

Thesis Degree Discipline: 

Engineering, Mechanical

Parent Collection: 

Theses and Dissertations

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