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Foot-ankle complex injury risk curves using calcaneus bone mineral density data
Narayan Yoganandan1, Sajal Chirvi2, Liming Voo3
1Department of Neurosurgery, Medical College of Wisconsin, Milwaukee, WI, USA; Orthopaedic Surgery, Medical College of Wisconsin, Milwaukee, WI, USA.
Summary
Pre-scaling bone mineral density (BMD) data is a more accurate method than using covariates for developing human injury risk curves from post mortem human subject (PMHS) experiments. This approach improves injury prediction for different age groups in biomechanical studies.
Area of Science:
- Biomechanics
- Human injury prediction
- Anthropometric testing
Background:
- Post mortem human subject (PMHS) experiments are crucial for developing human injury risk curves and criteria used in automotive safety and federal standards.
- Human bone strength naturally decreases with age, necessitating adjustments in injury risk models that utilize data from PMHS specimens of varying ages.
- Bone mineral density (BMD) offers a more direct measure of bone strength than age, presenting an opportunity to refine injury risk curve development.
Purpose of the Study:
- To investigate and compare two methods for incorporating BMD into human injury risk curves: treating BMD as a covariate versus pre-scaling test data based on BMD.
- To determine which method provides a more accurate representation of injury risk, particularly considering age-related bone strength variations.
Main Methods:
- Simulated underbody blast (UBB) loading experiments were conducted on twelve PMHS lower leg-foot-ankle complexes.
- Calcaneus BMD was quantified using quantitative computed tomography (QCT), and fracture forces were recorded.
- Survival analysis using a Weibull distribution model was employed to compare the covariate and pre-scaling methods, with normalized confidence intervals (NCIS) analyzed.
Main Results:
- The pre-scaling method yielded higher mean injury forces (5.4 kN for 5% and 9.2 kN for 50% probability) compared to the covariate method (3.9 kN and 8.6 kN, respectively).
- Risk curves derived using the pre-scaling method exhibited tighter confidence intervals (0.24-0.66) than those from the covariate method (0.52-1.00).
- Calcaneus BMD-based pre-scaling demonstrated a greater force at the same risk level compared to using spine BMD.
Conclusions:
- Pre-scaling biomechanical test data using BMD is a more accurate and recommended approach than using BMD as a covariate for developing human injury risk curves.
- Utilizing calcaneus BMD for pre-scaling is suggested for future underbody blast and similar loading studies focused on the foot-ankle complex due to its proximity to impact.
- This refined method enhances the accuracy of human injury probability curves for the foot-ankle complex, improving safety standards and research.
