Towards the Inclusion of Pelvis Population Variance in Human Body Models

With a future large-scale introduction of autonomous vehicles, the proportion of intersection crashes on the total number of motor vehicle crashes is expected to increase. The pelvis is frequently exposed to high loads in several of these impacts. In addition, autonomous driving is expected to result in new seating positions where reclined seating increases the risk of the pelvis sliding under the lap belt, producing submarining induced injuries. If unaddressed, submarining may result in an increased prevalence of abdominal and spinal injuries, and if addressed by advanced restraint systems, the risk of pelvic fractures may increase due to higher pelvis loads. Finite Element Human Body Models (FE-HBMs) represent the most advanced tool available to use in the design of safety systems for current and future vehicles. FE-HBMs represent the human anatomy, anthropometry, and physical properties to predict a biomechanical response to external loading via computer simulations. To date, these models are typically defined based on an average male or female subject in terms of global measurements like age, stature, and weight. However, individual variability is an intrinsic property of humans that must be considered in order to capture the vulnerable population and maximise the efficiency of vehicle safety systems. FE-HBMs provides the opportunity to include both geometrical and material variability in the analysis. In this thesis, methods/tools that enable inclusion of pelvis population variance in HBMs were developed. As part of this work, the population variance in pelvis shape has been described and a morphometric model capable of predicting pelvis shape was developed. A new generic pelvis FE-model was generated from the average pelvis geometry, which can be morphed to the population variance in pelvis shape. The model was validated for lateral impacts followed by a sensitivity analysis on model response to input variance. Results show that while 90% of the population shape variance was captured in the analysis, only 29% was predicted by a morphometric model using sex, age, stature, and BMI, as independent variables. The sensitivity analysis found that material properties account for the majority of the response variance (≈50-65%) in pelvis lateral impacts, and that input variables controlling shape contribute by a similar magnitude (≈35-40%). Increased knowledge about population variability, and inclusion in future safety evaluations, can result in more robust systems that would reduce the risk of pelvis injuries in real-world accidents

Predicting pelvis geometry using a morphometric model with overall anthropometric variables

Pelvic fractures have been identified as the second most common AIS2+ injury in motor vehicle crashes, with the highest early mortality rate compared to other orthopaedic injuries. Further, the risk is associated with occupant sex, age, stature and body mass index (BMI). In this study, clinical pelvic CT scans from 132 adults (75 females, 57 males) were extracted from a patient database. The population shape variance in pelvis bone geometry was studied by Sparse Principal Component Analysis (SPCA) and a morphometric model was developed by multi- variate linear regression using overall anthropometric variables (sex, age, stature, BMI). In the analysis, SPCA identified 15 principal components (PCs) describing 83.6% of the shape variations. Eight of these were signifi- cantly captured (α < 0.05) by the morphometric model, which predicted 29% of the total variance in pelvis geometry. The overall anthropometric variables were significantly related to geometrical features primarily in the inferior-anterior regions while being unable to significantly capture local sacrum features, shape and position of ASIS and lateral tilt of the iliac wings. In conclusion, a new detailed morphometric model of the pelvis bone demonstrated that overall anthropometric variables account for only 29% of the variance in pelvis geometry. Furthermore, variations in the superior-anterior region of the pelvis, with which the lap belt is intended to interact, were not captured. Depending on the scenario, shape variations not captured by overall anthropometry could have important implications for injury prediction in traffic safety analysis

Postoperative stability following a triple pelvic osteotomy is affected by implant configuration: a finite element analysis

BackgroundThe triple pelvic osteotomy is an established surgical method with multiple modifications regarding surgical technique and choice of implant. The stability of the osteotomy is affected by numerous factors, and among these, the three-dimensional implant configuration is a scientifically less explored aspect.MethodsWe used a finite element model of a hemi-pelvis with a standardized triple osteotomy to calculate relative flexibility for loads in all translational degrees of freedom for five different implant configurations. Two of the configurations used entry points only feasible when implant removal was not necessary.ResultsThe stability of the osteotomy improved with an increased distance between the implants in the plane of the osteotomy as well as for a more perpendicular angle relative to the osteotomy plane. The implant configurations with more entry points available made this easier to adhere to.ConclusionThe use of bioabsorbable implants may provide better opportunities for optimal implant constructs which can, to a certain degree, compensate for the lesser mechanical stiffness of bioabsorbable polymers as compared to metal implants

Validation of the SAFER Human Body Model Kinematics in Far-Side Impacts

Human Body Models are essential for real-world occupant protection assessment. With the overall purpose to create a robust human body model which is biofidelic in a variety of crash situations, this study aims to evaluate the biofidelity of the SAFER human body model in far-side impacts. The pelvis, torso and the upper and lower extremities of the SAFER human body model were updated. In addition, the shoulder area was updated for improved shoulder belt interaction in far-side impacts. The model was validated using kinematic corridors based on published human subject test data from two far-side impact set-ups, one simplified and one vehicle-based. The simplified far-side set-up included six configurations with different parameter settings, and the vehicle-based included two configurations: with and without far-side airbag, respectively. The updated SAFER HBM was robust and in general the model predicted the published human subject responses (kinematic CORA score > 0.65) for all configurations in both test set-ups. An exception was a 90 degree far-side impact with the D-ring in the forward position, in the simplified set-up. Here the model could not predict the shoulder belt retention, resulting in a low CORA score. Based on the overall results, the model is considered valid to be used for assessment of far-side impact countermeasures

Population Variance in Pelvic Response to Lateral Impacts - A Global Sensitivity Analysis

Pelvic fracture remains the third most common moderate to severe injury in motor vehicle crashes, and the dominating lower extremity injury in lateral impacts. An essential tool for analysis of injury, and real-world occupant protection, are finite element human body models. However, today\u27s state-of-the-art pelvis models do not adequately consider the variability in shape and size naturally occurring in human populations. In this study, we developed a new detailed pelvis finite element model, morphable to enable representation of the population shape variance. The model was validated using force-displacement data from post-mortem human subjects, in lateral loading of the denuded pelvis, followed by a global sensitivity analysis. The results suggests that in lateral impacts to the pelvis, pelvic shape contributes to the model response variance by the same magnitude as pelvic bone material stiffness, and that each of these contributions are approximately twice that of the cortical bone thickness. Hence, to model pelvic response for a general population accurately, future studies must consider both pelvic shape and the material properties in the analysis. Increased knowledge about population variability, and inclusion in safety evaluations, can result in more robust systems that reduce the risk of pelvic injuries in real-world accidents

Active Human Body Model Predictions Compared to Volunteer Response in Experiments with Braking, Lane Change, and Combined Manoeuvres

Active human body models are an important tool to study occupant interaction with safety systems in evasive manoeuvres such as braking and/or steering. In this study a finite element human body model with and without closed-loop active muscle control in the neck and lower trunk was compared to volunteer occupants in six different load cases with lane change, braking, and combined manoeuvres using standard and prepretensioned seat belts. Seven different muscle controllers, using two different muscle activation strategies based either on head and torso displacements or muscle length, and one with the controller turned off have been compared to volunteer kinematics. Cross-correlation analysis with CORA was used to evaluate the model biofidelity. The results show an improvement in CORA scores when using active muscles, compared to the model with muscle activity turned off, for one load case and similar CORA scores between the models for five load cases. CORA scores ranged from 0.78 to 0.88 for the active models and 0.70 to 0.82 from the model with muscles turned off. The active model gave a kinematic response with good biofidelity in lane change with braking, pure braking, and lane change with pre-pretensioned seat belt, but the biofidelity of the model was rated as fair in lane change with standard seat belt