Pelvis and femur geometry: Relationships with impact characteristics during sideways falls on the hip

Femur geometry and body composition influence femoral neck stresses: A combined fall simulation and beam modelling approach

Metrics of femur geometry and body composition have been linked to clinical hip fracture risk. Mechanistic explanations for these relationships have generally focused on femur strength; however, impact loading also modulates fracture risk. We evaluated the potential effects of femur geometry and body composition on femoral neck stresses during lateral impacts. Fifteen female volunteers completed low-energy sideways falls on to the hip. Additionally, participants completed ultrasound and dual-energy x-ray absorptiometry imaging to characterize trochanteric soft tissue thickness (TSTT) over the hip and six metrics of femur geometry, respectively. Subject-specific beam models were developed and utilized to calculate peak femoral neck stress (σ_Neck), utilizing experimental impact dynamics. Except for femoral neck axis length, all metrics of femur geometry were positively correlated with σ_Neck (all p < 0.05). Larger/more prominent proximal femurs were associated with increased force over the proximal femur, whereas a wider neck-shaft angle was associated with greater stress generation independent of force (all p < 0.05). Body mass index (BMI) and TSTT were negatively correlated with σ_Neck (both p < 0.05). Despite strong correlations, these metrics of body composition appear to influence femoral neck stresses through different mechanisms. Increased TSTT was associated with reduced force over the proximal femur, whereas increased BMI was associated with greater resistance to stress generation (both p < 0.05). This study provided novel insights into the mechanistic pathways through which femur geometry and body composition may modulate hip fracture risk. Our findings complement clinical findings and provide one possible explanation for incongruities in the clinical fracture risk and femur strength literature.

Factors that influence the distribution of impact force relative to the proximal femur during lateral falls

In-vivo fall simulations generally evaluate hip fracture risk through differences in impact force magnitude; however, the distribution of force over the hip likely modulates loading and subsequent injury risk of the underlying femur. The current study characterized impact force distribution over the hip during falls, and the influence of biological sex and trochanteric soft tissue thickness (TSTT). Forty young adults completed fall simulation protocols (FSP) including highly controlled vertical pelvis and more dynamic kneeling and squat releases. At the instant of peak force, percentage of impact force applied in a circular region (r = 5 cm) centered over the greater trochanter (F_GT%) was determined to characterize force localization. To assess the need for anatomically aligned pressure analysis, this process was repeated utilizing peak pressure location as a surrogate for the greater trochanter (F_PP%). F_GT% was 10.8 and 21.9% greater in pelvis release than kneeling and squat releases respectively. F_GT% was 19.1 and 30.4% greater in males and low-TSTT individuals compared to females and high-TSTT individuals. TSTT explained the most variance (43.7-55.3%) in F_GT% across all protocols, while sex explained additional variance (5.3-19.0%) during dynamic releases. In all FSP, TSTT-groups and sexes, average peak pressure location was posterior and distal to the GT. F_PP% overestimated F_GT% by an average of 15.7%, highlighting the need for anatomically aligned pressure analysis. This overestimation was FSP and sex dependent, minimized during pelvis release and in males. The data have important implications from clinical and methodological perspectives, and for implementation in tissue-level computational models.

Test systems for the biomechanical evaluation of hip protectors: a systematic review

Various mechanical and biomechanical test systems to evaluate the effectiveness of hip protectors designed to prevent hip fracture as a result of falls were examined in this review. The articles considered were selected systematically. The effect of differences in design criteria was demonstrated, and it was observed that the impact energy employed during testing dramatically affects the performance of the hip protector. Over the past three decades, researchers have continuously experimented with various systems to determine the efficacy of various hip protectors. The primary aim has been to make informed decisions in optimizing hip protector design. This article provides a systematic review of various test systems employed in the determination of the biomechanical efficacy of hip protectors. A systematic literature search was carried out, and 28 relevant articles were included to demonstrate the effect of test systems in the evaluation of the biomechanical effectiveness of hip protectors. Methodological studies illustrated the appropriate use of impact testing systems for the simulation of hip anatomy and fall dynamics in evaluating the effectiveness of hip protectors in preventing a hip fracture. This systematic review has demonstrated the effect of the variability of test systems on the evaluation of impact attenuation by various hip protectors. The lack of standardized test systems accounts for the inconsistencies in the test results of the efficacy of hip protectors. This has been a major challenge in the efforts of researchers to optimize the interventions. The standardization of test systems may require needed improvements immediately as opposed to the development of new interventions in order to ensure that only hip protectors with adequately proven efficacies are deployed for clinical trials or for the protection of the hips of vulnerable individuals from sideways impact.