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Levine I, Pretty SP, Mourtzakis M, Laing AC. Force magnitude and distribution during impacts to the hip are affected differentially by body size and body composition. J Biomech 2024; 172:112213. [PMID: 38968649 DOI: 10.1016/j.jbiomech.2024.112213] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2024] [Revised: 06/07/2024] [Accepted: 06/27/2024] [Indexed: 07/07/2024]
Abstract
Hip fractures are a severe health concern among older adults. While anthropometric factors have been shown to influence hip fracture risk, the low fidelity of common body composition metrics (e.g. body mass index) reduces our ability to infer underlying mechanisms. While simulation approaches can be used to explore how body composition influences impact dynamics, there is value in experimental data with human volunteers to support the advancement of computational modeling efforts. Accordingly, the goal of this study was to use a novel combination of subject-specific clinical imaging and laboratory-based impact paradigms to assess potential relationships between high-fidelity body composition and impact dynamics metrics (including load magnitude and distribution and pelvis deflection) during sideways falls on the hip in human volunteers. Nineteen females (<35 years) participated. Body composition was assessed via DXA and ultrasound. Participants underwent low-energy (but clinically relevant) sideways falls on the hip during which impact kinetics (total peak force, contract area, peak pressure) and pelvis deformation were measured. Pearson correlations assessed potential relationships between body composition and impact characteristics. Peak force was more strongly correlated with total mass (r = 0.712) and lean mass indices (r = 0.510-0.713) than fat mass indices (r = 0.401-0.592). Peak deflection was positively correlated with indices of adiposity (all r > 0.7), but not of lean mass. Contact area and peak pressure were positively and negatively associated, respectively, with indices of adiposity (all r > 0.49). Trochanteric soft tissue thickness predicted 59 % of the variance in both variables, and was the single strongest correlate with peak pressure. In five-of-eight comparisons, hip-local (vs. whole body) anthropometrics were more highly associated with impact dynamics. In summary, fall-related impact dynamics were strongly associated with body composition, providing support for subject-specific lateral pelvis load prediction models that incorporate soft tissue characteristics. Integrating soft and skeletal tissue properties may have important implications for improving the biomechanical effectiveness of engineering-based protective products.
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Affiliation(s)
- Iris Levine
- Department of Kinesiology and Health Sciences, University of Waterloo, 200 University Ave West, Waterloo, Ontario, Canada; The Kite Research Institute, Toronto Rehabilitation Institute-UHN, 5500 University Ave, Toronto, ON M5G 2A2, Canada
| | - Steven P Pretty
- Department of Kinesiology and Health Sciences, University of Waterloo, 200 University Ave West, Waterloo, Ontario, Canada
| | - Marina Mourtzakis
- Department of Kinesiology and Health Sciences, University of Waterloo, 200 University Ave West, Waterloo, Ontario, Canada
| | - Andrew C Laing
- Department of Kinesiology and Health Sciences, University of Waterloo, 200 University Ave West, Waterloo, Ontario, Canada.
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Effects of hip muscle activation on the stiffness and energy absorption of the trochanteric soft tissue during impact in sideways falls. J Mech Behav Biomed Mater 2023; 138:105622. [PMID: 36538838 DOI: 10.1016/j.jmbbm.2022.105622] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2022] [Revised: 12/06/2022] [Accepted: 12/11/2022] [Indexed: 12/23/2022]
Abstract
The trochanteric soft tissue attenuates impact force or absorbs impact energy during a fall on the hip (thereby helps to reduce a risk of hip fracture). While the benefits should be affected by contractions of muscles spanning the hip joint, no information is available to date. We examined how the stiffness (force attenuation capacity) and energy absorption of the trochanteric soft tissue were affected by hip muscle activation during a fall. Thirteen healthy young individuals (5 males, 8 females) participated in the pelvis release experiment. Falling trials were acquired with three muscle contraction conditions: 0-20% ("relaxed"), 20-50% ("moderate"), and 60-100% ("maximal") of the maximal voluntary isometric contraction of the gluteus medius muscle. During trials, we measured real-time force and deformation behaviour of the trochanteric soft tissue. Outcome variables included the stiffness and energy absorption of the soft tissue. The stiffness and energy absorption ranged from 56.1 to 446.9 kN/m, and from 0.15 to 2.26 J, respectively. The stiffness value increased with muscle contraction, and 59% greater in "maximal" than "relaxed" condition (232.2 (SD = 121.4) versus 146.1 (SD = 49.9)). However, energy absorption decreased with muscle contraction, and 58.9% greater in "relaxed" than "maximal" condition (0.89 (SD = 0.63) versus 0.56 (SD = 0.41)). Our results provide insights on biomechanics of the trochanteric soft tissue ("natural" padding device) during impact stage of a fall, suggesting that soft tissues' protective benefits are largely affected by the level of muscle contraction.
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Femur geometry and body composition influence femoral neck stresses: A combined fall simulation and beam modelling approach. J Biomech 2022; 141:111192. [PMID: 35764013 DOI: 10.1016/j.jbiomech.2022.111192] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2021] [Revised: 06/08/2022] [Accepted: 06/08/2022] [Indexed: 11/23/2022]
Abstract
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 (σNeck), utilizing experimental impact dynamics. Except for femoral neck axis length, all metrics of femur geometry were positively correlated with σNeck (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 σNeck (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.
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The Effects of Body Position on Trochanteric Soft Tissue Thickness-Implications for Predictions of Impact Force and Hip Fracture Risk During Lateral Falls. J Appl Biomech 2021; 37:556-564. [PMID: 34784585 DOI: 10.1123/jab.2020-0156] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2020] [Revised: 01/28/2021] [Accepted: 09/16/2021] [Indexed: 11/18/2022]
Abstract
Trochanteric soft tissue thickness (TSTT) is a protective factor against fall-related hip fractures. This study's objectives were to determine: (1) the influence of body posture on TSTT and (2) the downstream effects of TSTT on biomechanical model predictions of fall-related impact force (Ffemur) and hip fracture factor of risk. Ultrasound was used to measure TSTT in 45 community-dwelling older adults in standing, supine, and side-lying positions with hip rotation angles of -25°, 0°, and 25°. Supine TSTT (mean [SD] = 5.57 [2.8] cm) was 29% and 69% greater than in standing and side-lying positions, respectively. The Ffemur based on supine TSTT (3380 [2017] N) was 19% lower than the standing position (4173 [1764] N) and 31% lower than the side-lying position (4908 [1524] N). As factor of risk was directly influenced by Ffemur, the relative effects on fracture risk were similar. While less pronounced (<10%), the effects of hip rotation angle were consistent across TSTT, Ffemur, and factor of risk. Based on the sensitivity of impact models to TSTT, these results highlight the need for a standardized TSTT measurement approach. In addition, the consistent influence of hip rotation on TSTT (and downstream model predictions) support its importance as a factor that may influence fall-related hip fracture risk.
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Pretty SP, Levine IC, Laing AC. Factors that influence the distribution of impact force relative to the proximal femur during lateral falls. J Biomech 2021; 127:110679. [PMID: 34418865 DOI: 10.1016/j.jbiomech.2021.110679] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2021] [Revised: 07/27/2021] [Accepted: 08/02/2021] [Indexed: 11/29/2022]
Abstract
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 (FGT%) 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 (FPP%). FGT% was 10.8 and 21.9% greater in pelvis release than kneeling and squat releases respectively. FGT% 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 FGT% 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. FPP% overestimated FGT% 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.
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Affiliation(s)
- Steven P Pretty
- Injury Biomechanics and Aging Laboratory, Department of Kinesiology, University of Waterloo, 200 University Ave West, Waterloo, Ontario N2L 3G1, Canada
| | - Iris C Levine
- KITE-Toronto Rehabilitation Institute, University Health Network, 550 University Ave, Toronto, ON M5G 2A2, Canada
| | - Andrew C Laing
- Injury Biomechanics and Aging Laboratory, Department of Kinesiology, University of Waterloo, 200 University Ave West, Waterloo, Ontario N2L 3G1, Canada; Schlegel-UW Research Institute for Aging, 250 Laurelwood Drive, Waterloo, Ontario, N2J 0E2, Canada.
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Pretty SP, Levine IC, Laing AC. Anatomically Aligned Loading During Falls: Influence of Fall Protocol, Sex and Trochanteric Soft Tissue Thickness. Ann Biomed Eng 2021; 49:3267-3279. [PMID: 34494215 DOI: 10.1007/s10439-021-02852-6] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2021] [Accepted: 08/07/2021] [Indexed: 11/24/2022]
Abstract
Fall simulations provide insight into skin-surface impact dynamics but have focused on vertical force magnitude. Loading direction and location (relative to the femur) likely influence stress generation. The current study characterized peak impact vector magnitude, orientation, and center of pressure over the femur during falls, and the influence of biological sex and trochanteric soft tissue thickness (TSTT). Forty young adults completed fall simulations including a vertical pelvis release, as well as kneeling and squat releases, which incorporate lateral/rotational motion. Force magnitude and direction varied substantially across fall simulations. Kneeling and squat releases elicited 57.4 and 38.8% greater force than pelvis release respectively, with differences accentuated in males. With respect to the femoral shaft, kneeling release had the most medially and squat release the most distally directed loading vectors. Across all fall simulations, sex and TSTT influenced force magnitude and center of pressure. Force was 28.0% lower in females and was applied more distally than in males. Low-TSTT participants had 16.8% lower force, applied closer to the greater trochanter than high-TSTT participants. Observed differences in skin-surface impact dynamics likely interact with underlying femur morphology to influence stress generation. These data should serve as inputs to tissue-level computational models assessing fracture risk.
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Affiliation(s)
- Steven P Pretty
- Injury Biomechanics and Aging Laboratory, Department of Kinesiology, Faculty of Applied Health Sciences, University of Waterloo, 200 University Ave West, Waterloo, ON, N2L 3G1, Canada
| | - Iris C Levine
- KITE Research Institute, Toronto Rehabilitation Institute - University Health Network, 13-000, 550 University Avenue, Toronto, ON, M5G 2A2, Canada
| | - Andrew C Laing
- Injury Biomechanics and Aging Laboratory, Department of Kinesiology, Faculty of Applied Health Sciences, University of Waterloo, 200 University Ave West, Waterloo, ON, N2L 3G1, Canada.
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Modig K, Erdefelt A, Mellner C, Cederholm T, Talbäck M, Hedström M. "Obesity Paradox" Holds True for Patients with Hip Fracture: A Registry-Based Cohort Study. J Bone Joint Surg Am 2019; 101:888-895. [PMID: 31094980 DOI: 10.2106/jbjs.18.01249] [Citation(s) in RCA: 51] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
BACKGROUND Hip fractures are associated with high mortality and reduced quality of life. Studies have reported a high body mass index (BMI) as being positively associated with survival when linked to old age and some chronic diseases. This phenomenon is called the "obesity paradox." The association between BMI and survival after hip fracture has not been thoroughly studied in large samples, nor has to what extent the association is altered by comorbidities, sex, and age. The objective of this study was to investigate the association of BMI with survival after hip fracture and with the probability of returning to living at home after hip fracture. METHODS This cohort study was based on data from a prospectively maintained national registry of patients with hip fracture. A total of 17,756 patients ≥65 years of age who were treated for hip fracture during the period of 2013 to 2016, and followed until the end of 2017, were included. BMI was clinically assessed at hospital admission, comorbidity was measured with the American Society of Anesthesiologists (ASA) score, and the date of death was retrieved from a national database. Self-reported data on living arrangements were assessed on admission and 4 months after fracture. Multivariable regression models were used to estimate the associations. RESULTS Despite ASA scores being similar among all BMI groups, obese patients had the highest 1-year survival and patients with a BMI of <22 kg/m had the lowest. Adjustment for potential confounders strengthened the associations. For the chance of returning to living at home, no advantage was seen for obese patients, but patients with a BMI of <22 kg/m had clearly worse odds compared with patients who were of normal weight, overweight, or obese. CONCLUSIONS The obesity paradox appears to be true for hip fracture patients aged 65 and older. Attention should be given to patients with malnutrition and underweight status rather than to those with overweight status or obesity when developing the orthogeriatric care. LEVEL OF EVIDENCE Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.
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Affiliation(s)
- Karin Modig
- Unit of Epidemiology, Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden
| | | | - Carl Mellner
- Department of Surgical and Perioperative Sciences, Umeå University, Umeå, Sweden
| | - Tommy Cederholm
- Karolinska University Hospital, Stockholm, Sweden.,Department of Public Health and Caring Sciences, Clinical Nutrition and Metabolism, Uppsala University, Uppsala, Sweden.,Department of Geriatrics, Uppsala University Hospital, Uppsala, Sweden
| | - Mats Talbäck
- Unit of Epidemiology, Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden
| | - Margareta Hedström
- Karolinska University Hospital, Stockholm, Sweden.,Department of Clinical Science, Intervention and Technology, Karolinska Institutet, Stockholm, Sweden
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Pelvis and femur geometry: Relationships with impact characteristics during sideways falls on the hip. J Biomech 2018; 80:72-78. [PMID: 30201251 DOI: 10.1016/j.jbiomech.2018.08.029] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2018] [Revised: 08/21/2018] [Accepted: 08/22/2018] [Indexed: 11/23/2022]
Abstract
While metrics of pelvis and femur geometry have been demonstrated to influence hip fracture risk, attempts at linking geometry to underlying mechanisms have focused on fracture strength. We investigated the potential effects of femur and pelvis geometry on applied loads during lateral falls on the hip. Fifteen female volunteers underwent DXA imaging to characterize two pelvis and six femur geometric features. Additionally, participants completed low-energy sideways falls on the hip; peak impact force and pressure, contact area, and moment of force applied to the proximal femur were extracted. No geometric feature was significantly associated with peak impact force. Peak moment of force was significantly associated with femur moment arm (p = 0.005). Peak pressure was positively correlated with pelvis width and femur moment arm (p < 0.05), while contact area was negatively correlated with metrics of pelvis width and femur neck length (p < 0.05). This is the first study to link experimental measures of impact loads during sideways falls with image-based skeletal geometry from human volunteers. The results suggest that while skeletal geometry has limited effects on overall peak impact force during sideways falls, it does influence how impact loads are distributed at the skin surface, in addition to the bending moment applied to the proximal femur. These findings have implications for the design of protective interventions (e.g. wearable hip protectors), and for models of fall-related lateral impacts that could incorporate the relationships between skeletal geometry, external load magnitude/distribution, and tissue-level femur loads.
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