Hip Force Research Articles

Mechanical Design and Finite element Analysis for Acetabular cup

Hip replacements typically consist of a four-part piece. Our research will focus primarily on the acetabular component. Several different types of materials can be used when creating a hip replacement implant ranging from plastic to titanium. Different materials are used to accommodate for allergic reactions or circumventing potential health risks. Aside from the material, the size of the components plays a factor in terms of durability; a larger diameter head might avoid dislodgement though it could increase wear and tear on the stems through constant friction. A patient’s force applied to the hip replacement is usually measured through a number of physical assessments. Finite element analysis (FEA), a computer-based method of data observation, allows for us to accurately simulate hip forces and their impact on the hip replacements. Through this, it becomes easier to predict and calculate the performance of specific designs. Generative systems can also be used to support performance analysis and optimization through assessing a multitude of cases, many of which apply in real-world scenarios. By applying both systems, we designed and modeled an acetabular cup that when measured decreased the mass from 129 grams initially down to 52 grams, a 60% decrease in total mass. Furthermore, the design we created lessened the trauma on the piece through distributing force across the entirety of the piece rather than specific segments only. This shows an increased durability and life expectancy when compared to usual acetabular cups.

Systematic review of pre-operative planning modalities for correction of acetabular dysplasia.

Acetabular dysplasia, related to developmental dysplasia of the hip, causes the abnormal distribution of hip joint forces. Surgical correction of acetabular dysplasia involves repositioning the acetabulum to achieve improved coverage of the femoral head. However, ideal placement of the acetabular fragment is challenging, and has led to an increased interest in pre-operative planning modalities. In this study, we used the PubMed and EBSCO host databases to systematically review all the modalities for pre-operative planning of acetabular dysplasia proposed in the current literature. We included all case-series, English, full-text manuscripts pertaining to pre-operative planning for congenital acetabular dysplasia. Exclusion criteria included: total hip arthroplasty (THA) planning, patient population mean age >35, and double/single case studies. A total of 12 manuscripts met our criteria for a total of 186 hips. Pre-operative planning modalities described were: Amira (Thermo Fischer Scientific; Waltham, MA, USA) 12.9%, OrthoMap (Stryker Orthopaedics; Mahwah, NJ, USA) 36.5%, Amira + Biomechanical Guidance System 5.9%, Mills et al. method 16.1%, Klaue et al. method 16.1%, Armand et al. method 6.5%, Tsumura et al. method 3.8% and Morrita et al. method 2.2%. As a whole, there was a notable lack of prospective studies demonstrating these modalities’ efficacy, with small sample sizes and lack of commercial availability diminishing their applicability. Future studies are needed to comprehensively compare computer-assisted planning with traditional radiographic assessment of ideal osteotomy orientation.

Hip stress distribution - Predictor of dislocation in hip arthroplasties. A retrospective study of 149 arthroplasties.

Dislocation after hip arthroplasty is still a major concern. Recent study of the volumetric wear of the cup has suggested that stresses studied in a one-legged stance model could predispose arthroplasty dislocation. The aim of this work was to study whether biomechanical parameters of contact stress distribution in total hip arthroplasty during a neutral hip position can predict a higher possibility of the arthroplasty dislocating. Biomechanical parameters were determined using 3-dimensional mathematical models of the one-legged stance within the HIPSTRESS method. Geometrical parameters were measured from standard anteroposterior X-ray images of the pelvis and proximal femora. Fifty-five patients subjected to total hip arthroplasty that later suffered dislocation of the head and, for comparison, ninety-four total hip arthroplasties that were functional at least 10 years after the implantation, were included in the study. Arthroplasties that suffered dislocation had on average a 6% higher resultant hip force than the control group (p = 0.004), 11% higher peak stress on the load-bearing area (p = 0.001) and a 50% more laterally positioned stress pole (p = 0.026), all parameters being less favorable in the group of unstable arthroplasties. There was no statistically significant difference in the gradient index or in the functional angle of the weight bearing. Our study showed that arthroplasties that show a tendency to push the head out of the cup in the representative body position—the one-legged stance—are prone to dislocation. An unfavorable resultant hip force, peak stress on the load bearing and laterally positioned stress pole are predictors of arthroplasty dislocation.

Predicting growth plate orientation with altered hip loading: potential cause of cam morphology.

Proximal femoral deformities can result from altered hip joint loading patterns during growth. The growth plate hyaline cartilage has low resistance to shear stress. Therefore, we hypothesized that the growth plate orients in a direction which minimizes the shear stress on its surface. A finite element model of the proximal femur was generated with a simplified flat growth plate. Hip joint forces were estimated for standing upright and standing in hip flexion. We also parametrically studied the effects of posteriorly and laterally directed loads. An algorithm was developed to predict the shape of the femoral growth plate in a plane of minimum shear (along the principal stress vectors). To characterize and compare the growth plate shapes, we represented the distance from the growth plate to a reference plane as a two-dimensional contour plot, providing information of shape and orientation across the entire surface. We also assessed the clinical measures of growth plate shape to compare our predicted growth plates with previous clinical studies data. The shape of the growth plate predicted for an upright standing load correlated closely with morphological properties of the growth plane of a typically developing child. The shape of the growth plate predicted for femoral hip flexion force was similar to the growth plate in subjects with cam morphology, a hip shape that has documented growth plate changes. The model proposed here allows for investigation of the relation between joint forces and growth plate shape, which will help predict the development of bony deformities.

Human Knee Inverse Dynamics Model of Vertical Jump Exercise

Abstract This work deals with the dynamics of the human knee during vertical jump exercise. The focus is on the joint forces necessary to produce the jump and to dissipate energy during landing. A two-dimensional (2D) sagittal plane, inverse dynamics human leg model is developed. This model uses data from a motion capture system and force plates in order to predict knee and hip joint forces during the vertical jump exercise. The model consists of three bony structures femur, tibia, and patella, ligament structures to include both cruciate and collateral ligaments, and knee joint muscles. The inverse dynamics model is solved using optimization in order to predict joint forces during this exercise. matlab software package is used for the optimization computations. Results are compared with data available in the literature. This work provides insight regarding contact forces and ligaments forces, muscle forces, and knee and hip contact forces in the vertical jump exercise.

Joint Contact Forces with Changes in Running Stride Length and Midsole Stiffness

The purpose of this study was to determine if lower extremity joint loading was influenced by stride length or shoe midsole cushioning. Ten subjects completed 10 trials of overground running at an average speed of 4.43 m/s in each of three conditions: normal running, running with a stride length (SL) reduced by 10% of normal, and running with a cushioned midsole stiffness (i.e., mechanical impact reduction of 13.7–10.9 g). Reaction forces calculated from inverse dynamics were summed with muscle forces estimated from a musculoskeletal model using static optimization to obtain joint contact forces at the hip, knee and ankle joints. Peak components of the contact forces [axial, anterior–posterior, and medial–lateral (ML)] were examined using parametric statistics (α = 0.05). Reducing stride length resulted in significant decreases in absolute peak ankle contact forces in the axial direction (normal: − 14.5 ± 1.5 BW; reduced SL: − 14.0 ± 1.6 BW) and the ML direction (normal: 0.67 ± 0.23 BW; reduced SL: 0.61 ± 0.21 BW). Reducing stride length also reduced the peak absolute axial forces at the knee (normal: − 10.6 ± 1.3 BW; reduced SL: − 9.8 ± 1.2 BW) and the hip (normal: − 7.26 ± 2.24 BW; reduced SL: − 6.75 ± 2.10 BW). The cushioned shoe did not statistically reduce the peak absolute contact forces from the normal stride condition at any of the joints. Post hoc stress analysis suggested that the observed changes in anterior hip force would increase stress more than any of the other statistically significant results. Reductions in stride length appear to decrease some joint contact variables but cushioning in the heel region of the shoe does not.

Secondary hip dysplasia increases risk for early coxarthritis after Legg-Calve-Perthes disease. A study of 255 hips

The biomechanical parameters of the hip joint articular surface were analysed in 141 adult hips after Legg-Calve Perthes Disease, and 114 contralateral unaffected hips (controls), by using HIPSTRESS mathematical models. Geometrical parameters, assessed from anteroposterior and axial radiograms, were used as input to models for resultant hip force and contact hip stress. Results confirm previous indications that head enlargement after the Legg-Calve-Perthes Disease compensates the values of hip stress. Furthermore, it was found that an increased risk for coxarthritis development after the disease is secondary to concomitant hip dysplasia, with considerable and statistically significantly lower centre-edge angle and unfavourable distribution of stress.

Admittance Shaping-Based Assistive Control of SEA-Driven Robotic Hip Exoskeleton

This paper presents an admittance shaping-based assistive control for a series elastic actuator (SEA) driven robotic hip exoskeleton that can assist individuals with hip muscle weakness to restore normative mobility. The motivation for this paper is to develop a unified controller framework for designing an SEA-driven hip exoskeleton to assist walking and enhance gait stability. The controller design aims to modify the dynamic response of a coupled human-exoskeleton system, i.e., the relationship between the net muscle torque exerted by the human and the resulting angular motion, to ensure strong human-exoskeleton synergy to provide the effective assistance. This controller was preliminarily evaluated on a healthy subject walking on a treadmill at a speed of 1.0 m/s. Results showed that the exoskeleton can effectively provide walking assistance to the human by reducing electromyography (EMG) activation and increasing agility during locomotion. Specifically, EMG was reduced 3.3%–38% when walking with the hip exoskeleton when compared to walking without wearing the hip exoskeleton. In addition, timing of the maximum hip flexion angle increased by 10% (moved from 42% to 32% of gait cycle) when the controller had an inertia compensation of 60%. The faster onset of the maximum flexion angle will allow the wearer to more quickly generate reactive steps when trying to avoid a fall. Future work will aim to apply the hip exoskeleton to persons having hip muscle weakness or other musculoskeletal impairment, to restore hip movement and enough hip force to walk normally.

The effect of arthroscopic capsulotomy and repair on native resting hip joint forces using a non-destructive extra-articular method

AbstractPrevious methods for measuring intra-articular forces require significant soft tissue dissection and intra-articular insertion of sensory instruments. This study demonstrates a minimally invasive method of measuring native resting hip joint force without disrupting the soft tissue envelope. This method is then utilized to determine the effect of capsulotomy and repair on these forces. Twenty fresh-frozen human cadaver hemipelves were percutaneously instrumented with an iliac crest locking plate and retrograde femoral nail to allow for testing using a distracting force. Force–displacement curves were generated in the native state, and after joint venting, an anterior hip approach, capsulotomy, capsular repair and soft tissue dissections. Mean native resting hip joint force was 110.5 N (SD 54.3 N). Capsular venting resulted in a significant decrease in hip joint force compared with the native state (100.2 N, SD 45.2 N, P = 0.026). A further decrease in hip joint force was observed with a T-capsulotomy (79.9 N, SD 40.1 N, P < 0.001 compared with anterior hip approach), with restoration of these forces after capsular repair (84.8 N, SD 40.5, P = 0.014 versus T-capsulotomy and P = 0.67 versus anterior hip approach). Soft tissue dissection resulted in a large decrease in hip joint force compared with the hip’s native state (59.7 N, SD 28.4 N, P = 0.002). Taken together, the findings suggest that this method is effective in measuring hip joint force and may be more accurate than those requiring significant soft tissue dissection. Furthermore, the data suggest that capsular repair likely plays an important role in the restoration of biomechanical forces in the hip after capsulotomy.

Does Wearable Crutch Walking Excessively Load the Hip Joint?

PURPOSE: As an alternative to using traditional axillary crutches for non-weightbearing, the use of a wearable crutch has been associated with better functional outcomes. However, hip and back pain have been reported as side effects. This may be due to the reduced ability of the lower extremity to attenuate ground reaction forces. The primary objective was to compare compressive forces at the hip between wearable crutch walking, normal walking and axillary crutch walking. It was hypothesized that hip forces would be higher with wearable crutch walking compared with normal walking and axillary crutch walking. METHODS: Three-dimensional kinematics and ground reaction forces were measured in 12 healthy subjects (11 men, 1 woman, age 36±10 yr) during normal gait, axillary crutch ambulation and wearable crutch walking (iWalk 2.0). Hip and trunk range of motion, as well as peak vGRF and peak hip and low back compressive force during the stance phase, were compared for the three conditions using repeated-measures ANOVA. RESULTS: Gait speed while wearing the wearable crutch was reduced 44% compared to normal gait and 33% compared to crutch ambulation (P < 0.001). Frontal and sagittal plane hip range of motion were both significantly reduced during both crutch conditions compared to normal gait (P<0.001). Trunk range of motion in both planes was greatest during wearable crutch walking compared to both normal gait and crutch ambulation (P<0.001). Peak vGRF while wearing the hands-free crutch was 12% lower than normal gait (P<0.001) and 30% lower than crutch ambulation (P<0.001). Peak compressive hip force during wearable crutch walking was 11% lower than during normal walking (P = 0.026) and 30% lower than during axillary crutch walking (P<0.001). Low back compressive force during wearable crutch walking was 18% higher than during normal walking (P=0.03) but not different than during axillary crutch walking (1.4 % difference P>0.05) CONCLUSIONS: Despite a reduction in the shock-absorbing ability of the lower extremity, vGRF and compressive hip forces were not increased during wearable crutch walking. Although low back compressive force did increase with this device, it did not exceed the forces during axillary crutch walking. Therefore, the wearable crutch seems to be safe for patients who are required to be non-weightbearing.

The sidestep cutting manoeuvre requires exertion of lumbosacral lateral flexion torque to avoid excessive pelvic obliquity

ABSTRACT During sidestep cutting, the pelvis is supported only on one side; this affects the athlete’s posture. This study investigated the mechanism to avoid excessive pelvic obliquity during sidestep cutting. Ten physically active men performed sidestep cutting with maximal effort, and we captured the kinematics and kinetics with force platforms and an eight-camera motion capture system. Our results indicated that the stance hip exerted little abduction torque; however, lumbosacral lateral flexion torque was exerted towards the free-leg side (peak value: 3.39 ± 0.91 N m/kg). Although bilateral hip joint forces acted to drop the free-leg side of the pelvis, the net torque around pelvic elevation/drop axis was nearly zero during the entire stance phase and the change in the angular momentum around the pelvic elevation/drop axis from touchdown to toe-off was negligible (−0.004 ± 0.003 N m s/kg). The integrated components of lateral flexor for elevating the free-leg side of the pelvis (0.220 ± 0.072 N m s/kg) were significantly larger than any other integrated components, which were all negligible (<0.010 N m s/kg). Thus, sidestep cutting requires the lumbosacral lateral flexion torque exertion to neutralise the passive action that drops the free-leg side of the pelvis.

High Hip Center Reduces the Dynamic Hip Range of Motion and Increases the Hip Load: A Gait Analysis Study in Hip Arthroplasty Patients With Unilateral Developmental Dysplasia

BackgroundLong-term favorable clinical outcomes of anatomical or high hip center techniques in total hip arthroplasty (THA) are reported in patients with developmental dysplasia of the hip (DDH). However, there is little information about the effect of the hip center location on gait characteristics. The purpose of this study was to compare these surgical techniques with gait analysis, analyze the effect of the hip rotation center location on gait parameters, and discuss the possible problems that may arise. MethodsA total of 40 patients who underwent THA due to unilateral coxarthrosis secondary to Crowe type III-IV DDH and completed 5 years of follow-up were included in the study. Group 1 included 20 patients who underwent anatomical hip center reconstruction, while group 2 included 20 patients who underwent high hip center reconstruction. Gait analysis was performed, and the groups were compared according to the gait characteristics. ResultsThe mean temporospatial values were similar between the groups. The extension of the operated side was significantly lower in group 2 (−9.11 ± 8.92) than in group 1 (−1.87 ± 11.51) (P = .04). The mean longitudinal hip joint force was found to be significantly higher in group 2 (8.92 N/kg ± 0.54) than in group 1 (8.16 N/kg ± 0.66) (P = .04). The high hip center technique has been shown to increase the load on the hip and restrict the dynamic range of motion. ConclusionThe high hip center technique can decrease the survival of the implant and increase the fall risk as it increases the load on the hip and reduces the dynamic range of motion. The hip center should be reconstructed anatomically when possible in DDH patients who undergo unilateral THA.

Biomechanical Analysis Using FEA and Experiments of Metal Plate and Bone Strut Repair of a Femur Midshaft Segmental Defect.

This investigation assessed the biomechanical performance of the metal plate and bone strut technique for fixing recalcitrant nonunions of femur midshaft segmental defects, which has not been systematically done before. A finite element (FE) model was developed and then validated by experiments with the femur in 15 deg of adduction at a subclinical hip force of 1 kN. Then, FE analysis was done with the femur in 15 deg of adduction at a hip force of 3 kN representing about 4 x body weight for a 75 kg person to examine clinically relevant cases, such as an intact femur plus 8 different combinations of a lateral metal plate of fixed length, a medial bone strut of varying length, and varying numbers and locations of screws to secure the plate and strut around a midshaft defect. Using the traditional “high stiffness” femur-implant construct criterion, the repair technique using both a lateral plate and a medial strut fixed with the maximum possible number of screws would be the most desirable since it had the highest stiffness (1948 N/mm); moreover, this produced a peak femur cortical Von Mises stress (92 MPa) which was below the ultimate tensile strength of cortical bone. Conversely, using the more modern “low stiffness” femur-implant construct criterion, the repair technique using only a lateral plate but no medial strut provided the lowest stiffness (606 N/mm), which could potentially permit more in-line interfragmentary motion (i.e., perpendicular to the fracture gap, but in the direction of the femur shaft long axis) to enhance callus formation for secondary-type fracture healing; however, this also generated a peak femur cortical Von Mises stress (171 MPa) which was above the ultimate tensile strength of cortical bone.

A subject-specific integrative biomechanical framework of the pelvis for gait analysis.

Analysis of the human locomotor system using rigid-body musculoskeletal models has increased in the biomechanical community with the objective of studying muscle activations of different movements. Simultaneously, the finite element method has emerged as a complementary approach for analyzing the mechanical behavior of tissues. This study presents an integrative biomechanical framework for gait analysis by linking a musculoskeletal model and a subject-specific finite element model of the pelvis. To investigate its performance, a convergence study was performed and its sensitivity to the use of non-subject-specific material properties was studied. The total hip joint force estimated by the rigid musculoskeletal model and by the finite element model showed good agreement, suggesting that the integrative approach estimates adequately (in shape and magnitude) the hip total contact force. Previous studies found movements of up to 1.4 mm in the anterior-posterior direction, for single leg stance. These results are comparable with the displacement values found in this study: 0-0.5 mm in the sagittal axis. Maximum von Mises stress values of approximately 17 MPa were found in the pelvic bone. Comparing this results with a previous study of our group, the new findings show that the introduction of muscular boundary conditions and the flexion-extension movement of the hip reduce the regions of high stress and distributes more uniformly the stress across the pelvic bone. Thus, it is thought that muscle force has a relevant impact in reducing stresses in pelvic bone during walking of the finite element model proposed in this study. Future work will focus on including other deformable structures, such as the femur and the tibia, and subject-specific material properties.

Patient-specific musculoskeletal modeling of the hip joint for preoperative planning of total hip arthroplasty: A validation study based on in vivo measurements

Validation of musculoskeletal models for application in preoperative planning is still a challenging task. Ideally, the simulation results of a patient-specific musculoskeletal model are compared to corresponding in vivo measurements. Currently, the only possibility to measure in vivo joint forces is to implant an instrumented prosthesis in patients undergoing a total joint replacement. In this study, a musculoskeletal model of the AnyBody Modeling System was adapted patient-specifically and validated against the in vivo hip joint force measurements of ten subjects performing one-leg stance and level walking. The impact of four model parameters was evaluated; hip joint width, muscle strength, muscle recruitment, and type of muscle model. The smallest difference between simulated and in vivo hip joint force was achieved by using the hip joint width measured in computed tomography images, a muscle strength of 90 N/cm2, a third order polynomial muscle recruitment, and a simple muscle model. This parameter combination reached mean deviations between simulation and in vivo measurement during the peak force phase of 12% ± 14% in magnitude and 11° ± 5° in orientation for one-leg stance and 8% ± 6% in magnitude and 10° ± 5° in orientation for level walking.

Effects of barefoot and shod running on lower extremity joint loading, a musculoskeletal simulation study

The aim of the current investigation was to utilize a musculoskeletal simulation-based approach, to examine the effects of barefoot and shod running on lower extremity joint loading during the stance phase. Twelve male runners, ran over an embedded force plate at 4.0 m/s, in both barefoot and shod conditions. Kinematics of the lower extremities were collected using an eight-camera motion capture system. Lower extremity joint loading was also explored using a musculoskeletal simulation and mathematical modelling approach, and differences between footwear conditions were examined using paired samples t tests. Peak Achilles tendon force was significantly larger (P = 0.039) when running barefoot (6.85 BW) compared to shod (6.07 BW). In addition, both medial (P = 0.013) and lateral (P = 0.007) tibiofemoral instantaneous load rates were significantly larger in the barefoot (medial 289.17 BW/s and lateral 179.59 BW/s) in relation to the shod (medial 167.57 BW/s and lateral 116.40 BW/s) condition. Finally, the barefoot condition (9.70 BW) was associated with a significantly larger (P = 0.037) peak hip force compared to running shod (8.51 BW). The current investigation indicates that running barefoot may place runners at increased risk from the biomechanical factors linked to the etiology of chronic lower extremity pathologies. However, future analyses using habitual barefoot runners, are required before more definitive affirmations regarding injury predisposition can be made.

Analysis of the elastic bending characteristics of cementless short hip stems considering the valgus alignment of the prosthetic stem

BackgroundThe resultant hip force causes a varus torque which must be compensated by a shear force couple depending on the stem alignment of the prosthesis. Since the prosthesis is substantially less flexible than the bone, the interior of the femur is stiffened over the entire prosthesis length. The present study thus aims at analyzing short-stem prostheses for its elastic bending characteristics, considering inappropriate valgus alignment of the prosthetic stem. MethodsFive short stem prostheses were implanted each in synthetic femora in a standardized manner – in neutral and valgus stem alignments. Bending movements were recorded applying a tilting torque MX of ±3.5 Nm in medio-lateral direction. Variance analyses and Friedman tests were used. A P-value <.05 was considered statistically significant. FindingsBending movements b1-b6 showed significant differences (P < .05). It could be shown that different stem alignments (P < .05) and different measuring points had a highly significant influence (P < .001) on the relative movements. Compared to the AIDA®, the MiniHip™ as well as the Metha® stiffened the femur to a higher degree (P < .001). InterpretationRegarding the elastic bending behavior we see a relevant influence of the stems´ design. We conclude that the short-stem principle does not necessarily require the shortest possible prosthesis but rather a long and thin extending stem tip to optimize the lever ratios, ensuring a more physiological bending behavior of the femur. In addition, without sufficient anchoring of the prosthesis, the valgus stem alignment could favor tilting of the implant and should therefore be avoided.

Biomechanical characterization of slope walking using musculoskeletal model simulation.

Upslope and downslope walking are basic activities necessary for normal daily living in community, and they impose greater joint load on the lower extremities than during level walking. Thus, the purpose of this study was to quantify the resultant and shear forces in the hip and knee joints during slope walking. Twelve healthy volunteers were evaluated when walking under level and 10° up- and downslope conditions. Three-dimensional gait analysis was conducted using a 7-camera optoelectronic motion analysis system combined with a force plate to measure ground reactive force. Joint forces in the hip and knee joints were estimated using musculoskeletal model simulation. Results showed that the resultant hip force was increased significantly to 117.2% and 126.9%, and the resultant knee force was increased to 133.5% and 144.5% in up- and downslope walking, respectively, compared to that of level walking. Furthermore, increased shear force in the hip and knee joints was noted during both slope walking conditions. This information may be beneficial for therapists advising elderly people or patients with osteoarthrosis on an appropriate gait pattern, gait assistive devices, or orthoses according to their living environment.

Plausibility and parameter sensitivity of micro-finite element-based joint load prediction at the proximal femur

A micro-finite element-based method to estimate the bone loading history based on bone architecture was recently presented in the literature. However, a thorough investigation of the parameter sensitivity and plausibility of this method to predict joint loads is still missing. The goals of this study were (1) to analyse the parameter sensitivity of the joint load predictions at one proximal femur and (2) to assess the plausibility of the results by comparing load predictions of ten proximal femora to in vivo hip joint forces measured with instrumented prostheses (available from www.orthoload.com). Joint loads were predicted by optimally scaling the magnitude of four unit loads (inclined -20^{circ } to 100^{circ } with respect to the vertical axis) applied to micro-finite element models created from high-resolution computed tomography scans (30.3~upmu m voxel size). Parameter sensitivity analysis was performed by varying a total of nine parameters and showed that predictions of the peak load directions (range 10^{circ }–30^{circ }) are more robust than the predicted peak load magnitudes (range 2344.8–4689.5 N). Comparing the results of all ten femora with the in vivo loading data of ten subjects showed that peak loads are plausible both in terms of the load direction (in vivo: 18.2pm 2.0^{circ }, predicted: 20.0^{circ }) and magnitude (in vivo: 2707.6pm 443.3~hbox {N}, predicted: 3372.2pm 597.9~hbox {N}). Overall, this study suggests that micro-finite element-based joint load predictions are both plausible and robust in terms of the predicted peak load direction, but predicted load magnitudes should be interpreted with caution.

The Influence of Body Mass Index, Sex, & Muscle Activation on Pressure Distribution During Lateral Falls on the Hip.

Hip fracture incidence rates are influenced by body mass index (BMI) and sex, likely through mechanistic pathways that influence dynamics of the pelvis-femur system during fall-related impacts. The goal of this study was to extend our understanding of these impact dynamics by investigating the effects of BMI, sex, and local muscle activation on pressure distribution over the hip region during lateral impacts. Twenty participants underwent "pelvis-release experiments" (which simulate a lateral fall onto the hip), including muscle-'relaxed' and 'contracted' trials. Males and low-BMI individuals exhibited 44 and 55% greater peak pressure, as well as 66 and 56% lower peripheral hip force, compared to females and high-BMI individuals, respectively. Local muscle activation increased peak force by 10%, contact area by 17%, and peripheral hip force by 11% compared to relaxed trials. In summary, males and low-BMI individuals exhibited more concentrated loading over the greater trochanter. Muscle activation increased peak force, but this force was distributed over a larger area, preventing increased localized loading over the greater trochanter. These findings suggest potential value in incorporating sex, gender, and muscle activation-specific force distributions as inputs into computational tissue-level models, and have implications for the design of personalized protective devices including wearable hip protectors.