The effects of walking speed on tibiofemoral loading estimated via musculoskeletal modeling

The future of in-field sports biomechanics: wearables plus modelling compute real-time in vivo tissue loading to prevent and repair musculoskeletal injuries

This paper explores the use of biomechanics in identifying the mechanistic causes of musculoskeletal tissue injury and degeneration. It appraises how biomechanics has been used to develop training programmes aiming to maintain or recover tissue health. Tissue health depends on the functional mechanical environment experienced by tissues during daily and rehabilitation activities. These environments are the result of the interactions between tissue motion, loading, biology, and morphology. Maintaining health of and/or repairing musculoskeletal tissues requires targeting the "ideal" in vivo tissue mechanics (i.e., loading and deformation), which may be enabled by appropriate real-time biofeedback. Recent research shows that biofeedback technologies may increase their quality and effectiveness by integrating a personalised neuromusculoskeletal modelling driven by real-time motion capture and medical imaging. Model personalisation is crucial in obtaining physically and physiologically valid predictions of tissue biomechanics. Model real-time execution is crucial and achieved by code optimisation and artificial intelligence methods. Furthermore, recent work has also shown that laboratory-based motion capture biomechanical measurements and modelling can be performed outside the laboratory with wearable sensors and artificial intelligence. The next stage is to combine these technologies into well-designed easy to use products to guide training to maintain or recover tissue health in the real-world.

Hamstrings vibration reduces tibiofemoral compressive force following anterior cruciate ligament reconstruction

Individuals who have undergone anterior cruciate ligament reconstruction (ACLR) are at greater risk of developing knee osteoarthritis (OA). This elevated risk of knee OA is associated with high tibiofemoral (TF) compressive force, due to a combination of low knee flexion angles and increased co-contraction of the hamstrings and quadriceps during limb loading. Prolonged vibration of the hamstrings fatigues the intrafusal muscle fibers, which reduces autonomic reflexive excitation of the hamstrings and alleviates reciprocal inhibition to the quadriceps. The aim of this study was to examine the effect of prolonged hamstrings vibration on TF compressive force in individuals who have undergone ACL reconstruction. Fourteen participants with unilateral ACLR and 14 participants without knee injury performed a single-leg drop-land task before and after prolonged (20 min) vibration of the hamstrings. Peak TF compressive force, knee flexion angle, and hamstrings/quadriceps co-contraction were calculated during the deceleration phase of the drop-land task before and after vibration. The ACLR group experienced an 18% decrease in TF compressive force, a 32% increase in knee flexion angle, and a 38% decrease in hamstrings/quadriceps co-contraction after hamstrings vibration. There was no difference in any of the parameters in the noninjured group after vibration. These data suggest that acute prolonged hamstrings vibration has the potential to mitigate TF compressive force, which may protect the knee joint in the long term. Clinical significance: The results of this research are expected to lead to improved clinical care for ACLR patients because it holds promise for mitigating altered joint mechanics and perhaps slowing down the onset of posttraumatic knee osteoarthritis.

A framework based on subject-specific musculoskeletal models and Monte Carlo simulations to personalize muscle coordination retraining

Excessive loads at lower limb joints can lead to pain and degenerative diseases. Altering joint loads with muscle coordination retraining might help to treat or prevent clinical symptoms in a non-invasive way. Knowing how much muscle coordination retraining can reduce joint loads and which muscles have the biggest impact on joint loads is crucial for personalized gait retraining. We introduced a simulation framework to quantify the potential of muscle coordination retraining to reduce joint loads for an individuum. Furthermore, the proposed framework enables to pinpoint muscles, which alterations have the highest likelihood to reduce joint loads. Simulations were performed based on three-dimensional motion capture data of five healthy adolescents (femoral torsion 10°-29°, tibial torsion 19°-38°) and five patients with idiopathic torsional deformities at the femur and/or tibia (femoral torsion 18°-52°, tibial torsion 3°-50°). For each participant, a musculoskeletal model was modified to match the femoral and tibial geometry obtained from magnetic resonance images. Each participant's model and the corresponding motion capture data were used as input for a Monte Carlo analysis to investigate how different muscle coordination strategies influence joint loads. OpenSim was used to run 10,000 simulations for each participant. Root-mean-square of muscle forces and peak joint contact forces were compared between simulations. Depending on the participant, altering muscle coordination led to a maximum reduction in hip, knee, patellofemoral and ankle joint loads between 5 and 18%, 4% and 45%, 16% and 36%, and 2% and 6%, respectively. In some but not all participants reducing joint loads at one joint increased joint loads at other joints. The required alteration in muscle forces to achieve a reduction in joint loads showed a large variability between participants. The potential of muscle coordination retraining to reduce joint loads depends on the person's musculoskeletal geometry and gait pattern and therefore showed a large variability between participants, which highlights the usefulness and importance of the proposed framework to personalize gait retraining.

Walking speed differentially affects lower extremity biomechanics in individuals with anterior cruciate ligament reconstruction compared to uninjured controls

BACKGROUND

Walking biomechanics are commonly affected after anterior cruciate ligament reconstruction and differ compared to uninjured controls. Manipulating task difficulty has been shown to affect the magnitude of walking impairments in those early after knee surgery but it is unclear if patients in later phases post-op are similarly affected by differing task demands. Here, we evaluated the effects of manipulating walking speed on between-limb differences in ground reaction force and knee biomechanics in those with and without anterior cruciate ligament reconstruction.

METHODS

We recruited 28 individuals with anterior cruciate ligament reconstruction and 20 uninjured control participants to undergo walking assessments at three speeds (self-selected, 120%, and 80% self-selected speed). Main outcomes included sagittal plane knee moments, angles, excursions, and ground reaction forces (vertical and anterior-posterior).

FINDINGS

We observed walking speed differentially impacted force and knee-outcomes in those with anterior cruciate ligament reconstruction. Between-limb differences increased at fast and decreased at slow speeds in those with anterior cruciate ligament reconstruction while uninjured participants maintained between-limb differences regardless of speed (partial η2 = 0.13-0.33, p < 0.05). Anterior cruciate ligament reconstruction patients underloaded the surgical limb relative to both the contralateral, and uninjured controls in GRFs and sagittal plane knee moments (partial η2 range = 0.13-0.25, p < 0.05).

INTERPRETATION

Overall, our findings highlight the persistence of walking impairments in those with anterior cruciate ligament reconstruction despite completing formal rehabilitation. Further research should consider determining if those displaying larger changes in gait asymmetries in response to fast walking also exhibit poorer strength and/or joint health outcomes.

Unilateral transfemoral osseointegrated prostheses improve joint loading during walking

People with unilateral transfemoral amputation using socket prostheses are at increased risk for developing osteoarthritis in both the residual hip and intact lower-limb joints. Osseointegrated prostheses are a surgical alternative to socket prostheses that directly attach to the residual femur via a bone-anchored implant, however their multi-joint loading effect is largely unknown. Our objective was to establish how osseointegrated prostheses influence joint loading during walking. Motion capture data (kinematics, ground reaction forces) were collected from 12 participants at baseline, with socket prostheses, and 12-months after prosthesis osseointegration during overground walking at self-selected speeds. Subject-specific musculoskeletal models were developed at each timepoint relative to osseointegration. Internal joint moments were calculated using inverse dynamics, muscle and joint reaction forces (JRFs) were estimated with static optimization. Changes in internal joint moments, JRFs, and joint loading-symmetry were compared using statistical parametric mapping (p≤ 0.05) before and after osseointegration. Amputated limb hip flexion moments and anterior JRFs decreased during terminal stance (p = 0.002, <0.001; respectively), while amputated limb hip abduction moments increased during mid-stance (p < 0.001), amputated hip rotation moment changed from internal to external throughout early stance (p < 0.001). Intact limb hip extension and knee flexion moments (p = 0.028, 0.032; respectively), superior and resultant knee JRFs (p = 0.046, 0.049; respectively) decreased during the loading response following prosthesis osseointegration. These results may indicate that the direct loading transmission of these novel prostheses create a more typical mechanical environment in bilateral joints, which is comparable with loading observed in able-bodied individuals and could decrease the risk of development or progression of osteoarthritis.

Simulated Tibiofemoral Joint Reaction Forces for Three Previously Studied Gait Modifications in Healthy Controls

Gait modifications, such as lateral trunk lean (LTL), medial knee thrust (MKT), and toe-in gait (TIG), are frequently investigated interventions used to slow the progression of knee osteoarthritis. The Lerner knee model was developed to estimate the tibiofemoral joint reaction forces (JRF) in the medial and lateral compartments during gait. These models may be useful for estimating the effects on the JRF in the knee as a result of gait modifications. We hypothesized that all gait modifications would decrease the JRF compared to normal gait. Twenty healthy individuals volunteered for this study (26.7 ± 4.7 years, 1.75 ± 0.1 m, 73.4 ± 12.4 kg). Ten trials were collected for normal gait as well as for the three gait modifications: LTL, MKT, and TIG. The data were used to estimate the JRF in the first and second peaks for the medial and lateral compartments of the knee via opensim using the Lerner knee model. No significant difference from baseline was found for the first peak in the medial compartment. There was a decrease in JRF in the medial compartment during the loading phase of gait for TIG (6.6%) and LTL (4.9%) and an increasing JRF for MKT (2.6%). but none was statistically significant. A significant increase from baseline was found for TIG (5.8%) in the medial second peak. We found a large variation in individual responses to gait interventions, which may help explain the lack of statistically significant results. Possible factors influencing these wide ranges of responses to gait modifications include static alignment and the impacts of variation in muscle coordination strategies used, by participants, to implement gait modifications.

Independently ambulatory children with spina bifida experience near-typical knee and ankle joint moments and forces during walking

BACKGROUND

Spina bifida, a neurological defect, can result in lower-limb muscle weakness. Altered ambulation and reduced musculoskeletal loading can yield decreased bone strength in individuals with spina bifida, yet individuals who remain ambulatory can exhibit normal bone outcomes.

RESEARCH QUESTION

During walking, how do lower-limb joint kinematics and moments and tibial forces in independently ambulatory children with spina bifida differ from those of children with typical development?

METHODS

We retrospectively analyzed data from 16 independently ambulatory children with spina bifida and 16 children with typical development and confirmed that tibial bone strength was similar between the two groups. Plantar flexor muscle strength was measured by manual muscle testing, and 14 of the children with spina bifida wore activity monitors for an average of 5 days. We estimated tibial forces at the knee and ankle using motion capture data and musculoskeletal simulations. We used Statistical Parametric Mapping t-tests to compare lower-limb joint kinematic and kinetic waveforms between the groups with spina bifida and typical development. Within the group with spina bifida, we examined relationships between plantar flexor muscle strength and peak tibial forces by calculating Spearman correlations.

RESULTS

Activity monitors from the children with spina bifida reported typical daily steps (9656 [SD 3095]). Despite slower walking speeds (p = 0.004) and altered lower-body kinematics (p < 0.001), children with spina bifida had knee and ankle joint moments and forces similar to those of children with typical development, with no detectable differences during stance. Plantar flexor muscle weakness was associated with increased compressive knee force (p = 0.002) and shear ankle force (p = 0.009).

SIGNIFICANCE

High-functioning, independently ambulatory children with spina bifida exhibited near-typical tibial bone strength and near-typical step counts and tibial load magnitudes. Our results suggest that the tibial forces in this group are of sufficient magnitudes to support the development of normal tibial bone strength.

Effect of rearfoot valgus on biomechanics during barbell squatting: A study based on OpenSim musculoskeletal modeling

Background

Barbell squats are commonly used in daily training and rehabilitation. Injuries are not common when the posture is standard, but the wrong posture can lead to injuries. Rearfoot valgus is a common foot abnormality that may increase the risk of injury during sports. The purpose of this study was to compare the biomechanics of lower limbs in normal foot and valgus patients during barbell squat.

Methods

In this study, 10 participants with normal foot shape and 10 participants with rearfoot valgus were enrolled. The joint angle, joint moment, and range of motion of hip, knee, and ankle joints were collected under 0, 30, and 70% one-repetition maximum (RM) load, where discrete data are statistically analyzed using the independent sample t-test, and continuous data are statistically analyzed using one-dimensional parameter statistical mapping.

Results

In barbell squats, the range of motion and the joint moment of the hip, knee, and ankle in the rearfoot valgus participants were significantly larger than those in normal foot participants (p < 0.05). The participants with rearfoot valgus had a more significant knee valgus angle when squatting to the deepest (p < 0.05). In addition, with the increase in load, the participants with rearfoot valgus showed greater standardized medial knee contact force (p < 0.05). In the process of barbell squats, the participants with rearfoot valgus showed no significant difference in the foot valgus angle when compared with the normal foot shape (p > 0.05).

Conclusions

The valgus population showed a greater range of joint motion when performing barbell squats and showed genu valgus and greater medial knee contact force, which may increase the risk of musculoskeletal and soft tissue damage such as meniscus wear. In addition, there was no significant difference in the rearfoot valgus angle between people with rearfoot valgus and people with normal foot shape during squatting, so barbell squatting may correct valgus to a certain extent.

The Kinematic and Kinetic Responses of the Trunk and Lower Extremity Joints during Walking with and without the Spinal Orthosis

Spinal orthoses are an effective option for restoring the spine to its original position and controlling poor posture. However, the effects of poor posture and spinal orthoses on the kinematics and kinetics of trunk and lower extremity joints remain unclear. A six-camera Vicon motion capture system and two AMTI force plates were employed to collect gait parameters, including joint angle (spine, thorax, hip, knee, and ankle), range of motion (ROM), and ground reaction forces (GRFs). Furthermore, joint moments and joint reaction forces (JRFs) were calculated using a full-body musculoskeletal model in OpenSim. One-way repeated-measures ANOVA (p < 0.05) was used to compare significant differences among three trial conditions. These three conditions were walking in a normal posture, poor posture, and spinal orthosis. The results showed that spine ROM in the coronal and transverse plane was significantly lower when walking with a spinal orthosis compared to walking in normal and poor posture (p < 0.05). Compared to normal posture, the lumbar moments and back compressive forces were significantly increased when walking in poor posture (p < 0.05). However, when walking with a spinal orthosis, there was a significant decrease in trunk moments and reaction forces compared to walking in poor posture (p < 0.05). Individuals with poor posture could potentially induce instability and disorders, as evidenced by an increase in trunk moments and JRF compared to the normal posture. Spinal orthosis not only restricts spine ROM but also reduces the load on the spine and thus increases balance and stability.

Variable Stiffness Shoes for Knee Osteoarthritis: An Evaluation of 3-Dimensional Gait Mechanics and Medial Joint Contact Forces

The study aim was to quantify the impact of a commercially available variable stiffness shoe (VSS) on 3-dimensional ankle, knee, and hip mechanics and estimated knee contact forces compared with a control shoe. Fourteen participants (10 females) with knee osteoarthritis completed gait analysis after providing informed consent. Shoe conditions tested were control shoe (New Balance MW411v2) and VSS (Abeo SMART3400). An OpenSim musculoskeletal model with static optimization was used to estimate knee contact forces. There were no differences in joint kinematics or in the knee adduction or flexion moments (P = .06; P = .2). There were increases in the knee internal and external rotation (P = .02; P = .03) and hip adduction and internal rotation moments for VSS versus control (P = .03; P = .02). The estimated contact forces were not different between shoes (total P = .3, medial P = .1, and lateral P = .8), but contact force changes were correlated with changes in the knee adduction moment (medial r2 = .61; P < .007). High variability in knee flexion moment changes and increases in the internal rotation moment combined with small decreases in the knee adduction moment did not lead to decreases in estimated contact forces. These results suggest that evaluation of VSS using only the knee adduction moment may not adequately capture its impact on osteoarthritis.

Hip Joint Contact Loading and Muscle Forces During Running With a Transtibial Amputation

People with unilateral transtibial amputations (TTA) have greater risks of bilateral hip osteoarthritis, related to asymmetric biomechanics compared to people without TTA. Running is beneficial for physical health and is gaining popularity. However, people with TTA may not have access to running-specific prostheses (RSPs), which are designed for running, and may instead run using their daily-use prosthesis (DUP). Differences in joint loading may result from prosthesis choice; thus, it is important to characterize changes in peak and impulsive hip joint contact loading during running. Six people with and without TTA ran at 3.5 m/s while ground reaction forces, kinematics, and electromyography were collected. People with TTA ran using their own RSP and DUP. Musculoskeletal models incorporating prosthesis type of each individual were used to quantify individual muscle forces and hip joint contact forces (HJCFs) during running. People using RSPs had smaller bilateral peak hip joint contact forces compared to when wearing DUPs during stance and swing, and a smaller impulse over the entire gait cycle. Greater amputated leg peak hip joint contact forces for people wearing DUPs compared to RSPs occurred with greater forces from the ipsilateral gluteus maximus during stance. People with TTA also had greater bilateral peak hip joint contact forces during swing compared to people without TTA, which occurred with greater peak gluteus medius forces. Running with more compliant RSPs may be beneficial for long-term joint health by reducing peak and impulsive hip loading compared to DUPs.

A Systematic Review of the Associations Between Inverse Dynamics and Musculoskeletal Modeling to Investigate Joint Loading in a Clinical Environment

The assessment of knee or hip joint loading by external joint moments is mainly used to draw conclusions on clinical decision making. However, the correlation between internal and external loads has not been systematically analyzed. This systematic review aims, therefore, to clarify the relationship between external and internal joint loading measures during gait. A systematic database search was performed to identify appropriate studies for inclusion. In total, 4,554 articles were identified, while 17 articles were finally included in data extraction. External joint loading parameters were calculated using the inverse dynamics approach and internal joint loading parameters by musculoskeletal modeling or instrumented prosthesis. It was found that the medial and total knee joint contact forces as well as hip joint contact forces in the first half of stance can be well predicted using external joint moments in the frontal plane, which is further improved by including the sagittal joint moment. Worse correlations were found for the peak in the second half of stance as well as for internal lateral knee joint contact forces. The estimation of external joint moments is useful for a general statement about the peak in the first half of stance or for the maximal loading. Nevertheless, when investigating diseases as valgus malalignment, the estimation of lateral knee joint contact forces is necessary for clinical decision making because external joint moments could not predict the lateral knee joint loading sufficient enough. Dependent on the clinical question, either estimating the external joint moments by inverse dynamics or internal joint contact forces by musculoskeletal modeling should be used.

Estimating Knee Joint Load Using Acoustic Emissions During Ambulation

Quantifying joint load in activities of daily life could lead to improvements in mobility for numerous people; however, current methods for assessing joint load are unsuitable for ubiquitous settings. The aim of this study is to demonstrate that joint acoustic emissions contain information to estimate this internal joint load in a potentially wearable implementation. Eleven healthy, able-bodied individuals performed ambulation tasks under varying speed, incline, and loading conditions while joint acoustic emissions and essential gait measures-electromyography, ground reaction forces, and motion capture trajectories-were collected. The gait measures were synthesized using a neuromuscular model to estimate internal joint contact force which was the target variable for subject-specific machine learning models (XGBoost) trained based on spectral, temporal, cepstral, and amplitude-based features of the joint acoustic emissions. The model using joint acoustic emissions significantly outperformed (p < 0.05) the best estimate without the sounds, the subject-specific average load (MAE = 0.31 ± 0.12 BW), for both seen (MAE = 0.08 ± 0.01 BW) and unseen (MAE = 0.21 ± 0.05 BW) conditions. This demonstrates that joint acoustic emissions contain information that correlates to internal joint contact force and that information is consistent such that unique cases can be estimated.

A Comparative Study on Loadings of the Lower Extremity during Deep Squat in Asian and Caucasian Individuals via OpenSim Musculoskeletal Modelling

Populations of different ethnicities may present different movement capacities and muscular function adaptations. The purpose of this study was to investigate the differences of motion and loading in the lower extremity during dynamic deep squats between Asian and Caucasian individuals using OpenSim modelling technique with a customized squat-specific musculoskeletal model. Twenty-four participants joined the test performing the step-squat test, with right foot stepping side, squatting, and returning. The one-dimensional statistical parametric mapping package was used for statistical analysis. The main findings of the current study were as follows: (1) significant lower squat depth was observed in the Asian individuals, (2) the greater knee range of motion and contact forces were found in the Asian individuals, and (3) the greater ankle contact forces in the Caucasian individuals were notable while performing the deep squat compared to the Asian group. Knowledge found in the current study may provide implication for exercise practitioners and physiotherapists while designing schemes for the prevention of loading accumulation in the lower extremity.

Knee joint biomechanics in transtibial amputees in gait, cycling, and elliptical training

Transtibial amputees may experience decreased quality of life due to increased risk of knee joint osteoarthritis (OA). No prior studies have compared knee joint biomechanics for the same group of transtibial amputees in gait, cycling, and elliptical training. Thus, the goal of this study was to identify preferred exercises for transtibial amputees in the context of reducing risk of knee OA. The hypotheses were: 1) knee biomechanics would differ due to participant status (amputee, control), exercise, and leg type (intact, residual) and 2) gait kinematic parameters would differ due to participant status and leg type. Ten unilateral transtibial amputee and ten control participants performed exercises while kinematic and kinetic data were collected. Two-factor repeated measures analysis of variance with post-hoc Tukey tests and non-parametric equivalents were performed to determine significance. Maximum knee compressive force, extension torque, and abduction torque were lowest in cycling and highest in gait regardless of participant type. Amputee maximum knee extension torque was higher in the intact vs. residual knee in gait. Amputee maximum knee flexion angle was higher in the residual vs. intact knee in gait and elliptical. Gait midstance knee flexion angle timing was asymmetrical for amputees and knee angle was lower in the amputee residual vs. control non-dominant knees. The results suggest that cycling, and likely other non-weight bearing exercises, may be preferred exercises for amputees due to significant reductions in biomechanical asymmetries and joint loads.

The effects of pediatric obesity on patellofemoral joint contact force during walking

BACKGROUND

Obesity increases a child's risk of developing knee pain across the lifespan, potentially through elevated patellofemoral joint loads that occur during habitual weight-bearing activities.

RESEARCH QUESTION

Do obese children have greater absolute and patellar-area-normalized patellofemoral joint forces compared to healthy weight children during walking?

METHODS

We utilized a cross-sectional design to address the aims of this study. Experimental biomechanics data were collected during treadmill walking in 10 healthy-weight and 10 obese 8-12 year-olds. We used radiographic images to develop subject-specific musculoskeletal models, generated walking simulations from the experimental data, and predicted patellofemoral joint contact force using established techniques.

RESULTS

We found that the obese children had 1.98 times greater absolute (p = 0.002) and 1.81 times greater patellar-area-normalized (p = 0.008) patellofemoral joint contact forces compared to the healthy-weight children. We observed a stronger relationship between absolute patellofemoral joint contact force and BMI (r²=0.58) than between patellofemoral joint contact force and body fat percentage (r²=0.38).

SIGNIFICANCE

Our results indicate that obese children walk with increased patellofemoral loads in absolute terms and also relative to the area of the articulating surfaces, which likely contributes to the increased risk of knee pain in this pediatric population. This information, which provides a baseline comparison for future longitudinal studies, also informs the type and frequency of physical activity prescription aimed at reducing the risk of knee injury and improving long-term outcomes.

Contributions of muscles and external forces to medial knee load reduction due to osteoarthritis braces

BACKGROUND

Braces for medial knee osteoarthritis can reduce medial joint loads through a combination of three mechanisms: application of an external brace abduction moment, alteration of gait dynamics, and reduced activation of antagonistic muscles. Although the effect of knee bracing has been reported independently for each of these parameters, no previous study has quantified their relative contributions to reducing medial knee loads.

METHODS

In this study, we used a detailed musculoskeletal model to investigate immediate changes in medial and lateral loads caused by two different knee braces: OA Assist and OA Adjuster 3 (DJO Global). Seventeen osteoarthritis subjects and eighteen healthy controls performed overground gait trials in unbraced and braced conditions.

RESULTS

Across all subjects, bracing reduced medial loads by 0.1 to 0.3 times bodyweight (BW), or roughly 10%, and increased lateral loads by 0.03 to 0.2 BW. Changes in gait kinematics due to bracing were subtle, and had little effect on medial and lateral joint loads. The knee adduction moment was unaltered unless the brace moment was included in its computation. Only one muscle, biceps femoris, showed a significant change in EMG with bracing, but this did not contribute to altered peak medial contact loads.

CONCLUSIONS

Knee braces reduced medial tibiofemoral loads primarily by applying a direct, and substantial, abduction moment to each subject's knee. To further enhance brace effectiveness, future brace designs should seek to enhance the magnitude of this unloader moment, and possibly exploit additional kinematic or neuromuscular gait modifications.

The Effects of Filter Cutoff Frequency on Musculoskeletal Simulations of High-Impact Movements

Estimation of muscle forces through musculoskeletal simulation is important in understanding human movement and injury. Unmatched filter frequencies used to low-pass filter marker and force platform data can create artifacts during inverse dynamics analysis, but their effects on muscle force calculations are unknown. The objective of this study was to determine the effects of filter cutoff frequency on simulation parameters and magnitudes of lower-extremity muscle and resultant joint contact forces during a high-impact maneuver. Eight participants performed a single-leg jump landing. Kinematics was captured with a 3D motion capture system, and ground reaction forces were recorded with a force platform. The marker and force platform data were filtered using 2 matched filter frequencies (10–10 Hz and 15–15 Hz) and 2 unmatched filter frequencies (10–50 Hz and 15–50 Hz). Musculoskeletal simulations using computed muscle control were performed in OpenSim. The results revealed significantly higher peak quadriceps (13%), hamstrings (48%), and gastrocnemius forces (69%) in the unmatched (10–50 Hz and 15–50 Hz) conditions than in the matched (10–10 Hz and 15–15 Hz) conditions (P < .05). Resultant joint contact forces and reserve (nonphysiologic) moments were similarly larger in the unmatched filter categories (P < .05). This study demonstrated that artifacts created from filtering with unmatched filter cutoffs result in altered muscle forces and dynamics that are not physiologic.

Influence of Gait Speeds on Contact Forces of Lower Limbs

While walking with fast speed aims to promote health and fitness of individuals, the potential risk on lower limb joint loading across walking speed is still unknown. In order to determine the joint contact force loading associated with different walking speeds, fifteen young male and fifteen female participants performed barefoot walking across different speeds (regular = 1.1 m/s, medium = 1.4 m/s, and fast = 1.7 m/s). The synchronized motion and ground reaction force (GRF) data were captured by Codamotion capture system and AMTI force platform. All kinematics and GRF information were input to the AnyBody musculoskeletal model to determine 3-dimensional knee contact forces. The results showed that increased walking speed was associated with a greater proximal-distal and anterior-posterior GRF during early impact phase, implying that the joint stability is more demanding at higher walking speed conditions (P < 0.05). In addition, higher proximal-distal and anterior-posterior knee contact forces were found when participants were walking at higher speeds (P < 0.05). Therefore, the risk of knee cartilage and ligament damage associated with the increased knee contact forces should require further attention.

Effect of hammer mass on upper extremity joint moments

This study used an OpenSim inverse-dynamics musculoskeletal model scaled to subject-specific anthropometrics to calculate three-dimensional intersegmental moments at the shoulder, elbow and wrist while 10 subjects used 1 and 2 lb hammers to drive nails. Motion data were collected via an optoelectronic system and the interaction of the hammer with nails was recorded with a force plate. The larger hammer caused substantial increases (50-150%) in moments, although increases differed by joint, anatomical component, and significance of the effect. Moment increases were greater in cocking and strike/follow-through phases as opposed to swinging and may indicate greater potential for injury. Compared to shoulder, absolute increases in peak moments were smaller for elbow and wrist, but there was a trend toward larger relative increases for distal joints. Shoulder rotation, elbow varus-valgus and pronation-supination, and wrist radial-ulnar deviation and rotation demonstrated large relative moment increases. Trial and phase durations were greater for the larger hammer. Changes in moments and timing indicate greater loads on musculoskeletal tissues for an extended period with the larger hammer. Additionally, greater variability in timing with the larger hammer, particularly for cocking phase, suggests differences in control of the motion. Increased relative moments for distal joints may be particularly important for understanding disorders of the elbow and wrist associated with hammer use.

Osteoarthritis year in review 2016: mechanics

Inappropriate biomechanics, namely wear-and-tear, has been long believed to be a main cause of osteoarthritis (OA). However, this view is now being re-evaluated, especially when examined alongside mechanobiology and new biomechanical studies. These are multiscale experimental and computational studies focussing on cell- and tissue-level mechanobiology through to organ- and whole-body-level biomechanics, which focuses on the biomechanical and biochemical environment of the joint tissues. This review examined papers from April 2015 to April 2016, with a focus on multiscale experimental and computational biomechanical studies of OA. Assessing the onset or progression of OA at organ- and whole-body-levels, gait analysis, medical imaging and neuromusculoskeletal modelling revealed the extent to which tissue damage changes the view of inappropriate biomechanics. Traditional gait analyses studies reported that conservative treatments can alter joint biomechanics, thereby improving pain and function experienced by those with OA. Results of animal models of OA were consistent with these human studies, showing interactions among bone, cartilage and meniscus biomechanics and the onset and/or progression OA. Going down size scales, experimental and computational studies probed the nanosize biomechanics of molecules, cells and extracellular matrix, and demonstrated how the interactions between biomechanics and morphology affect cartilage dynamic poroelastic behaviour and pathways to OA. Finally, integration of multiscale experimental data and computational models were proposed to predict cartilage extracellular matrix remodelling and the development of OA. Summarising, experimental and computational methods provided a nuanced biomechanical understanding of the sub-cellular, cellular, tissue, organ and whole-body mechanisms involved in OA.

Soldier-relevant body borne loads increase knee joint contact force during a run-to-stop maneuver

The purpose of this study was to understand the effects of load carriage on human performance, specifically during a run-to-stop (RTS) task. Using OpenSim analysis tools, knee joint contact force, grounds reaction force, leg stiffness and lower extremity joint angles and moments were determined for nine male military personnel performing a RTS under three load configurations (light, ~6kg, medium, ~20kg, and heavy, ~40kg). Subject-based means for each biomechanical variable were submitted to repeated measures ANOVA to test the effects of load. During the RTS, body borne load significantly increased peak knee joint contact force by 1.2 BW (p<0.001) and peak vertical (p<0.001) and anterior-posterior (p=0.002) ground reaction forces by 0.6 BW and 0.3 BW, respectively. Body borne load also had a significant effect on hip (p=0.026) posture with the medium load and knee (p=0.046) posture with the heavy load. With the heavy load, participants exhibited a substantial, albeit non-significant increase in leg stiffness (p=0.073 and d=0.615). Increases in joint contact force exhibited during the RTS were primarily due to greater GRFs that impact the soldier with each incremental addition of body borne load. The stiff leg, extended knee and large braking force the soldiers exhibited with the heavy load suggests their injury risk may be greatest with that specific load configuration. Further work is needed to determine if the biomechanical profile exhibited with the heavy load configuration translates to unsafe shear forces at the knee joint and consequently, a higher likelihood of injury.

Reductions in knee joint forces with weight loss are attenuated by gait adaptations in class III obesity

A consensus exists that high knee joint forces are a precursor to knee osteoarthritis and weight loss reduces these forces. Because large weight loss also leads to increased step length and walking velocity, knee contact forces may be reduced less than predicted by the magnitude of weight loss. The purpose was to determine the effects of weight loss on knee muscle and joint loads during walking in Class III obese adults. We determined through motion capture, force platform measures and biomechanical modeling the effects of weight loss produced by gastric bypass surgery over one year on knee muscle and joint loads during walking at a standard, controlled velocity and at self-selected walking velocities. Weight loss equaling 412 N or 34% of initial body weight reduced maximum knee compressive force by 824 N or 67% of initial body weight when walking at the controlled velocity. These changes represent a 2:1 reduction in knee force relative to weight loss when walking velocity is constrained to the baseline value. However, behavioral adaptations including increased stride length and walking velocity in the self-selected velocity condition attenuated this effect by ∼50% leading to a 392 N or 32% initial body weight reduction in compressive force in the knee joint. Thus, unconstrained walking elicited approximately 1:1 ratio of reduction in knee force relative to weight loss and is more indicative of walking behavior than the standard velocity condition. In conclusion, massive weight loss produces dramatic reductions in knee forces during walking but when patients stride out and walk faster, these favorable reductions become substantially attenuated.

Modulating tibiofemoral contact force in the sheep hind limb via treadmill walking: Predictions from an opensim musculoskeletal model

Sheep are a predominant animal model used to study a variety of orthopedic conditions. Understanding and controlling the in-vivo loading environment in the sheep hind limb is often necessary for investigations relating to bone and joint mechanics. The purpose of this study was to develop a musculoskeletal model of an adult sheep hind limb and investigate the effects of treadmill walking speed on muscle and joint contact forces. We constructed the skeletal geometry of the model from computed topography images. Dual-energy x-ray absorptiometry was utilized to establish the inertial properties of each model segment. Detailed dissection and tendon excursion experiments established the requisite muscle lines of actions. We used OpenSim and experimentally-collected marker trajectories and ground reaction forces to quantify muscle and joint contact forces during treadmill walking at 0.25 m• s(-1) and 0.75 m• s(-1) . Peak compressive and anterior-posterior tibiofemoral contact forces were 20% (0.38 BW, p = 0.008) and 37% (0.17 BW, p = 0.040) larger, respectively, at the moderate gait speed relative to the slower speed. Medial-lateral tibiofemoral contact forces were not significantly different. Adjusting treadmill speed appears to be a viable method to modulate compressive and anterior-posterior tibiofemoral contact forces in the sheep hind limb. The musculoskeletal model is freely-available at www.SimTK.org.

How tibiofemoral alignment and contact locations affect predictions of medial and lateral tibiofemoral contact forces

Understanding degeneration of biological and prosthetic knee joints requires knowledge of the in-vivo loading environment during activities of daily living. Musculoskeletal models can estimate medial/lateral tibiofemoral compartment contact forces, yet anthropometric differences between individuals make accurate predictions challenging. We developed a full-body OpenSim musculoskeletal model with a knee joint that incorporates subject-specific tibiofemoral alignment (i.e. knee varus-valgus) and geometry (i.e. contact locations). We tested the accuracy of our model and determined the importance of these subject-specific parameters by comparing estimated to measured medial and lateral contact forces during walking in an individual with an instrumented knee replacement and post-operative genu valgum (6°). The errors in the predictions of the first peak medial and lateral contact force were 12.4% and 11.9%, respectively, for a model with subject-specific tibiofemoral alignment and contact locations determined through radiographic analysis, vs. 63.1% and 42.0%, respectively, for a model with generic parameters. We found that each degree of tibiofemoral alignment deviation altered the first peak medial compartment contact force by 51N (r(2)=0.99), while each millimeter of medial-lateral translation of the compartment contact point locations altered the first peak medial compartment contact force by 41N (r(2)=0.99). The model, available at www.simtk.org/home/med-lat-knee/, enables the specification of subject-specific joint alignment and compartment contact locations to more accurately estimate medial and lateral tibiofemoral contact forces in individuals with non-neutral alignment.

Effects of obesity on lower extremity muscle function during walking at two speeds

Walking is a recommended form of physical activity for obese adults, yet the effects of obesity and walking speed on the biomechanics of walking are not well understood. The purpose of this study was to examine joint kinematics, muscle force requirements and individual muscle contributions to the walking ground reaction forces (GRFs) at two speeds (1.25 ms(-1) and 1.50 ms(-1)) in obese and nonobese adults. Vasti (VAS), gluteus medius (GMED), gastrocnemius (GAST), and soleus (SOL) forces and their contributions to the GRFs were estimated using three-dimensional musculoskeletal models scaled to the anthropometrics of nine obese (35.0 (3.78 kg m(-2))); body mass index mean (SD)) and 10 nonobese (22.1 (1.02 kg m(-2))) subjects. The obese individuals walked with a straighter knee in early stance at the faster speed and greater pelvic obliquity during single limb support at both speeds. Absolute force requirements were generally greater in obese vs. nonobese adults, the main exception being VAS, which was similar between groups. At both speeds, lean mass (LM) normalized force output for GMED was greater in the obese group. Obese individuals appear to adopt a gait pattern that reduces VAS force output, especially at speeds greater than their preferred walking velocity. Greater relative GMED force requirements in obese individuals may contribute to altered kinematics and increased risk of musculoskeletal injury/pathology. Our results suggest that obese individuals may have relative weakness of the VAS and hip abductor muscles, specifically GMED, which may act to increase their risk of musculoskeletal injury/pathology during walking, and therefore may benefit from targeted muscle strengthening.