Knee Joint Reaction Forces Research Articles

Estimation of Joint Kinetics During Manual Material Handling Using Inertial Motion Capture: A Follow-Up Study.

Musculoskeletal models based on inertial motion capture (IMC) and ground reaction force (GRF) prediction hold great potential for field-based risk assessment of manual material handling (MMH). However, previous evaluations have identified inaccuracies in the methodology's estimation of spinal forces, while the accuracy of other key outcome variables is currently unclear. This study evaluated knee, shoulder, and L5-S1 joint reaction forces (JRFs) derived from a musculoskeletal model based on inertial motion capture and GRF prediction against a model based on simultaneously collected optical motion capture (OMC) and force plate measurements. Data from 19 healthy subjects performing lifts with various horizontal locations (HLs), deposit heights (DHs), and asymmetry angles (AAs) were analyzed, and the consistency and absolute agreement of the model estimates statistically compared. Despite varying levels of agreement across tasks and variables, considerable absolute differences were identified for the L5-S1 axial compression (AC) (root-mean-square error (RMSE) = 63.0-94.2%BW) and anteroposterior (AP) shear forces (RMSE = 40.9-80.6%BW) as well as the bilateral knee JRFs (RMSE = 78.9-117%BW). Glenohumeral JRFs and vertical GRFs exhibited the highest overall consistency (r = 0.33-0.91, median 0.78) and absolute agreement (RMSE = 7.63-34.9%BW), while the L5-S1 axial compression forces also showed decent consistency (r = 0.04-0.89, median 0.80). The findings generally align with prior evaluations, indicating persistent challenges with the accuracy of key outcome variables. While the modeling framework shows promise, further development of the methodology is encouraged to enhance its applicability in ergonomic evaluations.

A novel computational framework for the estimation of internal musculoskeletal loading and muscle adaptation in hypogravity.

Introduction: Spaceflight is associated with substantial and variable musculoskeletal (MSK) adaptations. Characterisation of muscle and joint loading profiles can provide key information to better align exercise prescription to astronaut MSK adaptations upon return-to-Earth. A case-study is presented of single-leg hopping in hypogravity to demonstrate the additional benefit computational MSK modelling has when estimating lower-limb MSK loading. Methods: A single male participant performed single-leg vertical hopping whilst attached to a body weight support system to replicate five gravity conditions (0.17, 0.25, 0.37, 0.50, 1 g). Experimental joint kinematics, joint kinetics and ground reaction forces were tracked in a data-tracking direct collocation simulation framework. Ground reaction forces, sagittal plane hip, knee and ankle net joint moments, quadriceps muscle forces (Rectus Femoris and three Vasti muscles), and hip, knee and ankle joint reaction forces were extracted for analysis. Estimated quadriceps muscle forces were input into a muscle adaptation model to predict a meaningful increase in muscle cross-sectional area, defined in (DeFreitas et al., 2011). Results: Two distinct strategies were observed to cope with the increase in ground reaction forces as gravity increased. Hypogravity was associated with an ankle dominant strategy with increased range of motion and net plantarflexor moment that was not seen at the hip or knee, and the Rectus Femoris being the primary contributor to quadriceps muscle force. At 1 g, all three joints had increased range of motion and net extensor moments relative to 0.50 g, with the Vasti muscles becoming the main muscles contributing to quadriceps muscle force. Additionally, hip joint reaction force did not increase substantially as gravity increased, whereas the other two joints increased monotonically with gravity. The predicted volume of exercise needed to counteract muscle adaptations decreased substantially with gravity. Despite the ankle dominant strategy in hypogravity, the loading on the knee muscles and joint also increased, demonstrating this provided more information about MSK loading. Discussion: This approach, supplemented with muscle-adaptation models, can be used to compare MSK loading between exercises to enhance astronaut exercise prescription.

The effect of running experience on muscle forces and knee joint reaction forces during running

The effect of running experience on muscle forces and knee joint reaction forces during running

Evaluation of knee joint reaction force for the back and front leg during the forward jump in soccer

Evaluation of knee joint reaction force for the back and front leg during the forward jump in soccer

Effect of stride length on the running biomechanics of healthy women of different statures.

Tibial stress fracture is a debilitating musculoskeletal injury that diminishes the physical performance of individuals who engage in high-volume running, including Service members during basic combat training (BCT) and recreational athletes. While several studies have shown that reducing stride length decreases musculoskeletal loads and the potential risk of tibial injury, we do not know whether stride-length reduction affects individuals of varying stature differently. We investigated the effects of reducing the running stride length on the biomechanics of the lower extremity of young, healthy women of different statures. Using individualized musculoskeletal and finite-element models of women of short (N = 6), medium (N = 7), and tall (N = 7) statures, we computed the joint kinematics and kinetics at the lower extremity and tibial strain for each participant as they ran on a treadmill at 3.0m/s with their preferred stride length and with a stride length reduced by 10%. Using a probabilistic model, we estimated the stress-fracture risk for running regimens representative of U.S. Army Soldiers during BCT and recreational athletes training for a marathon. When study participants reduced their stride length by 10%, the joint kinetics, kinematics, tibial strain, and stress-fracture risk were not significantly different among the three stature groups. Compared to the preferred stride length, a 10% reduction in stride length significantly decreased peak hip (p = 0.002) and knee (p < 0.001) flexion angles during the stance phase. In addition, it significantly decreased the peak hip adduction (p = 0.013), hip internal rotation (p = 0.004), knee extension (p = 0.012), and ankle plantar flexion (p = 0.026) moments, as well as the hip, knee, and ankle joint reaction forces (p < 0.001) and tibial strain (p < 0.001). Finally, for the simulated regimens, reducing the stride length decreased the relative risk of stress fracture by as much as 96%. Our results show that reducing stride length by 10% decreases musculoskeletal loads, tibial strain, and stress-fracture risk, regardless of stature. We also observed large between-subject variability, which supports the development of individualized training strategies to decrease the incidence of stress fracture.

Shear stress in the medial meniscus posterior root during daily activities

BackgroundMedial meniscus posterior root (MMPR) tears have been reported to occur in middle-aged patients with minor trauma. However, the injury mechanism of MMPR tears remains unclear. The purpose of this study was to evaluate the shear stress in the MMPR during daily activities using a finite-element analysis. MethodsSubject-specific finite-element models of the knee joint of a healthy middle-aged subject were developed from computed tomographic and magnetic resonance images. A three-dimensional motion capture system “VICON” was used to capture four daily activities: walking, jogging, descending stairs, and landing. The knee joint reaction force was estimated using the AnyBody modeling system. Based on these procedures, the shear stress in the MMPR was calculated during each motion. The shear stress in the lateral meniscus posterior root (LMPR) was also measured to compare the stress between the MMPR and LMPR. ResultsThe shear stress in the MMPR increased as the knee flexion angle increased during each motion. Descending stairs caused more than two-fold greater stress in the MMPR than walking and a similar or greater amount of stress than jogging. The LMPR tended to receive more shear stress than the MMPR throughout each motion. ConclusionsThe present study showed that descending stairs confers almost the same amount of shear stress to the MMPR as jogging. The results of the present study may suggest that descending motion of the knee is an important cause of MMPR tear, and the initiation of descending stairs should be delayed after MMPR repair.

The Effect of Running Experience on Muscle Forces and Knee Joint Reaction Forces during Running

The Effect of Running Experience on Muscle Forces and Knee Joint Reaction Forces during Running

Comparison of the knee joint reaction force between individuals with and without acute anterior cruciate ligament rupture during walking

BackgroundAnterior cruciate ligament plays a significant role in knee joint stability. It is claimed that the incidence of knee osteoarthritis increases in individuals with anterior cruciate ligament (ACL) rupture. The aim of this study was to evaluate the knee joints reaction force in ACL rupture group compared to normal subjects.MethodFifteen patients with acute ACL rupture and 15 healthy subjects participated in this study. The ground reaction force (GRF) and kinematic data were collected at a sampling rate of 120 Hz during level-ground walking. Spatiotemporal parameters, joint angles, muscle forces and moments, and joint reaction force (JRF) of lower extremity were analyzed by OpenSIM software.ResultsThe hip, knee and ankle joints reaction force at loading response and push-off intervals of the stance phase during walking was significantly higher in individuals with ACL rupture compared to healthy controls (p value < 0.05). Walking velocity (p value < 0.001), knee (p value = 0.065) and ankle (p value = 0.001) range of motion in the sagittal plane were significantly lower in the patients with ACL rupture compared to healthy subjects. The mean value of vertical GRF in the mid-stance, the peak of the hip adduction moment in loading response and push-off phases, the hip abductor, knee flexor and vastus intermedius part of quadriceps muscle forces were significantly higher compared to healthy subjects (p < 0.05) while vastus medialis and vastus lateralis produced significantly lower force (p < 0.001).ConclusionsBased on results of this study, lower limb JRF was higher in those with ACL rupture compared to healthy subjects may be due to the compensatory mechanisms used by this group of subjects. An increase in knee JRF in patients with ACL rupture may be the reason for the high incidence of knee OA.

Altering the strength of the muscles crossing the lower limb joints only affects knee joint reaction forces

BackgroundGeneric musculoskeletal models based on literature data are often used to estimate joint reaction forces (JRFs) that otherwise could only be measured invasively. Estimated JRFs are sensitive to changes in maximum isometric force (Fiso) of the muscles, but these are normally simply scaled using a multiplicative coefficient. The impact of varying Fiso, or strength, of muscles crossing each lower limb joint on estimated JRFs has not been systematically explored in musculoskeletal models of the lower limb. Research QuestionHow do alterations in the strength of joint-crossing muscles influence the lower limb JRF magnitudes computed through a generic musculoskeletal model? MethodsBy modifying Fiso of muscles crossing hip, knee, ankle, or all joints at once up to ± 40% in 10% increments, thirty-two models were created to simulate the gait of a patient with an instrumented tibial prosthesis (5th Grand Challenge dataset). A standard workflow (inverse kinematics, static optimization, joint reaction analysis) was utilized to calculate JRFs. Both alterations in JRF magnitudes due to joint crossing muscles’ strength modifications and their accuracy against in vivo knee loading measurements were quantified. ResultsThe knee JRF was the most sensitive force to changes in the joint-crossing muscles’ strength (variations ranging from −37.9 ± 0.5% to +37.9 ± 3.2%), while the hip and ankle JRFs were almost unaffected (maximum variation: +6.1%). Reducing the strength of knee and ankle-crossing muscles and intensifying the strength of hip-crossing muscles lowered the knee JRF. The knee JRF was best estimated (peak error: 0.42 ± 0.15 body weight, root mean squared error: 0.37 ± 0.06 body weight, coefficient of determination: 0.76 ± 0.10) by the model with -40% weakened knee-crossing muscles. SignificanceAltering strengths mainly affects knee JRF estimated with generic musculoskeletal models, suggesting that personalization of strength of joint-crossing muscles is required for accurate knee JRF estimations. Rehabilitation regimes meant to strengthen muscles crossing a joint should be carefully designed to avoid undesired effects on the other joints.

Investigating acute changes in osteoarthritic cartilage by integrating biomechanics and statistical shape models of bone: data from the osteoarthritis initiative.

ObjectiveThis proof-of-principle study integrates joint reaction forces (JRFs) and bone shape to assess acute cartilage changes from walking and cycling.MethodsSixteen women with symptomatic knee osteoarthritis were recruited. Biomechanical assessment estimated JRFs during walking and cycling. Subsamples had magnetic resonance imaging (MRI) performed before and after a 25-min walking (n = 7) and/or cycling (n = 9) activity. MRI scans were obtained to assess cartilage shape and composition (T2 relaxation time). Bone shape was quantified using a statistical shape model built from 13 local participants and 100 MRI scans from the Osteoarthritis Initiative. Statistical parametric mapping quantified cartilage change and correlations between cartilage change with JRFs and statistical shape model features.ResultsCartilage thickness (interior lateral, Δ − 0.10 mm) and T2 (medial, Δ − 4 ms) decreased on the tibial plateau. On the femur, T2 change depended on the activity. Greater tibiofemoral JRF was associated with more cartilage deformation on the lateral femoral trochlea after walking (r − 0.56). Knees more consistent with osteoarthritis showed smaller decreases in tibial cartilage thickness.DiscussionWalking and cycling caused distinct patterns of cartilage deformation, which depended on knee JRFs and bone morphology. For the first time, these results show that cartilage deformation is dependent on bone shapes and JRFs in vivo.Supplementary InformationThe online version contains supplementary material available at 10.1007/s10334-022-01004-8.

Patellofemoral and tibiofemoral joint loading during a single-leg forward hop following ACL reconstruction.

Altered biomechanics are frequently observed following anterior cruciate ligament reconstruction (ACLR). Yet, little is known about knee-joint loading, particularly in the patellofemoral-joint, despite patellofemoral-joint osteoarthritis commonly occurring post-ACLR. This study compared knee-joint reaction forces and impulses during the landing phase of a single-leg forward hop in the reconstructed knee of people 12-24 months post-ACLR and uninjured controls. Experimental marker data and ground forces for 66 participants with ACLR (28 ± 6 years, 78 ± 15 kg) and 33 uninjured controls (26 ± 5 years, 70 ± 12 kg) were input into scaled-generic musculoskeletal models to calculate joint angles, joint moments, muscle forces, and the knee-joint reaction forces and impulses. The ACLR group exhibited a lower peak knee flexion angle (mean difference: -6°; 95% confidence interval: [-10°, -2°]), internal knee extension moment (-3.63 [-5.29, -1.97] percentage of body weight × participant height (body weight [BW] × HT), external knee adduction moment (-1.36 [-2.16, -0.56]% BW × HT) and quadriceps force (-2.02 [-2.95, -1.09] BW). The ACLR group also exhibited a lower peak patellofemoral-joint compressive force (-2.24 [-3.31, -1.18] BW), net tibiofemoral-joint compressive force (-0.74 [-1.20, 0.28] BW), and medial compartment force (-0.76 [-1.08, -0.44] BW). Finally, only the impulse of the patellofemoral-joint compressive force was lower in the ACLR group (-0.13 [-0.23, -0.03] body weight-seconds). Lower compressive forces are evident in the patellofemoral- and tibiofemoral-joints of ACLR knees compared to uninjured controls during a single-leg forward hop-landing task. Our findings may have implications for understanding the contributing factors for incidence and progression of knee osteoarthritis after ACLR surgery.

Lead limb loading during a single-step descent in persons with and without a transtibial amputation in the trailing limb

BackgroundDecreased mechanical work done by the trailing limb when descending a single-step could affect load development and increase injury risk on the leading limb. This study assessed the effect of trailing limb mechanics on the development of lead limb load during a step descent by examining individuals with unilateral transtibial amputations who are known to exhibit reduced work in the prosthetic limb. MethodsEight amputees and 10 able-bodied controls walked 5 m along the length of a raised platform, descended a single-step of 14 cm height, and continued walking. The intact limb of amputees led during descent. Kinematic and kinetic data were recorded using integrated motion capture and force platform system. Lead limb loading was assessed through vertical ground reaction force, and knee moments and joint reaction forces. Sagittal-plane joint work was calculated for the ankle, knee, and hip in both limbs. FindingsNo differences were found in lead limb loading despite differences in trail limb mechanics evidenced by amputees performing 58% less total work by the trailing (prosthetic) limb to lower the centre of mass (P = 0.004) and 111% less for propulsion (P < 0.001). Amputees descended the step significantly slower (P = 0.003) and performed significantly greater lead limb ankle work (P = 0.017). After accounting for speed differences, initial loading at the knee was significantly higher in the lead limb of amputees versus controls. InterpretationIncreasing lead limb work and reducing forward velocity may be effective compensatory strategies to limit lead limb loading during a step descent, in response to reduced trailing limb work.

Manual material handling in the supermarket sector. Part 2: Knee, spine and shoulder joint reaction forces

Manual material handling is common in supermarkets and may be a contributing factor to the high prevalence of work-related musculoskeletal disorders, particularly to the lower back. This cross-sectional study applied state-of-the-art musculoskeletal models driven by kinematic data obtained in two supermarkets to estimate joint reaction forces in the knees, shoulders and lumbar spine under dynamic lifting conditions. Based on 1479 lifts from 15 workers, 8 tasks for which the compression or shear forces in the L5-S1 joint exceeded well-known biomechanical tolerance limits were identified. High shoulder forces were associated with lifting relatively heavy merchandise to high shelves, while the weight of the handled merchandise was the main predictor of high knee forces. The study addressed well-known limitations associated with traditional lifting analysis tools and was the first to present a detailed analysis of the biomechanical loads during manual material handling tasks in the supermarket sector based on field measurements.

Foot Rotation Gait Modifications Affect Hip and Ankle, But Not Knee, Stance Phase Joint Reaction Forces During Running.

Alterations of foot rotation angles have successfully reduced external knee adduction moments during walking and running. However, reductions in knee adduction moments may not result in reductions in knee joint reaction forces. The purpose of this study was to examine the effects of internal and external foot rotation on knee, hip, and ankle joint reaction forces during running. Motion capture and force data were recorded of 19 healthy adults running at 3.35 m/s during three conditions: (1) preferred (normal) and with (2) internal and (3) external foot rotation. Musculoskeletal simulations were performed using opensim and the Rajagopal 2015 model, modified to a two degree-of-freedom knee joint. Muscle excitations were derived using static optimization, including muscle physiology parameters. Joint reaction forces (i.e., the total force acting on the joints) were computed and compared between conditions using one-way analyses of variance (ANOVAs) via statistical parametric mapping (SPM). Internal foot rotation reduced resultant hip forces (from 18% to 23% stride), while external rotation reduced resultant ankle forces (peak force at 20% stride) during the stance phase. Three-dimensional and resultant knee joint reaction forces only differed at very early and very late stance phase. The results of this study indicate, similar to previous findings, that reductions in external knee adduction moments do not mirror reductions in knee joint reaction forces.

Design and Evaluation of Torque Compensation Controllers for a Lower Extremity Exoskeleton.

In this article, we present an integrated human-in-the-loop simulation paradigm for the design and evaluation of a lower extremity exoskeleton that is elastically strapped onto human lower limbs. The exoskeleton has three rotational DOFs on each side and weighs 23 kg. Two torque compensation controllers of the exoskeleton are introduced, aiming to minimize interference and maximize assistance, respectively. Their effects on the wearer's biomechanical loadings are studied with a running motion and predicted ground reaction forces (GRFs). It is found that the added weight of the passive exoskeleton substantially increases the wearer's musculoskeletal loadings. The maximizing assistance controller reduces the knee joint torque by 31% when compared with the normal running (without exoskeleton) and by 50% when compared with the passive exoskeleton case. When compared with the normal running, this controller also reduces the hip flexion and extension torques by 31% and 38%, respectively. As a result, the peak activations of the biceps short head, gluteus maximus, and rectus femoris muscles are reduced by more than a half. Nonetheless, the axial knee joint reaction force increases for all exoskeleton cases due to the added weight and higher ground reaction forces. In summary, the results provide sound evidence of the efficacy of the proposed controllers on reducing the wearer's musculoskeletal loadings. And it is shown that the human-in-the-loop simulation paradigm presented here can be used for virtual design and evaluation of powered exoskeletons and pave the way for building optimized exoskeleton prototypes for experimental evaluation.

A Finite Element Model for Estimation of Contact Dynamics During a Jumping Movement on a Trampoline

In order to fully understand contact dynamics on a trampoline, a simulation approach using a musculoskeletal model coupled with a dynamic model of the trampoline is essential. The purpose of the study was to examine dynamics and selected lower extremity muscle forces in a landing and jumping movement on a trampoline, using a combination of finite element modeling and musculoskeletal modeling. The rigid frame of the trampoline was modeled in ADAMS and coupled with a finite element model of the elastic trampoline net surface in ANSYS. A musculoskeletal model of an elite trampoline athlete was further developed in LifeMod and combined with the finite element model of the trampoline. The results showed that the peak trampoline reaction forces (TRF) were 3400 N (6.6 BW) and 2900 N (5.6 BW) for the left and right limb, respectively. The right hip, knee and ankle joint reaction forces reached the maximum between 3000-4000 N (5.8 – 7.7 BW). The gluteus maximum and quadriceps reached the maximum muscle force of 380 N (0.7 BW) and 780 N (1.5 BW), respectively. Asymmetric loading patterns between left and right TRFs and lower extremities joint reaction forces were observed due to the need to generate the rotational movement during the takeoff. The observed rigid and erect body posture suggested that the hip and knee extensors played important roles in minimizing energy absorption and maximizing energy generation during the trampoline takeoff.

Effects Of Foot Rotation On Knee Joint Reaction Forces During Running

PURPOSE: The purpose of this study was to examine the effects of internal and external foot rotation on knee joint reaction forces during running. METHODS: Motion capture and force data were recorded on nineteen healthy adult runners (22.3±4.0 years, 67.99±10.27 kg, and 1.77±0.10 m) running at 3.5 m/s with normal and maximal comfortable external (EXT) and internal (INT) foot rotation. Musculoskeletal simulations were performed using the Rajagopal 2015 model and OpenSim (SimTK). All data were low pass filtered at 10 Hz and normalized to a full stride (stance: 0-36% & swing: 37-100% stride). Models were scaled to each subject’s anthropometric parameters. Inverse dynamics were derived by combining inverse kinematics and force data. Muscle excitations were derived using Static Optimization, including muscle physiology parameters. Joint Reaction Forces were obtained by combining inverse kinematics, force data, and muscle excitations. Within-subjects ANOVAs via Statistical Parametric Mapping were used to determine differences in resultant knee joint reaction force waveforms. RESULTS: The EXT condition decreased early stance (0-2% stride) and late swing (92-100% stride) phase forces, but increased forces during early swing (44-46%) phase compared to normal. The INT condition reduced forces during very late swing phase (92-94% stride). The EXT reduced forces during early stance (0-1% stride) and late swing (97-100% stride) compared to INT. CONCLUSIONS: Despite the known success of altered foot rotation on reducing external knee abduction moments during walking and running, knee forces were only reduced during low-loading portions of running strides. Thus, it appears altered foot rotations does not improve knee loading during running.

Muscular Not Skeletal Components Of Leg Stiffness Are Significantly Correlated With Associated Biomechanical Variables During Running

Muscular (kMusc) and skeletal (kSkel) components of leg stiffness have been previously related to injury patterns in runners [1]. Though these components mirror proposed injury mechanisms in runners, their relationship to underlying biomechanical variables remains unclear. PURPOSE: to evaluate the association between components of leg stiffness (kMusc & kSkel) with common biomechanical variables of muscular (joint work) and skeletal loading (joint reaction forces) during a running task. METHODS: Thirteen recreational runners (8 male, 5 female) performed ten over ground running trials at 3.35 m/s (±5%) in each of four conditions with varying shoe and strike patterns. Kinematics and ground reaction forces (GRFs) were recorded using an 8-camera motion capture system (240 Hz, Qualisys) and force platform (1200 Hz, OR-7, AMTI). Visual3D (C-Motion) was used to calculate joint powers and compressive joint reaction forces (JRFs). MATLAB was used to calculate negative joint work values and stiffness variables. kMusc and kSkel were calculated as previously reported [1]. Prism 8.0 (GraphPad) was used to perform correlation analyses between muscular and skeletal contributions to load attenuation. RESULTS: kMusc had moderate and weak relationships with lower extremity work (p < 0.01; r = 0.55) and knee joint work (p = 0.01; r = 0.32). Weak correlations existed between kSkel and ankle (p = 0.25; r = -0.10), knee (p = 0.17; r = 0.14) and hip joint reaction forces (p = 0.46; r = 0.01). CONCLUSIONS: These data revealed moderate associations between kMusc and negative work values suggesting that kMusc is proportional to muscular contributions to load attenuation. JRFs had weak associations with kSkel, suggesting kSkel may not represent skeletal loading. These findings suggest this simplistic model may be insufficient to describe muscular and skeletal contributions to load attenuation. [1] Powell, Paquette & Williams, 2017.

A Pilot Study of Musculoskeletal Abnormalities in Patients in Recovery from a Unilateral Rupture-Repaired Achilles Tendon

The purpose of this study was to compare the inter-limb joint kinematics, joint moments, muscle forces, and joint reaction forces in patients after an Achilles tendon rupture (ATR) via subject-specific musculoskeletal modeling. Six patients recovering from a surgically repaired unilateral ATR were included in this study. The bilateral Achilles tendon (AT) lengths were evaluated using ultrasound imaging. The three-dimensional marker trajectories, ground reaction forces, and surface electromyography (sEMG) were collected on both sides during self-selected speed during walking, jogging and running. Subject-specific musculoskeletal models were developed to compute joint kinematics, joint moments, muscle forces and joint reaction forces. AT lengths were significantly longer in the involved side. The side-to-side triceps surae muscle strength deficits were combined with decreased plantarflexion angles and moments in the injured leg during walking, jogging and running. However, the increased knee extensor femur muscle forces were associated with greater knee extension degrees and moments in the involved limb during all tasks. Greater knee joint moments and joint reaction forces versus decreased ankle joint moments and joint reaction forces in the involved side indicate elevated knee joint loads compared with reduced ankle joint loads that are present during normal activities after an ATR. In the frontal plane, increased subtalar eversion angles and eversion moments in the involved side were demonstrated only during jogging and running, which were regarded as an indicator for greater medial knee joint loading. It seems after an ATR, the elongated AT accompanied by decreased plantarflexion degrees and calf muscle strength deficits indicates ankle joint function impairment in the injured leg. In addition, increased knee extensor muscle strength and knee joint loads may be a possible compensatory mechanism for decreased ankle function. These data suggest patients after an ATR may suffer from increased knee overuse injury risk.

Statistical Modeling of Lower Limb Kinetics During Deep Squat and Forward Lunge.

PurposeModern statistics and higher computational power have opened novel possibilities to complex data analysis. While gait has been the utmost described motion in quantitative human motion analysis, descriptions of more challenging movements like the squat or lunge are currently lacking in the literature. The hip and knee joints are exposed to high forces and cause high morbidity and costs. Pre-surgical kinetic data acquisition on a patient-specific anatomy is also scarce in the literature. Studying the normal inter-patient kinetic variability may lead to other comparable studies to initiate more personalized therapies within the orthopedics.MethodsTrials are performed by 50 healthy young males who were not overweight and approximately of the same age and activity level. Spatial marker trajectories and ground reaction force registrations are imported into the Anybody Modeling System based on subject-specific geometry and the state-of-the-art TLEM 2.0 dataset. Hip and knee joint reaction forces were obtained by a simulation with an inverse dynamics approach. With these forces, a statistical model that accounts for inter-subject variability was created. For this, we applied a principal component analysis in order to enable variance decomposition. This way, noise can be rejected and we still contemplate all waveform data, instead of using deduced spatiotemporal parameters like peak flexion or stride length as done in many gait analyses. In addition, this current paper is, to the authors’ knowledge, the first to investigate the generalization of a kinetic model data toward the population.ResultsAverage knee reaction forces range up to 7.16 times body weight for the forwarded leg during lunge. Conversely, during squat, the load is evenly distributed. For both motions, a reliable and compact statistical model was created. In the lunge model, the first 12 modes accounts for 95.26% of inter-individual population variance. For the maximal-depth squat, this was 95.69% for the first 14 modes. Model accuracies will increase when including more principal components.ConclusionOur model design was proved to be compact, accurate, and reliable. For models aimed at populations covering descriptive studies, the sample size must be at least 50.