Anterior Shear Force Research Articles

Biomechanical Analysis of Rectus Femoris Kinesio Taping Effects on Post-Muscle Fatigue Stop-Jump Task Performance

Objectives: This study aims to compare the effects of kinesio tape (KT) on the rectus femoris muscle in athletes and novices under pre- and post-fatigue conditions. Methods: Nineteen male volunteers took part, and fatigue was assessed using the Borg CR10 Scale. Kinematic and kinetic data were collected using Vicon MX13+ infrared cameras (250 Hz) and Kistler force platforms (1500 Hz), respectively. Visual 3D v5.0 software analyzed the data, focusing on parameters like angular displacement, ground reaction forces (GRFs), impulse, and joint moments during a stop-jump task. A two-way mixed-design ANOVA was used to assess group, fatigue, and KT effects. Results: There was a significant effect after applying KT. The results showed significant differences in knee flexion range of motion (ROM), hip flexion moment, vertical impulse, and peak vertical GRFs between pre- and post-fatigue conditions (all p < 0.05). The trained group exhibited less knee valgus ROM, higher hip flexion velocity at initial contact, and prolonged time to peak proximal tibia anterior shear force. Conclusions: KT application was found to reduce lower limb loading, improve force acceptance and joint stability, and alleviate fatigue-induced disparities. These findings highlight the potential of KT in enhancing lower limb strength and performance, particularly under fatigue.

Differential influence of quadriceps rate of torque development on single- and double-leg landing mechanics in anterior cruciate ligament reconstructed and control females.

The capacity to explosively contract quadriceps within the critical timeframe associated with anterior cruciate ligament (ACL) injury, quantified by the rate of torque development, is potentially essential for safe landing mechanics. This study aimed to investigate the influence of explosive quadricepsstrength on ACL-related sagittal-plane landing mechanics in females with and without ACL reconstruction (ACLR). Quadricepsexplosive strength and landing mechanics were assessed in 19 ACLR and 19 control females during isometric contractions and double-and single-leg jump landings. A stepwise multiple linear regression model determined the variance in each of the landing biomechanics variables for the ACLR limb and nondominant limb of controls that could be explained by the group, rate of torque developmentand/or their interaction. If peak kinetic variables could be predicted by the rate of torque development or interaction, additional analyses were conducted, accounting for knee flexion as a covariate in the regression model. During single-leg landings, ACLR females exhibited greater knee flexion at initial contact than controls (p = 0.04). Greater quadricepsrate of torque development predicted higher peak posterior ground reaction force and anterior tibial shear force in both groups (p = 0.04). However, after controlling for knee flexion angle at those peak forces, quadriceps rate of torque development was not predictive. In double-leg landings, greater explosive quadriceps strength was associated with quicker attainment of peak knee extension moment and posterior ground reaction force in the ACLR limb (p = 0.03). Regardless of ACL injury status, females with greater explosive quadriceps strength adopted safer single-leg landings through increased knee flexion, potentially mitigating ACL loading despite encountering higher peak forces. During double-leg landings, a greater explosive quadriceps strength of the ACLR limb is associated with faster achievement of peak force upon landing. Incorporating explosive quadriceps strengthening into post-ACLR rehabilitation and injury prevention programmes may enhance landing mechanics for reducing primary and subsequent ACL injury risks. Level II.

Ground reaction force analysis in flexible and rigid flatfoot subjects

BackgroundFlatfoot is a structural and functional deformity of the foot that might change ground reaction force variables of gait. Evaluating the components of ground reaction force in three dimensions during gait is considered clinically important. This study aimed to investigate the components of ground reaction force, impulse, and loading rate during gait in people with flexible and rigid flatfoot compared to healthy subjects. 20 young women with flatfoot in two experimental groups (10 with rigid flatfoot and 10 with flexible flatfoot) and 10 healthy women in the control group participated in this study. Ground reaction force components during gait were measured using two force plates. The peak of ground reaction forces, impulse, and loading rate were then extracted. Data were processed and analyzed using MATLAB and SPSS software. One-way ANOVA with a significant level (P˂0.05) was used for statistical analysis. The results showed that peak braking force was higher in the rigid flatfoot group than in the control group (p = 0.016) and the flexible flatfoot group (p = 0.003). The posterior force loading rate was significantly higher in the rigid flatfoot group than in the flexible flatfoot group (P = 0.04). There was no significant difference in vertical loading rate between groups (P˃0.05). Since the maximal posterior ground reaction force was higher in the subjects with rigid flatfoot than in those with flexible flatfoot and healthy subjects, the increase in posterior ground reaction force is associated with an increase in anterior shear force at the knee.

Biomechanical analysis of complications following T10-Pelvis spinal fusion: A population based computational study

Proximal junctional kyphosis (PJK) and proximal junctional failure (PJF) are challenging complications of long fusion constructs for the treatment of adult spinal deformity. The objective of this study is to understand the biomechanical stresses proximal to the upper instrumentation of a T10-pelvis fusion in a large patient cohort. The pre-fusion models were subject-specific thoracolumbar spine models that incorporate the height, weight, spine curvature, and muscle morphology of 250 individuals from the Framingham Heart Study Multidetector CT Study. To create post-fusion models, the subject-specific models were further modified to eliminate motion between the intervertebral joints from T10 to the pelvis. OpenSim analysis tools were used to calculate the medial lateral shear force, anterior posterior shear force, and compressive force on the T9 vertebra during the static postures. Differences between pre-fusion and post-fusion T9 biomechanics were consistent between increased segmental mobility and unchanged segmental mobility conditions.For all static postures, compression decreased (p < 0. 0005). Anterior-posterior shear force significantly increased (p < 0. 0005) during axial twist and significantly increased (p < 0. 0005) during trunk flexion. Medial lateral shear force significantly increased (p < 0. 0005) during axial twist. This computational study provided the first use of subject-specific models to investigate the biomechanics of long spinal fusions. Patients undergoing T10-Pelvis fusion were predicted to have increased shear forces and decreased compressive force at the T9 vertebra, independent of change in segmental mobility. The computational model shows potential for the investigation of spinal fusion biomechanics to reduce the risk of PJK or PJF.

Influencing factors on effectiveness of reverse total shoulder arthroplasty

To summarize the influencing factors on the effectiveness of reverse total shoulder arthroplasty (RTSA), so as to provide reference for clinical treatment. The related research literature of RTSA at home and abroad was extensively consulted, and the factors that may affect the effectiveness were summarized from the aspects of surgical technique, muscle condition, general condition of patients, psychological expectation, and lifestyle. For surgical techniques, different surgical approaches have their own advantages. The glenoid notch, poor bone ingrowth, increased bone resorption, and infection would lead to the loosening of glenoid prosthesis. In addition, the neck shaft angle and inclination angle of humeral prosthesis affect the occurrence of glenoid notch and the range of motion of joint internal/external rotation after operation, respectively. For muscle condition, the quality of teres minor and deltoid muscle has an important influence on joint stability after operation. Moderate increase of deltoid muscle tension can improve joint mobility after operation, and suture repair of subscapular tendon during operation can relieve joint pain and improve function, range of motion, and strength. For the general condition of patients, gender, age, and body mass index are all related to postoperative joint function and complications, and different occupations and postoperative exercise levels affect the recovery. The patients with severe degenerative diseases, poor preoperative function, and long disease duration have lower expectations and higher satisfaction with the effectiveness, and bad lifestyle has a negative impact on the effectiveness. The effectiveness of RTSA is related to surgical technique, muscle condition, general condition of patients, psychological expectation, and lifestyle. In order to avoid the loosening of glenoid prosthesis, the operator should choose humeral prosthesis with small neck shaft angle and large glenoid ball and put them down and inclined inferiorly during operation, and choose appropriate approach to eliminate space with drainage to reduce the risk of infection. After operation, patients should avoid activities that generate high anterior and posterior shear forces. In addition, the humeral prosthesis with a inclination angle of 10°-20° can achieve the best balance between the range of internal rotation and external rotation after operation. Proper deltoid tension can maintain joint stability and good range of motion. Suture of subscapular tendon is recommended.

Increased Posterior Tibial Slope Increases Force on the Posterior Medial Meniscus Root

Background: Posterior medial meniscus root (PMMR) tears have been associated with increased posterior tibial slope, but this has not been fully evaluated biomechanically. In addition, the effects of knee flexion and rotation on the PMMR are not well understood biomechanically because of technological testing limitations. A novel multiaxial force sensor has made it possible to elucidate answers to these questions. Purpose: (1) To determine if increased posterior tibial slope results in increased posterior shear force and compression on the PMMR, (2) to evaluate how knee flexion angle affects PMMR forces, and (3) to assess how internal and external rotation affects force at the PMMR. Study Design: Controlled laboratory study. Methods: Ten fresh-frozen cadaveric knees were tested in all combinations of 3 posterior tibial slopes and 4 flexion angles. A multiaxial force sensor was connected to the PMMR and installed below the posterior tibial plateau maintaining anatomic position. The specimen underwent a 500-N compression load followed by a 5-N·m internal torque and a 5-N·m external torque. The magnitude and direction of the forces acting on the PMMR were measured. Results: Under joint compression, an increased tibial slope significantly reduced the tension on the PMMR between 5° and 10° (from 13.5 N to 6.4 N), after which it transitioned to a significant increase in PMMR compression, reaching 7.6 N at 15°. Under internal torque, increased tibial slope resulted in 4.7 N of posterior shear at 5° significantly changed to 2.0 N of anterior shear at 10° and then 8.2 N of anterior shear at 15°. Under external torque, increased tibial slope significantly decreased PMMR compression (5°: 8.9 N; 10°: 4.3 N; 15°: 1.1 N). Under joint compression, increased flexion angle significantly increased medial shear forces of the PMMR (0°, 3.8 N; 30°, 6.2 N; 60°, 7.3 N; 90°, 8.4 N). Under internal torque, 90° of flexion significantly increased PMMR tension from 2.3 N to 7.5 N. Under external torque, 30° of flexion significantly increased PMMR compression from 4.7 N to 12.2 N. Conclusion: An increased posterior tibial slope affects compression and anterior shear forces at the PMMR. An increased flexion angle affects compression, tension, and medial shear forces at the PMMR. Clinical Relevance: The increase in compression and posterior shear force when the knee is loaded in compression may place the PMMR under increased stress and risk potential failure after repair. This study provides clinicians with information to create safer protocols and improve repair techniques to minimize the forces experienced at the PMMR.

Effect of Whole Body Parameters on Knee Joint Biomechanics: Implications for ACL Injury Prevention During Single-Leg Landings

Background: Previous studies have examined the effect of whole body (WB) parameters on anterior cruciate ligament (ACL) strain and loads, as well as knee joint kinetics and kinematics. However, articular cartilage damage occurs in relation to ACL failure, and the effect of WB parameters on ACL strain and articular cartilage biomechanics during dynamic tasks is unclear. Purposes: (1) To investigate the effect of WB parameters on ACL strain, as well as articular cartilage stress and contact force, during a single-leg cross drop (SLCD) and single-leg drop (SLD). (2) To identify WB parameters predictive of high ACL strain during these tasks. Study Design: Descriptive laboratory study. Methods: Three-dimensional motion analysis data from 14 physically active men and women were recorded during an SLCD and SLD. OpenSim was used to obtain their kinematics, kinetics, and muscle forces for the WB model. Using these data in kinetically driven finite element simulations of the knee joint produced outputs of ACL strains and articular cartilage stresses and contact forces. Spearman correlation coefficients were used to assess relationships between WB parameters and ACL strain and cartilage biomechanics. Moreover, receiver operating characteristic curve analyses and multivariate binary logistic regressions were used to find the WB parameters that could discriminate high from low ACL strain trials. Results: Correlations showed that more lumbar rotation away from the stance limb at peak ACL strain had the strongest overall association (ρ = 0.877) with peak ACL strain. Higher knee anterior shear force (ρ = 0.895) and lower gluteus maximus muscle force (ρ = 0.89) at peak ACL strain demonstrated the strongest associations with peak articular cartilage stress or contact force in ≥1 of the analyzed tasks. The regression model that used muscle forces to predict high ACL strain trials during the dominant limb SLD yielded the highest accuracy (93.5%), sensitivity (0.881), and specificity (0.952) among all regression models. Conclusion: WB parameters that were most consistently associated with and predictive of high ACL strain and poor articular cartilage biomechanics during the SLCD and SLD tasks included greater knee abduction angle at initial contact and higher anterior shear force at peak ACL strain, as well as lower gracilis, gluteus maximus, and medial gastrocnemius muscle forces. Clinical relevance: Knowledge of which landing postures create a high risk for ACL or cartilage injury may help reduce injuries in athletes by avoiding those postures and practicing the tasks with reduced high-risk motions, as well as by strengthening the muscles that protect the knee during single-leg landings.

Association Between the Medial-Lateral Quadriceps and Hamstring Muscle Thickness and the Knee Kinematics and Kinetics During Single-Leg Landing.

Muscle thickness can influence the joint kinematics and/or kinetics during dynamic activities. The relationship between the muscle thickness of individual quadriceps and hamstrings or medial-to-lateral thigh muscle thickness ratio and the knee kinematics/kinetics with respect to anterior cruciate ligament (ACL) injury risk remains unclear. Higher medial-to-lateral thigh muscle thickness ratio would be associated with lower knee valgus angle/moment and lower tibial internal rotation angle/moment during single-leg landing. Cross-sectional. Level 4. Muscle thickness of the vastus lateralis (VL), vastus medialis (VM), biceps femoris (BF), and semitendinosus (ST) of 30 healthy participants (16 males and 14 females) were measured using ultrasound. Knee joint kinematics and kinetics during single-leg landing were obtained. Stepwise multiple regression analysis, a follow-up Fisher's r to z test to examine the sex as a moderator, and independent t tests to evaluate sex difference were performed. Both knee valgus moment (R2 = 0.466, P < 0.001) and tibial external rotation moment (R2 = 0.330, P < 0.001) at peak anterior tibial shear force during single-leg landing were negatively correlated with medial-to-lateral (ie, (VM+ST):(VL+BF)) thickness ratio regardless of sex, whereas medial-to-lateral thigh muscle thickness ratio was not correlated with knee valgus and tibial external rotation angles. Male participants exhibited higher (VM+ST):(VL+BF) thickness ratio than female participants (P = 0.005), and lower knee valgus moment (P = 0.04) and tibial external rotation moment (P = 0.05), as well. The knee joint moments in frontal and transverse planes during single-leg landing were associated with the medial-to-lateral thigh muscle thickness ratio; thus, the medial-lateral thigh muscle thickness could be a potential contributor to frontal and transverse plane knee joint loading during dynamic movement. Strength training that aims to selectively strengthen the medial/lateral thigh muscles might be considered in a new ACL injury prevention training program to alter the biomechanical parameters associated with ACL injuries.

Dynamics of Two-Link Musculoskeletal Chains during Fast Movements: Endpoint Force, Axial, and Shear Joint Reaction Forces

This study provides a dynamic model for a two-link musculoskeletal chain controlled by single-joint and two-joint muscles. The chain endpoint force, and the axial and shear components of the joint reaction forces, were expressed analytically as a function of the muscle forces or torques, the chain configuration, and the link angular velocities and accelerations. The model was applied to upper-limb ballistic push movements involving transverse plane shoulder flexion and elbow extension. The numerical simulation highlights that the shoulder flexion and elbow extension angular acceleration at the initial phase of the movement, and the elbow extension angular velocity and acceleration at the later phase of the movement, induce a proportional medial deviation in the endpoint force direction. The forearm angular velocity and acceleration selectively affect the value of the axial and shear components of the shoulder reaction force, depending on the chain configuration. The same goes for the upper arm and elbow. The combined contribution of the elbow extension angular velocity and acceleration may give rise to anterior shear force acting on the humerus and axial forearm traction force as high as 300 N. This information can help optimize the performance and estimate/control of the joint loads in ballistic sport activities and power-oriented resistance exercises.

Correlation of Lower Limb Muscle Activity with Knee Joint Kinematics and Kinetics during Badminton Landing Tasks

A study on a single-leg landing task after an overhead stroke in badminton suggests that poor knee biomechanical indicators may be a risk factor for anterior cruciate ligament (ACL) injury. A preventive program targeting neuromuscular control strategies is said to alter the biomechanics of the knee joint and have a beneficial effect on reducing ACL injury. However, the relationship between muscle activity around the knee joint and knee biomechanical risk factors in the badminton landing task is unclear. The purpose of this study was to investigate the relationship between this movement pattern of muscle activity and knee kinematics and kinetics. This experiment analyzed knee muscle activity and biomechanical information in a sample of 34 badminton players (17 male, 17 female) during a badminton landing task. We assessed the relationship between the rectus femoris (RF), medial hamstring (MHAM), lateral hamstring (LHAM), medial gastrocnemius (MGAS), lateral gastrocnemius (LGAS), medial and lateral hamstring to quadriceps co-contraction ratio (MH/Q and LH/Q) with the knee flexion angle, valgus angle, extension moment, valgus moment, and proximal tibial anterior shear force. A moderate negative correlation was found between the peak knee flexion angle and electromyography (EMG) activity in LGAS (r = 0.47, p = 0.0046, R2 = 0.23, 95% CI: 0.16 to 0.70). Peak proximal tibial shear force showed strong and positive correlations with RF EMG activity (r = 0.52, p = 0.0016, R2 = 0.27, 95% CI: 0.22 to 0.73) and strong and negative correlations with MH/Q (r = 0.50, p = 0.0023, R2 = 0.25, 95% CI: 0.20 to 0.72). The knee extension moment showed moderate and positive correlations with RF EMG activity (r = 0.48, p = 0.0042, R2 = 0.23, 95% CI: 0.17 to 0.70) and strong and negative correlations with MH/Q (r = 0.57, p = 0.0004, R2 = 0.33, 95% CI: 0.29 to 0.76). The peak knee valgus moment showed strong and positive correlations with LH/Q (r = 0.55, p = 0.0007, R2 = 0.31, 95% CI: 0.26 to 0.75). Our findings suggest that there is a correlation between lower extremity muscle activity and knee kinematics and kinetics during the single-leg landing task in badminton; therefore, lower extremity muscle activity should be considered when developing rehabilitation or injury prevention programs.

Predicting the Effect of Localized ACL Damage on Neighbor Ligament Mechanics via Finite Element Modeling.

The anterior cruciate ligament (ACL) plays a pivotal role in support of the knee under loading. When damaged, it is known that substantial changes in the mechanics of the neighboring ligaments can be observed. However, a localized damage approach to investigating how ACL deficiency influences the neighboring ligaments has not been carried out. To do this, a finite element model, incorporating a continuum damage material model of the ACL, was implemented. Localized ACL damage was induced using high quadriceps force loading. Once damaged, anterior shear forces or tibial torque loadings were applied to the knee joint. The relative changes in stress contour and average mid-substance stress were examined for each of the neighboring ligaments following localized ACL damage. It was observed that localized ACL damage could produce notable changes in the mechanics of the neighboring knee ligaments, with non-homogenous stress contour shape changes and average stress magnitude being observed to increase in most cases, with a notable exception occurring in the MCL for both loading modes. In addition, the ligament bearing the most loading also changed with ACL deficiency. These changes carry implications as to morphological effects that may be induced following localized ACL damage, indicating that early diagnosis of ACL injury may be helpful in mitigating other complications post injury.

164. Biomechanical analysis of the endplate fixation methods of cervical total disc replacement (TDR) prostheses to shear force expulsion

<h3>BACKGROUND CONTEXT</h3> Current methods for achieving immediate endplate fixation with cervical TDR include the use of keels or spiked teeth. Nonphysiologic push-out or expulsion tests are typically used to measure the distraction force and mechanical work required to expulse the device. <h3>PURPOSE</h3> To determine the failure work and load required to expulse the upper and lower components of the 4 different cervical prostheses after undergoing multidirectional cyclic testing. Endplate configurations included single central keel, tripod keel, and spiked teeth. <h3>STUDY DESIGN/SETTING</h3> Each device was implanted in a cervical functional spinal unit (FSU) and cyclically loaded 2,000 times under physiological ranges of combined flexion/extension coupled with axial rotation at a rate of 2.5deg/s. Following cyclic testing, the specimens were disarticulated through the disc space, separated into upper and lower segments and mounted in a robotic testing platform for expulsion testing. <h3>PATIENT SAMPLE</h3> Sixteen (C4-C5) and 16 (C6-C7) FSUs were dissected from 8 male and 8 female cadaveric cervical spines with an average age of 55.9 +/- 9.7 years. Three FSUs were not usable due to poor tissue quality which reduced the sample size to 29 FSUs. <h3>OUTCOME MEASURES</h3> Shear expulsion force and distraction displacement were measured and combined to calculate the expulsion work, the resistive stiffness. The peak expulsion force was also obtained. Normality of the expulsion data was tested using the Shapiro-Wilk test (for p=0.05). If normality failed, a nonparametric Kruskal-Wallis test with Bonferroni correction was used to analyze the data between implant types. An additional test was done to compare the shear expulsion parameters between the upper and lower components of the same implant type. A similar normality test as above was used and a (2 tailed) Mann-Whitney U test was used here when normality failed. <h3>Methods</h3> Four ball and socket type cervical disc prostheses having different endplate fixation features were tested: 1. A clinically used and FDA approved single central keel (SCK), 2. A clinically used (outside the U.S.) low profile teeth (LPT) with domed endplate shape to allow a better fit in case of concave vertebral endplate, 3. A clinically used (outside the U.S.) tripod keel (TK), and 4. Small single keel (SSK). A minimum sample size of 6 implants per prosthesis type were used. Three additional TK disc prostheses and two additional LPT disc prostheses were implanted. A minimum of 6 implants per prosthesis type were used. Specimens were mounted in a robotic testing platform programmed to apply a 50N compressive load to the top surface of the disc, followed by an anterior shear force to the backside of the implant until the device was fully expulsed. <h3>Results</h3> Mean and standard deviations for peak expulsion forces were 69(41)N, 62(21)N, 110(71)N and 78(36)N, expulsion work were 321(225)Nmm, 399(161)Nmm, 463(305)Nmm, and 296(149)Nmm, and resistive stiffness were 81(61)N/mm, 44(42)Nmm, 163(207)Nmm, and 150(149)Nmm. No significant differences occurred between implant types for any of expulsion data. Further, no significant differences were found between the upper and lower components of any implant type except for the expulsion work term of the traditional central keel device (p=0.037). <h3>Conclusions</h3> The distraction failure strength of three different cervical disc prostheses was comparable to an existing FDA approved central-based keel designed disc prosthesis. <h3>FDA DEVICE/DRUG STATUS</h3> Prodisc C (Approved for this indication), Prodisc C Vivo (Investigational/Not approved), Prodisc C Nova (Investigational/Not approved), Prodisc C SK (Investigational/Not approved)

An Investigation of Differences in Lower Extremity Biomechanics During Single-Leg Landing From Height Using Bionic Shoes and Normal Shoes.

Bionic shoes utilizing an actual foot shape sole structure can alter lower limb’s biomechanics, which may help in the development of specific training or rehabilitation programs. The purpose of this study was to investigate the biomechanical differences in the lower limb during a single-leg landing task using bionic shoes (BS) and normal shoes (NS). Fifteen healthy male subjects participated in this study, sagittal, and frontal plane data were collected during the landing phase (drop landing from 35 cm platform). Our study showed that BS depicted a significantly greater minimum knee flexion angle at initial contact (p = 0.000), a significantly greater minimum (initial contact) hip flexion angle at initial contact (p = 0.009), a significantly smaller sagittal plane total energy dissipation (p = 0.028), a significantly smaller frontal plane total energy dissipation (p = 0.008), a significantly smaller lower limb total energy dissipation (p = 0.017) than NS during the landing phase. SPM analysis revealed that BS depicted a significantly smaller knee joint vertical reaction force during the 13.8–19.8% landing phase (p = 0.01), a significantly smaller anterior tibia shear force during the 14.2–17.5% landing phase (p = 0.024) than NS. BS appears to change lower limb kinematics at initial contact and then readjust the landing strategies for joint work and joint reaction force, thereby reducing the risk of lower limb skeletal muscle injury. BS have great potential for future development and application uses, which may help athletes to reduce lower limb injury risk.

Increased Ankle Range of Motion Reduces Knee Loads During Landing in Healthy Adults.

Decreased dorsiflexion range of motion (DROM) can be modified using static stretching and joint mobilizations and may attenuate known knee anterior cruciate ligament injury risk factors. It is not known how these interventions compare to each other and how they improve knee landing mechanics. This study's purpose was to determine the immediate effects of static stretching and joint mobilization interventions on DROM measurement changes and right-leg drop jump knee landing mechanics. Eighteen females and 7 males, all recreationally active, completed 2 study sessions. Active and passive DROM, the weight-bearing lunge test, the anterior reach portion of the Star Excursion Balance Test, and a right-leg drop jump landing task were completed before and after the intervention. Change in DROM (ΔDROM) was calculated for DROM assessments between preintervention and postintervention. Pairwise dependent t tests determined no differences in ΔDROM between interventions, and statistical parametric mapping determined increased knee flexion (P = .004) and decreased anterior shear force (P = .015) during landing after both interventions. Increased DROM improves sagittal plane displacement and loading at the knee. Stretching may be a more feasible option in a healthy population for those wanting to maintain range of motion and decrease knee injury risk without physical therapist involvement.

Exploring lumbar and lower limb kinematics and kinetics for evidence that lifting technique is associated with LBP

To investigate if lumbar and lower limb kinematics or kinetics are different between groups with and without a history of LBP during lifting. Secondly, to investigate relationships between biomechanical variables and pain ramp during repeated lifting. 21 LBP and 20 noLBP participants completed a 100-lift task, where lumbar and lower limb kinematics and kinetics were measured during lifting, with a simultaneous report of LBP intensity every 10 lifts. Lifts were performed in a laboratory setting, limiting ecological validity. The LBP group used a different lifting technique to the noLBP group at the beginning of the task (slower and more squat-like). Kinetic differences at the beginning included less peak lumbar external anterior shear force and greater peak knee power demonstrated by the LBP group. However, at the end of the task, both groups lifted with a much more similar technique that could be classified as more stoop-like and faster. Peak knee power remained greater in the LBP group throughout and was the only kinetic difference between groups at the end of the lifting task. While both groups lifted using a more comparable technique at the end, the LBP group still demonstrated a tendency to perform a slower and more squat-like lift throughout the task. Only one of 21 variables (pelvic tilt at box lift-off), was associated with pain ramp in the LBP group. Conclusions: Workers with a history of LBP, lift with a style that is slower and more squat-like than workers without any history of LBP. Common assumptions that LBP is associated with lumbar kinematics or kinetics such as greater lumbar flexion or greater forces were not observed in this study, raising questions about the current paradigm around 'safe lifting'.

Muscle force contributions to ankle joint contact forces during an unanticipated cutting task in people with chronic ankle instability

The purpose of this study was to compare muscle force contributions to ankle joint compression and anteroposterior shear forces between people with chronic ankle instability (CAI) and healthy controls (CON) during an unanticipated cutting task. Eleven people with CAI and 11 CON performed an unanticipated cutting task as three-dimensional motion capture, ground reaction force (GRF), and muscle activation data were collected. A musculoskeletal modeling was used to calculate talocrural joint compression and anteroposterior shear forces and parse out the contributions to these forces from ankle-spanning muscles and from GRF. Independent t-tests were used for statistical analysis. People with CAI exhibited greater anterior shear force peaks during early (p = 0.048, d = 0.98) and late (p = 0.017,d = 1.21) stance compared to CON. The difference in early stance shear force appeared to arise from greater GRF contribution (p = 0.026, d = 1.12) in CAI group, whereas the difference in late stance shear force appeared to arise from greater contribution of lateral gastrocnemius (p = 0.026, d = 1.12), medial gastrocnemius (p = 0.048, d = 0.98), tibialis posterior (p = 0.017, d = 1.22), fibularis brevis (p = 0.035, d = 1.05), and fibularis longus (p = 0.023, d = 1.15). People with CAI exhibit greater anterior shear, but not compressive forces in talocrural joint during an unanticipated cutting task. The differences in anterior shear force were the result of passive and active contributions from GRF during early stance and lower leg muscles during late stance, respectively.

Exposure to Sustained Flexion Impacts Lumbar Extensor Spinae Muscle Fiber Orientation.

The lumbar extensor spinae (LES) has an oblique orientation with respect to the compressive axis of the lumbar spine, allowing it to counteract anterior shear forces. This mechanical advantage is lost as spine flexion angle increases. The LES orientation can also alter over time as obliquity decreases with age and is associated with decreased strength and low back pain. However, it is unknown if LES orientation is impacted by recent exposures causing adaptations over shorter timescales. Hence, the effects of a 10-minute sustained spine flexion exposure on LES orientation, thickness, and activity were investigated. Three different submaximally flexed spine postures were observed before and after the exposure. At baseline, orientation (P < .001) and thickness (P = .004) decreased with increasingly flexed postures. After the exposure, obliquity further decreased at low (pairwise comparison P < .001) and moderately (pairwise comparison P = .008) flexed postures. Low back creep occurred, but LES thickness did not change, indicating that decreases in orientation were not solely due to changes in muscle length at a given posture. Activation did not change to counteract decreases in obliquity. These changes encompass a reduced ability to offset anterior shear forces, thus increasing the potential risk of anterior shear-related injury or pain after low back creep-generating exposures.

Greater explosive quadriceps strength is associated with greater knee flexion at initial contact during landing in females

ABSTRACT This study investigated the influences of explosive quadriceps strength and landing task on sagittal plane knee biomechanics. Forty female participants performed isometric knee extensions on a dynamometer and had lower extremity biomechanics assessed during double-leg jump-landings (DLJL) and single-leg jump-cuts (SLJC). Explosive quadriceps strength was quantified by calculating rate of torque development (RTD) between torque onset and 100 ms after onset on a dynamometer. Participants were stratified into high and low RTD groups. Landing biomechanics were compared using 2 (Group) × 2 (Task) mixed-model ANOVAs. The relationships between quadriceps RTD and landing biomechanics were also assessed using simple, bivariate correlations. Across RTD groups, greater knee flexion at initial contact (KFIC), peak vertical ground reaction force, peak anterior tibial shear force, and peak internal knee extension moment, and lesser peak knee flexion was observed during SLJC compared to DLJL. The high RTD group exhibited significantly greater KFIC than the low RTD group across landing tasks. Greater quadriceps RTD was significantly associated with greater KFIC during SLJC, but not during DLJL. As landing with lesser KFIC is a risk factor for ACL injury, greater explosive quadriceps strength capacity might be beneficial for facilitating the use of safer landing mechanics during athletic tasks.

Load-Sharing and Kinematics of the Human Cervical Spine Under Multi-Axial Transverse Shear Loading: Combined Experimental and Computational Investigation.

The cervical spine experiences shear forces during everyday activities and injurious events yet there is a paucity of biomechanical data characterizing the cervical spine under shear loading. This study aimed to (1) characterize load transmission paths and kinematics of the subaxial cervical spine under shear loading, and (2) assess a contemporary finite element cervical spine model using this data. Subaxial functional spinal units (FSUs) were subjected to anterior, posterior, and lateral shear forces (200 N) applied with and without superimposed axial compression preload (200 N) while monitoring spine kinematics. Load transmission paths were identified using strain gauges on the anterior vertebral body and lateral masses and a disc pressure sensor. Experimental conditions were simulated with cervical spine finite element model FSUs (GHBMC M50 version 5.0). The mean kinematics, vertebral strains, and disc pressures were compared to experimental results. The shear force-displacement response typically demonstrated a toe region followed by a linear response, with higher stiffness in anterior shear relative to lateral and posterior shear. Compressive axial preload decreased posterior and lateral shear stiffness and increased initial anterior shear stiffness. Load transmission patterns and kinematics suggest the facet joints play a key role in limiting anterior shear while the disc governs motion in posterior shear. The main cervical spine shear responses and trends are faithfully predicted by the GHBMC cervical spine model. These basic cervical spine biomechanics and the computational model can provide insight into mechanisms for facet dislocation in high severity impacts, and tissue distraction in low severity impacts.

Low-Profile Electromagnetic Field Sensors in the Measurement and Modelling of Three-Dimensional Jaw Kinematics and Occlusal Loading.

Dynamic occlusal loading during mastication is clinically relevant in the design and functional assessment of dental restorations and removable dentures, and in evaluating temporomandibular joint dysfunction. The aim of this study was to develop a modelling framework to evaluate subject-specific dynamic occlusal loading during chewing and biting over the entire dental arch. Measurements of jaw motion were performed on one healthy male adult using low-profile electromagnetic field sensors attached to the teeth, and occlusal anatomy quantified using an intra-oral scanner. During testing, the subject chewed and maximally compressed a piece of rubber between both second molars, first molars, premolars and their central incisors. The occlusal anatomy, rubber geometry and experimentally measured rubber material properties were combined in a finite element model. The measured mandibular motion was used to kinematically drive model simulations of chewing and biting of the rubber sample. Three-dimensional dynamic bite forces and contact pressures across the occlusal surfaces were then calculated. Both chewing and biting on the first molars produced the highest bite forces across the dental arch, and a large amount of anterior shear force was produced at the incisors and the second molars. During chewing, the initial tooth-rubber contact evolved from the buccal sides of the molars to the lingual sides at full mouth closure. Low-profile electromagnetic field sensors were shown toprovide a clinically relevant measure of jaw kinematics with sufficient accuracy to drive finite element models of occlusal loading during chewing and biting. The modelling framework presented provides a basis for calculation of physiological, dynamic occlusal loading across the dental arch.