Anterior Force Research Articles

The function of cruciate ligaments in bi-cruciate retaining Total knee arthroplasty with asymmetrical design

BackgroundBi-cruciate retaining total knee arthroplasty with an asymmetrical design may improve knee function and clinical outcomes. This study aimed to compare the kinematics, anteroposterior laxity, and in situ forces of the anterior and posterior cruciate ligaments of knees subjected to this treatment with those of healthy knees. MethodsSeven fresh-frozen cadaveric knees were tested using a robotic/universal force-moment sensor system. The kinematics during passive flexion-extension motion and anteroposterior laxity for native knee, treated knee, and treated knee with cruciate ligament transection states were investigated. The motions of the intact and treated knees during each test were repeated after anterior/posterior cruciate ligament transection to calculate the in situ force in the ligaments. FindingsThe screw-home movement of normal knees disappeared after treatment. The in situ force of the anterior cruciate ligament in treated knees was higher than that in intact knees at ˃15° during flexion and at 60° and 90° against an anterior force. The in situ force of the posterior cruciate ligament in treated knees was higher at 0°, 15°, and 30° during flexion and at all flexion angles against a posterior force. InterpretationThe screw-home movement of normal knees decreased, and the in situ force of the anterior and posterior cruciate ligaments increased after treatment.

Clinically Established Temporomandibular Involvement in Adults With Juvenile Idiopathic Arthritis.

To study clinical variables defining temporomandibular function in adults with juvenile idiopathic arthritis (JIA) and healthy controls. In this cross-sectional study, the temporomandibular joint (TMJ) screening protocol, mandibular range of motion (MROM), and anterior maximum voluntary bite force (AMVBF) were compared between adults with JIA and healthy controls. Unadjusted and adjusted models with corrections for sex and disease duration were constructed for active maximum interincisal mouth opening (AMIO) and AMVBF. A total of 100 adults with JIA and 59 healthy adults were included in this study. In adults with JIA, 56% had clinically established TMJ involvement. AMIO was the MROM variable most reduced by TMJ involvement; AMIO was 8.8 mm (95% CI -11.40 to -6.12; P < 0.001) less in adults with JIA with TMJ involvement compared to JIA without TMJ involvement. No differences of AMIO were found between healthy adults and adults with JIA without TMJ involvement (-2.52, 95% CI -5.13 to 0.10; P = 0.06). Male sex was associated with a higher AMIO, and disease duration was associated with a decreased AMIO. Collinearity between the subtype prebiologic era and disease duration was found. AMVBF did not differ between adults with JIA and healthy adults. The high prevalence of clinically established TMJ involvement in adults with JIA indicates the need for awareness of TMJ problems in adults with JIA. TMJ involvement negatively influenced AMIO and should therefore be part of the TMJ screening in adults with JIA. AMVBF seems to have less utility for TMJ screening in adult populations.

Changes in the distribution of occlusal forces in the course of the orthodontic retention phase : Aprospective cohort study.

Aim of the present study was to assess the relative distribution of occlusal forces after orthodontic treatment and during the first 3months of the retention phase using acomputerized occlusal analysis system (T-Scan, Tekscan Inc., Norwood, MA, USA). A total of 52patients were included in this prospective cohort study and underwent analysis of occlusal forces on the level of tooth, jaw-half, and -quadrant during a3-month period. Furthermore, differences between three retention protocols (groupI: removable appliances in both jaws; groupII: fixed 3-3 lingual retainers in both jaws; groupIII: removable appliance in the maxilla and fixed 3-3 lingual retainer in mandible) were assessed with Wilcoxon signed-rank tests at 5%. Directly after debonding, measured forces distribution were similar to published references for untreated samples. In the following, no significant difference was found between retention protocolsII andIII with regard to the asymmetry of the anterior occlusal forces. Both groups maintained an asymmetric force distribution in the anterior segment during the study period. There was also no difference between groupsII andIII in the distribution of occlusal forces for the posterior segments. Both retention concepts kept the symmetrical distribution of occlusal forces stable over the observation period. The retention concept of groupI demonstrated asymmetrical distribution of occlusal forces in the anterior segment after debonding and this remained stable during the 3‑month period. In the posterior segment, no improvement of the initially asymmetric masticatory force distribution could be observed. All three studied retention protocols showed stability in retaining their original symmetrical or asymmetrical occlusal force distribution posteriorly/anteriorly during the 3‑month observation period. Therefore, an even distribution of occlusal forces should be the aim of the finishing phase, as no relative benefit of any single retention scheme in terms of post-debond improvement during the retention phase was seen.

Musculoskeletal multibody dynamics investigation for the different medial-lateral installation position of the femoral component in unicompartmental knee arthroplasty

The surgical installation accuracy of the components in unicompartmental knee arthroplasty (UKA) is an important factor affecting the joint function and the implant life. Taking the ratio of the medial-lateral position of the femoral component relative to the tibial insert (a/A) as a parameter, and considering nine installation conditions of the femoral component, this study established the musculoskeletal multibody dynamics models of UKA to simulate the patients' walking gait, and investigated the influences of the medial-lateral installation positions of the femoral component in UKA on the contact force, joint motion and ligament force of the knee joint. The results showed that, with the increase of a/A ratio, the medial contact force of the UKA implant was decreased and the lateral contact force of the cartilage was increased; the varus rotation, external rotation and posterior translation of the knee joint were increased; and the anterior cruciate ligament force, posterior cruciate ligament force and medial collateral ligament force were decreased. The medial-lateral installation positions of the femoral component in UKA had little effect on knee flexion-extension movement and lateral collateral ligament force. When the a/A ratio was less than or equalled to 0.375, the femoral component collided with the tibia. In order to prevent the overload on the medial implant and lateral cartilage, the excessive ligament force, and the collision between the femoral component and the tibia, it is suggested that the a/A ratio should be controlled within the range of 0.427-0.688 when the femoral component is installed in UKA. This study provides a reference for the accurate installation of the femoral component in UKA.

Seated postural organization during bilateral upper limb symmetric and asymmetric pushing tasks in individuals after stroke compared to healthy controls

BackgroundAsymmetric weight distribution in sitting has been reported in people after stroke. However, postural strategies used during bilateral symmetric and asymmetric movements performed while seated require more evidence to inform rehabilitation strategies. Research questionsHow do symmetric and asymmetric effort levels exerted during upper limb (UL) pushing movements affect seated postural organization parameters (weight bearing (WB) between hands and hemibody sides, and forward trunk displacement) of stroke compared to healthy individuals? How are these parameters associated? MethodsUsing an instrumented exerciser, 19 post-stroke individuals were compared to 17 healthy individuals when executing four bilateral UL pushing movements in a seated position: symmetrical pushing at 30 % and 15 % of their maximal force (MF) and asymmetrical pushing with 15 % of their MF for one UL vs. 30 % of the MF for the other UL and vice versa. Anterior and vertical forces of the push, as well as vertical forces under each foot and thigh were compared between groups, sides and conditions. Forward trunk displacement was compared between groups and conditions. Correlations were used to determine the association between trunk displacement, hands and hemibody vertical forces. ResultsIncreasing pushing effort caused increased WB on thighs and decreased on WB on feet during the 30 % MF symmetric condition compared to the 15 % MF and asymmetric conditions (p < 0.05). Individuals post-stroke showed WB asymmetry and greater forward trunk displacement when compared to healthy persons (p < 0.05). For both groups, hemibody WB and trunk displacement showed moderate association (r > - 0.5) in the asymmetric condition executed with more resistance on the paretic or non-dominant hand. SignificanceIndividuals post-stroke presented a similar WB pattern to that of healthy persons during symmetric and asymmetric bilateral UL movements with greater forward trunk displacement and asymmetry. Increased effort and asymmetric force between both UL had effects on seated postural organization strategy.

Posterior-stabilized versus mid-level constraint polyethylene components in total knee arthroplasty.

Mid-level constraint designs for total knee arthroplasty (TKA) are intended to reduce coronal plane laxity. Our aims were to compare kinematics and ligament forces of the Zimmer Biomet Persona posterior-stabilized (PS) and mid-level designs in the coronal, sagittal, and axial planes under loads simulating clinical exams of the knee in a cadaver model. We performed TKA on eight cadaveric knees and loaded them using a robotic manipulator. We tested both PS and mid-level designs under loads simulating clinical exams via applied varus and valgus moments, internal-external (IE) rotation moments, and anteroposterior forces at 0°, 30°, and 90° of flexion. We measured the resulting tibiofemoral angulations and translations. We also quantified the forces carried by the medial and lateral collateral ligaments (MCL/LCL) via serial sectioning of these structures and use of the principle of superposition. Mid-level inserts reduced varus angulations compared to PS inserts by a median of 0.4°, 0.9°, and 1.5° at 0°, 30°, and 90° of flexion, respectively, and reduced valgus angulations by a median of 0.3°, 1.0°, and 1.2° (p ≤ 0.027 for all comparisons). Mid-level inserts reduced net IE rotations by a median of 5.6°, 14.7°, and 17.5° at 0°, 30°, and 90°, respectively (p = 0.012). Mid-level inserts reduced anterior tibial translation only at 90° of flexion by a median of 3.0 millimetres (p = 0.036). With an applied varus moment, the mid-level insert decreased LCL force compared to the PS insert at all three flexion angles that were tested (p ≤ 0.036). In contrast, with a valgus moment the mid-level insert did not reduce MCL force. With an applied internal rotation moment, the mid-level insert decreased LCL force at 30° and 90° by a median of 25.7 N and 31.7 N, respectively (p = 0.017 and p = 0.012). With an external rotation moment, the mid-level insert decreased MCL force at 30° and 90° by a median of 45.7 N and 20.0 N, respectively (p ≤ 0.017 for all comparisons). With an applied anterior load, MCL and LCL forces showed no differences between the two inserts at 30° and 90° of flexion. The mid-level insert used in this study decreased coronal and axial plane laxities compared to the PS insert, but its stabilizing benefit in the sagittal plane was limited. Both mid-level and PS inserts depended on the MCL to resist anterior loads during a simulated clinical exam of anterior laxity.

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.

Complete Restoration of Native Glenoid Width Improves Glenohumeral Biomechanics After Simulated Latarjet

Background: The amount of glenoid width that must be restored with a Latarjet procedure in order to reestablish glenohumeral stability has not been determined. Purpose/Hypothesis: The purpose of this article was to determine the percentage of glenoid width restoration necessary for glenohumeral stability after Latarjet by measuring anterior humeral head translation and force distribution on the coracoid graft. The hypothesis was that at least 100% of glenoid width restoration with Latarjet would be required to maintain glenohumeral stability. Study Design: Controlled laboratory study. Methods: Nine cadaveric shoulders were prepared and mounted on an established shoulder simulator. A lesser tuberosity osteotomy (LTO) was performed to allow accurate removal of glenoid bone. Coracoid osteotomy was performed, and the coracoid graft was sized to a depth of 10 mm. Glenoid bone was sequentially removed, and Latarjet was performed using 2 screws to reestablish 110%, 100%, 90%, and 80% of native glenoid width. The graft was passed through a subscapularis muscle split, and the LTO was repaired. A motion tracking system recorded glenohumeral translations, and force distribution was recorded using a TekScan pressure sensor secured to the glenoid face and coracoid graft. Testing conditions included native; LTO; Bankart tear; and 110%, 100%, 90%, and 80% of glenoid width restoration with Latarjet. Glenohumeral translations were recorded while applying an anteroinferior load of 44 N at 90° of humerothoracic abduction and 0° or 45° of glenohumeral external rotation. Force distribution was recorded without an anteroinferior load. Results: Anterior humeral head translation progressively increased as the proportion of glenoid width restored decreased. A marked increase in anterior humeral head translation was found with 90% versus 100% glenoid width restoration (10.8 ± 3.0 vs 4.1 ± 2.6 mm, respectively; P < .001). Greater glenoid bone loss also led to increased force on the coracoid graft relative to the native glenoid bone after Latarjet. A pronounced increase in force on the coracoid graft was seen with 90% versus 100% glenoid width restoration (P < .001). Conclusion: Anterior humeral head translation and force distribution on the coracoid graft dramatically increased when <100% of the native glenoid width was restored with a Latarjet procedure. Clinical Relevance: If a Latarjet is unable to fully restore the native glenoid width, surgeons should consider alternative graft sources to minimize the risk of recurrent instability or coracoid overload.

Comparing the Effects of Lumbar-pelvic and Pelvic Belts on the Activity of Pelvic Muscles in Pregnant Women With Back and Pelvic Pain

Objective The physical and hormonal changes occur in pregnant women, which may cause skeletal and muscular discomforts and back and pelvic pain. If the pelvic muscles mechanism is damaged, pelvic joints may have less stability, and the joint is more exposed to shearing force. As a result of this condition, the activity pattern of these muscles of the lumbar region may change, increased muscle activity compensates for the anterior forces, and bending moments may occur, especially when the abdomen volume is increased. In previous studies, the activity of pelvic muscles in the test of active straight leg raise (ASLR) was evaluated in pregnant women without using a pelvic belt. These belts are strapped at the level of the pelvic ring and do not fully support the lumbar region. The lumbar-pelvic belt can extend below the lower angle of the scapula, completely covering the lumbar region and supporting the waist and pelvis simultaneously. As a result, the whole body acts as a unit compared to a pelvic belt. The present study aims to compare the effect of the lumbar-pelvic belt with the pelvic belt in the activity of the pelvic muscles during the ASLR test of the lower limb in pregnant women with back and pelvic pain. Materials &amp; Methods This was a clinical trial study on 48 pregnant women with pregnancy-related back and pelvic pain referred to the Kawsar Specialized and Subspecialty Clinic in Arak City, Iran. The sampling method was convenience sampling based on inclusion and exclusion. All participants completed the written consent form, and then they were randomly divided into three groups: lumbar-pelvic belt (14 women), pelvic belt (14 women), and control (20 women). First, a demographic questionnaire was completed by the participants. Then the pelvic muscles’ muscle activity was evaluated using surface electromyography during the ASLR test at the beginning of the study and then three weeks later. Covariance analysis was used in SPSS version 26 software for data analysis, and the significance level was considered 0.05. Results After three weeks of using the devices, the activity of the right rectus femoris, left rectus femoris, right biceps femoris, and left biceps femoris muscles decreased in both groups who used the belts and increased in the control group during the ASLR test. The activity of the right biceps femoris and left biceps femoris muscles in the lumbar-pelvic belt group was significantly reduced compared to the pelvic belt group (P&lt;0.001). Although the activity level of the right rectus femoris and left rectus femoris muscles in the lumbar-pelvic belt group decreased more than the pelvic belt group, this decrease was not statistically significant. Conclusion The activity of the rectus femoris and biceps femoris muscles during the ASLR test decreased in both groups using the pelvic belts and increased in the control group after three weeks. This finding shows the effect of both pelvic belts on improving pelvic muscle activity. However, the lumbar-pelvic belt had a greater impact on improving the activity of the biceps femoris muscles than the pelvic belt during the ASLR test.

Gait speed and individual characteristics are related to specific gait metrics in neurotypical adults

Gait biofeedback is a well-studied strategy to reduce gait impairments such as propulsion deficits or asymmetric step lengths. With biofeedback, participants alter their walking to reach the desired magnitude of a specific parameter (the biofeedback target) with each step. Biofeedback of anterior ground reaction force and step length is commonly used in post-stroke gait training as these variables are associated with self-selected gait speed, fall risk, and the energy cost of walking. However, biofeedback targets are often set as a function of an individual’s baseline walking pattern, which may not reflect the ideal magnitude of that gait parameter. Here we developed prediction models based on speed, leg length, mass, sex, and age to predict anterior ground reaction force and step length of neurotypical adults as a possible method for personalized biofeedback. Prediction of these values on an independent dataset demonstrated strong agreement with actual values, indicating that neurotypical anterior ground reaction forces can be estimated from an individual’s leg length, mass, and gait speed, and step lengths can be estimated from individual’s leg length, mass, age, sex, and gait speed. Unlike approaches that rely on an individual’s baseline gait, this approach provides a standardized method to personalize gait biofeedback targets based on the walking patterns exhibited by neurotypical individuals with similar characteristics walking at similar speeds without the risk of over- or underestimating the ideal values that could limit feedback-mediated reductions in gait impairments.

Bayesian Calibration of Computational Knee Models to Estimate Subject-Specific Ligament Properties, Tibiofemoral Kinematics, and Anterior Cruciate Ligament Force With Uncertainty Quantification.

High-grade knee laxity is associated with early anterior cruciate ligament (ACL) graft failure, poor function, and compromised clinical outcome. Yet, the specific ligaments and ligament properties driving knee laxity remain poorly understood. We described a Bayesian calibration methodology for predicting unknown ligament properties in a computational knee model. Then, we applied the method to estimate unknown ligament properties with uncertainty bounds using tibiofemoral kinematics and ACL force measurements from two cadaver knees that spanned a range of laxities; these knees were tested using a robotic manipulator. The unknown ligament properties were from the Bayesian set of plausible ligament properties, as specified by their posterior distribution. Finally, we developed a calibrated predictor of tibiofemoral kinematics and ACL force with their own uncertainty bounds. The calibrated predictor was developed by first collecting the posterior draws of the kinematics and ACL force that are induced by the posterior draws of the ligament properties and model parameters. Bayesian calibration identified unique ligament slack lengths for the two knee models and produced ACL force and kinematic predictions that were closer to the corresponding in vitro measurement than those from a standard optimization technique. This Bayesian framework quantifies uncertainty in both ligament properties and model outputs; an important step towards developing subject-specific computational models to improve treatment for ACL injury.

Electrical stimulation to promote muscle and motor unit force and endurance after spinal cord injury.

Fatigue is a common feature of paralysed skeletal muscle, hindering performance when subjected to functional electrical stimulation (ES) for movement. We asked whether (1) 20Hz ES for 5% of each day (2.5s on and 2.5s off for 3h) increases tibialis anterior and medial gastrocnemius muscle and motor unit (MU) endurance after paralysis by hemisection and deafferentation (HSDA), and (2) muscle length or loading affects their isometric contractile properties. The daily 5% ES increased muscle endurance, largely independent of muscle length or loading, but to a lesser extent than the daily 50% ES (2.5s on and 2.5s off for 24h). The former was effective in counteracting the decline and slowing of muscle force promoted by the 50% ES. The altered muscle properties were confirmed at the MU level in final experiments once the properties had plateaued. Fast-fatigable MUs were converted to fatigue-intermediate and -resistant MUs that finally comprised ∼80% as compared to ∼10% of the total MU number in the daily 5% ES and the control normal groups, respectively. We conclude that the daily 5% ES regimen counteracts the fatigue of paralysed muscle without compromising contractile force, and thereby, is effective in conditioning muscle for effective movement. KEY POINTS: We asked whether 20Hz electrical stimulation (ES) for 5% of each day (2.5s on and 2.5s off for 3 h; 5% ES) preserves medial gastrocnemius and tibialis anterior muscle and MU isometric contractile forces and increases their endurance after paralysis. Daily 5% ES promoted increased muscle endurance irrespective of the muscle length or loading but to a lesser extent than daily 50% ES (20Hz ES 2.5s on and 2.5s off for 24 h). 5% ES was effective in counteracting decline and slowing of muscle force that resulted from 50% ES. Motor units (MUs) were converted from fast fatigable to fatigue intermediate and resistant MUs, comprising ∼80% as compared to ∼10% in the control normal groups. We conclude that the 5% ES regimen counteracts the fatigue of paralysed muscle without compromising contractile force, and thereby is effective in conditioning the muscle for effective movement.

Limiting the Use of Electromyography and Ground Reaction Force Data Changes the Magnitude and Ranking of Modelled Anterior Cruciate Ligament Forces

Neuromusculoskeletal models often require three-dimensional (3D) body motions, ground reaction forces (GRF), and electromyography (EMG) as input data. Acquiring these data in real-world settings is challenging, with barriers such as the cost of instruments, setup time, and operator skills to correctly acquire and interpret data. This study investigated the consequences of limiting EMG and GRF data on modelled anterior cruciate ligament (ACL) forces during a drop-land-jump task in late-/post-pubertal females. We compared ACL forces generated by a reference model (i.e., EMG-informed neural mode combined with 3D GRF) to those generated by an EMG-informed with only vertical GRF, static optimisation with 3D GRF, and static optimisation with only vertical GRF. Results indicated ACL force magnitude during landing (when ACL injury typically occurs) was significantly overestimated if only vertical GRF were used for either EMG-informed or static optimisation neural modes. If 3D GRF were used in combination with static optimisation, ACL force was marginally overestimated compared to the reference model. None of the alternative models maintained rank order of ACL loading magnitudes generated by the reference model. Finally, we observed substantial variability across the study sample in response to limiting EMG and GRF data, indicating need for methods incorporating subject-specific measures of muscle activation patterns and external loading when modelling ACL loading during dynamic motor tasks.

Predictive simulation of single-leg landing scenarios for ACL injury risk factors evaluation.

The Anterior Cruciate Ligament (ACL) rupture is a very common knee injury during sport activities. Landing after jump is one of the most prominent human body movements that can lead to such an injury. The landing-related ACL injury risk factors have been in the spotlight of research interest. Over the years, researchers and clinicians acquire knowledge about human movement during daily-life activities by organizing complex in vivo studies that feature high complexity, costs and technical and most importantly physical challenges. In an attempt to overcome these limitations, this paper introduces a computational modeling and simulation pipeline that aims to predict and identify key parameters of interest that are related to ACL injury during single-leg landings. We examined the following conditions: a) landing height, b) hip internal and external rotation, c) lumbar forward and backward leaning, d) lumbar medial and lateral bending, e) muscle forces permutations and f) effort goal weight. Identified on related research studies, we evaluated the following risk factors: vertical Ground Reaction Force (vGRF), knee joint Anterior force (AF), Medial force (MF), Compressive force (CF), Abduction moment (AbdM), Internal rotation moment (IRM), quadricep and hamstring muscle forces and Quadriceps/Hamstrings force ratio (Q/H force ratio). Our study clearly demonstrated that ACL injury is a rather complicated mechanism with many associated risk factors which are evidently correlated. Nevertheless, the results were mostly in agreement with other research studies regarding the ACL risk factors. The presented pipeline showcased promising potential of predictive simulations to evaluate different aspects of complicated phenomena, such as the ACL injury.

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.

Biomechanical Gender Differences in the Uninjured Extremity After Anterior Cruciate Ligament Reconstruction in Adolescent Athletes: A Retrospective Motion Analysis Study.

Introduction Subsequent anterior cruciate ligament (ACL) injury is more common in the pediatric population and encompasses graft failure and subsequent contralateral tears. Females are at a higher risk. The purpose of the present study was to compare the knee valgus angles at initial contact, knee extension moments, anterior and lateral knee joint forces, hip flexion angles, hip adduction moments, and ankle inversion during the drop vertical test in the uninjured extremity between adolescent males and females who had previously undergone an anterior cruciate ligament reconstruction (ACLR). Methods This IRB-approved retrospective chart review included patientsaged 8-18 years who were seen at the five to seven month postoperatively following ACL reconstruction. A total of 168 patients met our inclusion criteria (86 girls and 82 boys.) Using three-dimensional motion capture technology (CORTEX software, Motion Analysis Corp., Rohnert Park, CA), data were collected while the subject performed the drop vertical test over floor-mounted force plates (FP-Stairs, AMTI, Watertown, MA) under the direct supervision of a pediatric physical therapist. The Wilcoxon rank sum was used, and p < 0.05 was considered statistically significant. Results Females demonstrated a larger average knee joint extension moment (0.31 vs 0.28 N*m/kg, p = 0.0408), a larger anterior knee joint force at initial contact (3.51 vs. 2.79, N/kg, p = 0.0458), larger average hip flexion angle (41.50° vs. 35.99°, p = 0.0005), a smaller maximum hip adduction moment (0.92 vs. 1.16, N*m/kg, p = 0.0497), and a smaller average ankle inversion angle (5.08° vs. 6.41°, p = 0.03231). No significant differences were found regarding knee abduction angle or lateral knee joint force. Conclusions The biomechanical profile of the contralateral extremity varies significantly between the genders after ACLR. In the uninjured extremity, females may have larger hip flexion angles, smaller hip adduction moments, larger anterior knee joint forces, larger knee extension moments, and smaller ankle inversion angles as compared to males after ACLR. These findings may explain the higher incidence of subsequent contralateral injury in female adolescent athletes. Further work is required to develop a composite score that determines at-risk athletes.

Effects of Contralateral Trunk Tilt on Shoulder and Elbow Injury Risk and Pitching Biomechanics in Professional Baseball Pitchers

Background: Baseball pitchers employ various contralateral trunk tilt (CTT) positions when pitching depending on if they have an overhand, three-quarter, or sidearm delivery. There are no known studies that have examined how pitching biomechanics are significantly different in professional pitchers with varying amounts of CTT, which may provide insight into shoulder and elbow injury risk among pitchers with different CTT. Purpose: To assess differences in shoulder and elbow forces and torques and baseball pitching biomechanics in professional pitchers with maximum 30° to 40° CTT (MaxCTT), moderate 15° to 25° CTT (ModCTT), and minimum 0° to 10° CTT (MinCTT). Study Design: Controlled laboratory study. Methods: In total, 215 pitchers were examined, including 46 pitchers with MaxCTT, 126 pitchers with ModCTT, and 43 pitchers with MinCTT. All pitchers were tested using a 240-Hz, 10-camera motion analysis system, and 37 kinematic and kinetic parameters were calculated. Differences in kinematic and kinetic variables among the 3 CTT groups were assessed with a 1-way analysis of variance (P < .01). Results: Maximum shoulder anterior force and maximum elbow proximal force were significantly greater in ModCTT (403 ± 79 N) than MaxCTT (369 ± 75 N) and MinCTT (364 ± 70 N), while maximum elbow flexion torque and shoulder proximal force, respectively, were significantly greater in ModCTT (69 ± 11 N·m and 1176 ± 152 N, respectively) than MaxCTT (62 ± 12 N·m and 1085 ± 119 N, respectively). During arm cocking, maximum pelvis angular velocity was greater in MinCTT than MaxCTT and ModCTT, and maximum upper trunk angular velocity was greater in MaxCTT and ModCTT than MinCTT. At ball release, trunk forward tilt was greater in MaxCTT and ModCTT than MinCTT and greater in MaxCTT than ModCTT, while arm slot angle was less in MaxCTT and ModCTT than MinCTT and less in MaxCTT than ModCTT. Conclusion: The greatest shoulder and elbow peak forces occurred in ModCTT, which occurs in pitchers who throw with a three-quarter arm slot. More research is needed to assess if pitchers with ModCTT are at a higher risk of shoulder and elbow injury compared with pitchers with MaxCTT (overhand arm slot) and MinCTT (sidearm arm slot), although in the pitching literature, excessive elbow and shoulder forces and torques have been shown to correlate with elbow and shoulder injuries. Clinical Relevance: The results from the current study will help clinicians better understand if differences in kinematic and kinetic measures differ with pitching, or if differences in force, torque, and arm position occur at different arm slots.

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.

Reliability and measurement error of anterior maximum voluntary bite force in children with juvenile idiopathic arthritis and healthy children.

In children with juvenile idiopathic arthritis (JIA) the temporomandibular joint (TMJ) can be involved. As a consequence, the oral function can be impaired due to joint and/or muscle involvement of the masticatory system with a negative influence on the maximum bite force. The aim of this cross-sectional study was to establish the reliability of AMVBF in children with JIA and healthy children. Children with JIA and healthy children conducted three attempts of AMVBF. The reliability of AMVBF measurement was determined by the intra-class correlation coefficient (ICC) by age, standard error of measurement (SEM), smallest detectable change (SDC), and limits of agreement (LoA). A total of 298 children with JIA and 168 healthy children were examined. The AMVBF measurements showed an good to excellent reliability in children with JIA based on the ICCs corrected for age (0.782-0.979). In healthy children, the reliability was moderate to excellent (0.546-0.999). The SDC in our study indicated that values above 11.4N might be a clinical relevant change over time in children with JIA. The LoA showed a wide spread of variability in both children with JIA (-72.6-44.4N) and healthy children (-79.9-72.8N). The Bland-Altman plots indicated that the differences between the test and retest increased in value proportionally to the biteforce value.

Effect of Alteration in Hip Joint Alignment following Total Hip Arthroplasty on Hip Joint Contact Force during Gait

Purpose Investigation of the relationship between changes in hip-joint center and hip loading pre- and post- total hip arthroplasty (THA) is important in evaluating the effect of surgery on motor function. However, few longitudinal studies comparing pre- and post-THA have been reported. The purpose of this study was to determine the effect of changes in hip-joint center pre- and post-THA on the magnitude and direction of hip-joint contact force during the gait cycle, using a patient-specific musculoskeletal model. Methods The simulation program AnyBody was used to create musculoskeletal models incorporating patient specific hip-joint shape and hip-joint center position for 17 patients. The relationship between the displacement distance of the hip-joint center and the amount of change in hip-joint contact force was examined by correlation analysis. Results A decrease in the medial force (p ≤ 0.049) and an increase in the anterior force (p ≤ 0.001) acting on the hip joint were observed during gait post-THA compared to pre-THA. Mediolateral displacement of the hip-joint center post-THA compared to pre-THA was significantly positively correlated with the difference in anterior hip-joint contact force, and negatively to hip-joint medial contact force. Conclusions Longitudinal observations revealed the effects of change in hip-joint center position induced by THA on the hip-joint contact force during gait. Therefore, the change of hip-joint center position during THA can be an important factor for estimating the improvement of motor function following THA.