Finite Element Model of the Shoulder with Active Rotator Cuff Muscles: Application to Wheelchair Propulsion.

The rotator cuff is prone to injury, remarkably so for manual wheelchair users. To understand its pathomechanisms, finite element models incorporating three-dimensional activated muscles are needed to predict soft tissue strains during given tasks. This study aimed to develop such a model to understand pathomechanisms associated with wheelchair propulsion. We developed an active muscle model associating a passive fiber-reinforced isotropic matrix with an activation law linking calcium ion concentration to tissue tension. This model was first evaluated against known physiological muscle behavior; then used to activate the rotator cuff during a wheelchair propulsion cycle. Here, experimental kinematics and electromyography data was used to drive a shoulder finite element model. Finally, we evaluated the importance of muscle activation by comparing the results of activated and non-activated rotator cuff muscles during both propulsion and isometric contractions. Qualitatively, the muscle constitutive law reasonably reproduced the classical Hill model force-length curve and the behavior of a transversally loaded muscle. During wheelchair propulsion, the deformation and fiber stretch of the supraspinatus muscle-tendon unit pointed towards the possibility for this tendon to develop tendinosis due to the multiaxial loading imposed by the kinematics of propulsion. Finally, differences in local stretch and positions of the lines of action between activated and non-activated models were only observed at activation levels higher than 30%. Our novel finite element model with active muscles is a promising tool for understanding the pathomechanisms of the rotator cuff for various dynamic tasks, especially those with high muscle activation levels.

Trunk and glenohumeral joint adaptations to manual wheelchair propulsion over a cross-slope: An exploratory study.

BACKGROUND: Cross-slopes are often encountered by manual wheelchair users propelling within an urban setting. While propulsion over cross-slopes is more difficult than on level surfaces, little is known about how the users counter the downhill turning tendency of the wheelchair over cross-slopes. This study aimed to identify the adaptations of the manual wheelchair users to the presence of cross-slopes and examine how these might impact shoulder injury. METHODS: Nine manual wheelchair users propelled themselves across a cross-slope and over a level surface. The trunk and glenohumeral joint kinematics, as well as the handrim contact tangential force were compared between both conditions for the uphill and downhill limbs. FINDINGS: The uphill arm technique used to counter the downhill turning tendency varied greatly in terms of potential injury risk and efficiency between participants. Trunk flexion increased the turning tendency of the manual wheelchair, yet only one participant decreased his flexion when rolling over the cross-slope. Various potential pathomecanisms related to the trunk lateral flexion and the glenohumeral kinematics over a cross-slope were identified. INTERPRETATION: Both the uphill arm technique and trunk kinematics are important to propel over a cross-slope both efficiently and safely. Accordingly, tips about posture and kinematics are needed to teach this skill to manual wheelchair users. Additionally, as wheelchair positioning seems to influence the cross-slope skill, more research is needed to explore the impact of positioning devices (e.g., lateral supports) and wheelchair modifications (e.g., power assist wheels, handrim projections) on this skill.

Moment arms of the deltoid, infraspinatus and teres minor muscles for movements with high range of motion: A cadaveric study.

BACKGROUND: Moment arms are an indicator of the role of the muscles in joint actuation. An excursion method is often used to calculate them, even though it provides 1D results. As shoulder movement occurs in three dimensions (combination of flexion, abduction and axial rotation), moment arms should be given in 3D. Our objective was to assess the 3D moment arms of the rotator cuff (infraspinatus and teres minor) and deltoid muscles for movements with high arm elevation. METHODS: The 3D moment arms (components in plane of elevation, elevation and axial rotation) were assessed using a geometric method, enabling to calculate the moment arms in 3D, on five fresh post-mortem human shoulders. Movement with high range of motion were performed (including overhead movement). The humerus was elevated until it reaches its maximal posture in different elevation plane (flexion, scaption, abduction and elevation in a plane 30° posterior to frontal plane). FINDINGS: We found that the anterior deltoid was a depressor and contributes to move the elevation plane anteriorly. The median deltoid was a great elevator and the posterior deltoid mostly acted in moving the elevation plane posteriorly. The infraspinatus and teres minor were the greatest external rotator of the shoulder. The position of the glenohumeral joint induces changes in the muscular moment arms. The maximal shoulder elevation was 144° (performed in the scapular plane). INTERPRETATION: The knowledge of 3D moment arms for different arm elevations might help surgeons in planning tendon reconstructive surgery and help validate musculoskeletal models.

Effect of Expertise on Shoulder and Upper Limb Kinematics, Electromyography, and Estimated Muscle Forces During a Lifting Task.

OBJECTIVE: To highlight the working strategies used by expert manual handlers compared with novice manual handlers, based on recordings of shoulder and upper limb kinematics, electromyography (EMG), and estimated muscle forces during a lifting task. BACKGROUND: Novice workers involved in assembly, manual handling, and personal assistance tasks are at a higher risk of upper limb musculoskeletal disorders (MSDs). However, few studies have investigated the effect of expertise on upper limb exposure during workplace tasks. METHOD: Sixteen experts in manual handling and sixteen novices were equipped with 10 electromyographic electrodes to record shoulder muscle activity during a manual handling task consisting of lifting a box (8 or 12 kg), instrumented with three six-axis force sensors, from hip to eye level. Three-dimensional trunk and upper limb kinematics, hand-to-box contact forces, and EMG were recorded. Then, joint contributions, activation levels, and muscle forces were calculated and compared between groups. RESULTS: Sternoclavicular-acromioclavicular joint contributions were higher in experts at the beginning of the movement, and in novices at the end, whereas the opposite was observed for the glenohumeral joint. EMG activation levels were 37% higher for novices but predicted muscle forces were higher in experts. CONCLUSION: This study highlights significant differences between experts and novices in shoulder kinematics, EMG, and muscle forces; hence, providing effective work guidelines to ensure the development of a safe handling strategy is important. APPLICATION: Shoulder kinematics, EMG, and muscle forces could be used as ergonomic tools to identify inappropriate techniques that could increase the prevalence of shoulder injuries.

Glenohumeral joint and muscles functions during a lifting task.

The mobility of the healthy shoulder depends on complex interactions between the muscles spanning its glenohumeral joint. These interactions ensure the stability of this joint. While previous studies emphasized the complexity of the glenohumeral stability, it is still not clear how the kinematics and muscles interact and adapt to ensure a healthy function of the glenohumeral joint. To understand the function of each muscle and degree of freedom of the glenohumeral joint in executing an above-the shoulder box handling task while ensuring stability, we adapted an index-based approach previously used to characterize the functions of the lower limb joints and muscles during locomotion. Forty participants lifted two loads (6 Vs. 12 kg) from hip to eye level. We computed the mechanical powers of the glenohumeral joint and its spanning muscles. We characterized the function of muscles and degrees of freedom using function indices. The function of the glenohumeral joint underlined its compliancy and design for a large range of motion, while the rotator cuff indices emphasized their stabilizing function. The overall muscle functions underlined the complexity of the glenohumeral stability that goes beyond the rotator cuff. Additionally, the load increase was compensated with changes in the functions that seem to favor joint stability. The implemented approach represents a synthetized tool that could quantify the glenohumeral joint and muscles behavior during tridimensional upper limb tasks, which might offer additional insight into motor control strategies and functional alterations related to pathologies or external parameters (e.g., load).

Adapting the Wheelchair Skills Program for pediatric rehabilitation: recommendations from key stakeholders.

BACKGROUND: Backed by over 20 years of research development, the Wheelchair Skills Program (WSP) has proven to be a safe and effective program to improving wheelchair skills for adult wheelchair users. However, evidence is lacking for the pediatric population, which may help to explain the limited use of the WSP in pediatric settings. While additional evidence specific to the pediatric population is needed, concurrent implementation of the WSP into pediatric clinical practice is equally prudent to allow those users to benefit from the years of accumulated WSP evidence. To facilitate implementation of evidence-based programs into practice, adaptation is also often required to improve the fit between the program and the local context. Therefore, the objective of this study was to understand what adaptations, if any, are required for the WSP to be implementable in a pediatric setting. METHODS: A deductive qualitative descriptive study design was used, guided by the Knowledge to Action Framework and Consolidated Framework for Implementation Research (CFIR). Occupational Therapists (OTs) from a pediatric rehabilitation center and two specialized schools in Montreal, Canada were invited to participate in a 90-min focus group. The Framework Method was followed for the data analysis. RESULTS: One focus group in each site (n = 3) was conducted with a total of 19 participants. From the OTs' perspectives, our analysis revealed benefits of WSP use and various issues (e.g. some skills seem unrealistic) affecting its uptake in relation to the constructs of the CFIR Intervention Characteristics domain. The results provided guidance for the recommendations of adaptations (e.g. addition of a caregiver assistance score) to enhance implementation of the WSP in pediatric rehabilitation settings and helped to identify the need for the production of new knowledge and knowledge translation (KT) tools. CONCLUSIONS: Implementation of the WSP with the adaptations and KT tools proposed could allow pediatric manual wheelchair users to improve their wheelchair skills.

Three-Dimensional Upper Body Kinematics and Inter-articular Kinematic Sequence During a Canoe Polo Throw.

Canoe polo is an increasingly popular discipline requiring both kayaking and ball-handling skills. While the kinematics of the upper body during throw has been investigated for several overhead sports, the canoe polo throw has still to be studied. Therefore, the aim of this study is to analyze the canoe polo throw kinematics in terms of angles and inter-articular sequencing to understand its specificity. A secondary aim was to investigate whether adding pelvis mobility has an impact. Nineteen male players of canoe polo were equipped with reflective body markers for the throw analysis. They performed 5 throws with the pelvis fixed and 5 throws with additional pelvic mobility in rotation around a vertical axis. Inverse kinematics was performed with OpenSim providing pelvis, trunk, and glenohumeral rotations. Angular velocities were calculated to build the inter-articular sequences relative to these throws. Statistical parametric mapping was used to assess the effect of pelvis mobility on the throwing kinematics. Similar kinematics patterns as in other overhead sports were observed, however, a different inter-articular sequence was found for the canoe polo throw with a maximal angular velocity occurring sooner for the thorax in axial rotation than for the pelvis in rotation. While the limitation of rotation of the pelvis around a vertical axis has an influence on the pelvis and trunk kinematics, it did not modify the kinematic sequence.

Sex differences in upper limb musculoskeletal biomechanics during a lifting task.

Women experience higher prevalence of work-related upper limb musculoskeletal disorders compared to men. Previous studies have investigated the biological, kinematic and electromyographic sex-related differences during a lifting task but the actual differences in musculoskeletal loads remain unknown. We investigated the sex differences in three musculoskeletal indicators: the sum of muscle activations, the sum of muscle forces and the relative time spent beyond a shear-compression dislocation ratio. A musculoskeletal model was scaled on 20 women and 20 men lifting a 6 or 12kg box from hip to eye level. Women generated more muscle forces and activations than men, regardless of the lifted mass. Those differences occurred when the box was above shoulder level. In addition, women might spend more time beyond a shear-compression dislocation ratio. Our work suggests higher musculoskeletal loads among women compared to men during a lifting task, which could be the result of poor technique and strength difference.

High-Frequency Resonator Using A1 Lamb Wave Mode in LiTaO3 Plate.

Acoustic wave devices utilizing plate waves in thin lithium tantalate (LiTaO3) have the potential of achieving high resonance frequency with a suitable electromechanical coupling factor and a relatively small temperature coefficient of frequency (TCF). The influence of Euler angle and plate thickness on the characteristics of plate waves has been investigated. High-frequency resonators using first antisymmetric Lamb wave mode (A1) in (0°, 42°, 0°) LiTaO3 thin plates have been fabricated and optimized. The resonance frequency is as high as 5 GHz, with a relative bandwidth of 7.3% and an impedance ratio of 72 dB. Finally, the TCF of (0°, 42°, 0°) LiTaO3 has been evaluated. Therefore, it is proved that A1 Lamb wave mode propagating in LiTaO3 at a Euler angle close to (0°, 42°, 0°) is suitable for high-frequency devices.