The influence of altering push force effectiveness on upper extremity demand during wheelchair propulsion

Handrim kinetics and quantitative ultrasound parameters for assessment of subacromial impingement in wheelchair users with pediatric-onset spinal cord injury

BACKGROUND

Most manual wheelchair users with pediatric-onset spinal cord injury (SCI) will experience shoulder pain or pathology at some point in their life. However, guidelines for preservation of the upper limb in children with SCI are limited.

RESEARCH QUESTION

What are the relationships between manual wheelchair handrim kinetics and quantitative ultrasound parameters related to subacromial impingement in individuals with pediatric-onset SCI?

METHODS

Subacromial impingement risk factors including supraspinatus tendon thickness (SST), acromiohumeral distance (AHD), and occupation ratio (OR; SST/AHD) were measured with ultrasound in 11 manual wheelchair users with pediatric-onset SCI. Handrim kinetics were acquired during the stroke cycle, including peak resultant force (FR), peak rate of rise of resultant force (ROR) and fractional effective force (FEF). Variability of handrim kinetics was computed using the coefficient of variation and linear regression was performed to assess correlations between handrim metrics and quantitative ultrasound parameters.

RESULTS

Peak resultant force significantly increased 1.4 % and variability of FEF significantly decreased 8.0 % for every 0.1 cm increase in AHD. FEF decreased 3.5 % for every 0.1 cm increase in SST. Variability of peak resultant force significantly increased 3.6 % and variability of peak ROR of resultant force significantly increased 7.3 % for every 0.1 cm increase in SST. FEF variability significantly decreased 11.6 % for every 0.1 cm increase in SST. Peak ROR significantly decreased 1.54 % with every 10 % increase in OR. FEF variability significantly decreased 1.5 % with every 10 % increase in OR.

SIGNIFICANCE

This is the first study to investigate relationships among handrim kinetics and shoulder structure in manual wheelchair users with pediatric-onset SCI. Associations were identified between subacromial impingement risk factors and magnitude and variability of wheelchair handrim kinetics. These results indicate the critical need to further explore the relationships among wheelchair handrim kinetics, shoulder joint dynamics, and shoulder pathology in manual wheelchair users with pediatric-onset SCI.

Steering-by-leaning facilitates intuitive movement control and improved efficiency in manual wheelchairs

BACKGROUND

Manual wheelchair propulsion is widely accepted to be biomechanically inefficient, with a high prevalence of shoulder pain and injuries among users. Directional control during wheelchair movement is a major, yet largely overlooked source of energy loss: changing direction or maintaining straightforward motion on tilted surfaces requires unilateral braking. This study evaluates the efficiency of a novel steering-by-leaning mechanism that guides wheelchair turning through upper body leaning.

METHODS

16 full-time wheelchair users and 15 able-bodied novices each completed 12 circuits of an adapted Illinois Agility Test-course that included tilted, straight, slalom, and 180° turning sections in a prototype wheelchair at a self-selected functional speed. Trials were alternated between conventional and steering-by-leaning modes while propulsion forces were recorded via instrumented wheelchair wheels. Time to completion, travelled distance, positive/negative power, and work done, were all calculated to allow comparison of the control modes using repeated measures analysis of variance.

RESULTS

Substantial average energy reductions of 51% (able-bodied group) and 35% (wheelchair user group) to complete the task were observed when using the steering-by-leaning system. Simultaneously, able-bodied subjects were approximately 23% faster whereby completion times did not differ for wheelchair users. Participants in both groups wheeled some 10% further with the novel system. Differences were most pronounced during turning and on tilted surfaces where the steering-by-leaning system removed the need for braking for directional control.

CONCLUSIONS

Backrest-actuated steering systems on manual wheelchairs can make a meaningful contribution towards reducing shoulder usage while contributing to independent living. Optimisation of propulsion techniques could further improve functional outcomes.

A Dynamic Wheelchair Armrest for Promoting Arm Exercise and Mobility After Stroke

Arm movement recovery after stroke can improve with sufficient exercise. However, rehabilitation therapy sessions are typically not enough. To address the need for effective methods of increasing arm exercise outside therapy sessions we developed a novel armrest, called Boost. It easily attaches to a standard manual wheelchair just like a conventional armrest and enables users to exercise their arm in a linear forward-back motion. This paper provides a detailed design description of Boost, the biomechanical analysis method to evaluate the joint torques required to operate it, and the results of pilot testing with five stroke patients. Biomechanics results show the required shoulder flexion and elbow extension torques range from −25% to +36% of the torques required to propel a standard pushrim wheelchair, depending on the direction of applied force. In pilot testing, all five participants were able to exercise the arm with Boost in stationary mode (with lower physical demand). Three achieved overground ambulation (with higher physical demand) exceeding 2 m/s after 2–5 practice trials; two of these could not propel their wheelchair with the pushrim. This simple to use, dynamic armrest provides people with hemiparesis a way to access repetitive arm exercise outside of therapy sessions, independently right in their wheelchair. Significantly, Boost removes the requirements to reach, grip, and release the pushrim to propel a wheelchair, an action many individuals with stroke cannot complete.

Effect of Context-Dependent Modulation of Trunk Muscle Activity on Manual Wheelchair Propulsion

OBJECTIVE

The aims of the study were to reliably determine the two main phases of manual wheelchair propulsion via a simple wearable sensor and to evaluate the effects of modulated trunk and hip stimulation on manual wheelchair propulsion during the challenging tasks of ramp assent and level sprint.

DESIGN

An offline tool was created to identify common features between wrist acceleration signals for all subjects who corresponded to the transitions between the contact and recovery phases of manual wheelchair propulsion. For one individual, the acceleration rules and thresholds were implemented for real-time phase-change event detection and modulation of stimulation.

RESULTS

When pushing with phase-dependent modulated stimulation, there was a significant (P < 0.05) increase in the primary speed variable (5%-6%) and the subject rated pushing as "moderately or very easy." In the offline analysis, the average phase-change event detection success rate was 79% at the end of contact and 71% at the end of recovery across the group.

CONCLUSIONS

Signals from simple, wrist-mounted accelerometers can detect the phase transitions during manual wheelchair propulsion instead of elaborate and expensive, instrumented systems. Appropriately timing changes in muscle activation with the propulsion cycle can result in a significant increase in speed, and the system was consistently perceived to be significantly easier to use.

Is there an association between multiple sclerosis and osteoarthritis in Germany? A retrospective cohort study of 8,600 patients from Germany

OBJECTIVES

The goal of this retrospective cohort study was to investigate the multiple sclerosis-osteoarthritis relationship in adults followed in general practices in Germany.

METHODS

Patients aged 18-70 years who were diagnosed for the first time with multiple sclerosis in one of 1,193 general practices in Germany between 2005 and 2018 (index date) were included in this retrospective cohort study. Patients without multiple sclerosis were matched (1:1) to those with multiple sclerosis by sex, age, index year, general practice, obesity, injuries, and other types of arthritis (index date: a randomly selected visit date). The association between multiple sclerosis and the 10-year incidence of osteoarthritis was analyzed using Cox regression models.

RESULTS

There were 4,300 patients with multiple sclerosis and 4,300 patients without multiple sclerosis included in this study. The proportion of women was 69.3% and mean (SD) age was 43.6 (12.6) years. There was no significant association between multiple sclerosis and incident osteoarthritis in the overall sample (HR = 0.95, 95% CI: 0.83-1.09) as well as sex and age subgroups.

CONCLUSIONS

Based on these findings, multiple sclerosis is not significantly associated with osteoarthritis. Further studies of longitudinal nature are warranted to corroborate or invalidate these results.

Specialty Space: Breast Care Centers

As background, breast care centers around the world vary in interior design based on geographical location and the trends of the healthcare design process at the time of construction. However, at the forefront of healthcare interior design is the evidence-based design (EBD) process and the Universal Design (UD) guidelines. The Center for Health Design states that the EBD process differs from the linear design process, in that EBD uses relevant evidence to educate and guide the design decisions. The objective of this study was to support future EBD and UD use in the development of patient areas in breast care center interior design. The methods for this study incorporated an extensive review of the literature, examples of eight breast care centers around the world, observations, an interview, and a staff survey concerning the interior design of a local breast care center. The results revealed that using the EBD process and UD, to develop guidelines for patient areas in breast care centers' interior design, directors could use guidelines to evaluate existing breast care centers or preconstruction for new breast care centers. This study concluded with design guidelines for patient areas in breast care center interior design. The recommended guidelines targeted the following features: robes (vs. hospital gowns), spa-like atmosphere, monochromatic color scheme, use of wood and stone, private check-in areas, wayfinding, room temperature comfort, seating comfort, seating style choices including bariatric, personal items storage, access to natural light, indirect artificial lighting, living plants, views of nature, flooring comfort, and wheelchair accessibility.

Start-up propulsion biomechanics changes with fatiguing activity in persons with spinal cord injury

Objective: Shoulder pathology is a common condition in wheelchair users that can considerably impact quality of life. Shoulder muscles are prone to fatigue, but it is unclear how fatigue affects start-up propulsion biomechanics. This study determines acute changes in start-up wheelchair propulsion biomechanics at the end of a fatiguing propulsion protocol. Design: Quasi-experimental one-group pretest-postest design. Setting: Biomechanics laboratory. Participants: Twenty-six wheelchair users with spinal cord injury (age: 35.5 ± 9.8 years, sex: 73% males and 73% with a paraplegia). Interventions: Protocol of 15 min including maximum voluntary propulsion, right- and left turns, full stops, start-up propulsion, and rests. Outcome measures: Maximum resultant force, maximum rate of rise of applied force, mean velocity, mean fraction of effective force, and mean contact time at the beginning and end of the protocol during start-up propulsion. Results: There was a significant reduction in maximum resultant force (P < 0.001) and mean velocity (P < 0.001) at the end of the protocol. Also, contact time was reduced in the first stroke of start-up propulsion (P < 0.001). Finally, propelling with a shorter contact time was associated with a greater reduction in performance (maximum velocity) at the end of the protocol. Conclusion: There are clear changes in overground propulsion biomechanics at the end of a fatiguing propulsion protocol. While reduced forces could protect the shoulder, these reduced forces come with shorter contact times and lower velocity. Investigating changes in start-up propulsion biomechanics with fatigue could provide insight into injury risk.

Predictive Forward Dynamic Simulation of Manual Wheelchair Propulsion on a Rolling Dynamometer

Research studies to understand the biomechanics of manual wheelchair propulsion often incorporate experimental data and mathematical models. This project aimed to advance this field of study by developing a two-dimensional (2D) model to generate first of its kind forward dynamic fully predictive computer simulations of a wheelchair basketball athlete on a stationary ergometer. Subject-specific parameters and torque generator functions were implemented in the model from dual X-ray absorptiometry and human dynamometer measurements. A direct collocation optimization method was used in a wheelchair propulsion model for the first time to replicate the human muscle recruitment strategy. Simulations were generated for varying time constraints and seat positions. Similar magnitudes of kinematic and kinetic data were observed between simulation and experimental data of a first push. Furthermore, seat heights inferior to the neutral position were found to produce similar joint torques to those reported in previous studies. An anterior seat placement produced the quickest push time with the least amount of shoulder torque required. The work completed in this project demonstrates that fully predictive simulations of wheelchair propulsion have the potential of varying simulation parameters to draw meaningful conclusions.

Manual wheelchair propulsion cost across different components and configurations during straight and turning maneuvers

Aim

Maneuvering manual wheelchairs is defined by changes in momentum. The amount of effort required to maneuver a wheelchair is dependent on many factors, some of which reflect the design and configuration of the wheelchair.

Objective

The objective of this study was to measure the work required to propel a manual wheelchair configured with three weight distributions, three drive wheels and four casters.

Methods

A novel wheelchair-propelling robot was used as the test platform to measure work while traversing two surfaces using three different maneuvers which were defined to highlight different kinetic energies and energy loss mechanisms.

Results

Overall, propulsion cost decreased with an increase in load on the drive wheels. Pneumatic drive wheels exhibited lower propulsion costs compared to a solid tire. Two casters, a 4″ dia × 1.5″ and a 5″ dia × 1″, exhibited better overall performance compared to 5″ dia × 1.5″ solid and 6″ dia × 1″ pneumatic casters.

Discussion

The results indicate that drive wheel load and types of drive wheels and casters impact propulsion cost and their influences differ across maneuvers and surfaces. The approach is well suited to assess equivalency in components and configurations. Assessment of performance equivalency would empower clinicians and users with important knowledge when selecting components.

Reaction Force Generation and Mechanical Demand Imposed On the Shoulder When Initiating Manual Wheelchair Propulsion and At Self-selected Fast Speeds

Manual wheelchair (WC) users with spinal cord injury (SCI) experience shoulder pain and fatigue associated with their increased reliance on the upper extremity during activities of daily living [1]. We hypothesized that the mechanical demand imposed on the shoulder, represented as resultant shoulder net joint moment impulse, would be greater when initiating manual WC propulsion from a stationary position without momentum than when manually propelling at speed on a level sidewalk. Thirty manual WC users with paraplegia participated. Each individual initiated manual WC propulsion from a stationary position and propelled on a level sidewalk at their self-selected fast speed. Upper extremity kinematics and pushrim reaction forces (RFs) were measured and upper extremity joint kinetics were calculated and compared (a=0.05) between cycle 1, initiated without momentum, and cycle 3 with momentum. Results indicate that multiple factors contributing to the mechanical demand imposed on the shoulder were significantly greater when manual WC propulsion was initiated without momentum than with momentum. Significant differences in resultant shoulder net joint moment (NJM) impulse, push duration, orientation of RF relative to forearm, and resultant average shoulder NJMs during push were observed between momentum conditions. No significant differences in average resultant RF during push were found. These results indicate that mechanical loading of the shoulder during manual WC propulsion differs between momentum conditions; these differences in resultant shoulder NJM impulse during push need to be considered when assessing shoulder load exposure in stop-and-start activities.

On the influence of the shoulder kinematic chain on joint kinematics and musculotendon lengths during wheelchair propulsion estimated from multibody kinematics optimization

Multibody kinematic optimization is frequently used to assess shoulder kinematics during manual wheelchair (MWC) propulsion but multiple kinematics chains are available. It is hypothesized that these different kinematic chains affect marker tracking, shoulder kinematics and resulting musculotendon (MT) lengths. In this study, shoulder kinematics and MT lengths obtained from four shoulder kinematic chains (open-loop thorax-clavicle-scapula-humerus (M1), closed-loop with contact ellipsoid (M2), scapula rhythm from regression equations (M3), and a single ball-and- socket joint between the thorax and the humerus (M4) were compared. Right-side shoulder kinematics from seven subjects were obtained with 34 reflective markers and a scapula locator using an optoelectronic motion capture system while propelling on a MWC simulator. Data was processed based on the four models. Results showed the impact of shoulder kinematic chains on all studied variables. Marker reconstruction errors were found similar between M1 and M2 and lower than for M3 and M4. Few degrees of freedom (DoF) were noticeably different between M1 and M2, but all shoulder DoFs were significantly affected between M1 and M4. As a consequence of differences in joint kinematics, MT lengths were affected by the kinematic chain definition. The contact ellipsoid (M2) was found as a good trade-off between marker tracking and penetration avoidance of the scapula. The regression-based model (M3) was less efficient due to limited humerus elevation during MWC propulsion, as well as the ball-and-socket model (M4) which appeared not suitable for upper limbs activities, including MWC propulsion.

Changes in propulsion technique and shoulder complex loading following low-intensity wheelchair practice in novices

Background

Up to 80% of wheelchair users are affected by shoulder pain. The Clinical Practice Guidelines for preservation of upper limb function following spinal cord injury suggest that using a proper wheelchair propulsion technique could minimize the shoulder injury risk. Yet, the exact relationship between the wheelchair propulsion technique and shoulder load is not well understood.

Objective

This study aimed to examine the changes in shoulder loading accompanying the typical changes in propulsion technique following 80 min of low-intensity wheelchair practice distributed over 3 weeks.

Methods

Seven able-bodied participants performed the pre- and the post-test and 56 min of visual feedback-based low-intensity wheelchair propulsion practice. Kinematics and kinetics of propulsion technique were recorded during the pre- and the post-test. A musculoskeletal model was used to calculate muscle force and glenohumeral reaction force.

Results

Participants decreased push frequency (51→36 pushes/min, p = 0.04) and increased contact angle (68→94°, p = 0.02) between the pre- and the post-test. The excursion of the upper arm increased, approaching significance (297→342 mm, p = 0.06). Range of motion of the hand, trunk and shoulder remained unchanged. The mean glenohumeral reaction force per cycle decreased by 13%, approaching significance (268→232 N, p = 0.06).

Conclusions

Despite homogenous changes in propulsion technique, the kinematic solution to the task varied among the participants. Participants exhibited two glenohumeral reaction force distribution patterns: 1) Two individuals developed high force at the onset of the push, leading to increased peak and mean glenohumeral forces 2) Five individuals distributed the force more evenly over the cycle, lowering both peak and mean glenohumeral forces.

Forward dynamic optimization of handle path and muscle activity for handle based isokinetic wheelchair propulsion: A simulation study

Push-rim wheelchair propulsion is biomechanically inefficient and physiologically stressful to the musculoskeletal structure of human body. This study focuses to obtain a new, optimized propulsion shape for wheelchair users, which is within the ergonomic ranges of joint motion, thus reducing the probability of injuries. To identify the propulsion movement, forward dynamic optimization was performed on a 3D human musculoskeletal model linked to a handle based propulsion mechanism, having shape and muscle excitations as optimization variables. The optimization resulted in a handle path shape with a circularity ratio of 0.95, and produced a net propulsion power of 34.7 watts for an isokinetic propulsion cycle at 50 rpm. Compared to push-rim propulsion, the compact design of the new propulsion mechanism along with the ergonomically optimized propulsion shape may help to reduce the risk of injuries and thus improve the quality of life for wheelchair users.

Construction and evaluation of a model for wheelchair propulsion in an individual with tetraplegia

Upper limb overuse injuries are common in manual wheelchair users with spinal cord injury. Patient-specific in silico models enhance experimental biomechanical analyses by estimating in vivo shoulder muscle and joint contact forces. Current models exclude deep shoulder muscles that have important roles in wheelchair propulsion. Freely accessible patient-specific models have not been generated for persons with tetraplegia, who have a greater risk for shoulder pain and injury. The objectives of this work were to (i) construct a freely accessible, in silico, musculoskeletal model capable of generating patient-specific dynamic simulations of wheelchair propulsion and (ii) establish proof-of-concept with data obtained from an individual with tetraplegia. Constructed with OpenSim, the model features muscles excluded in existing models. Shoulder muscle forces and activations were estimated via inverse dynamics. Mean absolute error of estimated muscle activations and fine-wire electromyography (EMG) recordings was computed. Mean muscle activation for five consecutive stroke cycles demonstrated good correlation (0.15-0.17) with fine-wire EMG. These findings, comparable to other studies, suggest that the model is capable of estimating shoulder muscle forces during wheelchair propulsion. The additional muscles may provide a greater understanding of shoulder muscle contribution to wheelchair propulsion. The model may ultimately serve as a powerful clinical tool. Graphical abstract ᅟ.

Wheelchair propulsion: Force orientation and amplitude prediction with Recurrent Neural Network

The aim of this study was to use Recurrent Neural Network (RNN) to predict the orientation and amplitude of the applied force during the push phase of manual wheelchair propulsion. Trunk and the right-upper limb kinematics data were assessed with an optoeletronic device (Qualisys) and the force applied on the handrim was recorded with an instrumented wheel (SMARTWheel®). Data acquisitions were performed at 60/80/10/120/140% of the freely chosen frequency at submaximal and maximal conditions. The final database consisted of d = 5708 push phases. The input data were the trunk and right upper-limb kinematics (joint angle, angular velocity and acceleration) and anthropometric data (height, weight, segment length) and the output data were the applied forces orientation and amplitude. A ratio of 70/15/15 was used to train, validate and test the RNN (d_train = 3996, d_validation = 856 and d_test = 856). The angle and amplitude errors between the measured and predicted force was assessed from d_test. Results showed that for most of the push phase (∼70%), the force direction prediction errors were less than 12°. The mean absolute amplitude errors were less than 8 N and the mean absolute amplitude percentage errors were less than 20% for most of the push phase (∼80%).

Do relevant shear forces appear in isokinetic shoulder testing to be implemented in biomechanical models?

Isokinetic dynamometers measure joint torques about a single fixed rotational axis. Previous studies yet suggested that muscles produce both tangential and radial forces during a movement, so that the contact forces exerted to perform this movement are multidirectional. Then, isokinetic dynamometers might neglect the torque components about the two other Euclidean space axes. Our objective was to experimentally quantify the shear forces impact on the overall shoulder torque, by comparing the dynamometer torque to the torque computed from the contact forces at the hand and elbow. Ten healthy women performed isokinetic maximal internal/external concentric/eccentric shoulder rotation movements. The hand and elbow contact forces were measured using two six-axis force sensors. The main finding is that the contact forces at the hand were not purely tangential to the direction of the movement (effectiveness indexes from 0.26 ± 0.25 to 0.54 ± 0.20), such that the resulting shoulder torque computed from the two force sensors was three-dimensional. Therefore, the flexion and abduction components of the shoulder torque measured by the isokinetic dynamometer were significantly underestimated (up to 94.9%). These findings suggest that musculoskeletal models parameters should not be estimated without accounting for the torques about the three space axes.

Evaluation and validation of musculoskeletal force feasible set indices: Application to manual wheelchair propulsion

The aim of this work was to assess handrim wheelchair propulsion effectiveness, related to the applied forces on the handrim, through the force feasible set. For a given posture of the upper-limb, it represents the set of isometric forces that can be applied on the handrim in any direction. The force feasible set was predicted from a musculoskeletal model of the upper-limb and trunk (10 degrees of freedom and 56 muscles). The aim of the first part of the study was to compare the force feasible set prediction and the force currently applied on the handrim. The second part proposes the creation of a new index called "Musculoskeletal Postural Performance Index" (MPPI) derived from the force feasible set and its comparison with the Mechanical Efficiency Force (MEF). These comparisons were conducted at 60, 80, 100, 120 and 140% of the Freely Chosen Frequency at submaximal and maximal conditions on 5 different phases of the push phase. The values of the MPPI were significantly correlated with those of the MEF. During the course of the push phase, the orientation of the force feasible set main axis approached that of the measured force and the force effectiveness evaluated through the MPPI increased.

Relationship between linear velocity and tangential push force while turning to change the direction of the manual wheelchair

Wheelchair propulsion is a major cause of upper limb pain and injuries for manual wheelchair users with spinal cord injuries (SCIs). Few studies have investigated wheelchair turning biomechanics on natural ground surfaces. The purpose of this study was to investigate the relationship between tangential push force and linear velocity of the wheelchair during the turning portions of propulsion. Using an instrumented handrim, velocity and push force data were recorded for 25 subjects while they propel their own wheelchairs on a concrete floor along a figure-eight-shaped course at a maximum velocity. The braking force (1.03 N) of the inside wheel while turning was the largest of all other push forces (p<0.05). Larger changes in squared velocity while turning were significantly correlated with higher propulsive and braking forces used at the pre-turning, turning, and post-turning phases (p<0.05). Subjects with less change of velocity while turning needed less braking force to maneuver themselves successfully and safely around the turns. Considering the magnitude and direction of tangential force applied to the wheel, it seems that there are higher risks of injury and instability for upper limb joints when braking the inside wheel to turn. The results provide insight into wheelchair setup and mobility skills training for wheelchair users.

The influence of wheelchair propulsion hand pattern on upper extremity muscle power and stress

The hand pattern (i.e., full-cycle hand path) used during manual wheelchair propulsion is frequently classified as one of four distinct hand pattern types: arc, single loop, double loop or semicircular. Current clinical guidelines recommend the use of the semicircular pattern, which is based on advantageous levels of broad biomechanical metrics implicitly related to the demand placed on the upper extremity (e.g., lower cadence). However, an understanding of the influence of hand pattern on specific measures of upper extremity muscle demand (e.g., muscle power and stress) is needed to help make such recommendations, but these quantities are difficult and impractical to measure experimentally. The purpose of this study was to use musculoskeletal modeling and forward dynamics simulations to investigate the influence of the hand pattern used on specific measures of upper extremity muscle demand. The simulation results suggest that the double loop and semicircular patterns produce the most favorable levels of overall muscle stress and total muscle power. The double loop pattern had the lowest full-cycle and recovery-phase upper extremity demand but required high levels of muscle power during the relatively short contact phase. The semicircular pattern had the second-lowest full-cycle levels of overall muscle stress and total muscle power, and demand was more evenly distributed between the contact and recovery phases. These results suggest that in order to decrease upper extremity demand, manual wheelchair users should consider using either the double loop or semicircular pattern when propelling their wheelchairs at a self-selected speed on level ground.

Compensatory strategies during manual wheelchair propulsion in response to weakness in individual muscle groups: A simulation study

BACKGROUND

The considerable physical demand placed on the upper extremity during manual wheelchair propulsion is distributed among individual muscles. The strategy used to distribute the workload is likely influenced by the relative force-generating capacities of individual muscles, and some strategies may be associated with a higher injury risk than others. The objective of this study was to use forward dynamics simulations of manual wheelchair propulsion to identify compensatory strategies that can be used to overcome weakness in individual muscle groups and identify specific strategies that may increase injury risk. Identifying these strategies can provide rationale for the design of targeted rehabilitation programs aimed at preventing the development of pain and injury in manual wheelchair users.

METHODS

Muscle-actuated forward dynamics simulations of manual wheelchair propulsion were analyzed to identify compensatory strategies in response to individual muscle group weakness using individual muscle mechanical power and stress as measures of upper extremity demand.

FINDINGS

The simulation analyses found the upper extremity to be robust to weakness in any single muscle group as the remaining groups were able to compensate and restore normal propulsion mechanics. The rotator cuff muscles experienced relatively high muscle stress levels and exhibited compensatory relationships with the deltoid muscles.

INTERPRETATION

These results underline the importance of strengthening the rotator cuff muscles and supporting muscles whose contributions do not increase the potential for impingement (i.e., the thoracohumeral depressors) and minimize the risk of upper extremity injury in manual wheelchair users.

Contributions of muscle imbalance and impaired growth to postural and osseous shoulder deformity following brachial plexus birth palsy: a computational simulation analysis

PURPOSE

Two potential mechanisms leading to postural and osseous shoulder deformity after brachial plexus birth palsy are muscle imbalance between functioning internal rotators and paralyzed external rotators and impaired longitudinal growth of paralyzed muscles. Our goal was to evaluate the combined and isolated effects of these 2 mechanisms on transverse plane shoulder forces using a computational model of C5-6 brachial plexus injury.

METHODS

We modeled a C5-6 injury using a computational musculoskeletal upper limb model. Muscles expected to be denervated by C5-6 injury were classified as affected, with the remaining shoulder muscles classified as unaffected. To model muscle imbalance, affected muscles were given no resting tone whereas unaffected muscles were given resting tone at 30% of maximal activation. To model impaired growth, affected muscles were reduced in length by 30% compared with normal whereas unaffected muscles remained normal in length. Four scenarios were simulated: normal, muscle imbalance only, impaired growth only, and both muscle imbalance and impaired growth. Passive shoulder rotation range of motion and glenohumeral joint reaction forces were evaluated to assess postural and osseous deformity.

RESULTS

All impaired scenarios exhibited restricted range of motion and increased and posteriorly directed compressive glenohumeral joint forces. Individually, impaired muscle growth caused worse restriction in range of motion and higher and more posteriorly directed glenohumeral forces than did muscle imbalance. Combined muscle imbalance and impaired growth caused the most restricted joint range of motion and the highest joint reaction force of all scenarios.

CONCLUSIONS

Both muscle imbalance and impaired longitudinal growth contributed to range of motion and force changes consistent with clinically observed deformity, although the most substantial effects resulted from impaired muscle growth.

CLINICAL RELEVANCE

Simulations suggest that treatment strategies emphasizing treatment of impaired longitudinal growth are warranted for reducing deformity after brachial plexus birth palsy.

Benchmarking of dynamic simulation predictions in two software platforms using an upper limb musculoskeletal model

Several opensource or commercially available software platforms are widely used to develop dynamic simulations of movement. While computational approaches are conceptually similar across platforms, technical differences in implementation may influence output. We present a new upper limb dynamic model as a tool to evaluate potential differences in predictive behavior between platforms. We evaluated to what extent differences in technical implementations in popular simulation software environments result in differences in kinematic predictions for single and multijoint movements using EMG- and optimization-based approaches for deriving control signals. We illustrate the benchmarking comparison using SIMM-Dynamics Pipeline-SD/Fast and OpenSim platforms. The most substantial divergence results from differences in muscle model and actuator paths. This model is a valuable resource and is available for download by other researchers. The model, data, and simulation results presented here can be used by future researchers to benchmark other software platforms and software upgrades for these two platforms.

Computational sensitivity analysis to identify muscles that can mechanically contribute to shoulder deformity following brachial plexus birth palsy

PURPOSE

Two mechanisms, strength imbalance or impaired longitudinal muscle growth, potentially cause osseous and postural shoulder deformity in children with brachial plexus birth palsy. Our objective was to determine which muscles, via either deformity mechanism, were mechanically capable of producing forces that could promote shoulder deformity.

METHODS

In an upper limb computational musculoskeletal model, we simulated strength imbalance by allowing each muscle crossing the shoulder to produce 30% of its maximum force. To simulate impaired longitudinal muscle growth, the functional length of each muscle crossing the shoulder was reduced by 30%. We performed a sensitivity analysis to identify muscles that, through either simulated deformity mechanism, increased the posteriorly directed, compressive glenohumeral joint force consistent with osseous deformity or reduced the shoulder external rotation or abduction range of motion consistent with postural deformity.

RESULTS

Most of the increase in the posterior glenohumeral joint force by the strength imbalance mechanism was caused by the subscapularis, latissimus dorsi, and infraspinatus. Posterior glenohumeral joint force increased the most owing to impaired growth of the infraspinatus, subscapularis, and long head of biceps. Through the strength imbalance mechanism, the subscapularis, anterior deltoid, and pectoralis major muscles reduced external shoulder rotation by 28°, 17°, and 10°, respectively. Shoulder motion was reduced by 40° to 56° owing to impaired growth of the anterior deltoid, subscapularis, and long head of triceps.

CONCLUSIONS

The infraspinatus, subscapularis, latissimus dorsi, long head of biceps, anterior deltoid, pectoralis major, and long head of triceps were identified in this computational study as being the most capable of producing shoulder forces that may contribute to shoulder deformity following brachial plexus birth palsy.

CLINICAL RELEVANCE

The muscles mechanically capable of producing deforming shoulder forces should be the focus of experimental studies investigating the musculoskeletal consequences of brachial plexus birth palsy and are potentially critical targets for treating shoulder deformity.

A New Postural Force Production Index to Assess Propulsion Effectiveness During Handcycling

The aim of this study was to propose a new index called Postural Force Production Index (PFPI) for evaluating the force production during handcycling. For a given posture, it assesses the force generation capacity in all Cartesian directions by linking the joint configuration to the effective force applied on the handgrips. Its purpose is to give insight into the force pattern of handcycling users, and could be used as ergonomic index. The PFPI is based on the force ellipsoid, which belongs to the class of manipulability indices and represents the overall force production capabilities at the hand in all Cartesian directions from unit joint torques. The kinematics and kinetics of the arm were recorded during a 1-min exercise test on a handcycle at 70 revolutions per minute performed by one paraplegic expert in handcycling. The PFPI values were compared with the Fraction Effective Force (FEF), which is classically associated with the effectiveness of force application. The results showed a correspondence in the propulsion cycle between FEF peaks and the most favorable postures to produce a force tangential to the crank rotation (PFPI). This preliminary study opens a promising way to study patterns of force production in the framework of handcycling movement analysis.

Partitioning kinetic energy during freewheeling wheelchair maneuvers

This paper describes a systematic method to partition the kinetic energy (KE) of a free-wheeling wheelchair. An ultralightweight rigid frame wheelchair was instrumented with two axle-mounted encoders and data acquisition equipment to accurately measure the velocity of the drive wheels. A mathematical model was created combining physical specifications and geometry of the wheelchair and its components. Two able-bodied subjects propelled the wheelchair over four courses that involved straight and turning maneuvers at differing speeds. The KE of the wheelchair was divided into three components: translational, rotational, and turning energy. This technique was sensitive to the changing contributions of the three energy components across maneuvers. Translational energy represented the major component of total KE in all maneuvers except a zero radius turn in which turning energy was dominant. Both translational and rotational energies are directly related to wheelchair speed. Partitioning KE offers a useful means of investigating the dynamics of a moving wheelchair. The described technique permits analysis of KE imparted to the wheelchair during maneuvers involving changes in speed and direction, which are most representative of mobility in everyday life. This technique can be used to study the effort required to maneuver different types and configurations of wheelchairs.

Effects of intramuscular trunk stimulation on manual wheelchair propulsion mechanics in 6 subjects with spinal cord injury

OBJECTIVE

To quantify the effects of stabilizing the paralyzed trunk and pelvis with electrical stimulation on manual wheelchair propulsion.

DESIGN

Single-subject design case series with subjects acting as their own concurrent controls.

SETTING

Hospital-based clinical biomechanics laboratory.

PARTICIPANTS

Individuals (N=6; 4 men, 2 women; mean age ± SD, 46 ± 10.8y) who were long-time users (6.1 ± 3.9y) of implanted neuroprostheses for lower extremity function and had chronic (8.6 ± 2.8y) midcervical- or thoracic-level injuries (C6-T10).

INTERVENTIONS

Continuous low-level stimulation to the hip (gluteus maximus, posterior adductor, or hamstrings) and trunk extensor (lumbar erector spinae and/or quadratus lumborum) muscles with implanted intramuscular electrodes.

MAIN OUTCOME MEASURES

Pushrim kinetics (peak resultant force, fraction effective force), kinematics (cadence, stroke length, maximum forward lean), and peak shoulder moment at preferred speed over 10-m level surface; speed, pushrim kinetics, and subjective ratings of effort for level 100-m sprints and up a 30.5-m ramp of approximately 5% grade.

RESULTS

Three of 5 subjects demonstrated reduced peak resultant pushrim forces (P≤.014) and improved efficiency (P≤.048) with stimulation during self-paced level propulsion. Peak sagittal shoulder moment remained unchanged in 3 subjects and increased in 2 others (P<.001). Maximal forward trunk lean also increased by 19% to 26% (P<.001) with stimulation in these 3 subjects. Stroke lengths were unchanged by stimulation in all subjects, and 2 showed extremely small (5%) but statistically significant increases in cadence (P≤.021). Performance measures for sprints and inclines were generally unchanged with stimulation; however, subjects consistently rated propulsion with stimulation to be easier for both surfaces.

CONCLUSIONS

Stabilizing the pelvis and trunk with low levels of continuous electrical stimulation to the lumbar trunk and hip extensors can positively impact the mechanics of manual wheelchair propulsion and reduce both perceived and physical measures of effort.

A theoretical analysis of the influence of wheelchair seat position on upper extremity demand

BACKGROUND

The high physical demands placed on the upper extremity during manual wheelchair propulsion can lead to pain and overuse injuries that further reduce user independence and quality of life. Seat position is an adjustable parameter that can influence the mechanical loads placed on the upper extremity. The purpose of this study was to use a musculoskeletal model and forward dynamics simulations of wheelchair propulsion to identify the optimal seat position that minimizes various measures of upper extremity demand including muscle stress, co-contraction and metabolic cost.

METHODS

Forward dynamics simulations of wheelchair propulsion were generated across a range of feasible seat positions by minimizing the change in handrim forces and muscle-produced joint moments. Resulting muscle stress, co-contraction and metabolic cost were examined to determine the optimal seat position that minimized these values.

FINDINGS

Muscle stress and metabolic cost were near minimal values at superior/inferior positions corresponding to top-dead-center elbow angles between 110 and 120° while at an anterior/posterior position with a hub-shoulder angle between -10 and -2.5°. This coincided with a reduction in the level of muscle co-contraction, primarily at the glenohumeral joint.

INTERPRETATION

Deviations from this position lead to increased co-contraction to maintain a stable, smooth propulsive stroke, which consequentially increases upper extremity demand. These results agree with previous clinical guidelines for positioning the seat to reduce upper extremity overuse injuries and pain for wheelchair users.

Biomechanical contributions of posterior deltoid and teres minor in the context of axillary nerve injury: a computational study

PURPOSE

To determine whether transfer to only the anterior branch of the axillary nerve will restore useful function after axillary nerve injury with persistent posterior deltoid and teres minor paralysis.

METHODS

We used a computational musculoskeletal model of the upper limb to determine the relative contributions of posterior deltoid and teres minor to maximum joint moment generated during a simulated static strength assessment and to joint moments during 3 submaximal shoulder movements. Movement simulations were performed with and without simulated posterior deltoid and teres minor paralysis to identify muscles that may compensate for their paralysis.

RESULTS

In the unimpaired limb model, teres minor and posterior deltoid accounted for 16% and 14% of the total isometric shoulder extension and external rotation joint moments, respectively. During the 3 movement simulations, posterior deltoid produced as much as 20% of the mean shoulder extension moment, whereas teres minor accounted for less than 5% of the mean joint moment in all directions of movement. When we paralyzed posterior deltoid and teres minor, the mean extension moments generated by the supraspinatus, long head of triceps, latissimus dorsi, and middle deltoid increased to compensate. Compensatory muscles were not fully activated during movement simulations when posterior deltoid and teres minor were paralyzed.

CONCLUSIONS

Reconstruction of the anterior branch of the axillary nerve only is an appropriate technique for restoring shoulder abduction strength after isolated axillary nerve injury. When shoulder extension strength is compromised by extensive neuromuscular shoulder injury, reconstruction of both the anterior and posterior branches of the axillary nerve should be considered.

CLINICAL RELEVANCE

By quantifying the biomechanical role of muscles during submaximal movement, in addition to quantifying muscle contributions to maximal shoulder strength, we can inform preoperative planning and permit more accurate predictions of functional outcomes.

Reconfiguration of the upper extremity relative to the pushrim affects load distribution during wheelchair propulsion

OBJECTIVE

Repetitive loading during manual wheelchair propulsion (WCP) is associated with overuse injury to the upper extremity (UE). The aim of this study was to determine how RF redirection and load distribution are affected by changes upper extremity kinematic modifications associated with modifications in seat positions during a WCP task. The aim of this study was to determine how RF redirection and load distribution are affected by upper extremity kinematic changes associated with seat position adjustment during a WCP task.

DESIGN

Dynamic simulations using an experiment-based multi-link inverse dynamics model were used to generate solutions for redistributing UE mechanical load in different seating positions without decrements in WCP task performance.

METHODS

Experimental RF and kinematic data were collected for one subject propelling at a self-selected speed and used as input into the model. Shoulder/axle distance, wrist angular position, and RF direction were systematically modified to simulate how the mechanical demand imposed on the upper extremity (elbow and shoulder net joint moments (NJMs) and net joint forces) may vary.

RESULTS

Load distribution depended on UE orientation relative to the wheel. At peak force, lower shoulder/axle distances and more anterior wrist positions on the pushrim allowed for more extended elbow positions and reduced total NJM load.

INTERPRETATION

Simulation results incorporating subject-specific data may provide mechanically based information to guide clinical interventions that aim to maintain WCP performance and redistribute load by modifying RF direction, seat configuration and hand/rim interaction.

The influence of wheelchair propulsion technique on upper extremity muscle demand: a simulation study

BACKGROUND

The majority of manual wheelchair users will experience upper extremity injuries or pain, in part due to the high force requirements, repetitive motion and extreme joint postures associated with wheelchair propulsion. Recent studies have identified cadence, contact angle and peak force as important factors for reducing upper extremity demand during propulsion. However, studies often make comparisons between populations (e.g., able-bodied vs. paraplegic) or do not investigate specific measures of upper extremity demand. The purpose of this study was to use a musculoskeletal model and forward dynamics simulations of wheelchair propulsion to investigate how altering cadence, peak force and contact angle influence individual muscle demand.

METHODS

Forward dynamics simulations of wheelchair propulsion were generated to emulate group-averaged experimental data during four conditions: 1) self-selected propulsion technique, and while 2) minimizing cadence, 3) maximizing contact angle, and 4) minimizing peak force using biofeedback. Simulations were used to determine individual muscle mechanical power and stress as measures of muscle demand.

RESULTS

Minimizing peak force and cadence had the lowest muscle power requirements. However, minimizing peak force increased cadence and recovery power, while minimizing cadence increased average muscle stress. Maximizing contact angle increased muscle stress and had the highest muscle power requirements.

INTERPRETATION

Minimizing cadence appears to have the most potential for reducing muscle demand and fatigue, which could decrease upper extremity injuries and pain. However, altering any of these variables to extreme values appears to be less effective; instead small to moderate changes may better reduce overall muscle demand.

Coordinate transformation between shoulder kinematic descriptions in the Holzbaur et al. model and ISB sequence

Holzbaur et al. (2005) proposed a comprehensive 3-D biomechanical upper extremity model. Since then, this model has been adopted by many other studies for kinetic and kinematic analysis of the shoulder joint. Because of the 3-D anatomical structure, three angles are necessary to define or describe shoulder kinematics. In the Holzbaur et al. model, the three angles are shoulder elevation, elevation angle, and shoulder rotation. The computational implementation of the elevation angle degree of freedom is considered in a different way than described in the recommendation of the International Society of Biomechanics (ISB). This paper presents an analysis of the transformation between the coordinates of the shoulder kinematic defined in the Holzbaur et al. upper extremity model and those defined by the ISB. The results of this study could be used for comparing the coordinates between the different descriptions of the shoulder kinematics.

Musculotendon lengths and moment arms for a three-dimensional upper-extremity model

Generating muscle-driven forward dynamics simulations of human movement using detailed musculoskeletal models can be computationally expensive. This is due in part to the time required to calculate musculotendon geometry (e.g., musculotendon lengths and moment arms), which is necessary to determine and apply individual musculotendon forces during the simulation. Modeling upper-extremity musculotendon geometry can be especially challenging due to the large number of multi-articular muscles and complex muscle paths. To accurately represent this geometry, wrapping surface algorithms and/or other computationally expensive techniques (e.g., phantom segments) are used. This paper provides a set of computationally efficient polynomial regression equations that estimate musculotendon length and moment arms for thirty-two (32) upper-extremity musculotendon actuators representing the major muscles crossing the shoulder, elbow and wrist joints. Equations were developed using a least squares fitting technique based on geometry values obtained from a validated public-domain upper-extremity musculoskeletal model that used wrapping surface elements (Holzbaur et al., 2005). In general, the regression equations fit well the original model values, with an average root mean square difference for all musculotendon actuators over the represented joint space of 0.39 mm (1.1% of peak value). In addition, the equations reduced the computational time required to simulate a representative upper-extremity movement (i.e., wheelchair propulsion) by more than two orders of magnitude (315 versus 2.3 s). Thus, these equations can assist in generating computationally efficient forward dynamics simulations of a wide range of upper-extremity movements.

Simulated effect of reaction force redirection on the upper extremity mechanical demand imposed during manual wheelchair propulsion

BACKGROUND

Manual wheelchair propulsion is associated with overuse injuries of the shoulder. Reaction force redirection relative to upper extremity segments was hypothesized as a means to redistribute mechanical load imposed on the upper extremity without decrements in wheelchair propulsion performance.

METHODS

Two individuals performed wheelchair propulsion under simulated inclined (graded) conditions using self-selected control strategies. Upper extremity kinematics and reaction forces applied to the wheel were quantified and used as input into an experiment-based multi-link inverse dynamics model that incorporates participant-specific experimental results. Reaction force direction was systematically modified to determine the mechanical demand imposed on the upper extremity (elbow and shoulder net joint moments and net joint forces) during wheelchair propulsion. Results were presented as solution spaces to examine the upper extremity load distribution characteristics within and between participants across a range of reaction force directions.

FINDINGS

Redirection of the reaction force relative to the upper extremity segments provides multiple solutions for redistributing mechanical demand across the elbow and shoulder without decrements in manual wheelchair propulsion performance. The distribution of load across RF directions was participant specific and was found to vary with time during the push phase.

INTERPRETATION

Solution spaces provide a mechanical basis for individualized interventions that aim to maintain function and redistribute load away from structures at risk for injury (e.g. reduce demand imposed on shoulder flexors (reduce shoulder net joint moment) or reduce potential for impingement (reduce shoulder net joint force).

Measurement of shoulder joint loads during wheelchair propulsion measured in vivo

BACKGROUND

Recent in vivo measurements show that the loads acting in the glenohumeral joint are high even during activities of daily living. Wheelchair users are frequently affected by shoulder problems. With previous musculoskeletal shoulder models, shoulder joint loading was mostly calculated during well-defined activities like forward flexion or abduction. For complex movements of everyday living or wheelchair propulsion, the reported loads vary considerably.

METHODS

Shoulder joint forces and moments were measured with telemeterized implants in 6 subjects. Data were captured on a treadmill at defined speeds and inclinations. Additional measurements were taken in 1 subject when lifting the body from the wheelchair, using his arms only, and in 2 subjects when rapidly accelerating and stopping the wheelchair. The influence of the floor material on shoulder joint loading was accessed in 2 subjects. In general, the maximum shoulder loads did not exceed those during daily living but the time courses and magnitudes of the loads intra-individually varied much.

FINDINGS

The highest forces acted during maximum acceleration and lifting from the wheelchair (128% and 188% of body weight). Grass was the only surface which led to a general load increase, compared to a smooth floor.

INTERPRETATION

The increased incidence of overuse injuries in wheelchair users are probably not caused by excessive load magnitudes during regular propulsion. The high number of repetitions is assumed to be more decisive.

Computer simulation of nerve transfer strategies for restoring shoulder function after adult C5 and C6 root avulsion injuries

PURPOSE

Functional ability after nerve transfer for upper brachial plexus injuries relies on both the function and magnitude of force recovery of targeted muscles. Following nerve transfers targeting either the axillary nerve, suprascapular nerve, or both, it is unclear whether functional ability is restored in the face of limited muscle force recovery.

METHODS

We used a computer model to simulate flexing the elbow while maintaining a functional shoulder posture for 3 nerve transfer scenarios. We assessed the minimum restored force capacity necessary to perform the task, the associated compensations by neighboring muscles, and the effect of altered muscle coordination on movement effort.

RESULTS

The minimum force restored by the axillary, suprascapular, and combined nerve transfers that was required for the model to simulate the desired movement was 25%, 40%, and 15% of the unimpaired muscle force capacity, respectively. When the deltoid was paralyzed, the infraspinatus and subscapularis muscles generated higher shoulder abduction moments to compensate for deltoid weakness. For all scenarios, movement effort increased as restored force capacity decreased.

CONCLUSIONS

Combined axillary and suprascapular nerve transfer required the least restored force capacity to perform the desired elbow flexion task, whereas single suprascapular nerve transfer required the most restored force capacity to perform the same task. Although compensation mechanisms allowed all scenarios to perform the desired movement despite weakened shoulder muscles, compensation increased movement effort. Dynamic simulations allowed independent evaluation of the effect of restored force capacity on functional outcome in a way that is not possible experimentally.

CLINICAL RELEVANCE

Simultaneous nerve transfer to suprascapular and axillary nerves yields the best simulated biomechanical outcome for lower magnitudes of muscle force recovery in this computer model. Axillary nerve transfer performs nearly as well as the combined transfer, whereas suprascapular nerve transfer is more sensitive to the magnitude of reinnervation and is therefore avoided.

Individual muscle contributions to push and recovery subtasks during wheelchair propulsion

Manual wheelchair propulsion places considerable physical demand on the upper extremity and is one of the primary activities associated with the high prevalence of upper extremity overuse injuries and pain among wheelchair users. As a result, recent effort has focused on determining how various propulsion techniques influence upper extremity demand during wheelchair propulsion. However, an important prerequisite for identifying the relationships between propulsion techniques and upper extremity demand is to understand how individual muscles contribute to the mechanical energetics of wheelchair propulsion. The purpose of this study was to use a forward dynamics simulation of wheelchair propulsion to quantify how individual muscles deliver, absorb and/or transfer mechanical power during propulsion. The analysis showed that muscles contribute to either push (i.e., deliver mechanical power to the handrim) or recovery (i.e., reposition the arm) subtasks, with the shoulder flexors being the primary contributors to the push and the shoulder extensors being the primary contributors to the recovery. In addition, significant activity from the shoulder muscles was required during the transition between push and recovery, which resulted in increased co-contraction and upper extremity demand. Thus, strengthening the shoulder flexors and promoting propulsion techniques that improve transition mechanics have much potential to reduce upper extremity demand and improve rehabilitation outcomes.