DirkJan Veeger

Recording scapular motion using an acromion marker cluster

Disorders of the shoulder complex can be accompanied by changes in the movement pattern of the scapula. However, scapular motion is difficult to measure. A possible non-invasive method for dynamic three-dimensional kinematic measurement of the human scapula is the use of a marker cluster placed on the flat part of the acromion. A small light-weight acromion marker cluster (AMC) is presented in this study. In order to assess validity, kinematics obtained with the AMC were compared to simultaneous scapula locator (SL) recordings in a series of postures. The test/retest variability of replacement of the AMC, was also assessed. Measurement errors appeared to be sensitive for the plane of movement, the degree of humerus elevation, and replacement of the AMC. The AMC generally under-estimated scapula motion, compared to the SL. Some significant differences were found between the two methods, although the absolute differences were small (maximum mean difference 8.4 degrees in extreme position). In humerus forward flexion and abduction the maximum mean differences were 6 degrees or lower. In conclusion, the AMC is a valid method of measuring scapular movement during arm elevation that could be used in shoulder pathologies. Placement and planes of movement should be carefully considered and elevation of the humerus should not exceed 100 degrees.

Mechanical loading of the low back and shoulders during pushing and pulling activities

The objective of this study was to quantify the mechanical load on the low back and shoulders during pushing and pulling in combination with three task constraints: the use of one or two hands, three cart weights, and two handle heights. The second objective was to explore the relation between the initial and sustained exerted forces and the mechanical load on the low back and shoulders. Detailed biomechanical models of the low back and shoulder joint were used to estimate mechanical loading. Using generalized estimating equations (GEE) the effects were quantified for exerted push/pull forces, net moments at the low back and shoulders, compressive and shear forces at the low back, and compressive forces at the glenohumeral joint. The results of this study appeared to be useful to estimate ergonomics consequences of interventions in the working constraints during pushing and pulling. Cart weight as well as handle height had a considerable effect on the mechanical load and it is recommended to maintain low cart weights and to push or pull at shoulder height. Initial and sustained exerted forces were not highly correlated with the mechanical load at the low back and shoulders within the studied range of the exerted forces.

Alternative modes of manual wheelchair ambulation : An overview

van der Woude LHV, Dallmeijer AJ, Janssen TWJ, et al: Alternative modes of manual wheelchair ambulation: An overview. Am J Phys Med Rehabil 2001;80:765–777.An estimated 90% of all wheelchairs are hand-rim propelled, a physically straining form of ambulation that can lead to repetitive strain injuries in the arms and, eventually, to secondary impairments and disability. Further disability in wheelchair-dependent individuals can lead to a sedentary lifestyle and thereby create a greater risk for cardiovascular problems. Studies on lever-propelled and crank-propelled wheelchairs have shown that these propulsion mechanisms are less straining and more efficient than hand-rim–propelled wheelchairs. This article reviews these studies and substantiates that the frequent use of these alternative propulsion mechanisms may help prevent some of the secondary impairments that are seen among today’s wheelchair-user population.

Kinematic alterations in the ipsilateral shoulder of patients with hemiplegia due to stroke

Meskers CGM, Koppe PA, Konijnenbelt H, Veeger HEJ, Janssen TWJ: Kinematic alterations in the ipsilateral shoulder of patients with hemiplegia due to stroke. Am J Phys Med Rehabil 2005;84:97–105. Objective:To evaluate the assumption that shoulder kinematic patterns of the ipsilateral, nonparetic shoulder in hemiplegia are similar to kinematics recorded in a healthy population. Design:Case control study of a convenience sample of ten patients with hemiplegia due to stroke in the subacute phase compared with a control group of similar age. Three-dimensional positions of the scapula and humerus were measured and expressed in Euler angles as a function of active arm elevation in the frontal and sagittal plane and during passive humeral internal/external rotation at an elevation angle of 90 degrees in the frontal and sagittal plane. Results:Compared with controls, in the ipsilateral shoulder of patients, we found both a statistically significant diminished scapular protraction during elevation in the sagittal plane (35 ± 5 vs. 51 ± 8 degrees at 110 degrees of humeral elevation) and humeral external rotation during arm elevation in the frontal plane (51 ± 7 vs. 69 ± 14 degrees at 110 degrees of humeral elevation). Maximal passive humeral external rotation was found to be impaired in the frontal (64 ± 13 vs. 98 ± 14 degrees) and sagittal planes (65 ± 11 vs. 94 ± 12 degrees). In addition, there was significantly diminished anterior spinal tilt during humeral internal rotation (−5 ± 10 vs. −20 ± 9 degrees) and diminished posterior spinal tilt during external rotation in the frontal plane (−14 ± 8 vs. −3 ± 6 degrees). Maximal thoracohumeral elevation in patients was significantly impaired (126 ± 12 vs. 138 ± 8 degrees). Conclusion:Clear kinematic changes in the ipsilateral shoulder in patients with hemiplegia were found, indicating underlying alterations in muscle contraction patterns. The cause remains speculative. These results suggest that the ipsilateral shoulder should not be considered to function normally beforehand.

Kinematics of the contralateral and ipsilateral shoulder: a possible relationship with post-stroke shoulder pain.

OBJECTIVE Post-stroke shoulder pain is a common phenomenon in hemiplegia and impedes rehabilitation. The aim of this study was to identify a possible relationship between post-stroke shoulder pain, scapula resting position and shoulder motion. METHODS Shoulder kinematics of 27 patients after stroke (17 men) were compared with 10 healthy age-matched control subjects. Using an electromagnetic tracking device, the kinematics of both the contralateral and ipsilateral (i.e. paretic and non-paretic) arm during active and passive abduction and forward flexion were measured and expressed in Euler angles. RESULTS Scapular lateral rotation relative to the thorax was increased in patients with post-stroke shoulder pain compared with both patients without post-stroke shoulder pain and control subjects at rest as well as during arm abduction and forward flexion. Additionally, glenohumeral elevation was decreased in patients with post-stroke shoulder pain during passive abduction. No differences were found regarding scapula position (displacement relative to the thorax). CONCLUSION In patients with post-stroke shoulder pain a particular kinematical shoulder pattern was established, characterized by enhanced scapular lateral rotation and diminished glenohumeral mobility.

Clinical applications of musculoskeletal modelling for the shoulder and upper limb

Musculoskeletal models have been developed to estimate internal loading on the human skeleton, which cannot directly be measured in vivo, from external measurements like kinematics and external forces. Such models of the shoulder and upper extremity have been used for a variety of purposes, ranging from understanding basic shoulder biomechanics to assisting in preoperative planning. In this review, we provide an overview of the most commonly used large-scale shoulder and upper extremity models and categorise the applications of these models according to the type of questions their users aimed to answer. We found that the most explored feature of a model is the possibility to predict the effect of a structural adaptation on functional outcome, for instance, to simulate a tendon transfer preoperatively. Recent studies have focused on minimising the mismatch in morphology between the model, often derived from cadaver studies, and the subject that is analysed. However, only a subset of the parameters that describe the model’s geometry and, perhaps most importantly, the musculotendon properties can be obtained in vivo. Because most parameters are somehow interrelated, the others should be scaled to prevent inconsistencies in the model’s structure, but it is not known exactly how. Although considerable effort is put into adding complexity to models, for example, by making them subject-specific, we have found little evidence of their superiority over current models. The current trend in development towards individualised, more complex models needs to be justified by demonstrating their ability to answer questions that cannot already be answered by existing models.

The effect of experimental shortening of the clavicle on shoulder kinematics

BACKGROUND Malunion after mid shaft clavicle fractures has recently been recognized as a cause of pain and dysfunction of the shoulder. The mechanism that causes these complaints is however yet unclear. In this study we describe the kinematic changes that occur in the shoulder girdle due to clavicle shortening. METHODS An experimental cadaveric study was performed on five shoulders of three fresh frozen specimens. The specimens were fixed in an upright position that allowed free motion of the shoulder girdle. We measured position of the bony structures with an opto-electronic system (Northern Digital Inc., Waterloo, Ontario Canada) in rest and during in a series of motions. Measurements were done with a normal clavicle and after shortening of the clavicle by 1.2, 2.4 and 3.6 cm. The shoulders were moved manually by one of the researchers. We examined for changes in resting position and during movement that resulted from the experimental shortening of the clavicle. FINDINGS In the resting position, winging of the scapula increased with resultant changes in the orientation of the glenoid, acromio-clavicular and sterno-clavicular joints and an altered position of the clavicle. On average protraction increased by 20°, lateral rotation changed 12° and posterior tilt decreased by 7°. Clavicle shortening affected sterno-clavicular joint rotations but did not do so in the acromio-clavicular joint. In arm elevation the offset in scapula orientation at resting position stayed relatively constant over the full range of motion but the amount of disposition is progressive in relation to the amount of shortening. INTERPRETATION Shortening of the clavicle leads to significant changes in the shoulder girdle in resting position and in movement.

Force direction in manual wheel chair propulsion: balance between effect and cost

OBJECTIVE To evaluate the relationship between mechanical effect and musculoskeletal cost in wheelchair propulsion. DESIGN Simulation of force direction, based on experimental data from wheelchair users. METHODS For nine wheelchair users driving at 20 W, 1.39 m/s, the force direction was compared to simulation results based on a criterion defined as the ratio of mechanical effect and musculoskeletal cost. RESULTS Simulation data compare well to the actual force direction for the middle and final parts of the push. CONCLUSIONS The musculoskeletal cost of the exerted force must be taken into account to explain the observed propulsion pattern. Experienced users appear to optimize the force pattern by balancing mechanical effect and musculoskeletal cost of the pushing action. RelevanceThe effect-cost ratio may be a useful tool in analysing and improving wheelchair design.

Seat height : effects on submaximal hand rim wheelchair performance during spinal cord injury rehabilitation

OBJECTIVE To evaluate the effects of wheelchair seat height on wheeling efficiency and technique during rehabilitation in subjects with a spinal cord injury. DESIGN Laboratory-based study. SUBJECTS Twelve persons with spinal cord injury (age range 19-77 years, lesion level: C5/C6-L2; 7 men; 8 incomplete). METHODS Subjects conducted 8 submaximal hand rim wheelchair exercise tests (4 min) on a computerized ergometer at 8 seat heights (elbow angle: 70-140 degrees , full extension = 180 degrees) in a counter-balanced order (individualized fixed power output (5.4-13.9 W) and speed). Last-minute physiological and technique parameters were evaluated using repeated measures analysis of variance (ANOVA) and multilevel regression analysis (p < 0.05). RESULTS Physical strain and mechanical efficiency changed significantly (p < 0.05) with seat height, with optimal values at 100-130 degrees . Lower seat heights were clearly detrimental. Forces on the hand rims were affected by seat height, showing lower forces with increasing seat height. Lesion level was not a confounder of seat height with respect to mechanical efficiency, oxygen uptake or fraction effective force. CONCLUSION Mean physiological data indicate a tendency to optimize at 100-130 degrees seat height. This does not relate to the trends seen in force and technique data. Optimization of seat height during spinal cord injury rehabilitation may lead to more efficient and less straining conditions for manual wheeling.

The influence of task variation on manifestation of fatigue is ambiguous - a literature review

Task variation has been proposed to reduce shoulder fatigue resulting from repetitive hand–arm tasks. This review analyses the effect of task variation, both ‘temporal (i.e. change of work–rest ratio)’ and ‘activity (i.e. job rotation)’ variation, on physiological responses, endurance time (ET) and subjective feelings. Pubmed was searched and complemented with references from selected articles, resulting in 17 articles. Temporal variation had some positive effects on the objective parameters, as blood pressure decreased and ET increased, and on the subjective feelings, as perceived discomfort decreased. The observed findings of activity variation showed both positive and negative effects of increased activity variation, while hardly any effects were found on electromyography manifestations of fatigue. In conclusion, the evidence for positive effects of increasing the level of variation is scarce. The number of studies on variation is limited, while in most studies the findings were not controlled for the amount or intensity of work. Practitioner Summary: Some laboratory-controlled studies showed some positive effects of increasing temporal variation, providing limited support for introducing frequent interruptions in work. Activity variation showed ambiguous effects, meaning there is no evidence for practical implication. In practice, however, other positive effects of activity variation may occur, for example job enrichment and increased motivation.