External rotation in the glenohumeral joint during elevation of the arm

Individualized workplace ergonomics using motion capture

Production workers suffer from musculoskeletal disorders (MSDs) due to excessive workloads that exceed the individual physical capabilities. In order to assess and subsequently reduce the risk to suffer from a MSD at a specific workplace, companies use ergonomic screening methods. However, the current approaches have two major downsides: Firstly, they do not take the individual worker and his/her capabilities into account. Applied thresholds for joint angles or physical loads are standard values that do not address physical limitations, such as age-related loss of flexibility or muscle strength. Secondly, the methods only provide a risk assessment that indicates which workplaces and/or working postures are ergonomically hazardous. Necessary workplace improvements are decoupled from the results and require extensive ergonomic knowledge. This paper presents a method that uses an individualized ergonomics analysis to improve workplaces according to individual needs and helps the industrial engineer to find necessary workplace improvements.

Effect of intraarticular pressure on glenohumeral kinematics during a simulated abduction motion: a cadaveric study

BACKGROUND

The current understanding of glenohumeral joint stability is defined by active restrictions and passive stabilizers including naturally-occurring negative intraarticular pressure. Cadaveric specimens have been used to evaluate the role of intraarticular pressure on joint stability, although, while the shoulder's negative intraarticular pressure is universally acknowledged, it has been inconsistently accounted for.

HYPOTHESIS

During continuous, passive humeral abduction, releasing the native intraarticular pressure increases joint translation, and restoring this pressure decreases joint translations.

STUDY DESIGN

Descriptive Laboratory Study.

METHODS

A validated shoulder testing system was used to passively abduct the humerus in the scapular plane and measure joint translations for seven (n = 7) cadaveric specimens. The pressure within the glenohumeral joint was measured via a 25-gauge needle during passive abduction of the arm, which was released and subsequently restored. During motion, the rotator cuff muscles were loaded using stepper motors in a force feedback loop and electromagnetic sensors were used to continuously measure the position of the humerus and scapula. Joint translation was defined according to the instant center of rotation of the glenohumeral head according to the recommendations by the International Society of Biomechanics.

RESULTS

Area under the translation versus abduction angle curve suggests that releasing the pressure within the capsule results in significantly less posterior translation of the glenohumeral head as compared to intact (85-90˚, p < 0.05). Posterior and superior translations were reduced after 70˚ of abduction when the pressure within the joint was restored.

CONCLUSION

With our testing system employing a smooth continuous passive motion, we were able to show that releasing intraarticular pressure does not have a major effect on the path of humeral head motion during glenohumeral abduction. However, both violating the capsule and restoring intraarticular pressure after releasing alter glenohumeral translations. Future studies should study the effect of simultaneous external rotation and abduction on the relationship between joint motion and IAP, especially in higher degrees of abduction.

CLINICAL RELEVANCE

Thoroughly simulating the glenohumeral joint environment in the cadaveric setting may strengthen the conclusions that can be translated from this setting to the clinic.

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).

Beyond Euler/Cardan analysis: True glenohumeral axial rotation during arm elevation and rotation

BACKGROUND

Based on Euler/Cardan analysis, prior investigations have reported up to 80° of glenohumeral (GH) external rotation during arm elevation, dependent on the plane of elevation (PoE). However, the subtraction of Euler/Cardan angles does not compute the rotation around the humerus' longitudinal axis (i.e. axial rotation). Clinicians want to understand the true rotation around the humerus' longitudinal axis and rely on laboratories to inform their understanding of underlying shoulder biomechanics, especially for the GH joint since its motion cannot be visually ascertained. True GH axial rotation has not been previously measured in vivo, and its difference from Euler/Cardan (apparent) axial rotation is unknown.

RESEARCH QUESTION

What is the true GH axial rotation during arm elevation and external rotation, and does it vary from apparent axial rotation and by PoE?

METHODS

Twenty healthy subjects (10 M/10 F, ages 22-66) were recorded using biplane fluoroscopy while performing arm elevation in the coronal, scapular and sagittal planes, and external rotation in 0° and 90° of abduction. Apparent GH axial rotation was computed using the xz'y'' and yx'y'' sequences. True GH axial rotation was computed by integrating the projection of GH angular velocity onto the humerus' longitudinal axis. One-dimensional statistical parametric mapping was utilized to compare apparent versus true axial rotation, axial rotation versus 0°, and detect differences in axial rotation by PoE.

RESULTS

In contrast to apparent axial rotation, true GH axial rotation does not differ by PoE and is not different than 0° during arm elevation at higher elevation angles. The spherical area between the sequence-specific and actual humeral trajectory explains the difference between apparent and true axial rotation.

SIGNIFICANCE

Proper quantification of axial rotation is important because biomechanics literature informs clinical understanding of shoulder biomechanics. Clinicians care about true axial rotation, which should be reported in future studies of shoulder kinematics.

Kinematic Differences between Two Types of Forward Elevations of the Shoulder Joint: Flexion and Reaching Elevation

Background:

Extension of the elbow joint is maintained during shoulder flexion. In contrast, the arm starts from the flexed position of the elbow joint and the joint gradually extends during reaching elevation.

Objectives:

This study aimed to compare the kinematic elements and electromyographic (EMG) activities of the rotator cuff muscles between flexion and reaching elevation.

Methods:

The study included 10 healthy young men. (average age, 21.5 ± 3.4 years), and measurements were performed on their dominant arms. A three-dimensional motion analyzer was used to record the following elements during shoulder flexion and reaching elevation: the angles of glenohumeral joint elevation and scapular upward rotation, scapulohumeral rhythm, external rotation of the humerus, and glenohumeral plane shifting from the coronal plane. The EMG activities in the supraspinatus, infraspinatus, subscapularis, and teres minor were recorded simultaneously.

Results:

The plane of reaching elevation was retained at 60° from the coronal plane. The glenohumeral planes (P < 0 .01) and the external rotation angles of the humerus below 90° of elevation (P < 0.05) were significantly different between both the motions. The EMG activities in the supraspinatus (P < .01), infraspinatus (P < 0.05), and teres minor (P < 0.01) were significantly lower while reaching elevation than those during flexion.

Conclusion:

The motion plane at 60° from the coronal plane, movement of the humeral external rotation, and EMG activities of the rotator cuff muscles were different during reaching elevation and shoulder flexion.

Influence of humeral abduction angle on axial rotation and contact area at the glenohumeral joint

BACKGROUND

Although the elevation angle of the arm affects the range of rotation, it has not been evaluated up to the maximal abduction angle. In this study we conducted an evaluation up to maximal abduction and determined the contact patterns at the glenohumeral (GH) joint.

METHODS

Fourteen healthy volunteers (12 men and 2 women; mean age, 26.9 years) with normal shoulders (14 right and 8 left) were instructed to rotate their shoulders at 0°, 90°, 135°, and maximal abduction for each shoulder at a time. Using 2-dimensional and 3-dimensional single-plane image registration, the internal rotation (IR), external rotation (ER), and range of motion (ROM; ie, axial rotations) at the thoracohumeral (TH) and GH joints, and the contribution ratio (%ROM = GH-ROM/TH-ROM) were calculated for each abduction. The glenoid position with respect to the humeral head was also analyzed.

RESULTS

The TH-IR and TH-ER shifted toward an ER with increasing abduction angle, whereas the TH-ROM significantly decreased except at abduction between 0° and 90° (P < .001). The GH-IR and GH-ROM significantly decreased except at abduction between 0° and 90° (P < .001), but the GH-ER remained constant regardless of the abduction. The contribution ratio exceeded 80% for every abduction angle. The glenoid moved on the central and posterior areas of the humeral head at 0° and 90° abduction, respectively, and on the posterosuperior and anterosuperior areas at 135° and maximal abduction, respectively.

CONCLUSION

Our results provide new knowledge about wide axial rotation up to maximal abduction and constant GH-ER at any abduction.

Can optimal marker weightings improve thoracohumeral kinematics accuracy?

Local and global optimization algorithms have been developed to estimate joint kinematics to reducing soft movement artifact (STA). Such algorithms can include weightings to account for different STA occur at each marker. The objective was to quantify the benefit of optimal weighting and determine if optimal marker weightings can improve humerus kinematics accuracy. A pin with five reflective markers was inserted into the humerus of four subjects. Seven markers were put on the skin of the arm. Subjects performed 38 different tasks including arm elevation, rotation, daily-living tasks, and sport activities. In each movement, mean and peak errors in skin- vs. pins-orientation were reported. Then, optimal marker weightings were found to best match skin- and pin-based orientation. Without weighting, the error of the arm orientation ranged from 1.9° to 17.9°. With weighting, 100% of the trials were improved and the average error was halved. The mid-arm markers weights were close to 0 for three subjects. Weights of a subject applied to the others for a given movement, and weights of a movement applied to others for a given subject did not systematically increased accuracy of arm orientation. Without weighting, a redundant set of marker and least square algorithm improved accuracy to estimate arm orientation compared to data of the literature using electromagnetic sensor. Weightings were subject- and movement-specific, which reinforces that STA are subject- and movement-specific. However, markers on the deltoid insertion and on lateral and medial epicondyles may be preferred if a limited number of markers is used.

Assessment of shoulder external rotation range-of-motion on throwing athletes: the effects of testing end-range determination (active versus passive)

The purpose of this study was to compare the effects of active or passive end-range determination (supine position) for external rotation range of motion (ROM) in overhead throwing athletes and verify if athletes' ROM is similar to non-athletes. Kinematic data from the dominant shoulder of 24 healthy male subjects, divided into two groups (12 athletes and 12 non-athletes) were recorded at end-range external rotation, thoracohumeral and glenohumeral external rotation angles were compared and a 2-way repeated-measures ANOVA was used to calculate the effects of end-range determination (passive versus active) across groups (athlete and non-athlete). A significant main effect (p < 0.001) on both thoracohumeral and glenohumeral external end-range angles was observed while the highest end-range determination values were associated with passive motion. No differences were observed between the athletic or non-athletic groups for either thoracohumeral (p = 0.784) or glenohumeral (p = 0.364) motion.

Glenohumeral relationship in maximum elevation

Purpose

The purpose of this study was to clarify rotational relationships between the anatomical landmarks of the glenohumeral joint in maximum elevation.

Methods

Twenty-five healthy volunteers (20 men, 5 women; mean age, 31 years) held the arm in maximum elevation in an open MRI system. In each three-dimensionally computer-generated image, elevation angle of the humerus in the plane of elevation was measured, based on the glenoid and the scapular planes. Using the equator set on the head surface by the plane parallel to the humeral axis, involving the head center and the bicipital groove, glenoid location and rotational relationships were investigated.

Results

The elevation angle was 102° ± 9° in the plane 7° ± 8° anterior to the scapular plane, and axial rotation was fixed with the glenoidal long axis parallel to the equator (within 2°). Each glenoid center located on antero-superior portion of the humeral head, and the direction from the top of the head to its location was the same as that of the shaft tilting, indicating the glenoid only translated without rotation after reaching the top of the head on the equator.

Conclusions

Before reaching maximum elevation, the glenohumeral joint would be locked in axial rotation. The position when the glenoid is on the top of the humeral head with the humeral shaft perpendicular to the glenoid is considered to be essentially the final position of elevation, above which the glenohumeral joint only translates without axial rotation even if the humerus is more elevated.

Electronic supplementary material

The online version of this article (doi:10.1007/s00276-014-1257-y) contains supplementary material, which is available to authorized users.

In vitro biomechanical comparison of three different types of single- and double-row arthroscopic rotator cuff repairs: analysis of continuous bone-tendon contact pressure and surface during different simulated joint positions

HYPOTHESIS

We assessed bone-tendon contact surface and pressure with a continuous and reversible measurement system comparing 3 different double- and single-row techniques of cuff repair with simulation of different joint positions.

MATERIALS AND METHODS

We reproduced a medium supraspinatus tear in 24 human cadaveric shoulders. For the 12 right shoulders, single-row suture (SRS) and then double-row bridge suture (DRBS) were used. For the 12 left shoulders, DRBS and then double-row cross suture (DRCS) were used. Measurements were performed before, during, and after knot tying and then with different joint positions.

RESULTS

There was a significant increase in contact surface with the DRBS technique compared with the SRS technique and with the DRCS technique compared with the SRS or DRBS technique. There was a significant increase in contact pressure with the DRBS technique and DRCS technique compared with the SRS technique but no difference between the DRBS technique and DRCS technique.

CONCLUSIONS

The DRCS technique seems to be superior to the DRBS and SRS techniques in terms of bone-tendon contact surface and pressure.

External rotation during elevation of the arm

BACKGROUND

Knowledge about the pattern of rotation during arm elevation is necessary for a full understanding of shoulder function, and it is also useful for planning of rehabilitation protocols to restore range of motion in shoulders in disorder. However, there are insufficient in vivo data available. METHODS; We investigated dynamic arm rotation during elevation in different planes using 30 shoulders in 15 healthy men (age range 21-33 years). Both arms were moved from neutral dependent position to maximum elevated position in 4 planes from laterally to anteriorly, and each dynamic course of motion was traced using a 3-dimensional motion capture system.

RESULTS

Patterns of rotation were categorized as being one of 2 types, depending on whether or not external rotation peaked before the arm reached the maximum elevated position. External rotation peaked at 122 degrees (SD14) of abduction, then decreased according to the arm movement in the lateral planes, but increased gradually to maximum elevated position in the anterior planes. Mean maximal angles of external rotation (in degrees) during elevation were 27 (SD11), 13 (SD13), 3 (SD9), and 3 (SD5), from laterally to anteriorly.

INTERPRETATION

There were differences in rotational patterns, and more external rotation was needed to reach maximum elevation in lateral planes than in anterior planes.

Scapulohumeral rhythm and associated spinal motion

BACKGROUND

To investigate the coordination of humeral, scapular and thoracolumbar spine motions during a number of unilateral and bilateral upper limb movements in a range of movement conditions.

METHODS

Thirty-two healthy women performed unilateral and bilateral arm elevations in three planes-sagittal, coronal and scapular. Scapular, humeral and spinal orientations were measured at 100 Hz using a multi-sensor, 6-degree-of-freedom electromagnetic tracking system. Segmental displacements were computed following International Society of Biomechanics recommendations.

FINDINGS

Humeral, scapular and thoracic segments demonstrate consistent, synchronous interactions. Scapular upward rotation is significantly greater on the non-dominant side than the dominant in all planes of movement and in both unilateral and bilateral arm movement. Unilateral and bilateral arm movements produce significantly different ranges and patterns of spinal motion and ranges of scapular external rotation. There does not appear to be any effect of age, height or weight on the ranges or patterns of motion of the shoulder girdle and spine during arm elevation.

INTERPRETATION

Movement of the arm into elevation, irrespective of the plane of motion, has significant implications for the shoulder girdle and the thoracic spine. Clinical assessment of the shoulder should include the thoracic spine.

A proposal for a new definition of the axial rotation angle of the shoulder joint

The Euler/Cardan angles are commonly used to define the motions of the upper arm with respect to the trunk. This definition, however, has a problem in that the angles of both the horizontal flexion/extension and the axial rotation of the shoulder joint become unstable at the gimbal-lock positions. In this paper, a new definition of the axial rotation angle was proposed. The proposed angle was stable over the entire range of the shoulder motion. With the new definition, the neutral position of the axial rotation agreed with that in the conventional anatomy. The advantage of the new definition was demonstrated by measuring actual complex motions of the shoulder with a three-dimensional motion capture system.

The three-dimensional motions of glenohumeral joint under semi-loaded condition during arm abduction using vertically open MRI

BACKGROUND

Magnetic resonance imaging is an accurate non-invasive tool for visualizing muscles, tendons, and bones. It also provides 3D coordinate values. The purpose of the present study was to visualize and quantify the 3D positions of the glenohumeral joint during isometric abduction of the arm using vertically open magnetic resonance imaging.

METHODS

We examined 14 shoulders of seven healthy volunteers. Magnetic resonance images were obtained in a seated position and in seven static positions of the arm from 0 degrees to maximum abduction using vertically open magnetic resonance imaging. 3D surface models were created and 3D movements of each bone in the glenohumeral joint were calculated using a computer algorithm. We analyzed the translation and contact pattern of the glenohumeral joint.

FINDINGS

In supero-inferior direction, the humeral head translated slight inferiorly from +1.9 (SD 1.0) mm at 0 degrees to +0.8 (SD 1.8) mm at the maximum abduction. In antero-posterior direction, the humeral head translated anteriorly from 0 degrees to 90 degrees (mean +2.4, SD 2.6 mm) and posteriorly from 90 degrees to 150 degrees of abduction (mean -1.4, SD 2.7 mm). Furthermore, the humeral head had a unique contact patterns with the glenoid; the contact part of the humeral head with the glenoid changed from the central part to the posterior in the midrange of abduction.

INTERPRETATION

The humeral head showed a small translation in the antero-posterior direction between 90 degrees and 150 degrees of abduction. In addition, the posterior part of the humeral head contacted the glenoid in this range of abduction. These findings of motion patterns in asymptomatic subjects will be necessary when comparing the kinematics with pathologic condition such as the glenohumeral instability and rotator cuff tear.

Pathological Teres Major activation in patients with massive rotator cuff tears alters with pain relief and/or salvage surgery transfer

BACKGROUND

Massive rotator cuff tears impose restraints on overhand arm functionality and are often accompanied by pain. After musculotendinous Teres Major transfer, overhand arm function is generally restored and pain is reduced. The assumed mechanical abduction insufficiency and Teres Major muscle function adaptation will be experimentally verified.

METHODS

Principal Teres Major muscle activation (surface IEMG averaged over 3s) is recorded for 12-24 isometric and isotonic force directions perpendicular to the 60 degrees forward flexed humerus in three conditions: prior to surgery (n = 6 patients), prior to surgery and after subacromial anaesthetic (n = 6) and post-surgery (n = 3). Principal direction and on-, offset directions were estimated.

FINDINGS

Teres Major activation adapts both to pathological and post surgery conditions: the normal activation during adduction changes into activation during forward flexion or abduction. Glenohumeral stabilisation, not abduction torque, seems to be the explanation for post surgery Teres Major transfer success.

INTERPRETATIONS

The pathological absence of Supraspinatus and Infraspinatus forces during forward flexion result in increased upward glenohumeral instability. The superior translations are compensated for by Teres Major activity during forward flexion. This translation-'force' function conflicts with the adduction-generating rotation-'torque' function. This may explain the pain-induced reduction of arm elevation in these patients. Musculotendinous transfer solves the force-torque conflict by changing the moment arm of the Teres Major from adduction to abduction. Teres Major can now both compensate for the loss of Supraspinatus and Infraspinatus forces needed for glenohumeral stabilisation and contribute to forward flexion of the arm.

Effects of shoulder muscle fatigue caused by repetitive overhead activities on scapulothoracic and glenohumeral kinematics

The purpose of this study was to determine the effects of shoulder muscle fatigue on three dimensional scapulothoracic and glenohumeral kinematics. Twenty healthy subjects participated in this study. Three-dimensional scapulothoracic and glenohumeral kinematics were determined from electromagnetic sensors attached to the scapula, humerus, and thorax. Surface electromyographic (EMG) data were collected from the upper and lower trapezius, serratus anterior, anterior and posterior deltoid, and infraspinatus muscles. Median power frequency (MPF) values were derived from the raw EMG data and were used to indicate the degree of local muscle fatigue. Kinematic and EMG measures were collected prior to and immediately following the performance of a shoulder elevation fatigue protocol. Following the performance of the fatigue protocol subjects demonstrated more upward and external rotation of the scapula, more clavicular retraction, and less humeral external rotation during arm elevation. All muscles with the exception of the lower trapezius showed EMG signs of fatigue, the most notable being the infraspinatus and deltoid muscles. In general, greater scapulothoracic motion and less glenohumeral motion was observed following muscle fatigue. Further studies are needed to determine what effects these changes have on the soft tissues and mechanics of the shoulder complex.

Soft tissue artefact assessment in humeral axial rotation

The accuracy of upper-limb kinematic data acquired from optoelectronic systems with retro-reflective markers is poor, mainly due to soft tissue artefact (STA). For the upper-arm, humeral internal/external rotation (HIER) is the movement most affected by STA, which is measured as a percentile fraction (K) of the effective humeral axial rotation performed. The aim of this work was to quantify STA during HIERs, with independently varying attitude of the humerus and elbow flexion, and to test the possibility of estimating its mean value over the tested upper-limb orientations using one simple trial. Six able-bodied subjects performed a series of HIERs in combination with elbow flexion for different humeral planes and degrees of elevation. During the trials the instantaneous attitudes of two humeral anatomical frames were compared, one being affected by the STA to be measured, and the other assumed as the gold standard. K was found to range from 20% to 48% of the effective humeral axial rotation performed, depending on the subject, humeral attitude and elbow flexion. These last two factors comparably affect STA and resulted in mean K coefficients of variation among the subjects of about 9% and 7%, respectively. Common patterns of K with elbow flexion and humerus elevation are discussed. The data also show that the mean of K of a subject is very close to the value assessed in a specific upper-limb configuration consistent among the subjects. This result from this study could be used to build up a time-saving STA compensation procedure suitable for clinical applications.

Three-dimensional in vivo displacements of the shoulder complex from biplanar radiography

The goal of this study was to adapt roentgen photogrammetry to in vivo studies of shoulder skeletal motion during arm elevation in the scapular plane. Numerous in vitro and in vivo studies have been published describing shoulder bone movements. They involve plain radiographic measurements and utilize a three-dimensional (3D) approach. Measurements are either direct using pins implanted in bones, or indirect recording points on medical images. Roentgen photogrammetry locates points in space from two projections obtained from two different radiographic incidences. The technique has been applied in vivo by implanting metallic balls in bones. However, to be used as a standard clinical procedure, the technique must be adapted to be less invasive. In vivo photogrammetric reconstruction of known points in 3D space requires that the subject is strictly motionless between the successive radiographic exposures or that the exposures are obtained simultaneously. Methods used in this study were developed to allow subsequent exposures to be used for analysis. Numerical tools have been developed to align the two projections of a point in 3D space which have moved slightly between two successive exposures. The standard photogrammetric technique is completed by geometric modeling of the shoulder complex and humerus, and by the control of their mutual proximity at the level of joints. Bones are modeled as a set of simple volumes linked together using geometric shapes described by shape parameters. The coincidence between real bone contours and radiographic projections of the modeled bone gives the values of the shape parameters and the accurate location in space. Results focus on two different topics: errors related to the use of roentgen photogrammetry with successive exposures, and results obtained by applying roentgen photogrammetry to the in vivo shoulder complex. Results describing shoulder bone and joint displacements are presented for comparison with previously published results. The technique of roentgen photogrammetry can successfully be applied to patients. The radiographic protocol is simple, and data can be obtained easily and quickly from the digitized films. The data obtained from asymptomatic shoulders compared favorably with published values. Future research will focus on comparisons between kinematics of the symptomatic and asymptomatic contralateral limbs in volunteers.