Repetitive Shoulder Research Articles

Rating Distal Clavicle Resection per the Guides, Sixth Edition

Rating Distal Clavicle Resection per the Guides, Sixth Edition

The influence of job rotation and task order on muscle fatigue: A deltoid example

Despite frequent use in industry, job rotation lacks robust confirmation as an effective method to limit exposure. This study investigated two tasks that involved the deltoid muscle. We examined two major factors in the context of muscle fatigue: the presence of rotation between tasks, and the order of task rotation if rotation was present. Participants performed four task combinations (coded AA, AB, BA, BB) of two tasks that were intended to produce fatigue (A: repetitive shoulder flexion; B: repetitive shoulder abduction). All tested conditions resulted in lower maximum force production capability (mean range of 78-88% of original strength), in this order of decreasing magnitude: BB --> AB --> BA --> AA, though differences between successive levels were not always significant. Specific muscle results supported this progression of strength decreases. For tasks with different muscular demands (AB and BA), it was less fatiguing to rotate between them than to only perform the more demanding task (BB). The order of rotation between tasks (AB vs. BA) did not influence muscle fatigue indicators. These findings help to assess the effectiveness of rotating between different tasks in reducing muscular fatigue or exposure. They also indicated a low apparent influence of task order on terminal fatigue characteristics for the task combinations evaluated.

Posture-movement changes following repetitive motion-induced shoulder muscle fatigue

Repetitive motion-induced fatigue not only alters local motion characteristics but also provokes global reorganization of movement. However, the three-dimensional (3D) characteristics of these reorganization patterns have never been documented in detail. The goal of this study was to assess the effects of repetitive reaching-induced arm fatigue on the whole-body, 3D biomechanical task characteristics. Healthy subjects ( N = 14) stood and performed a continuous reaching task (RRT) between two targets placed at shoulder height to fatigue. Whole-body kinematic (Vicon ©), kinetic (AMTI © force platforms) and electromyographic (EMG, Noraxon ©) characteristics were recorded. Maximal voluntary isometric efforts (MVIE) of the shoulder and elbow were measured pre- and post-RRT. Post-RRT shoulder elevation MVIE was reduced by 4.9 ± 8.3% and trapezius EMG amplitude recorded during the RRT increased by 46.9 ± 49.9% from the first to last minute of the RRT, indicating that arm fatigue was effectively induced. During fatigued reaching, subjects elevated their shoulder (11.7 ± 10.5 mm) and decreased their average shoulder abduction angle by 8.3 ± 4.4°. These changes were accompanied by a lateral shift of the body’s center of mass towards the non-reaching arm. These findings suggest a compensatory strategy to decrease the load on the fatigued shoulder musculature.

Posterior Shoulder Pain: A Dynamic Study of the Spinoglenoid Ligament and Treatment With Arthroscopic Release of the Scapular Tunnel

The purpose of this study was to determine the pressure exerted on the suprascapular nerve by compression of the spinoglenoid ligament during glenohumeral range of motion. In addition, a 2-portal technique was described to arthroscopically visualize and safely release the spinoglenoid ligament while visualizing the suprascapular nerve, artery, and vein. Ten cadaveric shoulders were used for visual observation of variation in the position and tension of the spinoglenoid ligament. In 15 additional shoulders, a transducer was used to sense the pressure changes and was recorded in voltage. Pressure changes created by the spinoglenoid ligament on the distal suprascapular nerve in the scapular tunnel during glenohumeral motion were recorded. Internal rotation, rather than external rotation, in any position of the shoulder created a visual increase of tension in the spinoglenoid ligament. Increased pressure readings were noted with internal rotation and with 90 degrees of abduction, full abduction, and full adduction of the shoulder. The suprascapular nerve occupying the space created by the spinoglenoid ligament experiences an increased pressure during glenohumeral range of motion and positions that mimic overhead throwing. The dynamic nature of the ligament with its insertion on the posterior capsule required a new minimally invasive technique for its release that can be safe and straightforward. The spinoglenoid ligament was affected by the position of the glenohumeral joint. These changes in pressure in combination with repetitive shoulder movement are likely components that cause repeated trauma or compression on the distal suprascapular nerve created by a scapular tunnel syndrome. The surgical technique provides a treatment option when conservative treatment fails in the patient with posterior shoulder pain. The spinoglenoid ligament was affected by the position of the shoulder, with the most pressure noted with the arm in full adduction and internal rotation. This pressure can be treated with arthroscopic release.

Effectiveness of workstation design on reducing musculoskeletal risk factors and symptoms among semiconductor fabrication room workers

The aim of this study was to evaluate the effect of ergonomic workstation design on musculoskeletal risk factors (MRFs) and musculoskeletal symptoms (MSSs) reduction among female semiconductor fabrication room (fab) worker. A prospective study was conducted to follow up 40 female fab workers over 3 months after intervention. The intervention program focused on reducing shoulder loadings for 20 female fab workers by redesigning nine workstations. Simultaneous comparisons were made for the other 20 female fab workers using original workstations. One customized observation checklist and Nordic musculoskeletal questionnaire were used to evaluate workers’ MRFs and MSSs, respectively. One month after intervention, MRFs of awkward shoulder postures and repetitive motions and MSSs in shoulders for the intervention group were significantly lower than those for the control group. The lowering effects persisted for 3 months on awkward shoulder postures but lasted for only 1 month on repetitive motions and shoulder symptoms after intervention. Relevance to industry This study demonstrates a systematic approach for assessing effectiveness of ergonomically redesigned workstations tailored for female fab workers on reducing their awkward shoulder postures and shoulder symptoms. Industries can use our findings to design or evaluate their ergonomic intervention programs in the workplace or use our workstation specifications to purchase their manufacturing equipments in the future.

Experimental muscle pain results in reorganization of coordination among trapezius muscle subdivisions during repetitive shoulder flexion

The aim of the study was to examine the effect of experimental unilateral upper trapezius muscle pain on the relative activation of trapezius muscle subdivisions bilaterally during repetitive movement of the upper limb. Surface EMG signals were detected from nine healthy subjects from the upper, middle and lower divisions of trapezius during a repetitive bilateral shoulder flexion task. Measurements were performed before and after injection of 0.5 ml hypertonic (pain condition) and isotonic (control) saline into the upper division of the right trapezius muscle in two experimental sessions. On the painful side, upper trapezius showed decreased EMG amplitude (average rectified value, ARV) and lower trapezius increased ARV throughout the entire task following the injection of hypertonic saline (40.0 +/- 22.2 vs. 26.0 +/- 17.4 microV, and 12.5 +/- 7.6 vs. 25.6 +/- 14.8 microV, respectively, at the beginning of the contraction). On the side contralateral to pain, greater estimates of ARV were identified for the upper division of trapezius as the task progressed (37.4 +/- 20.2 vs. 52.7 +/- 28.4 microV, at the end of the contraction). Muscle fiber conduction velocity did not change with pain in all three divisions of the right trapezius muscle. The results suggest that local elicitation of nociceptive afferents in the upper division of the trapezius induces reorganization in the coordinated activity of the three subdivisions of the trapezius in repetitive dynamic tasks.

Spatial dependency of trapezius muscle activity during repetitive shoulder flexion

The purpose of this study was to explore changes in spatial muscle activation within the three divisions of the trapezius muscle during a dynamic, cyclic task of the upper limb. Surface EMG signals were detected from thirteen healthy subjects from the upper, middle and lower divisions of the trapezius muscle at multiple electrode sites in the cephalad-caudal direction during a repetitive shoulder flexion task. Initial values and rate of change of average rectified value (ARV) and of instantaneous mean power spectral frequency (iMNF) were estimated at 45°, 90° and 120° of shoulder flexion throughout the 5-min task. The location of the electrodes had a significant effect on initial EMG ARV for both the upper and middle division of the trapezius muscle ( P < 0.05). Both the rate of change and normalized rate of change of ARV were greatest for the most cranial muscle fibers of the upper division ( P < 0.05). Initial values and rates of change of iMNF were also affected by electrode location for the upper and lower divisions of the trapezius muscle ( P < 0.05). These results demonstrate that muscle activity and its changes over time depend on position within the three divisions of the trapezius muscle during a dynamic, cyclic task of the upper limb. This suggests non-uniform muscle fiber distribution and/or recruitment. The results also highlight the importance of multiple recording sites when investigating trapezius muscle function in dynamic tasks.

Aetiology of work-related disorders of the rotator cuff tendons: Research and theory

This paper examines evidence and theories from epidemiological and biomechanical research regarding the work-relatedness of shoulder disorders affecting the rotator cuff tendons, often referred to as rotator cuff syndrome, one of the few more clearly defined musculoskeletal disorders of the shoulder region. Recent epidemiological studies and prior reviews were found to be generally consistent in their findings and conclusions regarding problems with repetitive work and elevated shoulder posture. However, most studies tended to employ fairly gross assessments of exposure. In considering more specific methods for assessing exposure, this paper identifies studies of shoulder biomechanics, tendon cell biology and animal models of tendinosis that are relevant to the design and development of exposure assessment methodologies specifically relevant to rotator cuff pathology. The authors concur with others regarding the need for more specific assessments of associations between disorders and exposures, in order to progress to the point where researchers can provide exposure-dose-response information for physical workplace factors in relation to musculoskeletal disorders. The paper concludes by listing several theoretical issues pertaining to the biomechanics of the shoulder that need to be addressed by the research community.

Acromioclavicular Joint Arthritis

Abstract Acromioclavicular joint (ACJ) arthritis is a common source of shoulder pain. Manifestations of the arthritis may include inferiorly projecting spurs that predispose an individual to impingement and rotator cuff tears and can result in permanent impairment due to shoulder weakness or motion loss. Rotator cuff tendinopathy generally is multifactorial, and tears usually result from a combination of intrinsic factors (loads transmitted, local blood supply, and age) and extrinsic factors (impingement, primarily). Surgery to eliminate impingement collectively is termed subacromial decompression. The AMA Guides to the Evaluation of Permanent Impairment provides no impairment rating for cheilectomy about acromioclavicular or other joints, and, because removal of this liability is beneficial, it results in no (and perhaps even negative) impairment. An individual whose job involves repetitive shoulder elevation and who develops impingement probably has a legitimate workers’ compensation claim, even if predisposed by preexisting bony prominences; in this scenario, the proximate cause was repetitive shoulder elevation. A case example demonstrates that if an individual with preexisting osteoarthritis of the ACJ is injured and disabled at work, the rotator cuff tear, although preexisting, was worsened during employment and probably will be covered under the claim. In legal terms, findings of disability associated with ACJ injuries may differ depending on the jurisdiction.

Atypical shoulder muscle activation in multidirectional instability

Objective Surface and intramuscular electromyography was used to investigate shoulder muscle activity in subjects with multidirectional instability (MDI). Methods Subjects (seven MDI, 11 control) performed repetitive shoulder abduction/adduction, flexion/extension and internal/external rotation movements on an isokinetic dynamometer. The activity of the deltoid, infraspinatus, supraspinatus, latissimus dorsi, and pectoralis major muscles were recorded using double-differential surface and intramuscular fine-wire electrodes. A repeated measures analysis of variance evaluated group differences in the amplitude, onset, termination and duration of the muscle activity. Results Significant activation parameter differences for the supraspinatus, infraspinatus, posterior deltoid and pectoralis major muscles were found in the subjects with MDI. The rotator cuff and posterior deltoid muscles demonstrated abbreviated periods of activity when performing internal/external rotation, despite activation amplitudes that were similar to the controls. In contrast, the activation of the pectoralis major differed from the control group in both the amplitude and time domains when performing shoulder extension. Conclusions MDI is associated with atypical patterns of muscle activity that occur even when highly constrained movements are used to elicit the activity. Significance In addition to glenohumeral hyperlaxity, the results suggest that dysfunctional neuromuscular control of the rotator cuff is also a contributing factor to the pathoetiology of MDI.

Effects of a home exercise programme on shoulder pain and functional status in construction workers

Background: Repetitive or sustained elevated shoulder postures have been identified as a significant risk factor for occupationally related shoulder musculoskeletal disorders. Construction workers exposed to routine overhead work have high...

A case of locking shoulder caused by longitudinal rotator cuff tear

Although crepitus is common in patients with rotator cuff tears, locking is a rare symptom. We encountered a case of repetitive shoulder locking in the elevated position with a longitudinal tear in the supraspinatus tendon and a marked subacromial spur.

Activity Levels As a Guide for Shoulder Girdle Exercise Progression

Traditional shoulder rehabilitation protocols have typically used either set time frames or achievement of certain criteria for determining when to advance patients from one level of rehabilitation to the next. Each system has its own unique set of advantages and disadvantages. Because of the disadvantages, we developed a new model that primarily uses patient activity levels and secondarily uses objective criteria as the system of advancement for our shoulder girdle rehabilitation protocol. Our purpose here is threefold: (1) to discuss the rationale behind this model of exercise progression, (2) to present the eight discrete shoulder activity levels that are combined into four functional activity levels, and (3) to present the components and rationale for a four-phase, 50-step shoulder rehabilitation program that can return a patient to high-level shoulder activity that includes rapid acceleration and deceleration and repetitive overhead shoulder activity with load.

A Decreased Ability to Relax Between Repetitive Muscle Contractions in Patients with Chronic Symptoms After Whiplash Trauma of the Neck

Objectives: The aim was to investigate if patients with common chronic symptoms after whiplash trauma had an inability to relax certain neck and shoulder muscles in pauses between repetitive shoulder forward flexions.Methods: The control group [27 clinically healthy females] and the patient group [22 female patients with chronic symptoms after whiplash trauma] performed maximum isokinetic shoulder flexions [100 contractions scheduled]. Surface-electromyography [EMG] was obtained from four neck/shoulder muscles. Peak torque and the signal amplitude ratio [SAR] of each contraction were determined. The SAR was calculated as the ratio [%] between root mean square [RMS] of the EMG of the passive extension and the RMS of the active flexion. The subjects rated their perceived fatigue of the shoulder flexors throughout the test.Results: The majority of the patient group was not able to perform the number of contractions scheduled. Significantly higher SAR of trapezius two portions and infraspinatus for the patien...

Musculoskeletal problems in the tomato growing industry: 'tomato trainer's shoulder'?

Tomato training entails highly repetitive shoulder muscle contractions, static contractions and work at shoulder level, factors linked in other working groups with neck and shoulder complaints. The frequency of musculoskeletal complaints was compared using the Nordic Questionnaire in 56 tomato trainers and 52 other matched glasshouse workers whose job did not include these work task factors. A higher 12- month (odds ratio (OR) = 5.9; [95% confidence interval (CI) = 2.4-16.7] and 7- day (OR = 3.6, CI = 1.2-11.1) period prevalence of shoulder complaint was recorded in trainers than in pickers and deleafers. Other upper limb and upper trunk complaints were also more common in tomato trainers, highlighting an area of ergonomic concern.

Arthroscopic shoulder stabilization using transglenoid sutures. A four-year minimum followup.

Thirty-seven of 41 consecutive patients with recurrent anterior instability of the shoulder were retrospectively observed for a mean of 5.6 years (range, 4 to 10) after an arthroscopic stabilization procedure had been performed. The operative technique involved the use of transglenoid sutures to repair the capsule and labrum. According to the criteria established by Rowe, 27 patients (74%) had good or excellent results, and 3 patients (7%) were graded as fair. Seven patients (19%) developed recurrent instability after the procedure and had failed results. Failure rates were equal in patients with a history of recurrent dislocation and those with recurrent subluxation. Absence of a Bankart lesion at operation was associated with postoperative instability (P = 0.03). The presence or size of humeral head defects did not influence the result. Eight of 12 athletes who engaged in sports requiring repetitive overhead shoulder motion returned to full activity, and none of the 12 developed instability after operation. Four of the 13 patients who participated in contact sports or recreational skiing developed postoperative instability (P = 0.21). All failures occurred within 2 years of the procedure.

Myxoid and Globular Degeneration of Nerves in the Shoulder Joint

Characteristic degeneration of the nerves in shoulder joints was recognized in 26 of 35 capsules (74.3%) from 20 cadavers. No left or right or gender differences were found. Histologic features of the nerves were (1) thickening of the perineurium, (2) myxoid degeneration in the endoneurium, and (3) hyaline globular structures with a whorled, oligocellular appearance regarded as Renaut bodies. The results of histochemical and electron microscopic studies showed prominent degenerated collagen fibers in the globular areas. These features resembled those found in the fusiform swelling in the axillary nerve branch to the teres minor muscle, believed to be caused by chronic nerve compression. Sixty percent of the degenerated nerves occurred in the anteroinferior and posteroinferior portions of the capsule, an area that is considered to be innervated by the axillary nerve. No correlation between age and severity of these degenerative nerve changes was noted. Compression of the axillary nerve and inferior joint capsule caused by repetitive shoulder movement such as forward flexion, abduction, and external rotation of the humerus might result in this form of nerve degeneration found histologically over a lifetime without necessarily causing clinical symptoms.

Muscle performance, electromyography and fibre type composition in fibromyalgia and work-related myalgia.

Muscle performance and fibre type composition were investigated in women with fibromyalgia, work-related trapezius myalgia and healthy volunteers. Each subject performed 100 repetitive shoulder flexions using an isokinetic dynamometer during simultaneous registration of surface electromyography. A biopsy from the trapezius muscle was obtained. The groups differed neither in mechanical performance nor in fibre type proportions. An inability to relax between contractions was found in all registered muscles in patients with fibromyalgia. The patients with work-related myalgia displayed an inability to relax only in the myalgic trapezius muscle. An inability to relax during repetitive movements might play an important role both in initiating and upholding muscle pain.

Prevalence rates and odds ratios of shoulder-neck diseases in different occupational groups.

The aim of the present study was to evaluate the association and impact of occupational exposure and diseases of the shoulder and neck. Prevalence rates, odds ratios, aetiological fractions, and their confidence intervals were computed for pooled and non-pooled data of previous published reports. By comparison with office workers and farmers, dentists had an increased odds ratio for cervical spondylosis (two studies) and for shoulder joint osteoarthrosis. Meat carriers, miners, and "heavy workers" also had significantly higher rates of cervical spondylosis compared with referents. Compared with iron foundry workers, civil servants had a significant odds ratio (4.8) of cervical disc disease and a 0.79 aetiological fraction. Whether this was due to exposure or healthy worker effect was not clear. In four occupational groups with high shoulder-neck load an odds ratio of 4.0 was found for thoracic outlet syndrome with an aetiological fraction of 0.75. Rotator cuff tendinitis in occupational groups with work at shoulder level (two studies) showed an odds ratio of 11 and an aetiological fraction of 0.91. Keyboard operators had an odds ratio of 3.0 for tension neck syndrome (five studies). Unfortunately, owing to the scanty description of the work task, the exposure could be analysed only by job title. Examination of published reports shows clearly that certain job titles are associated with shoulder-neck disorders. High rates and aetiological fractions for rotator cuff tendinitis and tension neck syndrome suggest that preventive measures could be effective. Although job descriptions are brief, the associations noted suggest that highly repetitive shoulder muscle contractions, static contractions, and work at shoulder level are hazardous exposure factors. In reports of cross sectional studies of occupational shoulder-neck disorders presentation of age, exposure, and effect distribution may help for future meta-analysis.

Work load and fatigue in repetitive arm elevations.

Six females performed continuous series of concentric and eccentric flexions in the shoulder between 0 and 90 degrees with 0 to 3.1 kg weights held in a powergrip. Heart rate (H R), perceived exertion (RPE) and myoelectric activity (EMG) from the descending part of the trapezius muscle, the anterior part of the deltoid muscle, and the biceps brachii were measured during the tasks. The increase of RPE was faster than the increase of HR with work load indicating an increased importance of local factors (i.e. strain on muscles and tendons) with load in the perceived exertion. The local muscular load determined by EMG on the trapezius muscle was closely correlated with the external torque produced in the glenohumeral joint. The time constants of EMG amplitude increase were correlated with work load, endurance time and with slope coefficients of RPE-HR linear regression. Symptoms and complaints 24 hours after the task were often localized to the descending part of the trapezius muscle. It is suggested that exertion of the descending part of the trapezius muscle in tasks involving repetitive shoulder flexion may promote discomfort and complaints referred to the neck.