Repetitiveness is commonly cited as an occupational factor leading to CTD of the upper extremity (8). It can be defined as cyclical or repeated motions requiring contraction of the same muscles to mobilize joints. The NIOSH conducted a 1997 review that found moderate evidence for repetition as a cause of work-related musculoskeletal disorders in neck and shoulder pain, CTS, and hand/wrist tendonitis. It did not find sufficient evidence in LBP or epicondylitis (1).

There is epidemiologic evidence to support the role of forceful exertions in the workplace in contributing to neck, lumbar back, elbow, and hand/wrist pain. Ergonomic design plays a critical role as force requirements may increase based upon several factors including poor body mechanics, high torque or speed of power tools, and friction between objects and the worker (16).

Improper postural mechanics during the performance of a task appears to play a significant role in the development of CTD, especially those involving the spine and upper extremities. Sustained wrist and forearm flexion-extension or radial-ulnar deviation may induce friction between tendons and adjacent anatomic surfaces. A good example of this is frequent radial deviation of the wrist and subsequent development of de Quervain’s tenosynovitis.

Another frequently mentioned risk factor in CTD is vibration (17). Exposure to vibration occurs in a variety of contexts: using power tools, holding an object as it is processed in a machine (e.g., wood in a power saw), or using percussion tools (e.g., hammering a nail). Vibration has been implicated as the cause of Hand-Arm Vibration Syndrome (HAVS).

The cervical spine is a complex structure consisting of eight individual motion segments, beginning with the articulation of the occiput on C1 (atlas) and ending with the articulation between C7 and T1. Cervical nerve roots exit bilaterally through intervertebral foramen to innervate the myotomes and dermatomes of the head, neck, and arms. The cervical musculature controls head movement and provides stability. Pain in the neck area can arise from overwork of the musculature, impingement of cervical nerve roots, or degenerative arthritis of the spine. Neck pain is commonly encountered in jobs requiring prolonged posturing of the neck, forceful exertions, and highly repetitive tasks with static postural loads. Because major neck muscles extend to the shoulder or base of the skull, shoulder pain and headache are commonly associated. Tension neck syndrome involves persistently stiff neck muscles resulting in aching discomfort at the base of the neck, upper back, and suboccipital region.

Poor neck posture has been strongly associated with occupational neck pain and appears to be the most significant factor in work-related neck disorders. Specifically, prolonged neck flexion or extension in combination with arm elevation is problematic. Mayoux-Benhamou and Revel used electromyography (EMG) to demonstrate improved neck muscle efficiency with neutral head position as compared to the flexed or extended position (18). Other studies have found associations between forward head posture and headaches (19), overhead arm tasks and radiating neck pain (20), and simultaneous head extension and arm elevation with neck/shoulder pain (21). The literature has also identified certain occupations involving overhead work with a higher incidence of neck pain. Neck symptoms were reported in 62% of dental hygienists and 66% of sewing machine operators with more than 15 years of experience (22, 23). Significant symptoms related to the neck have also been reported in dentists, meat carriers, miners, heavy labor workers, iron foundry workers, and civil servants (24).

Repetition and high exertional loads are important factors in neck pain as well. A cross-sectional study of 82 female assembly line workers who were exposed to repeated intermittent
neck flexion and shoulder abduction revealed an odd ratio (OR) of 4.6 for any neck/shoulder diagnosis and OR of 3.6 for diagnosis of neck tension syndrome (25). A smaller, but more quantitative, study measured trapezius activity on surface EMG in order to demonstrate that increased frequency of sustained, low muscle activity was positively correlated with neck discomfort in workers (26). For forceful exertions, the trapezius is the major muscle of the neck utilized to carry out work involving high forces. One longitudinal study found that workers with a reduced static trapezius load had less shoulder pain at 2-years follow-up (27). Another study found that postal workers, who carry heavy shoulder bags, consistently reported greater shoulder/neck disability compared to gas meter readers who perform a similar amount of walking as postal workers (28). This was the case after controlling for age, work years, and previous lifting work.

Management of neck pain involves avoiding prolonged static postures and introducing dynamic and varied work tasks (29). Exercise therapy for mechanical neck disorders has short-term benefits in terms of pain and function (30). Although no specific exercises can be clearly recommended over others based upon evidence, a reasonable regimen would include neck retraction exercises, stretching of the anterior shoulder capsule and pectoralis muscles, and strengthening of the trapezius and rhomboids. In general, treatments for neck pain arising from cumulative trauma have not been well studied, and management principles have been extrapolated from general mechanical neck pain studies. Pharmacotherapy can include NSAIDs, muscle relaxants, and opioids for severe pain. Manipulation alone is not helpful but may have benefit in conjunction with exercise therapy (31). There is moderate evidence for a lack of efficacy of botulinum toxin injections in chronic mechanical neck pain according to a recent systematic review (31). The therapeutic value of TENS, biofeedback, and acupuncture remain unclear. For further details regarding cervical spine pain, refer to Chapter 32.

The shoulder is a complex structure that affords great mobility at the expense of stability. Its stability can be divided into static and dynamic components. Statically, the bony glenoid, cartilaginous labrum, glenohumeral ligaments, and joint capsule provide moderate stability. Dynamically, the rotator cuff muscles and biceps tendon function to assist with shoulder stability. The most frequent CTDs of the shoulder are rotator cuff tendinopathy (especially involving the supraspinatus), biceps tendinopathy, and shoulder impingement.

The rotator cuff consists of the supraspinatus, infraspinatus, subscapularis, and teres minor and resides in the subacromial space, which is defined by the acromion, subacromial bursa, and coracoacromial ligament above; the coracoid process at the medial border; and the humeral head below. The rotator cuff plays an especially important role in the case of overhead elevation of the arm, which requires tonic contraction to keep the humeral head anchored in the shallow glenoid fossa (32). This explains why rotator cuff tendinopathy is particularly common in laborers who work with their arms overhead or athletes who throw repeatedly (7).

A disorder that often accompanies rotator cuff tendinopathy is impingement syndrome, in which there is progressive encroachment of the rotator cuff tendons in the subacromial space due to intrinsic or extrinsic sources (33). Intrinsic causes include trauma or degeneration of the rotator cuff with instability or laxity of the shoulder complex. The laxity results in cephalad migration of the humeral head resulting in impingement. Extrinsic causes include bony changes to the acromion, coracoid, acromioclavicular joint or greater tuberosity, cervical nerve root compression, and other systemic conditions, including rheumatic disorders. Acromial morphology (type I flat, type II curved, type III hooked) is another factor that can predispose one to impingement (34). Individuals with a hooked acromion are most likely to develop rotator cuff abnormalities. The positioning of the rotator cuff has also been reported as having a relationship to rotator cuff pathology. Rathbun and Macnab report the “wringing out” phenomenon, whereby a hypovascular region in the supraspinatus tendon is created when the arm is held in adduction (35). Overall, shoulder impingement, a mechanical compression process, often leads to rotator cuff tendinopathy, which can lead to further impingement.

The individual with rotator cuff tendinopathy or impingement syndrome will report pain deep within the shoulder or posteriorly, with referral to the deltoid muscle insertion region. There may also be loss of strength and motion secondary to the pain. The discomfort is worsened by activities at shoulder level or above. Pain will occasionally occur at night while resting on the involved shoulder, perhaps from a concomitant subacromial bursitis. On physical examination, a positive Hawkins’ or Neer’s sign is suggestive of impingement. Hawkins’ test involves passive internal rotation and abduction of the shoulder while the elbow is flexed at 90 degrees. Neer’s test involves forward shoulder flexion until the arm is overhead while simultaneously maintaining light pressure on the acromion. Other tests include diagnostic injection of local anesthetic into the subacromial space, which should provide temporary pain relief and improved ROM in these conditions. The differentiation of rotator cuff tendinopathy and impingement is often difficult. A helpful clinical maneuver to differentiate these conditions is to assess isometric strength testing of the rotator cuff muscles (i.e., resisted external rotation of shoulder or abduction), which should produce moderate to severe pain in rotator cuff tendonitis, but minimal discomfort in a pure impingement syndrome. Further evaluation can include imaging such as x-rays or MRI/MR arthrography, which may show narrowed subacromial space, calcified tendons, or partial tears.

Bicipital tendinopathy is another condition that can result from repetitive strain and overhead reaching. Patients typically complain of anterior shoulder pain localized to the region of the bicipital groove. On examination, a positive Yergason’s or Speed’s manuever (36) along with pain during active elbow flexion may be important clues. Diagnostic injection with local anesthetic or MRI may confirm this clinical diagnosis. Since other shoulder pathology frequently occurs in concert, the
clinician should also investigate for rotator cuff tendinopathy, impingement, or shoulder instability.

There have been numerous studies illustrating the association between repetitive movements and/or exertional force and shoulder pathology. Chiang et al. found an OR of 1.6 (95% CI 1.1 to 2.5) among fish-processing workers’ repetitive upper limb movement and shoulder girdle pain (37). Another cross-sectional study of fish industry workers revealed that repeated arm elevations and shoulder abductions as documented on videotape were significantly associated with shoulder and neck pain (25). Welch et al. noted a prevalence of 32% incidence of rotator cuff injury in sheet metal workers, with most occurring from overhead duct work (38). Other at-risk occupations for shoulder pain include electricians (39), garment workers (40), hospital workers (41), and construction workers (42). Herberts et al. reported 18% of shipyard welders and 16% of steel plate workers had rotator cuff pathology (especially supraspinatus tendonitis) (43). Overall, rotator cuff injury has been reported as the third most common diagnosis encountered in workers, accounting for 8.3% of cases (44).

In the industrial setting, treatment of shoulder impingement and tendinopathy emphasizes avoiding awkward postures and decreasing overhead work, especially tasks involving shoulder internal rotation. One study found that postural alterations could improve the range of shoulder motion at which pain was experienced, in spite of having no overall effect on pain intensity in symptomatic impingement patients (45). Acute interventions include NSAIDs, ice, and pain management. If persistent, corticosteroid injections into the subacromial space can be utilized. Range-of-motion exercises involving both the glenohumeral and scapulothoracic articulations will decrease the likelihood of asynchronous motion leading to impingement. Strengthening exercises should focus on the rotator cuff muscles and scapular stabilizers.