Category: Specific Disorders

Over the past several decades, a major retooling of industry has been undertaken to make the work environment more employee friendly. Ergonomics is the science behind the design and operation of machines within the work environment (5). The proper management of CTD requires a thorough understanding of ergonomics, as ergonomics factors often contribute to the development of CTD. Treating the symptoms without modifying the workplace is the primary reason for recurrence of CTD and magnifies the overall economic burden caused by these disorders.

ECONOMIC IMPACT

Musculoskeletal disorders are the leading cause of disability among persons during their working years (6). In 1995 alone, 308,000 musculoskeletal disorders due to repeated trauma were reported in U.S. workplaces, representing nearly 62% of all occupational illness cases reported to the United States Bureau of Labor Statistics. This led to $2.1 billion in workers’ compensation costs and $90 million in indirect costs (7). Injuries to the hand and wrist have continued to grow. Of these injuries, work-related carpal tunnel syndrome is the most disabling and is increasing, as the median number of workdays lost in 1995 was 30 (7). Low back pain is the most common musculoskeletal problem affecting the working population. Approximately $16 billion was spent in 1984 managing low back pain (8,9). The total cost of worker’s compensation was estimated at $50 billion in 1990, with back care alone representing $30 billion (10). The growing costs of managing CTD in industry place a significant economic burden on the employer that ultimately impacts the consumer.

ERGONOMICS

Ergonomic assessment of the injured worker is now commonly used in the industrial setting. It requires an understanding of human abilities and the limitations imposed by the work environment, machines, tools, and specific job tasks (11,12). Ergonomics has received significant attention as the prevalence of CTD has risen in the workplace. Cumulative trauma disorders have been shown to be costly to employers and employees, as they contribute to time lost from work, decreases in productivity, and poor employee morale, all of which are factors in disability (13,14).
Several elements contribute to occupational CTD, including forceful exertions, repetitiveness of a work task, biomechanical postures, vibration, temperature, localized contact stress, and tool use and design (12,14,15).
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Forceful Exertions

Forceful exertions in the workplace directly or indirectly cause CTD in combination with such environmental factors as friction, equipment issues, gravity, and inertia (11,12). Force requirements may increase, depending on the condition of the hand tool (e.g., sharpness versus dullness), poor body mechanics, high torque or speed of power tools, and friction between objects and the worker (15,16). Wearing gloves may also increase the force needed during certain activities. Using poor-quality or improperly fitted gloves may be detrimental by blunting sensory feedback, reducing friction between the tool and hand, and reducing strength (15,17).
High force requirements, in collaboration with other occupational factors (especially repetition), are reported to be responsible for the greatest frequency of CTD of the upper extremity. The incidence of carpal tunnel syndrome and tendinitis has been shown to increase with activities of food processing, carpentry, and secretarial work, where forceful buffing, polishing, cutting, and typing may be required (18).

Repetitiveness or Prolonged Activities

Repetitiveness is also commonly cited as an occupational factor leading to CTD of the upper extremity (14,19). Repetition may be defined as (a) repeated motions requiring the same muscles and joints or (b) prolonged posture within a job task (12,14). After variable periods of time, repetitive work activities may lead to impairment secondary to CTD. Compromise of soft-tissue function may produce inflammation of tendons within the upper extremity, leading to pain and/or loss of motion. It may also lead to compression of peripheral nerves, causing pain, numbness, and weakness in the involved nerve distribution. During muscle contraction, blood flow locally can be decreased by as much as 40%. If a contraction is maintained, the oxygen supply to the area is quickly diminished while metabolite levels increase, causing muscle fatigue and soreness (12).
Since levels of repetitiveness have not been determined, workplace modifications should be integrated as problems are identified. These may include avoiding repeated gripping motions, maintaining pinching force requirements under 7 pounds, alternating among work tasks with a 5-minute break at least every hour, restructuring work tasks to encourage synergistic rather than isolated muscle activity, and using machinery to complete portions of tasks while rotating workers among tasks (12,15). In the computerized workstation environment, microbreaks taken every 40 minutes reduced discomfort at the wrist extensors, neck, and low back without disrupting productivity (20).

Posture

Improper postural mechanics during the performance of a task is an important causative risk factor for CTD. Sustained wrist and forearm flexion-extension or radial-ulnar deviation may induce friction between tendons and adjacent anatomic surfaces. Carpal tunnel syndrome and tenosynovitis of the flexor and extensor tendons of the wrist may be directly associated with sustained wrist or hand position (21,22,23,24,25). This is often seen in jobs that require a significant amount of typing, cashiering, or playing a musical instrument such as the violin (21). Positioning the wrist in radial deviation has been associated with de Quervain’s tenosynovitis (25,26,27,28). Other problematic postures commonly cited include those for using pliers, knives, and other household items such as a vacuum cleaner (14). Common awkward postures during work tasks may include extreme elbow flexion-extension, pronation-supination, excessive shoulder elevation, and pinch grips (15,29).
To optimally control awkward postures during work tasks, either the workstation should be redesigned or equipment modification (such as the use of bent-handled tools or split computer keyboards) should be considered to improve body position and alignment (30).

Localized Contact Stress

Contact stresses are produced when soft tissues of the body come in contact with an object or tool. Compression or shearing of soft-tissue structures between bone and tool are the most common forms of contact stress (11). Activities that require the worker to rest the forearms on a work surface for prolonged periods of time or to grip a sharp-edged tool may be causative (14). A common injury from contact stress is trigger finger, caused by pressure to the A-1 annular pulley (Fig. 26-1). When the distal phalanx is used to control a tool’s trigger release, stress is applied to the retinacular ligaments (15). Stress can be ameliorated by adjusting the trigger design so that flexion of the middle phalanx occurs before flexion of the distal phalanx. Another adaptation may include the use of soft rubber-coated handles (12,15). Local contact stress may also cause compression of the digital nerves. Improper design or use of hand tools is commonly the cause of these stresses. To decrease local stress on specific anatomic structures, one must consider handle shape and size. Handles should be as large as possible for a given task, and sharp edges should be avoided (11). Copyright: Copyright©2005 Lippincott Williams & Wilkins – Physical Medicine & Rehabilitation: Principles and Practice – Joel A. Delisa

The shoulder is a complex structure that affords great mobility at the expense of stability. What stability is present has both static and dynamic components. Statically, the bony glenoid, cartilaginous labrum, glenohumeral ligaments, and joint capsule provide moderate stability. The rotator cuff (supraspinatus, infraspinatus, teres minor, and subscapularis) and the biceps tendon function dynamically to assist with stability. The rotator cuff plays a key role, especially with the arm in overhead elevation, where it must tonically contract to keep the humeral head anchored in the shallow glenoid fossa . The rotator cuff rests in the subacromial space, defined by the acromion, subacromial bursa, and coracoacromial ligament above; the coracoid process at the medial border; and the humeral head below. Numerous anatomic and pathophysiologic factors may lead to a narrowing of the space and predisposition to rotator cuff impingement. Bicipital tendonitis may occur in concert with rotator cuff tendonitis as the biceps passes underneath the subscapularis and supraspinatus tendons.
The impingement syndrome has been well described as a progression of changes to the rotator cuff eventually leading to a tearing of the tendons. The causes of rotator cuff impingement can be classified as intrinsic or extrinsic . Intrinsic causes include trauma or degeneration of the rotator cuff with instability or laxity of the shoulder complex. 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 . Morrison and Bigliani reported the relationship between acromial morphology (type I flat, type II curved, type III hooked) and rotator cuff impingement. Individuals with a hooked acromion were 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 reported the “wringing out” phenomenon, whereby a hypovascular region in the supraspinatus tendon was created with the arm held in adduction . Glenohumeral instability has been described as an inciting cause, with rotator cuff impingement occurring secondary to increased humeral motion . The torque placed on the rotator cuff is greatest at arm elevation of 90 degrees, which may predispose to overuse injury in the overhead position . Loss of scapular motion, or asynchrony between the scapulothoracic and glenohumeral musculature, may also predispose to impingement.
Rotator cuff injury was the third most common diagnosis encountered in workers, accounting for 8.3% of cases . In a fish-processing plant, shoulder girdle pain was encountered in 30.9% of workers and was more prevalent in workers who performed both repetitive and forceful movements of their upper limbs during work . Among electricians, 29% reported shoulder symptoms that occurred at least three times or lasted greater than 1 week . Shoulder pain was also reported in 37% of construction workers, 19.6% of garment workers, and 8.8% of hospital workers . Herberts et al. reported 18% of shipyard welders, and 16% of steel plate workers had shoulder pain . Welch noted a prevalence of 32% for rotator cuff injury in sheet metal workers, with most occurring from overhead duct work . Rotator cuff injury is more common overall in individuals who perform overhead activities or who require internal rotation of the shoulder, awkward or static postures; lack of rest, and vibration .
The individual with rotator cuff tendonitis or the 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, pain may be reproduced with palpation within the subacromial space or over the biceps tendon. Several methods are used to reproduce impingement of the rotator cuff (impingement signs). Hawkins described a method in which the arm is forward-flexed 90 degrees, and with the elbow flexed 90 degrees the arm is forcibly internally rotated . Neer described forced forward flexion of the arm, maintaining pressure on the acromion, so as to impinge the humeral head under the acromion . The impingement test was described as a method of obtaining pain relief from rotator cuff impingement . It is performed by the injection of lidocaine into the subacromial space and is interpreted as positive if there is a return of strength and an improved range after infiltration of the space. Strength testing of the rotator cuff should be performed in all involved subjects, with weakness and pain of the supraspinatus with or without external shoulder rotators usually most apparent. A complete neurologic examination should also be performed to rule out the presence of an underlying cervical radiculopathy. Further evaluation can occur with the use of x-rays, magnetic resonance imaging (MRI), and electrodiagnosis.
In the industrial setting, rehabilitation of shoulder impingement emphasizes decreasing overhead work, particularly for activities that also promote internal rotation of the shoulder. Acute intervention emphasizes pain reduction, including NSAIDs, ice, and occasionally, corticosteroid injection into the subacromial space. Range of motion of both the glenohumeral and scapulothoracic articulations will decrease the likelihood of asynchronous motion leading to impingement. Finally, strengthening of the glenohumeral and scapulothoracic musculature concentrically and eccentrically will help to prevent future injury. Strengthening of the scapular stabilizers should be started immediately; the remainder of the strengthening program (i.e., of the cuff itself) is prescribed when such activity no longer reproduces much pain. Copyright: Copyright©2005 Lippincott Williams & Wilkins – Physical Medicine & Rehabilitation: Principles and Practice – Joel A. Delisa