112: Repetitive Strain Injuries

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CHAPTER 112

Repetitive Strain Injuries

Kelly C. McInnis, DO

Synonyms

Cumulative trauma disorders

Occupational overuse syndromes

Upper extremity musculoskeletal disorders

Nonspecific work-related upper limb disorders

Repetitive overuse disorders

ICD-9 Codes

719.44  Hand pain

729.5   Limb pain

729.1   Myalgia and myositis, unspecified

ICD-10 Codes

M79.641  Pain in right hand

M79.642  Pain in left hand

M79.643  Pain in unspecified hand

M79.609  Pain in unspecified limb

G70.9   Myoneural disorder, unspecified (myalgia)

M60.9  Myositis, unspecified

Definition

Repetitive strain injury (RSI) describes nonspecific upper extremity pain that often develops in occupational settings. RSIs are thought to result from the performance of repetitive and forceful hand-intensive tasks. These conditions are also referred to as cumulative trauma disorders, occupational overuse syndromes, and nonspecific work-related upper limb disorders. The varying nomenclature is controversial because it provides little insight into anatomy affected, disease severity, appropriate treatment, or expected prognosis. Classification systems of work-related musculoskeletal disorders often include specific diagnoses, such as carpal tunnel syndrome and de Quervain tenosynovitis, as RSIs, but the consensus in recent years has been to consider RSI an entirely separate category of occupational disorder [1]. RSIs have symptom complexes that do not fit neatly into another diagnostic classification, such as specific tendinopathy or nerve entrapment. RSIs typically have few objective physical findings and little in the way of demonstrable pathologic change.

RSI is a significant medical concern; approximately 65% of reported cases of occupational illness are attributed to repeated trauma annually [2,3]. In fact, occupational musculoskeletal disorders of the hand and wrist are associated with the longest absences from work and have greater lost productivity and wages than those of other anatomic regions [2]. There is evidence that this condition is actually underreported [4]. Important risk factors appear to be repetitive motion of the arm or wrist, movements that require extremes of hand or arm position, prolonged static postures, and vibration. Other risk factors may be poor ergonomic work environment, task invariability, lack of autonomy, and high levels of psychological distress in the workplace. In addition, the female gender appears to be more susceptible to development of RSI [5]. RSIs can develop outside of the workplace in individuals who participate in hobbies or activities that expose them to repetitive motion and prolonged postures on a consistent basis. A study demonstrated that the adult acquired upper limb amputee population is at increased risk of musculoskeletal pain in the neck/upper back and residual limb as well as in the contralateral remaining arm [6].

According to the U.S. Department of Labor, Bureau of Labor Statistics, occupations that appear to be at greatest risk for RSIs are those in the service and manufacturing industries, including any job involving computer processing and keyboard use [2]. These occupations have the most demand for upper extremity intensive tasks. Because of limitations in the assessment of risk factors, quantitative levels of exposure that are “acceptable” in each occupation are not available [7]. Clinically, it appears that the onset and perpetuation of RSIs are multifactorial. There is no proven etiology of RSI, but it is thought to develop from repetitive microtrauma to muscle, tendon, nerve, loose connective tissue, or bone that exceeds the ability of the tissue to heal itself. In animal models, when chronic repetitive motion is induced, an acute inflammatory response is stimulated in the tissue. This initial response eventually subsides and is followed by a fibrotic response that may lead to complete tissue repair if loads and repetition are sufficiently low [8]. However, in the presence of high repetition or high force, the acute inflammatory response is followed by tissue degeneration and fibrosis that leads to scarring. It is this tissue reorganization that may lead to a nonspecific pattern of pain in RSI.

Abnormal muscle fatigability may also contribute to pain [9]. Reduction in muscle blood flow and localized tissue hypoxia have been demonstrated in trapezius muscle biopsy specimens taken from assembly-line workers with prolonged, static shoulder postures who developed chronic trapezius myalgia [10]. In addition, diminished local muscle oxygenation and blood flow has been demonstrated in the forearms of individuals with RSI during static contraction, compared with controls at similar working intensities [11]. The same investigators later demonstrated that patients with RSI have an attenuated exercise-induced brachial artery blood flow and an impaired vascular endothelial function in the affected arm [12]. A subsequent study found that blood flow and oxygen consumption after exercise are similarly attenuated in both the affected and contralateral unaffected arms of patients with unilateral RSI, indicating that systemic vascular adaptations may occur [13]. These findings indicate that the underlying vasculature may be impaired in this condition. It is unclear whether these data can be extrapolated to explain the pathophysiologic mechanism of all RSIs in the upper extremity.

There may also be a neurogenic origin for RSI. There is evidence of neural reorganization at multiple levels of the central nervous system after the performance of repetitive tasks [2]. The repeated stimulation of nociceptive afferent nerve fibers may cause the receptors to become hypersensitive, to expand their receptive fields, and to increase the excitability of secondary neurons in the spinal cord. These changes may contribute to the hyperalgesia associated with chronic pain in RSIs. Moreover, there may also be an element of central nervous system reorganization at the level of the somatosensory cortex with repetitive tasks [2]. Figure 112.1 illustrates the distribution of somatosensory pathways in the central nervous system.

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FIGURE 112.1 A, Spinothalamic and spinocerebellar tracts to muscle (blue) and from nociceptive receptor (red). B, Afferent sensory pathways from peripheral receptors to lumbosacral spine. DRG, dorsal root ganglion. (From Nolte J. Elsevier’s Integrated Neuroscience. St. Louis, Mosby, 2008.)

Regardless of the factors that contribute to the development of RSI, there is often a complex dynamic in managing patients with work-related musculoskeletal disorders. They are often involved in compensation claims. When the injured patient takes on the additional role of claimant, the perception of both patient and caregiver can change in many aspects of the healing and rehabilitation process. It is paramount for the physician treating RSI to take the medicolegal implications into account. Indeed, the workers’ compensation system has a great impact on the reporting and control of work-related disorders [14].

Symptoms

The predominant symptom in RSI is upper extremity pain. The discomfort often begins as a dull ache in the forearm or hand after the performance of tasks of repetitive motion. Initially, it may be intermittent and alleviated with rest. As the offending activity is repeated with regularity, the pain may increase in intensity and be triggered by minimal exertion in the workplace and even while performing simple activities of daily living, such as dressing or grooming. The symptoms usually begin in one region of the limb in a fairly localized area (e.g., wrist, elbow, or forearm) but may quickly spread to involve the entire arm and at times the contralateral arm. Pain tends to gradually increase during the workday, with peak intensity during the last hours of work. It appears to get better over the weekends and during vacations from work.

Other symptoms may include paresthesias, numbness, and weakness. If these symptoms are present, they may not follow dermatomal or peripheral nerve distributions. Patients may also complain of arm or hand muscle cramping, allodynia, stiffness, and slowing or incoordination of fine motor movements of the hand.

Patients often complain of night pain, resulting in poor sleep. A detailed investigation of sleep habits is important because sleep disruption is common in RSI. Psychological distress and depression may result if pain and sleeplessness persist. In fact, self-reported upper extremity–specific health status measured by the Disabilities of the Arm, Shoulder, and Hand (DASH) questionnaire appears to correlate with depression and pain anxiety in these patients [15]. Some patients may also exhibit maladaptive illness beliefs, such as catastrophizing and fear-avoidance.

In taking a patient’s history, the clinician should attain an accurate understanding of the patient’s job description and daily workstation. It is important to thoroughly evaluate the biomechanics of body position and posture as well as the physical layout of the work site. Special attention should be given to the details of specific job duties, including the frequency, duration, and conditions under which they are performed. For example, if the patient works a desk job and spends each day on a computer, it is important to inquire about desk and chair setup and placement of the computer monitor and keyboard. The clinician should also take note of the patient’s perception and satisfaction with the workplace. This information can give the clinician valuable insight as dissatisfied workers are notorious for work-related medical claims.

Physical Examination

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