eMedicine Specialties > Physical Medicine and Rehabilitation > Muscle Pain Syndromes
Overuse Injury
Updated: Mar 12, 2008
Introduction
Background
Overuse injuries, otherwise known as cumulative trauma disorders, are described as tissue damage that results from repetitive demand over the course of time. The term refers to a vast array of diagnoses, including occupational, recreational, and habitual activities.
Pathophysiology
The pathophysiology of overuse injuries is based on the idea that tissues adapt to the stresses placed on them over time. These stresses include shear, tension, compression, impingement, vibration, and contraction. Mechanical fatigue within tendons, ligaments, neural tissue, and other soft tissues results in characteristic changes depending on their individual properties. This fatigue is theorized to initially lead to adaptations of these tissues. As the tissues attempt to adapt to the demands placed on them, they can incur injury unless they have appropriate time to heal. The rate of injury simply exceeds the rate of adaptation and healing in the tissue. Evidence also suggests that chemical mediators are involved in the initiation and propagation of overuse injuries.
Nerve tissues are at particular risk for ischemic injuries. This ischemia leads to characteristic changes in the nerve itself. The timeline generally begins with subperineurial edema, followed by thickening of the perineurium, thickening of the internal and external epineurium, thinning of the peripheral myelin, and, eventually, axonal degeneration.
One hypothesis is that the development of muscular pain originates from the nearly continuous activation of low-threshold motor units that occurs in muscles performing continuous or slow, repetitive tasks, causing depletion of adenosine 5'-triphosphate (ATP) in those fibers. With insufficient ATP, sarcoplasmic reuptake of Ca++ could be reduced, resulting in high concentrations in the cytosol, allowing Ca++ –dependent activation of phospholipase, the generation of free radicals, and damage to the muscle fibers involved. This theory has a rational physiologic basis, but it remains to be proven. Multiple studies have shown that patients with more significant work-related, upper extremity disorders exhibit more muscular activity on electromyelography (EMG) findings; however, these studies are observational and not designed to exhibit causality.
Increasing data in in vitro and in vivo human and animal models shows that there are tissue-level changes associated with repetitive stress. Prostaglandin E2 has been found to be present in high quantities in overuse tissues in rat and chicken models.1 This mediator has been suggested to influence cell proliferation, increase collagenase, and decrease collagen synthesis. Increasing loads on these tissues alters the amount of nitric oxide and prostaglandin E2. However, another hypothesis based on rat-model observations suggests that overuse may lead to an understimulation of tendon cells, rather than to overstimulation.2
Alterations in the regulation of genes within tendons undergoing overuse have been shown in the rat model.3 These changes include upregulation of genes associated with cartilage, and down-regulation of genes associated with tendon. This suggests that overuse may cause a morphologic alteration of tendon tissue, causing it to become more cartilaginous.
Moderate (40 N) and high (60 N) cyclic loads are reported to create an acute neuromuscular disorder characterized by delayed hyperexcitability in the lower back. This delay is characteristic of an inflammatory state. Microtears within muscle tissue have been shown to be related to higher repetition loads and cyclic rate.4,5,6,7
Psychosocial factors have been implicated in overuse injuries for decades.8 A partial list includes work satisfaction, perceived physical health, perceived mental health, coping mechanisms of the patient and his/her family, perception of work-readiness, and anxiety.
A review of the English-language literature revealed specific articles focusing on ultrasonographers, equestrian athletes, ballet dancers, bicyclists, baseball players, swimmers, triathletes, golfers, bull riders, martial artists, sign language interpreters, skeletally immature patients, college students, heavy computer users, assembly line workers, tailors (seamstresses), surgeons, dentists, and nurses. This list dramatizes the point that at least the perception exists that many common and some uncommon ailments are associated with repetitive motion.
See also the following related eMedicine topic:
Nerve Entrapment Syndromes
Frequency
United States
The incidence of overuse injuries as a whole is nearly impossible to estimate given the sheer volume of included diagnoses, as well as the difficulty in establishing clear diagnostic criteria.9 However, several long-term, retrospective, work-related studies have estimated the annual incidence of upper extremity disorders at 4.5-12.7% per year. The frequency of injury in each diagnostic category is more appropriately left to more focused literature.
Mortality/Morbidity
Overuse injuries are not associated with direct mortality. Morbidity, however, is significant. The impact of these injuries varies from the occasional annoyance to loss of function as a result of frank tissue destruction. In many performing artists, musicians, craftsmen, and workers, loss of function at even a minor level can result in a significant loss of livelihood (leading to the various difficulties associated with this loss). The direct economic impact of overuse injury in the workplace is immense. The indirect impact is nearly incalculable if the number of health care dollars involved is considered. Of particular note, one interesting review of worker demographic data suggested that workers with cumulative trauma disorders were subjected to employment discrimination. Depression and quality-of-life issues have been described after a diagnosis of chronic overuse injury.
Race
Race is not a differentiating factor for overuse injury incidence.
Sex
For a variety of hypothesized reasons, differences in sex play a role in certain overuse injuries.10 Most notably, a significant female predominance in carpal tunnel syndrome has been noted. This has a variety of possible causes, including anatomical differences in the carpal tunnel, hormonal differences, and, importantly, differences in the activities performed by men and woman. Other biomechanical differences have also been implicated; elbow carrying angles, Q-angles, femoral anteversion, and lean body mass are the most commonly stated. Psychosocial and cultural phenomena also play roles.
Age
Age would be expected to be an independent risk factor for overuse injury; however, given the dependence of overuse injury on activity and the changes in activity that typify aging, the contribution of age as a risk factor is difficult to determine.
Clinical
History
The first and most crucial step is obtaining comprehensive information on the onset, timing, and frequency of symptoms; any associated symptoms; and alleviating and exacerbating factors. More detailed information about the culprit activity or technique problem is also key. Systemic symptoms should be elicited, if present. Other hallmark symptoms may include a history of popping, clicking, rubbing, erythema, or vascular phenomena.11 When interviewing an athlete, specific attention must be paid to training details, equipment fit, and technique.
Physical
The examination should begin with the basics of inspection, palpation, and passive and active range of motion (ROM). Tenderness and guarding are often present. Crepitus, painful or painless, is often found during the ROM examination. Obvious erythema, swelling, and anatomic derangement raise the possibility of an acute injury or infection, as well as the presence of an inflammatory disease. For physical findings associated with specific injuries, refer to the specific article in Differentials.
Causes
The most important factor leading to overuse injury is repetitive activity, although the specific type of force leads to different outcomes.
- One group of authors accurately described the issue as "a culprit and a victim," in which the victim is the injured tissue, and the culprit is the true biomechanical cause. All too frequently, physicians focus on the victim tissue and not on the culprit.
- Repetition is part of the definition of overuse injury. The concept is that overuse injury is associated with repeated challenge without sufficient recovery time.
- Cycles and fundamental cycles are terms used to describe activities repeated at work. A cycle is a large-scale activity that is repeated throughout the day. A fundamental cycle is a small component of a cycle that may be repeated several times during the performance of a cycle. If a job has cycles that are repeated many times a day, the job is designated as repetitive. The tendency in industry to specialize labor for the sake of efficiency and better productivity has resulted in fewer different tasks per job. These tasks are repeated frequently, and this repetition is believed to be a contributing factor to the increase of overuse injury claims. Repetitiveness and force exerted are features of a task that increase the risk of sustaining an overuse injury.
- However, studies have been performed that dispute this theory, finding that cycle times and repetitive motions do not specifically lead to overuse injury in the upper extremity. Most articles in the literature tend to implicate these repetitive motions as possible causes for injury.
- Vibration, especially over long periods, has long been shown to be a factor in increasing the risk of many injuries (eg, lower back pain, intervertebral disk injury, wrist injury).
- The greater the forces involved, the greater the likelihood of developing an overuse injury.
- Malpositioning limbs away from their neutral position increases the risk for overuse injury. Multiple articles in dental and surgical literature emphasize this point. Ergonomics is the field that focuses primarily on designing devices that lend themselves to good positioning. A massive increase has occurred in the amount of ergonomically designed work equipment, especially keyboards and mouses. The literature remains divided on their effectiveness in decreasing injuries.
- A literature review found a moderate association between hand-arm symptoms and increasing duration of mouse use.12 There was a weaker association between neck-arm symptoms and mouse use. Nevertheless, prolonged computer and mouse use does not typically result in chronic neck and shoulder pain.13 However, certain psychosocial factors may be predictive of chronic pain.
More on Overuse Injury |
 Overview: Overuse Injury |
| Differential Diagnoses & Workup: Overuse Injury |
| Treatment & Medication: Overuse Injury |
| Follow-up: Overuse Injury |
| References |
| Next Page » |
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Further Reading
Keywords
repetitive stress disorder, repetition strain injury, cumulative trauma disorder, secondary gain, malingering, worker's compensation fraud, workers compensation fraud, worker's compensation abuse, workers compensation abuse, worker's compensation, workman's comp, overuse injuries, cumulative trauma disorder, repetitive demand injuries, occupational injury
