OVERUSE INJURY
Overuse injuries, otherwise known as cumulative trauma disorders, are described as tissue damage that results from repetitive demand over the course of time.
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. 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 under-stimulation of tendon cells, rather than to overstimulation.
Alterations in the regulation of genes within tendons undergoing overuse have been shown in the rat model. 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.
Psychosocial factors have been implicated in overuse injuries for decades. 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.
SEX
For a variety of hypothesized reasons, differences in sex play a role in certain overuse injuries. 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. 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.
CAUSES
The most important factor leading to overuse injury is repetitive activity, although the specific type of force leads to different outcomes.
Ø 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.
Ø Repetition is part of the definition of overuse injury. The concept is that overuse injury is associated with repeated challenge without sufficient recovery time.
o 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.
o 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.
Ø 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).
Ø The greater the forces involved, the greater the likelihood of developing an overuse injury.
Ø 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.
Ø A literature review found a moderate association between hand-arm symptoms and increasing duration of mouse use. 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. However, certain psychosocial factors may be predictive of chronic pain.
DIAGNOSIS
LABORATORY STUDIES
Laboratory tests are rarely contributory to the evaluation of overuse injury. No laboratory results contribute to the diagnosis of overuse injury, although several tests are generally ordered during the initial workup to rule out other etiologies of pain, depending on the patient's presentation.
Erythrocyte sedimentation rate
Rapid plasma reagent testing
Antinuclear antibody testing
C-reactive protein
Complete blood count (CBC), B12, thyroid-stimulating hormone (TSH), comprehensive metabolic panel, and liver function tests are also used for initial evaluation.
IMAGING STUDIES
The diagnosis of most overuse injuries does not require imaging studies. However, if surgical intervention is considered, imaging studies are vital for the decision-making process.
Radiography
Bony avulsions are relatively common among people who participate in dance, athletic activity, and heavy physical labor. Radiography is useful for defining these bony avulsions.
Stress fractures; calcification of tendons, which occurs in persons with chronic tendonitis; joint mice; myositis ossificans; heterotopic ossification; and atrophy of cartilage generally are revealed with radiography.
Bone scanning - This may reveal stress fractures that are not evident on radiographs.
Magnetic resonance imaging (MRI)
Typically, MRI is most effective for acute injuries; findings are generally more subtle with chronic injuries.
MRI is increasingly effective for revealing the site of nerve compression when large nerves are involved (eg, ulnar, median, sciatic), but it is not yet definitive for smaller nerves. Its true sensitivity is still being determined for these uses.
MRI has been quite successful in revealing tendon, ligament, and muscle injuries. It is easily available, does not involve radiation, and can help to assess chronicity of soft-tissue injuries.
The presence of bone marrow edema on MRI scans may precede visualization of stress fractures of the cortical bone and indicates trauma to the trabecular portions of the bone.
OTHER TESTS
Electrodiagnostic testing (eg, EMG, nerve conduction studies) can be very useful when used appropriately. In cases of peripheral nerve compression or injury, such testing can provide evidence of the location and severity of the injury. EMG and nerve conduction studies are not tests with high specificity, although they can provide much-needed information when vague symptoms are the chief complaint. They are also very useful for documenting work-related injuries.
PROCEDURES
Steroid injections are the most commonly used procedure in the treatment of overuse injuries, although controversy surrounding this treatment is still readily apparent. Tendons and ligaments can become structurally weakened by the use of steroids, predisposing them to rupture. The use of local anesthetics and steroids should be reserved for patients with significant pain who have the ability to change the underlying cause behind their injury. Repeatedly injecting patients who will inevitably return to the same routine that initially caused the injury is not advisable.
Many steroid injections can be performed under ultrasonographic guidance to increase accuracy and decrease the possibility of intratendon or intraligament injection.
TREATMENT
PHYSICAL THERAPY
Relative rest, particularly avoidance of the inciting activity, is a hallmark component of treatment. Using the involved area in non painful ways often helps maintain ROM.
Total bed rest is virtually never advisable for these patients. Participation in a carefully planned physical therapy program is important for the following reasons:
v Patient education
v Supervised use of the injured part
v Appropriate use of modalities (eg, transcutaneous electrical nerve stimulation units, similar electrical treatments, ultrasound/phonophoresis, iontophoresis, heat/cold)
v Development of a home exercise program
v Psychosocial benefits related to frequent interaction with an active partner in the treatment regimen
The physical therapy program also offers the patient the chance to see that movement will not lead to ongoing tissue damage, thus preventing significant "sick behaviors" or kinesophobia.
Overuse injury in athletes is commonly caused by ill-fitting equipment (eg, in cycling), overtraining / over-reaching (eg, with regard to triathlons, marathons, etc.), or technique flaws.
Specialized bike-fitting is available, sports psychology is worthwhile in combating overtraining, and sport-specific coaching is often invaluable.
Coaches, athletes, and physicians must work together to correct these problems and maintain a healthy musculoskeletal system.
OCCUPATIONAL THERAPY
Occupational therapists with experience in this field can help to identify workplace modifications. In cases of individuals with disabilities who develop overuse injuries as a result of the interface with adaptive equipment, occupational therapy may be of great benefit.
Often, simple modifications in the manner in which the patient performs activities of daily living or modifications in the equipment itself confer relief.
Vocational rehabilitation and work-hardening programs are often effective for bringing motivated patients back into the workforce. Integration of this type of program has proven to be effective in the corporate world and has decreased the overall financial impact of overuse injuries in the workplace.
SURGICAL INTERVENTION
Surgical intervention is undertaken if conservative approaches fail and if the injury is amenable to surgery. In overuse injury, decompression of nerves and repair of lax or failed ligaments are the most common problems that lead to surgery.
Surgeries that are performed solely to relieve pain in the absence of objective findings are notorious for suboptimal outcomes.
MEDICATION
Injection of involved structures with combinations of corticosteroids and local anesthetics frequently is quite helpful in persons with overuse injury. Pain relief enables more effective participation in therapy, and it may help to limit the likelihood that the patient will develop a chronic pain syndrome.
In most cases, injections should be performed after less invasive measures fail. Rarely, immediate relief of pain may be necessary to allow participation in an athletic or performing arts event, and this can be achieved through injection therapy.
Nonsteroidal anti-inflammatory drugs (NSAIDs) are mainstays in the treatment of overuse injuries. However, considerable evidence has been revealed that true inflammation is rarely a component of these disorders, especially tendinopathies. Consequently, the use of simple analgesics has become more prevalent in the treatment of such disorders.
Muscle relaxants, opiates, corticosteroids, tricyclic antidepressants, and sleep medications have a role in the tailored treatment of individuals with overuse injury.
CORTICOSTEROIDS
Have anti-inflammatory properties and cause profound and varied metabolic effects. Used for pain relief and reduction of inflammation.
CORTISONE (CORTONE)
Reduces inflammation. Decreases inflammation by suppressing migration of PMN leukocytes and reversing increased capillary permeability.
Adult: 25-300 mg/d PO/IM divided q12-24h
Pediatric: 0.5-0.75 mg/kg/d PO/IM or 20-25 mg/m2/d divided q8h; alternatively, 0.25-0.35 mg/kg/d IM qd or 12.5 mg/m2/d
Pregnancy
D - Fetal risk shown in humans; use only if benefits outweigh risk to fetus
Precautions
Caution in patients with hyperthyroidism, cirrhosis, nonspecific ulcerative colitis, osteoporosis, peptic ulcer, diabetes, and myasthenia gravis
NONSTEROIDAL ANTI-INFLAMMATORY DRUGS
Most commonly used for relief of mild to moderate pain. Effects in treatment of pain tend to be patient-specific.
DICLOFENAC (VOLTAREN, CATAFLAM)
Used to reduce inflammation; inhibits prostaglandin synthesis by decreasing activity of COX enzyme, which, in turn, decreases formation of prostaglandin precursors.
Adult: 25 mg PO bid/tid
If well tolerated, increase by 25 or 50 mg at weekly intervals until satisfactory response obtained or total daily dose of 150-200 mg reached; higher doses generally do not increase effectiveness
Pregnancy
B - Fetal risk not confirmed in studies in humans but has been shown in some studies in animals
D - Fetal risk shown in humans; use only if benefits outweigh risk to fetus
Precautions
Acute renal insufficiency, hyperkalemia, hyponatremia, interstitial nephritis, and renal papillary necrosis may occur; increases risk of acute renal failure in patients with pre-existing renal disease or compromised renal perfusion; low WBC counts occur rarely and usually return to normal in ongoing therapy; discontinuation of therapy may be necessary if persistent leukopenia, granulocytopenia, or thrombocytopenia occurs
MUSCLE RELAXANTS
Thought to work centrally by suppressing conduction in the vestibular cerebellar pathways. May have an inhibitory effect on the parasympathetic nervous system.
CYCLOBENZAPRINE (Flexeril)
Acts centrally and reduces motor activity of tonic somatic origins, influencing alpha and gamma motor neurons. Structurally related to TCAs. Skeletal muscle relaxants have modest, short-term benefit as adjunctive therapy for nociceptive pain associated with muscle strains and, used intermittently, for diffuse and certain regional chronic pain syndromes.
Long-term improvement over placebo has not been established. Often produces a "hangover" effect, which can be minimized by taking the nighttime dose 2-3 h before going to sleep.
Adult: 20-40 mg/d PO divided bid/qid; not to exceed 60 mg/d
Pregnancy
B - Fetal risk not confirmed in studies in humans but has been shown in some studies in animals
Precautions
Caution in angle-closure glaucoma and urinary hesitance
NARCOTIC ANALGESICS
Pain control is essential to quality patient care. It ensures patient comfort, promotes pulmonary toilet, and enables physical therapy regimens. Many analgesics have sedating properties, which are beneficial for patients who have sustained injuries.
HYDROCODONE & ACETAMINOPHEN (Vicodin, Norcet, Lortab)
Drug combination indicated for moderate to severe pain.
Adult: 1-2 tab or cap PO q4-6h prn; not to exceed total of 4 g/d acetaminophen
Pediatric:
<12 years: 10-15 mg/kg acetaminophen PO q4-6h prn; not to exceed 2.6 g/d acetaminophen
>12 years: 750 mg acetaminophen PO q4h; not to exceed 10 mg hydrocodone bitartrate per dose or 5 doses/24 h
Pregnancy
C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus
Precautions
Tab contains metabisulfite, which may cause hypersensitivity; caution in patients dependent on opiates, because this substitution may result in acute opiate-withdrawal symptoms; caution in severe renal or hepatic dysfunction
TRICYCLIC ANTIDEPRESSANTS
Used in the treatment of overuse injury, not for their antidepressant effects but as adjunct pain medications. Act synergistically with narcotic analgesics and appear to alter brainstem pain processing. Their sedating effects also may be used advantageously if the patient's sleep is disrupted.
AMITRIPTYLINE (ELAVIL)
Analgesic for certain chronic and neuropathic pain.
Adult: 30-100 mg/d PO hs
Pediatric:
Children: 0.1 mg/kg PO hs; increase, as tolerated, over 2-3 wk to 0.5-2 mg/d hs
Adolescents: 25-50 mg/d PO initially; increase gradually to 100 mg/d in divided doses
Pregnancy
D - Fetal risk shown in humans; use only if benefits outweigh risk to fetus
Precautions
Caution in cardiac conduction disturbances; history of hyperthyroidism or renal or hepatic impairment; avoid using in elderly patients
ANXIOLYTIC AGENTS
Sleep-inducing medications are used in overuse injury when the patient's sleep is disrupted because of discomfort from the injury.
ZOLPIDEM (AMBIEN)
Structurally dissimilar to benzodiazepine but similar in activity, with exception of having reduced effects on skeletal muscle and seizure threshold.
Adult: 10 mg PO hs; not to exceed 10 mg.