Industrial Medicine and Acute Musculoskeletal Rehabilitation. 7. Acute Industrial Musculoskeletal Injuries in the Aging Workforce

7.1 Educational Activity: To explain the current and future demographic trends in the aging population of workers in the United States 

THE AGING OF THE U.S. population has been well chronicled in both the medical literature and the general media. A greater proportion of U.S. citizens is over age 65 currently than at any other time in history, with projections for continued growth in this segment of the population over the next 30 years. According to the 2000 census, there was a 49% increase in the 45-to-54–year age group over the previous 10 years, the most rapid increase in any demographic group.1 This rise reflects the aging of the “baby boomer” generation, those born between 1946 and 1964. This generation remains quite active, and when polled, the American Association of Retired Persons reported that up to 79% of seniors (age ≥50y) plan to work part time or full time after “retirement.”2 With an “older worker” defined arbitrarily in the literature as age 40 years and older, this group will soon become a majority of the workforce in the very near future. Injuries in this “graying workforce” will present new challenges to the medical community, employers, and workers’ compensation insurance carriers.

7.2 Clinical Activity: To identify the factors intrinsic and extrinsic to a 65-year-old industrial worker that may predispose her to a workplace injury 

Many factors increase the risk of occupational injuries in older workers. Those commonly cited in the literature include a general decline in vision and hearing with increasing age. Findings from the Health and Retirement Study,3 validated by the National Health Interview Survey,4 and other studies5 affirm that diminished vision and hearing are independent risk factors for occupational injury. Diminished sensory input places older workers at risk for falls and is 1 of the leading causes of injury among all older adults, regardless of work status. Much of the literature, however, focuses on extrinsic, environmental sources of falls such as surface traction, contaminant control, and footwear.6 Among those workers presenting to an emergency department with an industrial musculoskeletal injury, workers over age 65 years are most likely to present with a fracture or dislocation, an injury resulting from a fall to the ground from the same level, and to require hospitalization.7 Besides diminished vision and hearing, older adults also experience depressed autonomic reflexes, which predisposes them to postural hypotension, syncopal episodes, and, hence, to falls. Concomitant medication usage, particularly antihypertensive medications, may compound this risk. Older workers also may have aging-related decreases in sensory and motor nerve conduction. Although the prevalence of these decreases in nerve function in older workers has not been established, affected workers may have clinically impaired vibratory sensation, reduced cutaneous pressure sensation, and prolonged sensory and motor latencies.8 Although the most common diagnosable cause of peripheral neuropathy in the United States remains diabetes mellitus, other etiologies occurring with increasing frequencies in older adults include peripheral neuropathies associated with herpes zoster, vitamin B12 deficiency, and carcinoma. Identifying these impairments and providing modifications in work requirements and work environment are crucial for successful rehabilitation and re-entry to the workforce.

Less commonly considered factors in older workers may also contribute to work-related injuries. The prevalence of depression tends to increase with age. Somatic manifestations may mimic acute musculoskeletal injury and should be sought out, especially in those patients not responding to treatment. In patients on cholesterol-lowering medications, side effects of muscle pains and myopathy9 may also mimic acute musculoskeletal injury and confound the etiology of these symptoms.

Older workers have long been considered predisposed to musculoskeletal injuries. The vicious cycle of musculotendinous overload presents a schematic and conceptual framework for this inherent risk (fig 1).10

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Fig 1. Vicious cycle of musculotendinous overload. From Kibler et al.10 Reprinted with permission.

The biomechanic deficits enumerated in figure 1 all occur, to varying degrees, with aging and cumulative trauma.11 Muscular weakness occurs after age 30 years in association with generalized muscle fiber atrophy, decreased muscle density, and increased intramuscular fat.12, 13 The resultant diminished muscle mass and strength may be further compounded by inactivity and aerobic deconditioning. This reduction in muscle mass, strength, and endurance appears to accelerate after age 70 years. The observed reductions in strength are 15% per decade between ages 50 to 70 years and 30% per decade thereafter.11, 12

Inflexibility results from shortening of muscle fiber length and diminished extensibility of tendons and connective tissues surrounding joints. With age, the tensile strength of tendons decreases.14 Coupled with the loss of strength is a decrease in both insoluble and total collagen.15 This combination results in decreased flexibility, which increases the likelihood of tissue trauma. Cumulative microtrauma from repetitive activities produces inflammation, or even “scarring,” and thickening of the tendinous sheath.16 In conjunction with the weakening musculature associated with aging, the resultant inflexibility and microtrauma further exacerbate muscle imbalances resulting from improper or compensatory strategies, improper body mechanics, and poor posture accumulating over years.15 Overstressing of these soft tissues leads to muscle strain, ligament sprain, tendon strain, or rupture as described by in the vicious cycle of musculotendinous overload.

7.3 Clinical Activity: To identify specific occupations and work-related activities that predispose an older worker to potential work-related injury 

The literature exploring this observation of an increased risk of musculoskeletal injury in older workers varies depending on the industry. In certain populations, such as workers in the coal mining17 and construction industries,18 age is clearly a risk factor for industrial musculoskeletal injury. Types of injuries within these groups may also differ when stratified for age. Older union carpenters are more likely to sustain fractures of the foot but less likely to sustain contusions of the hand or foot.19 Older workers in the service industries, agriculture, forestry, and fishing industries7 mechanics, repairers, and those performing heavy lifting3 have been observed by some investigators to be particularly at risk for musculoskeletal injury. However, another investigation20 suggested a lower injury rate among older workers than younger (age <25y) workers. In a study of poultry workers and data-entry personnel (groups known to have high rates of cumulative trauma disorders [CTDs]), there was no statistical increased susceptibility to CTDs such as nerve compression syndromes, tenosynovitis, epicondylitis, or tendinitis in older workers when compared with their younger counterparts.8 In a study21 of material handlers in a home improvement retail chain, musculoskeletal injury rates in workers over age 55 years were similar to those in younger workers, even when length of employment and lifting intensity were taken into consideration.

7.4 Educational Activity: To discuss the available literature addressing the impact of older age on functional outcomes in work-related injuries 

When observing outcome studies of injured workers, there is a clearer trend of longer periods of disability resulting from occupational injuries in older workers. In the study of material handlers cited earlier,21 although the prevalence of injury was no greater in the older cohort (age >55y), the amount of lost work time because of injury was significantly greater in this group. Among construction workers, a retrospective assessment determined that the risk of development of chronic symptoms after a musculoskeletal soft-tissue injury was significantly greater in older workers.22 Prospective trials affirm the significant correlation among lost work time in older workers, their decreased likelihood of return to work, and a higher probability of future disability.23 Considering the subset of workers with spine injuries, age was linearly associated with both pretreatment duration of disability and frequency of surgeries.24 Further, older workers have a higher level of posttreatment disability, and they have a higher likelihood of recurrent injury.23 A review25(p162) of the international literature suggests that older workers “sustain more serious injuries, take longer to recover, and are less likely to return to work than younger workers.” The risk of fatality associated with injury in the workplace clearly increases with age as well,20, 26 with death resulting from falls of lesser heights and lower energies of impact.27

7.5 Clinical Activity: To summarize how increasing age affects the differential diagnosis of low back pain 

Medical comorbidities in older workers present further confounding variables in their diagnosis and treatment. For example, low back injuries are the most common musculoskeletal injuries in the aging workforce and present unique diagnostic challenges. The maximal frequency of low back pain (LBP) occurs between the ages of 35 and 55 years, and the duration of symptoms increases with increasing age.28 The differential diagnosis for these symptoms should extend well beyond the colloquial lumbosacral sprain or strain. Spinal etiologies may include a lumbar annular tear or disk protrusion, a lumbar or lower-thoracic compression fracture, zygapophyseal joint mediated pain, or segmental injury and dysfunction with myofascial pain, that is, the sprain alluded to earlier. The degenerative cascade model of Kirkaldy-Willis provides a framework in which to conceptualize the dynamic changes that occur during aging of the lumbar spine.29 In this model, the 3-joint complex of the intervertebral disk and paired zygapophyseal joints undergo characteristic and somewhat predictable changes with aging. Initially, in stage I (dysfunction), the cumulative trauma of aging is manifest at the zygapophyseal joints by cartilage degeneration, joint synovitis, and subluxation. The intervertebral disk experiences tears within the annulus with breakdown of the nucleus pulposus matrix and, potentially, even disk herniation. This may explain the peak incidence of lumbar disk herniations that occurs in the third and fourth decades of life. Stage II (instability) is characterized by further collagen degradation within the zygapophyseal joint, associated with capsular laxity and increased rotational movement. Within the intervertebral disk, further annular tears with or without herniation and coalescence also increase annular laxity, with further increased translational forces. Stage III (stabilization) is marked by typical changes of osteoarthritis within the zygapophyseal joints. There is loss of joint surface cartilage and joint space narrowing, with fibrosis and osteophyte formation. The intervertebral disk undergoes further deterioration of the nucleus pulposus, with changes in collagen type, disk resorption, fibrosis, and loss of disk height. These advanced changes may account for the peak in lumbar spinal stenosis in the sixth and seventh decades of life. In older patients presenting with back and referred leg pain, the associated findings also include both central and foraminal stenosis.

7.6 Clinical Activity: To explain the various nonspine diagnoses that may present with back pain in the aging worker and delineate their specific diagnostic considerations 

Vascular etiologies for LBP are a potentially fatal cause that may be overlooked. Abdominal aortic aneurysms may occur in up to 4% of the population over the age of 50.30 Smoking is the risk factor most strongly associated with abdominal aortic aneurysms, followed by age, hypertension, hyperlipidemia, and atherosclerosis.31 Men are 10 times more likely than women to have a clinically significant abdominal aortic aneurysm (ie, 4cm or larger). There is also a genetic predilection, with a 30% increased risk in patients with a family history. On physical examination in slender people, a pulsatile mass may be appreciated. Plain film radiographs may show a widened aortic silhouette with a curvilinear calcification if there is significant atherosclerosis. Contrast-enhanced computed tomography (CT) and magnetic resonance angiography are the preferred studies to define aortic aneurysms in both the thoracic and abdominal regions.

Genitourinary causes of LBP also may occur with increasing frequency after the age of 40 years. Prostatitis can cause LBP, sacral pain, and pelvic pain.32 It generally is characterized as acute or chronic, bacterial, or abacterial. An acute bacterial prostatitis may be easily confirmed on prostate examination (tenderness, bogginess) and with a positive urine culture and sensitivity, indicating the need for an appropriate course of antibiotics. It may otherwise present as a chronic, ill-defined pelvic pain known as chronic pelvic pain syndrome.33 Because of the extensive overlap of symptoms among benign prostatic hypertrophy, chronic bacterial, and abacterial prostatitis, consultation with a urologist is recommended. Nephrolithiasis typically presents acutely with severe flank, low back, and, at times, pelvic pain. In a study of machinists exposed to high temperatures, there was a significantly increased prevalence of uric acid stones compared with the control group of machinists working in normal temperatures.34 Older employees working in occupations exposed to high heat appear particularly at risk for uric acid stones. Counseling regarding adequate fluid intake and avoidance of beverages that contain oxaloacetic acid (eg, black tea) are critical components to minimize this risk.

Gastrointestinal disorders can also present with low back and musculoskeletal-type symptoms. Gastric and duodenal ulcers typically present with boring abdominal pain associated with referred pain in the lumbar spine or sometimes with midback pain only. Risk factors include cigarette smoking, intake of aspirin and nonsteroidal anti-inflammatory medications, increased dietary salt, and excessive alcohol use.35 The risk of gastric and duodenal ulcer increases with age, fairly precipitously after age 60 years. This risk should be considered especially when prescribing nonsteroidal anti-inflammatory medications in the older worker. Workers performing rotating shift and night work and immigrant workers appear to be at significantly increased risk for the development of gastric and duodenal ulcers,36, 37, 38 which are presumed to be related to sleep disturbance and disruption of circadian rhythm in these workers. Pancreatitis is also a potentially overlooked cause of back pain in older workers. Pancreatitis should be especially considered in workers with significant alcohol and tobacco use. In the Health and Retirement Study, older male workers were more likely to answer 3 out of 4 CAGE alcoholism screening questions positively and consume 4+ drinks per day.39 The CAGE acronym stands for trying to cut down alcohol use (C), angry when discussing alcohol use (A), feeling guilty about alcohol use (G), and taking an eye opener (E).

Rheumatologic disorders may also present with acute musculoskeletal pain including LBP. Polymyalgia rheumatica typically presents with shoulder girdle pain and stiffness, but a subset of these patients present with hip girdle symptoms. Age at onset is invariably greater than 50 years, with most over the age of 60 years. It affects women twice as often as men. Erythrocyte sedimentation rates (ESR) of 80 to 100mm per hour (or greater) are highly suggestive of this diagnosis, although elevated C-reactive protein levels may be a more sensitive indicator of disease presence.40 Dramatic response to low-dose prednisone (10–20mg/d) provides both confirmation and treatment. The potential development of temporal arteritis and its inherent risk of blindness must be given careful consideration in this population. Diffuse idiopathic skeletal hyperostosis (DISH) presents generally after the age of 50 years. Flowing syndesmophytes in the thoracic and potentially the lumbar spine give the appearance of a “bamboo spine” in these patients. In addition to causing a gradual decrease in spine flexibility and range of motion, even trivial trauma may result in fractures in DISH patients. Whenever there is a history of DISH in the setting of trauma, the clinician must maintain a high index of suspicion for underlying fracture and thus pursue early and aggressive radiologic investigation.

Osteoporosis is 1 of the more common underlying comorbidities increasing the risk of injury in older workers. Risk factors for osteoporosis include being postmenopausal, particularly in a woman of eastern European descent, hyperthyroidism, previous steroid treatments, excessive alcohol intake, calcium deficiency, eating disorders, and smoking. The single greatest risk factor for injury from fall in older patients is osteoporosis, with vertebral compression fracture a likely result.41 Despite this, there is a paucity of research on the effects of osteoporosis on work-related injuries and their prevention. For working women in Canada older than 60 years, there is a significantly increased risk of hand fractures in the workplace compared with younger cohorts and men, likely associated with the increased prevalence of osteoporosis in this population.42 In addition, research43 shows predictable fracture patterns in older women compared with men, with women more likely than older men to sustain forearm and wrist fractures, presumably from osteoporosis. Recognition of these injury patterns and identification of osteoporosis in this patient population is critical. Within the workers’ compensation system, instructions on weight-bearing exercise and fall prevention in the workplace are appropriate and important for the prevention of future injury. Involvement of the primary care physician outside the workers’ compensation system for medical investigation and treatment of the osteoporosis is vital as well.

A higher index of suspicion for malignancy in older workers must also be maintained, especially in workers over the age of 50 years. Malignancies creating back and spine pain may represent a primary malignancy, most commonly multiple myeloma, or metastatic disease. The most common malignancies that metastasize to the spine are those of the prostate, lung, thyroid, breast, and renal cell. Red flags that signal the possibility of malignancy in the history and presentation of these patients44 are outlined in appendix 1.

The presence of weight loss greater than 4.5kg (10lb) in 6 months and ESR higher than 50mm per hour, especially in combination, are reasonably sensitive and specific indicators of malignancy in the setting of LBP.45 Serologic studies should include a complete blood count with differential, because the presence of anemia rivals elevated ESR in sensitivity for malignancy. Serum calcium and alkaline phosphatase levels may indicate states of rapid bone turnover seen with some malignancies. Serum and urine immunoelectrophoresis studies to exclude a monoclonal protein spike, as seen in multiple myeloma, may also be helpful. Anteroposterior (AP) and lateral lumbosacral plain film radiographs are the initial radiologic screen and may show compression fracture or more subtle osteolytic or osteoblastic lesions. Because of the predilection of metastatic tumor to be harbored in more highly vascular sites, particular attention should be paid to the pedicle region when reviewing these images. A triple-phase bone scan can be a sensitive indicator of metastatic disease in the spine but may appear normal in the setting of multiple myeloma. CT of the spine has proven both sensitive and specific in differentiating benign and malignant lesions46 and in detecting metastatic lesions in the spine.47 Magnetic resonance imaging (MRI) with gadolinium remains the criterion standard for identification of spinal malignancies because of its superior soft-tissue resolution and staging of malignant spinal cord compression.48

7.7 Clinical Activity: To discuss appropriate historical and diagnostic considerations in a 62-year-old dock worker presenting with LBP after a fall 

Given the complexities noted above, the investigation for older workers must be tailored to their symptoms. For instance, younger workers with back and leg pain most likely have a diskogenic source for their radicular symptoms. In older workers, spinal stenosis, whether central or foraminal, can cause neurogenic claudication, with bilateral leg pain that mimics vascular claudication. Differentiating these conditions is important. Walking uphill tends to improve the symptoms of neurogenic claudication but worsen those of vascular claudication. After symptom onset, standing still tends to improve the symptoms of vascular claudication, whereas the prolonged erect posture would typically cause persistence or worsening of the leg symptoms of neurogenic claudication. Neurogenic claudication symptoms may improve with walking behind and leaning forward on a shopping cart (the “shopping cart sign”), which generally results in no benefit for patients with vascular claudication. Noninvasive arterial studies including arterial ultrasound and ankle-brachial indices may further help differentiate neurogenic versus vascular claudication. The radiographic investigation has special considerations as well. It is generally accepted that AP and lateral films of the lumbar spine represent an adequate screening study, with the possible exception of clinical suspicion of a pars interarticularis fracture (spondylolysis), which may be missed with these studies alone.49, 50, 51 Additional oblique radiographs may increase the diagnostic yield in this clinical setting. Indications for plain film radiographs in the setting of acute LBP44 are outlined in appendix 2.

When a bone scan is ordered to evaluate for spinal fracture52 or malignancy,53 requesting single-photon emission computed tomography (SPECT) significantly increases the diagnostic yield, sensitivity, and specificity of this diagnostic modality. When malignancy or fracture is suspected, routine inclusion of SPECT imaging is recommended. When ordering CT or MRI, clinicians should be mindful that these yield increasing rates of false-positive results with advancing age.54, 55, 56 The history, physical examination, and imaging studies should all be correlated to arrive at an appropriate working diagnosis.

7.8 Clinical Activity: To analyze the effect of advancing age on the determination of causation in the workers’ compensation system 

The establishment of causation of injury in older workers presents yet another challenge to clinicians. The American Medical Association Guides to the Evaluation of Permanent Impairment, 5th Edition, define causation as “an identifiable factor (eg, accident or exposure to hazards or disease) that results in a medically identifiable condition.”57(p11) Inherent in this definition is the general concept of a sentinel event or set of conditions—that is, environmental exposure or cumulative trauma—that either results in clear injury or exacerbates an underlying condition. For an older worker, underlying conditions such as spondylosis can significantly affect this determination. By age 60 years, 100% of the population will have histologic changes of osteoarthritis.58 Employers and workers’ compensation insurance carriers have an economic interest in relating symptoms to preexisting conditions. Thus, sentinel events that bring an otherwise quiescent condition to a symptomatic state become crucial to document. Ultimate compensability of an injury or symptom complex relies on the particular policy of each individual state’s workers’ compensation system.

7.9 Educational Activity: To summarize factors specific to the employee or employer that affect the functional outcomes of older workers 

In the rehabilitation of older workers, goals should include resolution of symptoms, reduction of the risk of further injury, and successful return to the workplace. An injury at work precipitates an earlier-than-planned retirement in up to 11% of workers and correlates with preinjury dissatisfaction with their job or medical care and poor physical and mental health status.59 Successful return to work is enhanced by rehabilitation that emphasizes improved flexibility, increased aerobic fitness, strengthening, education on fall prevention and lifting techniques, and early return to the worksite.60 Older workers in general may be more likely to return to their previous employments because of their longer workplace attachment.61 Meanwhile, various return-to-work factors are under the control of employers. Employers who are deemed rigid, inflexible, and nonsupportive are less likely to see their older workers return.62 Employer policies that promote shared governance between unions and management with emphasis on joint safety programs and appropriate workplace modifications will provide more accommodating environments for worker return.63 Employers who value experience and transition workers to more supervisory roles may also realize greater retention of older workers.