Back pain is one of the most common chief complaints in the emergency department. It is also a leading cause of disability and high healthcare expenses globally as it affects patients of all ages and backgrounds. Mechanical back strain is a subtype of back pain where the etiology is the spine, intervertebral discs, or the surrounding soft tissues. While the majority of cases of mechanical back strains that present to the emergency department can be managed conservatively, healthcare providers must be aware of the common red flags that signal more emergent causes of back pain and that are associated with high morbidity and mortality when the diagnosis is delayed.
Historically, references to mechanical back pain have used many other vague terms like "non-specific back pain," "lumbar strain," or "lumbago." This terminology was due to the absence of proper diagnostic methods in the past. However, more recent advances in imaging technology and a better clinical understanding of spinal anatomy and the body's innervation have allowed more accurate terminology and diagnoses, depending on the underlying cause. Hence, more specific diagnoses are made based on the etiology of mechanical back strain, which is typically due to pathology involving the anatomy of the spine. While the lower back is usually affected the most, mechanical back pathology may involve any part of the bones, spinal ligaments, intervertebral discs, facet joints, spinal cord, spinal nerves, or paraspinal muscles. Common examples of pathology involving these structures include the following diseases :
Greater than 80% of people will suffer from low back pain during their lifetime. The global point prevalence of low back pain is 12 to 33%. There is a higher prevalence among women and people ages 40 to 80 years old. Due to missed work days and decreased wages, 100 to 200 billion dollars are estimated to be spent each year in the United States due to lower back pain.
Obtaining a complete history and performing an in-depth physical exam is crucial to the diagnosis of mechanical back strains. The goal of evaluation in the acute setting is to ensure there are no red flags that warrant more advanced imaging and surgical consultation. These red flag symptoms include fevers, involuntary weight loss, night sweats, bladder or bowel incontinence, significant trauma, frequent falls, and history of cancer, anticoagulant use, chronic systemic steroid use, intravenous drug abuse, or an immunocompromised state. Physical exam red flags compromise assessing for focal neurologic deficits, including weakness, ataxia, saddle anesthesia, decreased deep tendon reflexes, and diminished rectal tone.
Acute mechanical back strains may be triggered by physical or non-physical activity, with lifting being the most commonly recalled event. However, one-third of patients may not necessarily remember an inciting incident. More specific spinal pathology may have classically associated symptoms. For example, herniated discs will present with radicular pain that radiates from the lower back in L4 to S1 distribution, and pain may be reproducible to the affected side on straight leg raise. Spinal stenosis may demonstrate back pain and bilateral posterior leg pain that worsens with ambulation and spine extension but is relieved by rest and spine flexion. Patients on chronic steroids or at risk for osteoporosis are at increased risk for vertebral compression fractures even after seemingly minor trauma. Compression fractures tend to be focally tender on palpation.
In the absence of the red flags discussed above, no laboratory or radiographic studies are necessary for the diagnosis or management of mechanical back strains in the acute setting. Inflammatory biomarkers, such erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP), are useful for risk stratification of patients who have risk factors for infectious spinal pathology or malignancy but have no neurologic deficits on examination. Routine imaging for mechanical back strains is not recommended, as many may have incidental abnormal findings that are unrelated to their pain. More advanced imaging is needed in the setting of trauma, failure of conservative management, worsening of symptoms, and new neurologic deficits. Plain radiographs and computed tomography are useful when suspecting fractures. However, patients with signs of spinal cord compression or red flag symptoms need magnetic resonance imaging for making the diagnosis.
Management of mechanical back strains depends on the chronicity of symptoms, the patient's comorbidities, and the specific etiology. The American College of Physicians published an updated guideline in 2017 with recommendations regarding non-invasive options for treating low back pain. First-line nonpharmacologic therapy for acute low back pain includes spinal manipulation, acupuncture, massage, and superficial heat application, while first-line pharmacologic therapy for acute low back pain is nonsteroidal anti-inflammatory drugs and muscle relaxants. The use of acetaminophen and systemic corticosteroids showed no improvement of acute back pain when compared to placebo according to low-quality evidence. There was insufficient evidence to determine the benefits of other pharmacologic agents, such as benzodiazepines, antidepressants, antiepileptic medications, and opioids. According to the clinical policy by American College of Emergency Physicians, opioids should not be routine pharmaceutical therapy but saved for those whose pain is severe or uncontrolled with other medications.
For chronic low back pain, non-pharmacologic approaches were recommended as the first-line agents, including exercise, tai-chi, yoga, multidisciplinary rehabilitation, spinal manipulation, acupuncture, psychotherapy, low-level laser therapy, and electromyogram biofeedback. Nonsteroidal anti-inflammatory drugs were again the first-line pharmacologic agents recommended followed by tramadol and duloxetine as the second-line treatments. Recommendations for opioid therapy are only if the previously mentioned therapies failed and based on an individualized decision to determine if the benefit outweighs the risk.
The American Pain Society also has published recommendations by a multidisciplinary panel in 2009 regarding the use of more invasive procedures for diagnostic and therapeutic purposes to treat non-radicular low back pain, radicular low back pain, and spinal stenosis. The panel emphasized the use of intensive interdisciplinary rehabilitation for chronic non-radicular low back pain, as it has similar efficacy to fusion surgery. Epidural steroid injection showed variable evidence of short-term benefit for radicular low back pain; thus, the panel recommended a shared decision-making process for the appropriate patient.
For surgical management options, standard open discectomy and microdiscectomy have a moderate short-term benefit in treating persistent, debilitating radiculopathy secondary to herniated disc disease. Similarly, decompressive laminectomy has a moderate short-term benefit in treating severe, debilitating spinal stenosis. The panel noted that these benefits tend to decrease over time, and a shared decision-making process is also appropriate in these patients before surgical intervention. Lastly, spinal cord stimulation may be an option for patients who underwent surgery for herniated disc disease but continue to have debilitating radiculopathy.
While the majority of acute episodes of mechanical back pain resolve spontaneously within 12 weeks, up to one-third of patients may continue to have chronic symptoms. However, even those whose acute symptoms resolve have a 20 to 40% chance of symptom recurrence during the first year and 85% of lifetime recurrence. Various environmental and psychosocial factors may influence the prognosis of mechanical back strains. These include a body mass index greater than 25, smoking, poor health, depression, fear avoidance, strenuous work demand, job dissatisfaction, and presence of compensation.
The possible complications of mechanical back strains depend on the specific etiology, with the most common complication being the persistence of symptoms and the development of lasting disability. Rarer physical complications include cauda equina syndrome and physical deformities. Other health complications may arise as side effects from long-term pharmacologic therapies, such as NSAID use, or from more invasive therapeutic procedures, such as injections and surgeries. Many financial and social complications also exist for both the patients with chronic, disabling mechanical back pain and their employers due to lost wages and missed work days.
Reduction of strenuous physical requirements is the main primary prevention for mechanical back strains; however, secondary prevention rather than primary prevention is more practical due to the high prevalence of the condition and since the greatest risk factor is the recurrence of a previous episode. Some interventions by employers that may aid in injury prevention are stretching exercises at the workplace, appropriate rest breaks, and ergonomic modifications. Ergonomic modifications refer to adaptations in the work environment to reduce the physical stress of the employees. Also, educating patients regarding the importance of maintaining proper posture and correct lifting techniques may also aid in prevention. Other prevention techniques that can be used by patients aim at reducing the risk factors of having a poor prognosis, including exercising, smoking cessation, weight loss for obese patients, and resuming normal physical activity.
Healthcare professionals of many specialties are involved in providing care for patients with mechanical back strains. Physicians and nurses, especially in the acute setting, must be familiar with red flag symptoms of back pain that may require more urgent interventions and possible surgical consultation. Conservative management of acute mechanical back strains after a complete assessment is reasonable as the course is usually self-limited; this includes superficial heat, nonsteroidal anti-inflammatory drugs, and muscle relaxants. [Level II]
Chronic mechanical back strains require an interprofessional approach due to the psychosocial factors involved. Initial non-pharmacologic therapy includes exercise, an interprofessional rehabilitation, manipulation, and acupuncture. First-line pharmacologic therapy is nonsteroidal anti-inflammatory drugs followed by duloxetine or tramadol as second-line therapy. [Level II] Patients with persistent disabling chronic non-radicular low back pain may benefit from interprofessional rehabilitation, described as rehabilitation along with a psychological, social, or occupational component. Patients with persistent chronic radicular pain due to herniated discs or spinal stenosis may benefit from surgical interventions. [Level I]
Mechanical back pain requires an interprofessional team approach, including physicians, specialists, specialty-trained nurses, physical therapists, chiropractors, and pharmacists, all collaborating across disciplines to achieve optimal patient results. [Level V]
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