Mechanical Back Strain

Etiology

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 spine's anatomy. 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[3]: 

• Spinal foraminal stenosis
• Herniated discs
• Spinal stenosis
• Degenerative disc disease
• Vertebral fractures
• Sacroiliac joint dysfunction
• Facet joint syndrome
• Ligamentous and muscular injury
• Myofascial pain syndrome

Epidemiology

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. Due to missed workdays and decreased wages, 100 to 200 billion dollars are estimated to be spent each year in the United States due to lower back pain.[2][4]

History and Physical

Obtaining a complete history and performing an in-depth physical exam is crucial to diagnosing mechanical back strains. The goal of evaluation in the acute setting is to ensure no red flags 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, history of cancer, anticoagulant use, chronic systemic steroid use, intravenous drug abuse, or an immunocompromised state. Physical exam red flags compromise assessing focal neurologic deficits, including weakness, ataxia, saddle anesthesia, decreased deep tendon reflexes and diminished rectal tone.[3][5]

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.[1][6]

Evaluation

In the absence of the red flags discussed above, no laboratory or radiographic studies are necessary to diagnose or manage mechanical back strains in the acute setting. Inflammatory biomarkers, such as erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP), are useful for risk stratification of patients with 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 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 an accurate diagnosis.[3][5][7]

Treatment / Management

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. According to low-quality evidence, the use of acetaminophen and systemic corticosteroids showed no improvement of acute back pain compared to placebo. 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 the American College of Emergency Physicians, opioids should not be routine pharmaceutical therapy but should be saved for those whose pain is severe or uncontrolled with other medications.[8][9](A1)

Physical therapy is an integral component in the treatment of mechanical back pain. When initial conservative measures fail, a referral is appropriate. Studies have shown that early physical therapy intervention, when compared to the implementation of physical therapy after lower back pain was chronic, resulting in a reduction in healthcare costs, a decrease in opioid use, and a reduction in spinal surgery rates.[10][11](A1)

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.[8](A1)

The American Pain Society also 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.[12](A1)

Differential Diagnosis

The differential diagnoses for mechanical back strains are other nonmechanical causes of back pain. These include but are not limited to the following categories and diseases[1][5][13]: 

• Rheumatologic - ankylosing spondylitis, Reiter syndrome, psoriatic spondylitis, polymyalgia rheumatica   
• Oncologic - metastatic disease, spinal cord tumor, lymphomas, leukemia, multiple myeloma 
• Infectious - spinal epidural abscess, osteomyelitis, discitis 
• Gastrointestinal - pancreatitis, cholecystitis, bowel perforation 
• Vascular - aortic aneurysm, spinal epidural hematoma, aortoiliac disease
• Renal - pyelonephritis, nephrolithiasis, perinephric abscess
• Genitourinary - endometriosis, prostatitis, pelvic inflammatory disease

Prognosis

While most 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.[2][8] 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 demands, job dissatisfaction, and the presence of compensation.[1][3][6]

Complications

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 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 workdays.[1][8]

5% to 10% of adults with low back pain develop chronic pain. Recurrence of low back pain occurs in 20 to 72% of patients. In adults with low back pain severe enough to cause them to miss work, 60 to 70% return to work by 6 weeks, and 80 to 90% return by 12 weeks.