Low Back Pain
Last updated: November 4, 2014
ICD-9 Codes: Low back pain, 724.5; cervical OA, 721.0; neck pain, 723.1; lumbosacral OA, 721.3; degenerative disc disease, 722.6; lumbosacral strain, 846.0; herniated intervertebral disc, 722.2.
Definition: Low back pain is the most common acute musculoskeletal complaint in general practice. Although acute or episodic low back pain will affect as much as 75% of the adult population, most cases will resolve and ~10% of patients will develop chronic low back pain. The societal ramifications of low back pain are enormous, in terms of disability, psychosocial impact, and legal implications. It has been estimated that the total annual costs related to patients with low back pain exceed $24 billion.
Anatomic Considerations: Back pain can derive from many structures in the area of the lower back, including joints, bursae, ligaments, nerves, tendons, muscles, and bone/cartilage (Table 23).
Etiology: Inciting stimuli for pain in these structures can include acute trauma, repetitive trauma, degeneration, inflammation, bony hypertrophy, infection, and tumor. In ~90% of patients with low back pain, the etiology relates to a mechanical or degenerative cause; 10% have pain associated with a systemic illness. Inflammatory low back pain is a small subset of those with chronic low back pain but is distinguished by onset age of 15 to 30 years, pain that is usually worse in the morning or in the middle of the night, pain that is improved by activity, and elevated ESR or CRP levels.
Demographics: Overall, low back pain is second only to upper respiratory ailments as the most common reason why patients seek medical attention. Low back pain is most prevalent in persons between 45 and 64 years of age. The annual incidence of low back pain is ~5%. Moreover, between 60% and 85% of the population experience this symptom at some time in their lives.
|Table 23: Differential Diagnosis of Back Pain|
|Soft tissue injury (affecting ligaments, muscles, and other nonosseous structures)|
|Myofascial pain (injury sometimes referred to as sprain)|
|Often secondary to trauma or overuse (mechanical pain)|
|Arthritis (e.g., affecting facet, uncovertebral, sacroiliac joints)|
|Osteoarthritis (with or without osteophyte formation)|
|Intervertebral disc disease|
|Herniation (of the nucleus pulposus)|
|Neurologic/spinal cord injury|
|Cauda equina compression syndrome|
|Radicular (nerve root) entrapment (sciatica)|
|Infection (meninges, epidural space)|
|Lumbosacral bone disease|
|Spondylosis, spondylolysis, spondylolisthesis|
|Diffuse idiopathic skeletal hyperostosis|
|Osteoporosis (with compression fracture)|
|Infections (vertebral body)|
|Pelvic bone disease|
|Insufficiency fractures (e.g., sacral) caused by trauma or osteoporosis|
|Abdominal/pelvic sources of pain|
|Piriformis syndrome (pain from the piriformis muscle)|
Evaluation: The primary objective in the assessment of a patient with low back pain is to make a timely diagnosis, relieve pain, and return the patient to regular activity as soon as possible. Also, it is important to identify the uncommon, but serious, causes of low back pain, including the cauda equina syndrome, abdominal aortic aneurysm, fracture, infection, or tumor (“red flag” conditions).
Because most patients with low back pain have a readily discernable cause, the workup need not be extensive. Generally, a history focusing on recent overuse, strain, or trauma will identify the inciting cause. In concert with a focused physical examination, this will also frequently identify the involved pathology. A thorough neurologic examination is often indicated because it not only might help define the severity of the problem but may also provide some guidance for optimal therapy. In unusual cases or in patients without a clear inciting cause, a history and physical examination looking for systemic conditions associated with back pain (e.g., infection, tumor, autoimmune disease) are indicated.
Cardinal Findings: In the vast majority of patients with low back pain, the pain originates in muscles, ligaments, or other soft tissues as opposed to bones or joints. The pain may occur acutely, with stress or related to excess lifting or turning. In addition, many patients experience similar symptoms recurrently or chronically, sometimes with minimal exertion. Patients with myofascial pain uncomplicated by spine or nerve involvement should have a normal neurologic examination. They may report tenderness on palpation of the paraspinous muscles, and a good deal of the pain probably derives from continuous contraction (spasm) of the paraspinous musculature. Several factors may predispose patients to development of myofascial injury, including occupational factors (work that requires repetitive lifting in the forward bent and twisted position), exposure to vibrations, deconditioning, obesity, and poor posture. Psychologic factors such as job dissatisfaction and depression are often associated with chronic low back pain. Variations in spinal posture such as scoliosis do not appear to increase the risk of low back pain.
Several joints in the lumbosacral spine and pelvis may be involved in low back pain. These joints can be affected by inflammatory (e.g., RA, AS) or, more commonly, by degenerative arthritis of the spine. However, radiographic changes consistent with OA are quite common, particularly with advancing age. Many patients with radiographic evidence of OA are asymptomatic, and even in patients with low back pain, finding degenerative arthritis on x-ray does not establish it as the source of pain in a given patient.
The intervertebral disc may be a source of low back pain. Classically, patients with discogenic pain have increased pain with maneuvers that increase intraabdominal pressure (e.g., Valsalva maneuver, coughing, laughing). In addition, in contrast to spinal stenosis, patients may find relief by walking around. Degeneration of the intervertebral disc is common with aging. Tears of the circumferential annulus fibrosus may allow herniation of the central nucleus pulposus. Mild bulging or protrusion of the disc into the spinal canal is common and can be demonstrated in approximately half of asymptomatic normal persons by sensitive techniques such as MRI. Therefore, demonstration of such findings does not prove that the disc is the source of the pain.
Patients with arthritis (particularly with bony spur formation), disc disease, and other pathophysiologic changes may have impingement on the spinal cord or nerve roots and consequent neurologic symptoms. If such lesions are central, they may cause spinal stenosis. More commonly, bony spurs near the neural foramina impinge on the exiting nerve root, resulting in radiculopathy. Depending on the severity, impairment of neurologic function may be demonstrable. Radicular pain originating in the lower lumbar nerve roots is commonly known as sciatica.
Sciatica, defined as pain that radiates from the gluteal region and down the posterolateral leg below the knee is often associated with mechanical impingement of nerve. Sciatica may be exacerbated by flexion or extension. Lumbar flexion- or sitting-induced pain may be caused by a herniated intervertebral disc (often involving L5 or S1 nerve roots). Extension- or standing-induced pain may be related to spinal stenosis. Both forms of sciatica should be treated with conservative measures, NSAIDs, and muscle relaxants. If these are ineffective, epidural injection with corticosteroids may be helpful.
Low back pain associated with anterior thigh (with or without groin) pain may be caused by hip disease, inguinal hernia, femoral neuropathy, tumor, aortic aneurysm, kidney disease, or retroperitoneal fibrosis. Anterior thigh pain may imply involvement of nerve roots L1-3 (see Dermatomal Map).
Low back pain associated with posterior thigh pain (above the knee) may be caused by lumbosacral strain or a herniated lumbar disc (usually L3-4).
Cauda equina syndrome is an uncommon and serious cause of low back pain and may be suggested by findings of incontinence and saddle anesthesia (e.g., cauda equina syndrome). Tumor may be suggested by fever, weight loss, or pain exacerbated by sleep or recumbency. Fracture may manifest as focal bone pain worsened by manual pressure or standing.
Diagnostic Testing: Laboratory testing is seldom needed to determine the cause of low back pain. ESR or CRP may provide nonspecific evidence of a systemic, inflammatory, or infectious process. HLA-B27 is only needed if a spondyloarthropathy is suspected
Imaging: Radiographs are not routinely recommended because of their low yield (i.e., most patients with low back pain do not have conditions visible on radiographs as the cause) and low specificity (as above, many older patients have findings of OA that may be of no consequence). Radiographs should be obtained if there is history of serious trauma, suspicion of malignant disease, suspicion of infection or fracture, or neurologic deficit. If abnormalities are seen on plain films, tomograms or CT scans may give further delineation. If neurologic impairments are suspected (e.g., spinal stenosis), MRI may be the imaging procedure of choice because it allows definition of bone, nerve, and soft tissue.
Therapy: Historically, patients with low back pain were put at strict bed rest for several weeks to rest the affected structures. However, more recent studies have shown that most patients with acute back pain do as well with continuing ordinary activities as well as bed rest or back-mobilizing exercises. No more than 2 days of bed rest is advised and should be followed by progressive mobilization and exercise. Treatment of back pain often involves several modalities. Local pain may respond well to cold or warm compresses and should be determined by patient preference. Many patients respond to NSAIDs or simple analgesics, such as acetaminophen. More potent analgesics such as narcotics may be necessary in the acute setting. However, many patients have chronic symptoms, and such agents must be used with caution. Because muscle spasm may be an important contributor to the pain, muscle relaxants are sometimes useful adjuncts. Spinal manipulation is effective for some patients. Although there has been anecdotal support for the analgesic efficacy of electrical stimulation (transcutaneous electrical nerve stimulation units), controlled trials have not shown it to be beneficial. Chronically, back-strengthening exercises may be of some value. Although they are widely used, lumbar belts have not been proven to be of benefit. Surgery is rarely indicated and should be reserved for those proven to have tumor, infections, fractures, or dislocations.
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