Low Back Pain

Hallett H. Whitman III

Daniel J. Clauw

John F. Beary III

KEY POINTS

Low back pain (LBP) is the second most common condition seen in primary care practice, and the most common problem seen by musculoskeletal specialists. It is essential that physicians be comfortable with the nuances of diagnosis and treatment of LBP.
Less common causes of LBP such as infection (fever and focal pain) and cancer (weight loss, unexplained pain, and oncologic risk factors) must not be overlooked. If the pain persists and is unexplained, then the case must be investigated further.
Magnetic resonance imaging (MRI) images have a 30% false-positive rate, and therefore must be used in a discriminating manner. Remember that most patients with acute LBP and without neurologic signs and symptoms will respond to conservative therapy, and need no diagnostic tests.
Prolonged bed rest is harmful. An extended period of inactivity is a risk factor for converting acute LBP into chronic LBP. Start an appropriate regimen of exercise as soon as possible to preserve strength and flexibility in the muscles that support the lumbar spine.
Sensitization of peripheral or central pain processing systems will explain some cases of chronic LBP that persist despite the correction of the anatomical factors. Therefore, the first 3 to 6 months
of assessment and treatment of patients with LBP are critical with regard to preserving and optimizing function of the lumbar spine.

INTRODUCTION

Low back pain (LBP) can affect up to 80% of the population at some point in their lives, making it second only to the common cold as an illness affecting the general population, and the fourth or fifth most common reason for a visit to the physician’s office in the United States.
Acute LBP usually resolves spontaneously, but up to 10% progress to chronic LBP resulting in temporary or permanent disability. This results in a loss of more than 1,000 work days per 1,000 workers each year, costing more than $20 billion annually, and disabling several million individuals in the United States alone at any one time.
Risk factors for the development of LBP include heavy manual work, poor job satisfaction, exposure to vibration, cigarette smoking, and pregnancy. A sedentary lifestyle is also probably a cause.
Most patients with acute and chronic LBP have “idiopathic” LBP, meaning that despite testing, no clear cause can be found for their pain.
Most patients who present with acute LBP in the absence of significant neurologic physical findings need no diagnostic tests and will respond to conservative management.
Patients who do not respond to a conservative regimen may need imaging studies, and rarely surgery.

ETIOPATHOGENESIS

Any of the components of the lumbosacral spine when combined with related conditions listed in the subsequent text may be responsible for LBP.

VERTEBRAL BODY (fracture, osteoporosis, metastatic disease, sickle cell disease, and infection).
INTERVERTEBRAL DISC (herniation and infection).
JOINTS (osteoarthritis and ankylosing spondylitis).
- Apophyseal joints.
- Sacroiliac joints.
LIGAMENTS (strain and rupture).
- Anterior and posterior longitudinal ligaments.
- Interspinous and supraspinous ligaments.
- Iliolumbar ligaments.
- Apophyseal ligaments.
NERVE ROOTS (herniated nucleus pulposus and spinal stenosis).
PARASPINAL MUSCULATURE (strain and spasms).
PAIN FROM ADJACENT STRUCTURES (referred pain).
- Kidney (pyelonephritis and perinephric abscess).
- Pelvic structures (pelvic inflammatory disease, ectopic pregnancy, endometriosis, and prostate disease).
- Vascular (aortic aneurysm and mesenteric thrombosis).
- Intestinal (diverticulitis).
PAIN AMPLIFICATION SYNDROMES where there is no identifiable abnormality of the peripheral tissue, but there is localized or widespread hyperalgesia (e.g., myofascial pain and regional forms of fibromyalgia).

PREVALENCE

Prevalence of LBP ranges from 38 to 93 per 1,000 population, with female sex, white ancestry, and increasing age being independent risk factors for increased incidence.

CLINICAL MANIFESTATIONS

Clinical history of the patient is of great importance in obtaining information regarding associated symptoms and establishing a pattern of pain. A thorough review of symptoms that would suggest a nonmechanical cause for LBP is required.
- Fever or chills would raise the possibility of an infectious process.
- Weight loss, chronic cough, change in bowel habits, or night pain may suggest malignancy.
- Similar pain or morning stiffness in different areas of the body would increase the suspicion of a more generalized rheumatic condition such as ankylosing spondylitis, psoriatic arthritis, or reactive arthritis (ReA).
- If fatigue or sleep disturbance is present, in the setting of a diffuse pain syndrome, the diagnosis of fibromyalgia should be considered.
- Morning stiffness or back pain that improves with exercise should prompt consideration of a spondyloarthropathy such as ankylosing spondylitis.
PAIN. The quality of pain, its distribution, and modulating factors are helpful in determining etiology.
- Onset of pain
  - Sudden onset especially following trauma suggests injury.
  - Indolent onset suggests a nonmechanical cause.
  - Episodic or colicky pain suggests an intra-abdominal or pelvic source.
- Localization of pain
  - Localized pain provides a focus for the diagnostic workup.
  - Radicular pain, suggesting nerve root impingement.
  - Pain that is not easily localized, migratory, or multifocal suggests fibromyalgia.
- Modulating factors
  - Exercise-induced pain, especially on walking, suggests osteoarthritis or spinal stenosis, whereas pain that improves with exercise especially following morning stiffness suggests an inflammatory process, for example, a spondyloarthropathy.
  - Valsalva maneuvers such as coughing, sneezing, or bowel movements that worsen pain suggest nerve root impingement.
NEUROLOGIC SYMPTOMS. The presence of neurologic symptoms should be specifically sought in patients with LBP. Their presence can not only help to delineate the site of the abnormality but also can prompt more rapid intervention.
- Weakness, numbness, or paresthesias in a dermatomal distribution suggests nerve root impingement (Table 20-1) (see also the dermatome figure in Appendix B).
  - The most common cause of nerve root impingement in individuals between the ages of 20 and 50 years is a herniated nucleus pulposus.
  - Radicular symptoms in individuals older than 60 are more likely to be secondary to spinal stenosis resulting from osteoarthritis.
- Bowel or bladder dysfunction suggests the presence of cauda equina syndrome and should prompt emergent investigation.
- LBP in the presence of fever and neurologic symptoms should trigger the mind to the possibility of an epidural abscess.

PHYSICAL EXAMINATION

Specific abnormalities and provocative maneuvers designed to elicit pain associated with certain syndromes should be tested for in patients with LBP.

I. PATIENT IN STANDING POSITION

Note the alignment of the spine looking for a pelvic tilt that may indicate a paravertebral spasm, for loss of normal lumbar lordosis that could indicate either spasm or ankylosis, and for evidence of structural scoliosis.

Table 20-1 Signs and Symptoms of Common Disc Lesions

Site	Pain	Sensory findings	Motor weakness	Reflexes
L3-4^a	Anterolateral thigh, medial knee	Anterolateral thigh	Knee extensors	Patellar decreased
L4-5^b	Posterior thigh, lateral calf, dorsum of foot, great toe	Posterolateral calf, dorsum of foot, web of great toe	Ankle dorsiflexors, extensor of great toe	No specific reflex change
L5-S1^c	Buttock, posterior thigh, calf, heel, ball of foot, lateral toes	Buttock, posterior thigh, calf, lateral foot, or lateral two toes	Normal or weak plantar strength of ankle	Achilles decreased
^a L3-4 disc affects the L4 nerve root. ^b L4-5 disc affects the L5 nerve root. ^c L5-S1 disc affects the S1 nerve root.