Definition

Lumbar radiculopathy refers to a pathologic process involving the lumbar nerve roots. Lumbar radiculitis refers to an irritation or inflammation of a nerve root. These terms should not be confused with disc herniation, which is a displacement of the lumbar disc from its anatomic location between the vertebrae (often into the spinal canal) (Fig. 47.1). Although lumbar radiculopathy is often caused by a herniated lumbar disc, this is not invariably the case. Many pathologic processes, such as bone encroachment, tumors, and metabolic disorders (e.g., diabetes), can also result in lumbar radiculopathy. It is of utmost significance that disc herniation is often an incidental finding on imaging of the lumbar spine of asymptomatic individuals [1,2]. Therefore, without a clear correlation with the history and physical examination, imaging studies alone can be more misleading than beneficial. When disc herniation results in radiculopathy, the precise cause of the pain is not fully understood. The two possibilities are mechanical compression and inflammation. It has been demonstrated that in a “nonirritated” nerve, mechanical stimulus rarely leads to pain. In contrast, an “irritated” nerve usually results in pain. Furthermore, inflammatory mediators have experimentally been shown to cause radicular pain in the absence of compression [3–5]. It is likely that both factors may be at work individually or together in any given patient. As a result of the imaging findings in asymptomatic individuals and the various causes of pain in radiculopathy, it should be no surprise that disc herniations and nerve root compression can be present in asymptomatic patients [2] and that patients can have radiculopathy without visible disc herniations or nerve root compression [6].

The prevalence of lumbar radiculopathy in the general population varies from 2.2% to 8%, depending on the study, and the incidence ranges from 0.7% to 9.6% [7,8]. One study found a higher incidence in men (67%), with the highest prevalence in individuals 45 to 65 years old [9], and an association with obesity and smoking as well as a correlation with occupations requiring very heavy physical activity.

Symptoms

The most common symptom in lumbar radiculopathy is pain, which may vary in severity and location. The pain may be severe and is often exacerbated or precipitated by standing, sitting, coughing, and sneezing. The location of the pain depends on the nerve root involved, with a great deal of overlap among the dermatomes. Most commonly, S1 radiculopathy produces posterior thigh and calf pain; L5, buttocks and anterolateral leg pain; L4, anterior thigh, anterior or medial knee, and medial leg pain; and L3, groin pain. The patient usually cannot pinpoint the precise onset of pain. Location of pain at onset may be in the back; however, by the time the patient is evaluated, the pain may be present only in the buttocks or limb.

Paresthesias are also common and occur in the dermatomal distribution of the involved nerve root (rarely is the sensory loss complete). On occasion, the patient may present with complaints of weakness. Rarely, there is bladder and bowel involvement, which may be manifested as urinary retention or bowel incontinence.

Physical Examination

The most important elements in the evaluation of lumbar radiculopathy are the history and physical examination [10].

A thorough musculoskeletal and peripheral neurologic examination should be performed. Examine the back for asymmetry or a shift over one side of the pelvis. Evaluate back motion and see whether radicular symptoms (pain radiating to an extremity) in the distribution of the patient’s complaints are produced. In an L5 or S1 radiculopathy, forward flexion of the back while standing is equivalent to a straight-leg raising test and may produce pain in the buttock or posterior thigh. In an L4 or L3 radiculopathy, extension may produce groin or anterior thigh pain.

Manual muscle testing is a vital part of the examination for radiculopathy. The major muscle weakness in relation to the nerve root involved is as follows: L3, hip flexors; L4, knee extensors and hip adductors; L5, hip abductors, knee flexors, ankle dorsiflexors, foot evertors, foot inverters, and great toe extensor; S1, ankle plantar flexors (Table 47.1). Try to detect weakness in the distribution of two peripheral nerves arising from the same nerve root. Proximal muscle weakness in the appropriate nerve root distribution is useful in distinguishing bilateral radiculopathy from peripheral neuropathy.

The straight-leg raising test can be performed with the patient sitting or supine. The leg is raised straight up by the examiner, and the test result is positive if the patient complains of pain in the extremity (not the back), typically in a specific nerve root distribution. If pain occurs only in the back, this is not an indicator of radiculopathy and is most often seen with nonspecific low back pain. On occasion, the process of lumbar radiculopathy may start with low back pain, and several days or weeks later, the symptom will occur in the leg. It is possible that the initial process of nucleus pulposus rupture through the anulus may result in the initial back pain, but the pathogenesis is not completely known at this time. Compare side to side to confirm a positive response to the straight-leg raise as opposed to the pain associated with passive hamstring stretch. Rectal examination and perianal and inguinal sensory testing should be done if there is history of bowel or bladder incontinence or retention or recent onset of erectile dysfunction.

Waddell signs are a group of indicators that a nonorganic process is interfering with the accuracy of the physical examination. The signs are superficial—nonanatomic tenderness; simulation—axial loading or rotation of the head causes complaints of back pain; distraction—sitting straight-leg raising versus supine; regional disturbance—weakness or sensory loss in a region of the body that is in a nonanatomic distribution; and overreaction—what is described commonly as excessive pain behavior. These signs are often present in patients with compensation, litigation, or psychoemotional issues [11]. Evaluation for presence of Waddell signs should be a routine part of the examination in patients with pain complaints, particularly if they are long-standing or the history reveals that some of these issues are present.

Functional Limitations

The functional limitations depend on the severity of the symptoms and weakness. Limitations usually occur because of pain but may occasionally occur because of weakness. Standing and walking may be limited, and sitting tolerance is often decreased. Patients with an L4 radiculopathy are at risk of falling down stairs if the involved leg is their “trailing” (power) leg on the stairs. They would also have difficulty ascending stairs or rising from a seated position, depending on the degree of weakness (although that is not as dangerous as descending stairs). Patients with a severe S1 radiculopathy will be unable to run because of calf weakness, even when the pain resolves. Patients with L5 radiculopathy may catch the foot on curbs or, if weakness is severe, on the ground. They may require a brace (ankle dorsiflexion assist). In patients with acute radiculopathy that is severe, the pain will usually preclude them from a whole range of activities—household, recreation, and work. In the majority of patients, once the acute process is ameliorated, they can return to most activities except for heavy household and work activity. After about 3 to 6 months, they can return to all activities unless there is residual weakness, in which case they would be functionally limited as noted before, depending on the radiculopathy level.

Diagnostic Studies

Diagnostic testing takes two forms: one to corroborate the diagnosis and the second to determine the etiology. For simple cases, despite the current “rush toward imaging,” diagnostic testing is usually not needed and the clinical picture can guide the treatment. A history that includes trauma, cancer, bacterial infection, human immunodeficiency virus infection, or diabetes would be an indication for earlier diagnostic testing.

Electromyography

Electromyography and nerve conduction studies, when performed by an individual well versed in the diagnosis of neuromuscular disorders, can be valuable in the diagnosis of lumbar radiculopathy. They can also help with differential diagnoses and in clarifying the diagnosis in patients whose physical examination is not reliable. Electromyography has the advantage over imaging techniques of high specificity, and recordings will rarely be abnormal in asymptomatic individuals [12]. Electrodiagnostic studies, however, do not give direct information about the cause of the radiculopathy.

Imaging

Imaging techniques in relation to lumbar radiculopathy usually refer to lumbosacral spine radiography, computed tomography (CT) scan, and magnetic resonance imaging (MRI).

Plain radiography can be useful to exclude traumatic bone injury or metastatic disease. It allows visualization of the disc space but not the contents of the spinal canal or the nerve roots. CT and MRI allow visualization of the disc, spinal canal, and nerve roots (Fig. 47.2). There is a high incidence of abnormal findings in asymptomatic people, with rates of disc herniation ranging from 21% in the 20- to 39-year age group to 37.5% in the 60- to 80-year age group [2