Does the patient have sciatica or another nerve root compression syndrome?
The obvious manifestation of nerve root irritation is usually sciatica, a sharp or burning pain radiating down the posterior or lateral aspect of the leg usually to the foot or the ankle and often associated with numbness or paresthesias. The pain is sometimes aggravated by coughing, sneezing, or the Valsalva maneuver. It is most commonly seen in lumbar disk herniation, cauda equina syndrome, and spinal stenosis.
Might the patient have spinal stenosis?
More than 20% of people over age 60 have radiographic evidence of lumbar spinal canal stenosis, even if they have no symptoms.5 For this reason, the diagnosis of spinal stenosis as a cause of low back pain must be based on the history and physical examination.
The classic history of spinal stenosis is that of neurogenic claudication (“pseudoclaudication”), which is pain that occurs in the legs after walking or prolonged standing and is relieved with sitting. It may sometimes be associated with a varying and transient neurologic deficit. Lumbar flexion increases and lumbar extension decreases the cross-sectional area of the spinal canal—hence, the relief of symptoms of spinal stenosis on stooping or bending forward. Pain is commonly perceived in the back, buttock, or thigh and is elicited by prolonged lumbar extension.
On neurologic examination, about 50% of patients with spinal stenosis have a deficit in vibratory sensibility, temperature sensitivity, or muscle strength. The nerve root involved is most commonly L5, followed by S1 and L4.
Many patients have balance disturbance (wide-based gait or Romberg sign), particularly later in the course of the disorder, with normal cerebellar signs (“pseudocerebellar” presentation).
Patients with bilateral hip osteoarthritis may present with similar symptoms of buttock or thigh pain, which can be distinguished with the above clinical examination. Rotation of the hip is painful in osteoarthritis but not in spinal stenosis. If both conditions overlap, injection of a steroid or lidocaine in the painful hip should decrease the pain associated with hip osteoarthritis.
Does the patient have evidence of neurologic compromise?
Muscle strength is tested by examining the:
- L2 nerve root (which supplies the iliopsoas muscle and is tested by hip flexion)
- L3 nerve root (quadriceps, tested by knee extension)
- L4 nerve root (tibialis anterior, assessed by evaluating ankle dorsiflexion and inversion at the subtalar joint)
- L5 nerve root (extensor hallucis longus and extensor digitorum longus, tested by asking the patient to dorsiflex the great toe, then the other toes)
- S1 nerve root (flexor hallucis longus, flexor digitorum longus, and tendoachilles, tested by asking the patient to plantar-flex the great toe, then the other toes, and then the ankle).
The patient is also asked to walk a few steps on the toes and then on the heels. Inability to toe-walk indicates S1 nerve root involvement; inability to heel-walk may indicate L4 or L5 involvement. If the patient cannot heelwalk, ask him or her to squat; inability to do so indicates L4 problems.6
Radiculopathy. Detecting and locating the cause of radiculopathy may be helpful. In L3–L4 disk herniation, there is pain and paresthesia with numbness and hypalgesia in the anteromedial thigh and the knee. In L4–L5 disk herniation, there is usually involvement of the exiting L5 nerve root, which presents as numbness or paresthesias in the anterolateral calf, great toe, first web space, and medial foot. In L5-S1 disk herniation, the S1 nerve root is involved, presenting as numbness and hypalgesia in the fifth toe, lateral aspect of the foot, sole, and posterolateral calf and thigh.
Reflexes. Exaggerated or decreased reflexes do not always indicate a neurologic abnormality, but reflex asymmetry is significant. The knee-jerk reflex is diminished in L3–L4 nerve root involvement, and the ankle-jerk reflex is diminished with S1 nerve root involvement. The Babinski sign indicates pyramidal tract involvement.
Gait. Observe the patient’s gait as he or she rises and moves to the examining table, to determine whether it is shortened, asymmetrical, or antalgic.7 Also note any foot drop, which may indicate a potentially serious problem (L5 radiculopathy).
What is an adequate examination of the back?
A good back examination can elicit important information about the cause and the extent of back pain. It includes inspection, palpation, and range of movement of the spine along with a detailed neurologic examination.
Inspect it for any deformities, scoliosis, asymmetry, paraspinal muscle spasm, unusual hair growth, listing to one side, decrease or increase in lumbar lordosis, or muscle atrophy or fasciculation.
Palpate it for paraspinal muscle spasm, warmth, and localized bone pain.
Move it. The normal ranges of motion of the lumbar spine are 15 degrees of extension, 40 degrees of flexion, 30 degrees of lateral bending, and 40 degrees of lateral rotation to each side.
Assess it. This includes estimating the tone and nutrition of the muscles, testing their strength (Table 2), examining vibratory or proprioception and pinprick sensation in each dermatome (see below), testing the Achilles and patellar reflexes, and looking for the Babinski sign and clonus. In addition, perform the straight-leg-raising and the cross-straightleg-raising tests, which are positive in most patients with lower lumbar disk herniations.
The femoral stretch test is usually positive in upper lumbar disk herniations (L2–L3, L3– L4). It is performed with the patient in the prone position, with the knee being gradually flexed from full extension. Pain radiating along the anterior aspect of the thigh indicates a positive test.
The examination of the spine must be supplemented with examination of the hip and sacroiliac joints, since back pain may be a referred symptom from any pathology affecting these joints.