The interpretation of leg pain

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One of the most common mistakes is to assume that all leg pain is sciatica, and must be due to a disk prolapse pressing on a nerve. That is false logic. Leg pain may be nerve root pain due to a disk prolapse pressing on a root, but more often it is not. Most leg pain is not nerve root pain, and has nothing to do with a disk prolapse. There is so much confusion about the term "sciatica" that it is better not to use it. Sciatica is pain in the distribution of the sciatic nerve, but different doctors and therapists use the term differently, varying from any leg pain to a precise definition of nerve root pain. We will think and communicate more clearly if we talk about referred leg pain and nerve root pain.

It is nearly 60 years since Kellgren (1939) showed that stimulation of any of the tissues of the back can cause pain down one or both legs. Seventy percent of patients with back pain have some radiation of pain to their legs. This referred pain can come from the fascia, muscles, ligaments, periosteum, facet joints, disk, or epidural structures. It is usually a dull, poorly localized ache that spreads into the buttocks and thighs (Fig. 2.5). It may affect both legs. It usually does not go much below the knee. Referred pain is not due to anything pressing on a nerve. It is not sciatica.

Stimulation of the nerve root gives a quite different pain, which is sharp and well localized (Fig. 2.6). At the common L5 or SI levels, nerve root pain usually radiates to the foot or toes. It at least approximates to a dermatomal distribution. Patients often describe the pain with sensory qualities such as pins and needles, or numbness. It usually affects one leg only and is greater than back pain. Nerve root pain is much less common than referred leg pain.

Triage should distinguish referred leg pain from nerve root pain. You can usually make a provisional decision from the patient's description of the pain. If a patient presents with back pain alone and no leg pain or neurologic symptoms, a nerve root problem is very unlikely. There is then no need for any neurologic exam. If the patient does have leg

Figure 2.5 Referred leg pain is dull, ill-localized, and usually does not radiate much below the knee(s). From Waddell (1982), with permission.

Figure 2.6 Nerve root pain usually radiates to the foot or toes and at least approximates to a dermatome. From Waddell (1982), with permission.

Figure 2.5 Referred leg pain is dull, ill-localized, and usually does not radiate much below the knee(s). From Waddell (1982), with permission.

Figure 2.6 Nerve root pain usually radiates to the foot or toes and at least approximates to a dermatome. From Waddell (1982), with permission.

pain then you should examine the legs for signs of nerve irritation or nerve compression.

Nerve irritation and compression signs help to confirm the diagnosis of nerve root pain. Ninety-eight percent of disk prolapses are at L4/L5 or L5/S1 and affect the L5 or SI roots, and most clinical tests look at these levels. Textbooks emphasize motor, sensory, and reflex signs, but these only occur when there is actual compromise of nerve function. Nerve irritation signs are earlier and more common, and just as important for diagnosis.

Root irritation signs

Nerve irritation signs depend on tests that stretch or press on an irritable nerve root to cause root pain. The diagnostic finding is this reproduction of symptomatic nerve pain. Straight leg raising is the most widely used test for nerve irritation (Deville et al 2000) but many doctors and therapists still misinterpret it. Limited straight leg raising in itself is not a sign of nerve irritation. The key finding is not the limitation, but the reason for it. Limitation due to back pain or hamstring spasm probably has nothing to do with irritation of a nerve. The specific sign of nerve irritation is limited straight leg raising due to reproduction of nerve pain down the leg (Edgar & Park 1974; Fig. 2.7). Pain may only radiate to the thigh and not down the full length of the dermatome. Passive dorsiflexion of the foot at the limit of straight leg raising may increase the leg pain or make it radiate more distally.

Other signs of nerve irritation also depend on reproducing nerve pain. A positive cough impulse is pain down the leg, not back pain alone. The well-leg raising test or cross-over sign uses passive straight

Straight Leg Test Interpretation
Figure 2.7 The diagnostic feature of straight leg raising is reproduction of the symptomatic root pain.
Bowstring Test
Figure 2.8 The diagnostic feature of the bowstring test is reproduction of the symptomatic root pain or paresthesia.

leg raising of the painfree leg to give nerve pain in the symptomatic leg. The bowstring test is better known in North America than in Europe (Fig. 2.8). At the end of the straight leg raising test, slightly flex the knee to relieve pain. Then press your thumb on the nerve where it is bowstrung across the popliteal fossa. With an irritable nerve, you may produce pain or paresthesia radiating up or down the leg. Local pain beneath your thumb is not diagnostic.

If the pattern of pain suggests an upper lumbar nerve root, then you should also do the femoral

Figure 2.9 (A, B) The diagnostic feature of the femoral stretch test is reproduction of the symptomatic root pain.

stretch test (Fig. 2.9). The diagnostic finding of nerve irritation is again radiating nerve pain in the anterior thigh and not back pain. You should distinguish that from hip disease or a tight quadriceps muscle.

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