Surgical disorders of the thoracic and lumbar spine: a guide for neurologists.

Mixter and Barr in 1934 first described the herniated disc to be a cause of segmental leg pain (sciatica or femoralgia). Acute low back pain is a relatively common condition and is accompanied by sciatica in only 1–2% of cases. Patients presenting with acute low back pain alone are therefore unlikely to have a disc prolapse. Lumbar intervertebral disc prolapse is most prevalent between the ages of 30–50 years, and the L5/S1 and L4/5 intervertebral discs account for 95% of all lumbar prolapses. A lumbar disc prolapse typically presents with gradual or sudden onset localised back pain radiating through the buttock or hip area into the leg. The episode may have been precipitated by heavy axial loading, flexion or rotation of the spine, but may also occur at rest. The onset of sciatica often coincides with improvement in localised back pain. The sciatica is initially severe and is often described as a dull aching pain with occasional sharp or shooting exacerbations. The pain may be aggravated by coughing, sneezing, bending or prolonged sitting. The compromised nerve root is usually identified by noting the specific dermatomal distribution of the pain or associated sensory disturbances. The myotomal distribution of any muscle weakness and hyporeflexia further refines the clinical impression. Muscle wasting is rarely seen unless the symptoms have been present for several months. Bilateral leg symptoms, peri-anal or saddle sensory disturbances, and urinary or anal sphincter dysfunction signify a cauda equina syndrome (table 1) caused by the presence of a large central disc prolapse. These patients warrant urgent investigation and treatment. The straight leg raising test (Lasegue’s sign) elicits dermatomal pain in the presence of abnormal nerve root tension caused by a disc prolapse at the L4/5 or L5/S1 level. A positive femoral stretch test (hip extension with maximal knee flexion) signifies the presence of an L2, L3 or L4 radiculopathy. This may be caused by a lumbar disc protrusion or other pathology such as a psoas abscess, haematoma, or diabetic femoral neuropathy. It is important to distinguish between true sciatica and hip related pain. Pain on weight bearing or hip movements, particularly on external rotation and extension, suggests the presence of joint related pathology—for example, trochanteric bursitis or arthritis.