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Am Fam Physician. 1999;60(6):1666

to the editor: The recent article on the evaluation and treatment of herniated lumbar disc by Humpreys and Eck1 is excellent in most respects, but clarification of a few points might be useful. The authors correctly note that bed rest is often overused for musculoskeletal disorders, but both studies they cited excluded patients with acute sciatica from their research populations.2,3

The assertion that nonorganic physical signs (Waddell signs) “may identify patients with pain of a psychologic or socioeconomic basis” seems wide of the mark. Biologic and psychosocial factors often coexist; the presence of one does not exclude the other. Waddell and colleagues4 have cautioned medical personnel repeatedly about the hazards of overinterpreting the significance of the signs that bear his name; they state that “Isolated signs should not be overinterpreted. Multiple signs suggest that the patient does not have a straightforward physical problem, but that psychological factors also need to be considered. . . . Behavioral signs are not on their own a test of credibility or faking.”

A more complete discussion of the straight-leg raising test would have been helpful. This test is classically performed with the patient lying in the supine position. The examiner places a hand under the patient's heel and lifts the fully extended leg until pain is reported or increasing resistance is felt. The normal limit in subjects without sciatic nerve embarrassment may be anywhere between 60 and 120 degrees depending on the patient's age, habitus and physical condition. The amount of pain-free flexion is less important than variation between legs. Dorsiflexing the foot of a patient with sciatica when the hip is flexed to the limit of comfort may make the pain worse; plantar flexion should not.

A patient's anxiety or other behavioral factors can lead to a falsely abnormal supine straight-leg raising test. This situation can usually be clarified by testing the patient in the seated position. It is sometimes helpful to note the supine test findings and move to other parts of the examination for a few minutes. Then, with the patient seated on the examining table with his or her legs hanging over the side, the examiner might say, “I need to cheek your knees,” or something similar. While seeming to check the knee ligaments, or perhaps while actually doing so, the examiner extends each leg at the knee. The ability to extend the knee joint fully is the equivalent of a normal supine straight-leg raising test. A significant discrepancy between the results of the two procedures is the equivalent of a positive Waddell's sign.

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This series is coordinated by Kenny Lin, MD, MPH, deputy editor.

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