Diurnal changes in straight leg raising.

Diurnal changes in straight leg raising were measured in 28 patients with criteria of lower lumbar disc protrusion, having first established an acceptable intra-observer repeatability using an oil-filled precision goniometer. Eight patients showed little change between the straight leg raising after a night of recumbancy, and after 180 minutes in the upright posture. Twenty patients, however, had 10 or more degrees of improvement in straight leg raising, with a mean improvement of 16.9 degrees (SD 7.1 degrees); most of the increase occurred in the first hour of being upright. The measurement returned again to the base level after 120 minutes of further recumbancy. Five of the eight patients who showed little diurnal change had discectomy, and four had a complete annular tear. Only one of the 20 patients with more than 10 degrees of diurnal change required surgery. Diurnal change in straight leg raising is probably related to the disc's proteoglycan content, its hydration, the tension of the protrusion and the presence of intact peripheral annular fibers.