Instrumental straight-leg raising: a new approach to Lasègue's test.

In clinical practice the outcome of Lasègue's test is interpreted with respect to two variables: (1) the maximum angle between the leg and the horizontal plane to which the leg can be lifted, and (2) the pain that is provoked by the movement. For a number of reasons it is difficult in many patients to interpret the test outcome; predominantly, it is because of the lack of information it yields concerning the activity of the muscles. To get more information, an instrumental test was developed that imitates Lasègue's test. In this setup, which is based on a simple biomechanical model, the leg is passively raised in a lift installation. During lifting, the angles between leg and horizontal plane and between leg and pelvis are measured with electrogoniometers; the lift moment is determined with the help of a force transducer; pelvic rotation is assessed with a lordosis meter; and surface electromyography is used to record electric transducer; pelvic rotation is assessed with a lordosis meter; and surface electromyography is used to record electric activity in the erector spinae, the gluteus maximus, and the semimembranosus. The method, called instrumental straight-leg raising, makes it possible to determine the extensibility, elasticity, and electric activity of the hamstrings and back muscles during Lasègue's test. This information provides a better basis for the interpretation of the test outcome.