[Electromyographical study of the straight leg raising test in lumbar disc herniation]

The straight leg raising test is one of the most reliable test for the diagnosis of the disc herniation. It is well known that the pain is produced by the increased tension of the affected root. However, the patient's response to the pain evoked by the straight leg raising test is not uniform. In some patients the leg is raised beyond the straight leg raising positive angle without resistance and some young patients show the tight hamstrings phenomenon. To elucidate these phenomena, the muscle action of erector spinae, gluteus maximus and biceps femoris evoked by this test was studied electromyographically. The results are as follows: 1) The muscle action patterns in the patients of disc herniation which are not observed in normal group are classified into four groups, namely LGB type (erector spinae, gluteus maximus and biceps femoris act), GB type (gluteus maximus and biceps femoris act), G type (gluteus maximus only acts), B type (biceps femoris only act). These abnormal muscle actions disappear under general anesthesia and are different from the actions which are recorded when the patients resist passive straight leg raising intentionally. 2) In the case of L4-5 intervertebral disc herniation mainly gluteus maximus acts as the resisting force against the passive straight leg raising. On the other hand, biceps femoris acts mainly in the case of L5-S1 disc herniation. 3) The group of younger age and less degenerated disc shows more resistance against straight leg raising and records the action potential of resisting muscles in earlier stage of the leg raising test.