OBJECTIVE: To examine whether there is a significant difference in gnostic sensibility between affected and unaffected legs of patients suffering from lumbosacral radicular syndrome (LRS) resulting from a disc herniation and to determine the validity of the sensibility test for detecting a disc herniation.

DESIGN: Observer blind study of sensibility testing.

SETTING: Four general hospitals (neurology department) and one practice of physical and manual therapy.

SUBJECTS: Fifty-one patients with radicular pain in the lumbosacral nerve roots for at least 4 wk and/or neurological deficits.

METHODS: The gnostic sensibility of 51 patients with a unilateral LRS was tested using Semmes-Weinstein monofilaments for the L4, L5 and S1 dermatomes.

RESULTS: Gnostic hypoesthetic impairments in the L4, L5 and S1 dermatomes were found in 84.6% of the 43 patients in which the presence of disc herniation was confirmed by CT. There was significant difference in gnostic sensibility between the affected and unaffected legs in the L4, L5, and S1 dermatomes for disc herniation at the L4-L5 level and for the L5 and S1 dermatomes for a disc herniation at the L5-S1 level. There was no significant difference in gnostic sensibility in the L4 dermatome for a disc herniation at the L5-S1 level.

CONCLUSION: The gnostic sensibility of the affected leg is hypoesthetic compared with the unaffected leg. The specificity of the sensibility test using monofilaments is acceptable, but the sensitivity is not. The monofilament test is a useful and practical tool for excluding the presence of a disc herniation at dermatomes L4, L5 and S1 and disc herniations at the L4-L5, L5-S1 level.

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