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Evaluation of lumbosacral nerve root lesions using evoked potentials recorded by a surface electrode technique
Toru Osawa1, Taku Ogura, Tatsuro Hayashida
1Department of Orthopaedic Surgery, Kyoto Prefectural University of Medicine, Kamigyo, Kyoto, Japan.
Study Design:
Patients with lumbar disc herniation were studied with lumbosacral evoked potentials (EPs).
Objectives:
To evaluate lumbosacral EPs for the functional diagnosis of nerve root lesions in patients with lumbar disc herniation.
Summary Of Background Data:
No clinical studies have been conducted using lumbosacral EPs elicited by body surface leads.
Methods:
Lumbosacral EPs elicited by stimulating the posterior tibial nerve were recorded using surface electrodes placed over the interspinous processes of T12-S1. By subtracting the waveform recorded at NT12 (T12/L1 potential) from that at NL3 (L3/L4 potential), NL3' (residual potential) potentials were clearly identified. NT12 and NL3' potentials were classified into four groups based on the degree of the reduction of amplitude and/or the prolongation of latency.
Results:
Significant correlations were found between the NL3' score and the straight-leg raising test score (r = 0.36, P < 0.05) and between the NT12 amplitude and sensory disturbance (r = 0.37, P < 0.02). The NL3' score was 1.2 +/- 0.5 points before surgery, and it significantly improved to 2.5 +/- 0.5 points 2 months after surgery (P < 0.05). Short-term, the NT12 amplitude did not change significantly. Twelve months after surgery, the NT12 amplitude improved significantly to 1.1 +/- 0.5 microV (P < 0.05).
Conclusions:
The results of this study indicated that the NL3' score may reflect impairment of the impulse traversing the nerve root in the acute clinical stage, whereas the NT12 amplitude reflects a neurologic deficit. The postoperative clinical course can be estimated by observing recovery of the NL3' score and NT12 amplitude.