Motor Conduction Time Along the Cauda Equina in Patients With Lumbar Spinal Stenosis

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Study Design.

Magnetic lumbar stimulation was used to detect spinal nerve degeneration in patients with lumbar spinal stenosis (LSS).


To evaluate delays in the motor conduction time in the cauda equina of patients with LSS.

Summary of Background Data.

Previous studies suggested a bilateral slowing of motor conduction in the cauda equina in LSS. Among several methods, only magnetic stimulation is sufficiently sensitive for detecting potential degeneration in LSS. A recent study demonstrated the direct calculation of the cauda equina motor conduction time using magnetic stimulation at proximal and distal sites of the cauda equina. We used this technique to determine potential degeneration in patients with LSS.


Twenty adult subjects and 15 patients with LSS were investigated. Lumbosacral roots were stimulated at intervertebral levels L1–L2 and L5–S1 by magnetic coil stimulation. The muscle responses to stimulation were recorded from the gastrocnemius-soleus, and anterior tibialis muscles on both sides with bipolar surface electrodes. The response latency from stimulations at the L5 spine level were subtracted from those at the L1 level on the same side. This value represented the conduction time from the proximal to distal ends of the cauda equina.


The mean conduction time along the cauda equina was significantly prolonged in patients with LSS compared with controls. The mean cauda equina motor conduction time was 1.97 ± 0.67 milliseconds in controls and 3.57 ± 2.22 milliseconds in patients with LSS (P = 0.00).


Determining the motor conduction time along the cauda equina using L1 and L5 magnetic stimulation provides an effective alternative method for evaluating the lumbar motor roots in patients with LSS.

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