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Correspondence  |   November 2004
Movement of the Cauda Equina during the Lateral Decubitus Position with Fully Flexed Leg
Author Affiliations & Notes
  • Shigeki Yamaguchi, M.D., Ph.D
    *
  • * Dokkyo University School of Medicine, Tochigi, Japan.
Article Information
Correspondence
Correspondence   |   November 2004
Movement of the Cauda Equina during the Lateral Decubitus Position with Fully Flexed Leg
Anesthesiology 11 2004, Vol.101, 1250. doi:
Anesthesiology 11 2004, Vol.101, 1250. doi:
To the Editor:—
Spinal anesthesia is performed in the lateral decubitus, sitting, or prone-jackknife position. The lateral decubitus position is the most common position for performance of spinal anesthesia because it allows patients to be more comfortable. We previously demonstrated that the cauda equina was dynamically shifted to the left side of subarachnoid space when patients were in the left lateral decubitus position. To perform spinal anesthesia, however, patients are usually placed in the lateral decubitus position, with the knees drawn up to the stomach, the leg fully flexed, and the neck flexed (fully flexed leg) to curve the back outward. However, there have thus far been no reports on the structural change of the cauda equina in the lateral decubitus position with fully flexed leg. We examined the influences of a fully flexed leg in the lateral decubitus position on structural change of the cauda equina using magnetic resonance imaging. Three healthy volunteers (age, 36 ± 11 yr; height, 160 ± 2 cm; weight, 55 ± 2 kg) were studied with magnetic resonance imaging, and their positions were changed as follows: the supine position, the lateral decubitus position without fully flexed leg, and the lateral decubitus position with fully flexed leg. An interesting movement of the cauda equina was observed by changing position to fully flexed leg in the lateral decubitus position. Figures 1A, B, and Cshow axial images of magnetic resonance in the supine position, the lateral decubitus position without fully flexed leg, and the lateral decubitus position with fully flexed leg, respectively. As in our previous study,1 the nerve roots of the cauda equina moved to the left side of the subarachnoid space with gravity in the left lateral decubitus position without fully flexed leg (fig. 1B). Furthermore, the fully flexed leg position moved the roots of the cauda equina to the ventral site and created a free space in the dorsal subarachnoid space (fig. 1C). This phenomenon was observed in all volunteers.
Fig. 1. Axial view of the cauda equina. Magnetic resonance images (T2 weighted, spin echo, TR 2,000/TE 100 ms) at the L3–L4 level in the same subject were obtained in the supine position (  A  ), the left lateral decubitus position without fully flexed leg (  B  ), and the left lateral decubitus position with fully flexed leg (  C  ). L = left; R = right; TE = echo time; TR = repetition time. 
Fig. 1. Axial view of the cauda equina. Magnetic resonance images (T2 weighted, spin echo, TR 2,000/TE 100 ms) at the L3–L4 level in the same subject were obtained in the supine position (  A  ), the left lateral decubitus position without fully flexed leg (  B  ), and the left lateral decubitus position with fully flexed leg (  C  ). L = left; R = right; TE = echo time; TR = repetition time. 
Fig. 1. Axial view of the cauda equina. Magnetic resonance images (T2 weighted, spin echo, TR 2,000/TE 100 ms) at the L3–L4 level in the same subject were obtained in the supine position (  A  ), the left lateral decubitus position without fully flexed leg (  B  ), and the left lateral decubitus position with fully flexed leg (  C  ). L = left; R = right; TE = echo time; TR = repetition time. 
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Previously, we have considered that the fully flexed leg position can be used to widen the interlaminal space. However, the lateral decubitus position with fully flexed leg also creates a free space in the dorsal subarachnoid space. Although we do not know whether these changes in the position of the cauda equina have any relevance to the risk of nerve injury during spinal anesthesia, this information should be useful to perform spinal anesthesia.
* Dokkyo University School of Medicine, Tochigi, Japan.
Reference
Reference
Takiguchi T, Yamaguchi S, Okuda Y, Kitajima T: Deviation of the cauda equine by changing position. Anesthesiology 2004; 100:754–5Takiguchi, T Yamaguchi, S Okuda, Y Kitajima, T
Fig. 1. Axial view of the cauda equina. Magnetic resonance images (T2 weighted, spin echo, TR 2,000/TE 100 ms) at the L3–L4 level in the same subject were obtained in the supine position (  A  ), the left lateral decubitus position without fully flexed leg (  B  ), and the left lateral decubitus position with fully flexed leg (  C  ). L = left; R = right; TE = echo time; TR = repetition time. 
Fig. 1. Axial view of the cauda equina. Magnetic resonance images (T2 weighted, spin echo, TR 2,000/TE 100 ms) at the L3–L4 level in the same subject were obtained in the supine position (  A  ), the left lateral decubitus position without fully flexed leg (  B  ), and the left lateral decubitus position with fully flexed leg (  C  ). L = left; R = right; TE = echo time; TR = repetition time. 
Fig. 1. Axial view of the cauda equina. Magnetic resonance images (T2 weighted, spin echo, TR 2,000/TE 100 ms) at the L3–L4 level in the same subject were obtained in the supine position (  A  ), the left lateral decubitus position without fully flexed leg (  B  ), and the left lateral decubitus position with fully flexed leg (  C  ). L = left; R = right; TE = echo time; TR = repetition time. 
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