An experimental study of the effects of nerve root retraction on the posterior ramus.
METHODS
The histologic and ultrastructural changes in the posterior ramus after posterior lumbar surgery were studied in rabbits.


OBJECTIVE
To investigate the structural changes in the posterior ramus after posterior lumbar surgery that may cause injury to the posterior ramus after the procedure.


BACKGROUND
Investigators in previous studies have pointed out that low back discomfort after lumbar discectomy relates to neurogenic changes and/or myogenic changes of paravertebral muscle. However, no previous study has demonstrated the effects of excessive nerve root retraction on spinal posterior rami.


METHODS
Eighteen male Japanese White rabbits were used. The posterior ramus arising from the S1 nerve root was examined after exposure of the lamina only, fenestration, or retraction of the S1 nerve root, with light microscopy and transmission electron microscopy at 2, 4, and 6 weeks after the procedure. Results were compared with a those in control specimens that did not undergo the procedure.


RESULTS
In the exposed group, no distinct difference was found compared with the control specimen. In the fenestration group, especially at 6 weeks, some attenuation and splitting of myelin sheaths was observed. In the retraction group, the structural alteration was most severe. Even at 2 weeks, fragmentation of many myelin sheaths was detected. Examination of specimens by electron microscopy indicated phagocytosis of myelinated fibers at 4 and 6 weeks.


CONCLUSIONS
Findings showed that posterior lumbar procedures, including retraction of paravertebral muscle, fenestration of the lamina, and retraction of the nerve root affect the posterior ramus. Excessive retraction of the nerve root has an especially disastrous effect on the posterior ramus. Such a violent maneuver within the spinal canal must be avoided.
Nagayama
R
R
Department of Orthopaedic Surgery, School of Medicine, Osaka City University, Japan. rnagayama@msic.med.osaka-cu.ac.jp
Nakamura
H
H
Yamano
Y
Y
Yamamoto
T
T
Minato
Y
Y
Seki
M
M
Konishi
S
S
D000818:Animals; D007796:Laminectomy; D008297:Male; D008854:Microscopy, Electron; D011817:Rabbits; D013126:Spinal Nerve Roots / Q000601:surgery* / Q000648:ultrastructure*; D013131:Spine / Q000601:surgery*; D013997:Time Factors