Spinal somatosensory evoked potential to evaluate neurophysiologic changes associated with postlaminotomy fibrosis: an experimental study.
METHODS
We evaluated electrophysiologic changes of the cauda equina after lumbar laminotomy in rats.


OBJECTIVE
To clarify immediate and long-term electrophysiologic and neurologic responses in an experimental postlaminotomy animal fibrosis model.


BACKGROUND
Postspinal surgery-induced epidural fibrosis is assessed using either Gadolinium- enhanced magnetic resonance imaging (MRI) or intraoperative observations. In experimental animal models mimicking this complication, many approaches are used: advanced imaging (computed tomography, CT; and MRI), functional observations, biomechanical techniques, and histologic examinations. However, no study has reported the substantial neurophysiologic changes of the cauda equina in such a model.


METHODS
Rats were given a sham operation (laminar exposure only), a left L5 hemilaminotomy alone, or a left L5 hemilaminotomy with extradural topical collagen. Mixed-nerve-elicited somatosensory-evoked potentials (M-SSEPs) and dermatomal (D)-SSEPs were recorded at the thoracolumbar junction after percutaneous stimulation of the posterior tibial nerve at the bilateral medial ankles and the L5 dermatomal field, respectively. Potentials recorded on the operated and nonoperated sides before surgery and then 30 minutes, 2 weeks, and 1, 2, and 3 months after surgery were compared. Walking track and thermal hyperalgesia test results and a final histologic analysis of perineural fibrosis were correlated.


RESULTS
Electrical stimulation yielded reproducible responses in all rats on all tests. Preoperative and postoperative measurements showed no statistically significant differences in M-SSEP or D-SSEP. Postoperative D-SSEPs in both experimental groups showed significant reductions in relative amplitude, but the M-SSEPs of all groups and D-SSEPs of the control groups remained constant.


CONCLUSIONS
SSEP is valuable for detecting electrophysiologic changes after laminotomy fibrosis, but acceptable accuracy requires proper stimulation and recording settings. D-SSEP monitoring provided reliable, useful information about the functional integrity of the cauda equina in this animal model. We recommend D-SSEP monitoring as a supplemental tool for quantifying the effect of postlaminotomy fibrosis on neuropathy.
Jou
I-Ming
IM
Department of Orthopedics, College of Medicine, National Cheng Kung University, Tainan, Taiwan. jming@mail.ncku.edu.tw
Tai
Ta-Wei
TW
Tsai
Ching-Lin
CL
Tsai
Tse-Min
TM
Yung
Wan-Sheng
WS
Jung
Yun-Chih
YC
D000818:Animals; D001416:Back Pain / Q000209:etiology / Q000473:pathology / Q000503:physiopathology; D001522:Behavior, Animal; D002420:Cauda Equina / Q000503:physiopathology*; D004195:Disease Models, Animal; D004558:Electric Stimulation; D004568:Electrodiagnosis; D004824:Epidural Space / Q000473:pathology*; D005073:Evoked Potentials, Somatosensory; D005355:Fibrosis / Q000175:diagnosis / Q000209:etiology; D007796:Laminectomy / Q000009:adverse effects*; D008159:Lumbar Vertebrae / Q000601:surgery*; D009483:Neuropsychological Tests; D010523:Peripheral Nervous System Diseases / Q000150:complications / Q000175:diagnosis* / Q000209:etiology / Q000473:pathology / Q000503:physiopathology; D011237:Predictive Value of Tests; D011843:Radiculopathy / Q000209:etiology / Q000473:pathology / Q000503:physiopathology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012720:Severity of Illness Index; D013997:Time Factors