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Effects of Vertebral Column Distraction on Transcranial Electrical Stimulation-Motor Evoked Potential and Histology of the Spinal Cord in a Porcine Model

Yang, Jae Hyuk MD; Suh, Seung Woo MD, PhD; Modi, Hitesh N. MS, PhD; Ramani, Easwar T. MBBS, DNB(Orth), MNAMS; Hong, Jae Young MD; Hwang, Jin Ho MD; Jung, Woon Yong MD, PhD

Journal of Bone & Joint Surgery - American Volume: 1 May 2013 - Volume 95 - Issue 9 - p 835–842
doi: 10.2106/JBJS.K.00575
Scientific Articles
Supplementary Content
Disclosures

Background: Spinal cord injury can occur following surgical procedures for correction of scoliosis and kyphosis, as these procedures produce lengthening of the vertebral column. The objective of this study was to cause spinal cord injury by vertebral column distraction and evaluate the histological changes in the spinal cord in relationship to the pattern of recovery from the spinal cord injury.

Methods: Global osteotomy of all three spinal columns was performed on the ninth thoracic vertebra of sixteen pigs. The osteotomized vertebra was distracted until transcranial electrical stimulation-motor evoked potential (TES-MEP) signals disappeared or decreased by >80% compared with the baseline amplitude; this was defined as spinal cord injury. The distraction distance at which spinal cord injury occurred was measured, the distraction was released, and the TES-MEP recovery pattern was observed. A wake-up test was performed, two days of observations were made, and histological changes were evaluated in relationship to the recovery pattern.

Results: Spinal cord injury developed at a distraction distance of 20.2 ± 4.7 mm, equivalent to 3.6% of the thoracolumbar spinal length, and the distraction distance was correlated with the thoracolumbar spinal length (r = 0.632, p = 0.009). No animals exhibited complete recovery according to TES-MEP testing, eleven exhibited incomplete recovery, and five exhibited no recovery. During the two days of observation, all eleven animals with incomplete recovery showed positive responses to sensory and motor tests, whereas none of the five animals with no recovery had positive responses. On histological evaluation, three animals that exhibited no recovery all showed complete severance of nerve fibers (axotomy), whereas six animals that exhibited incomplete recovery all showed partial white-matter injury.

Conclusions: Parallel distraction of approximately 3.6% of the thoracolumbar length after global osteotomy resulted in spinal cord injury and histological evidence of spinal cord damage. The pattern of recovery from the spinal cord injury after release of the distraction was consistent with the degree of axonal damage. Axotomy was observed in animals that exhibited no recovery on TES-MEP, and only hemorrhagic changes in the white matter were observed in animals that exhibited incomplete recovery.

Clinical Relevance: The information on TES-MEP changes and histological responses associated with distraction in an animal model may be useful in corrective surgery for spinal deformity in humans.

1Scoliosis Research Institute, Department of Orthopedics, Korea University, Guro Hospital, Guro dong 80, Guro-gu, Seoul, South Korea. E-mail address for S.W. Suh: spine@korea.ac.kr

2Division of Spine Surgery, Department of Orthopaedics, Ortho One Orthopaedic Speciality Centre, 657 Trichy Road, Singanallur, Coimbatore, Tamil Nadu 641005, India

3Department of Orthopedics, Korea University, Ansan Hospital, Gojan 1-dong, Danwon-gu, Ansan-si, Gyeonggi-do 425-707, South Korea

4Division of Pediatric Orthopaedics, Department of Orthopaedic Surgery, Yonsei University College of Medicine, Severance Children’s Hospital, Sinchon-Dong, Seodaemun-gu, Seaoul 120-752, South Korea

5Department of Pathology, Ulsan University, Asan Medical Center, Pungnap 2-dong, Songpa-gu, Seoul 138-736, South Korea

Copyright 2013 by The Journal of Bone and Joint Surgery, Incorporated
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