The safe ultimate antedisplacemental distance of the thoracic vertebrae in thoracic column antedisplacement and fixation: goat in vivo experiment

Abstract Objective To investigate the safe ultimate antedisplacemental distance of the thoracic vertebrae in the new surgical technique of thoracic column antedisplacement and fixation (TCAF) in living goat model. Methods A total of ten healthy goats were obtained, the T12, T13 and L1 were selected as the antedispalcemental vertebrae while T10, T11, L2 and L3 were chosen as fixed vertebrae. The X-ray was taken before surgery to measure the anteroposterior diameter of spinal canal and the width of the vertebrae of T12, T13 and L1. The TCAF was performed by using pedicle screw system to antedisplacethe vertebrae according to the adjustment of the length of the reserved thread under the somatosensory evoked potential (SSEP) monitoring. The SSEP measured after the T11/12 and L1/2 discs were resected was set as the baseline, and the SSEP decreased by 50% from the baseline amplitude and/or delayed by 10% relative to the baseline peak latency were set as positive results, which indicated spinal cord injury (SCI). The vertebrae were gradually antedisplaced until the SSEP monitoring just did not show a positive result, then the length of the reserved thread (T12, T13 and L1) were recorded, and the antedisplacemental distance measured by postoperative imaging was regard as the ultimate distance. Exploring whether there was a correlation and linear relationship between the ultimate antedisplacemental distance and the related parameters of the vertebrae. Hindlimb function was evaluated by the Tarlov scores on day 2 postoperatively. Results The ultimate antedisplacemental distance for TCAF was 8.0±0.2mm, and Pearson correlation test showed that there was a good correlation with the average anteroposterior diameter of spinal canal of the antedisplacemental segment and the average width of the vertebrae of the antedisplacemental segment. Linear regression analysis showed that there was a linear relationship between the ultimate antedisplacemental distance (Y) and the average anteroposterior diameter of spinal canal of the antedisplacemental segment (X)and the linear equation was Y=-7.769+1.648X. Conclusions In goat animal experiment, the ultimate antedisplacement distance for TCAF was 8.0 ± 0.2mm and there was a linear relationship between the ultimate antedisplacemental distance and the average anteroposterior diameter of spinal canal of the antedisplacemental segment. When the current displacement distance is less than this value, it will not cause spinal cord injury, that is, intraoperative real-time SSEP has no positive results. Thus, TCAF is a safe operation method.