Study on the safe limit of shortening of the spinal cord in thoracolumbar bivertebral column resections: an experimental study in goat

ABSTRACT OBJECTIVE To clarify the safe limit of shortening of the spinal cord in thoracolumbar bivertebral column resections in the goat model. METHODS Ten healthy goats were selected for animal experiment. The X-ray was taken before surgery to measure the height of T13, L1 and the initial osteotomy segment (the distance from the lower endplate of T12 to the upper endplate of L2). A procedure of thoracolumbar bivertebral column resections (T13, L1) was completed under the monitoring of somatosensory evoked potential (SSEP) monitoring. The SSEP measured after vertebral resection 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 was set as positive results, which indicated spinal cord injury. The initial height of osteotomy gap was measured first and the spinal column was gradually shortened until the SSEP monitoring just did not show a positive result. Then the height of the osteotomy gap was recorded again. The safe limit of shortening was measured and recorded when any morphologic change of the spinal cord was observed. Hindlimb function was evaluated by the Tarlov scores on day 2 postoperatively. RESULTS The safe limit of shortening of the spinal cord in thoracolumbar bivertebral columns resection was 35.2±2.6 mm, which was roughly equal to 127.6% of the mean osteotomy vertebral height and 57.1% of the initial osteotomy gap height. Pearson’s correlation test showed that the safe limit of shortening of the spinal cord was correlated with the height of T13, the height of L1, the mean height of T13 and L1, and the height of initial osteotomy gap. CONCLUSIONS The safe limit of shortening distance of the bivertebral column resectionswas roughly equal to 127.6% of the mean osteotomy vertebral height and 57.1% of the initial osteotomy gap height with a good correlation. Moreover, the safe limit of shortening distance of the bivertebral column resections was longer than that in single-vertebral column resection. Increasing the number of vertebral resected may prevent spinal cord injury(SCI) due to excessive shortening.