A sheep model of chronic cervical compressive myelopathy via an in-vitro control compression device/

English Keywords:Cervical spinal cord compression  Chronic  Animal model  Digital control

English Abstract:

  【Abstract】 Objectives: This study applied an in-vitro control compression device to sheep model of chronic cervical compressive myelopathy to make the compression digitalized and precisely controllable. Methods: The compression device consisted of two parts, intervertebral compression part and percutaneous control part, and was controlled by an Android phone in vitro. 12 male small tailed han sheep were divided into 3 groups randomly on average, control group (A), 10 weeks group (B) and 20 weeks group (C). The compression device was implanted into intervertebral space of C2/C3 and fixed. Control part was implanted subcutaneously. The control group (A) ran no compression after surgery. Group B and group C were pushed 0.1mm every two days while awake. Tarlov score was assessed in each group before and after push. The Tarlov score was recorded at 1 week, 5, 10, 15 and 20 weeks after surgery. CT scan was performed immediately, 1, 5, 10, 15 and 20 weeks after surgery and the spinal canal encroachment rate was calculated at the same time. Electrophysiology examination (SEP) was performed immediately, 1, 10 and 20 weeks after surgery. The spinal cord specimens at C2/3 level were collected, and HE, Nissl and TUNEL test were performed to observe the histology results at the end of experiment. Pearson correlation coefficien t(r) and general linear regression was used for the analysis of the encroachment rate(ER) of group B and C and time (t, week). The relationship between ER and Tarlov score was analysed with Pearson correlation coefficient(r). All results were analyzed via SPSS software. Results: One control part of sheep in group B broke down and was repaired after reoperation. No behavioral changes were noted in group A and all Tarlov scores were 5. The final Tarlov score was 5 in 2 sheep and 4 in 2 sheep of group B, 3 in 3 sheep and 2 in 1 sheep of group C. The results of Tarlov score showed significant difference(P<0.05). The final radiological findings showed that the average spinal canal encroachment rate was (33.0±1.8)% in group B and (64.8±1.9)% in group C. Pearson correlation coefficient(r) of ER of group B&C with time (t, week) was r=0.998 (P<0.001). The linear regression equation of ER and time (t, week) was ER=3.197t. ER and Tarlov score showed negative correlation(r=-0.862, P<0.001). The latency and amplitude of SEP during and immediately after surgery showed no obvious changes. The electrophysiology results revealed that there was no statistically difference between group B, C and A both for amplitude and latency immediately and 1 week after surgery, while the animals in group B&C showed obvious prolongation of latency and decrease of amplitude at 10 and 20 weeks. The histological results of group A showed normal structure of neuron and nerve fiber. The pathological examination of group B showed atrophy of anterior horn motor neurons and reduction of Nissl body. There were also mild demyelination and vacuolar degeneration of corticospinal tract in group B, while more remarkably in group C. The proportion of abnormal cell of three groups demonstrated significant difference (P<0.001). The amount of TUNEL positive cell obviously increased with the prolongation of compression time(P<0.001). Conclusions: This compression device can be used to establish a reliable and precisely controllable sheep model of chronic cervical compressive myelopathy.