Experimental Study for the Effect of Myelotomy on Acute Spinal Cord Injury

ABSTRACT

This study involved 29 adult cats with acute spinal cord injuries produced experimentally in which a myelotomy was performed in 10 cats one hour(1-hour myelotomy group) after and in remaining 9 animals 6 hours(6-hour myelotomy group) after the injury. The remaining 10 animals served as controls and were only subjected to the spinal cord injury. The spinal cord injury with 400gm-cm blow was inflicted by dropping a 20gm cylindrical weight from a height of 20cm onto the impounder rested epidurally over the entire dorsal surface of the cord at T10 or T12 vertebral level. Under the operating microscope, a myelotomy, dorsal midline longitudinal, approximately 1.0cm to 1.5cm long, was made at the injury site. The myelotomy extended 4mm into cord completely through to the anterior surface of the cord. Animals were evaluated neurologically after the injury in time sequence of 4 hours, 8 hours, 2 days 4 days and 7 days after which they were sacrified, and the spinal cord and meninges were removed for pathological study. Acute spinal cord injury produced in this study immediately resulted in total paralysis of both hind limbs in all animals after injury and the weakness lasted throughout whole experimental period. There was no significant improvement in recovery of neurological function in control and in 6-hour yelotomy groups, but there was a significant improvement in recovery of motor function in the group of 1-hour myelotomy animals as compaired with the other groups. Histopathological findings of injured spinal cord were mainly those of hemorrhage, necrosis of cavity formation in the central gray and degenerative changes in the white and gray matters, and of edema and swelling of the spinal cord. In the group treated with myelotomy after the injury, the degree of destruction of the spinal cord was lesser histologically than those in control group, and that, in the group of 1-hour myelotomy, no central cavitation or necrosis were observed. It was observed that the neurological functional deficits tended to correlate with the degree of destruction to the spinal cord, and when the myelotomy was done earlier in the post-traumatic period and extended for the full depth of the cord, the improvement of neurological function and the prevention of further destruction of the spinal cord were significant. It is well to say that a number of possible mechanism to account for this beneficial effectiveness of myelotomy may be attributed to drainage of blood and necrotic tissue from the injury site. Myelotomy may prevent cavitation of spinal cord, and thus prevent the surviving axons from further damage, and it may reduce tissue pressure.