An In Vitro Study on the Effects of Freezing, Spine Segment, Repeat Measurement, and Individual Cord Properties on Cord Interstitial Pressure

Abstract

In vitro study of the spinal cord tension and pressure relationships before and after thawing in 6 different spinal cord segment from 2 individual pigs. To determine if frozen and thawed spinal cord segments had different tension/cord interstitial pressure(CIP) relationships to fresh spinal cord segments. In addition, we will determine if the cord level, individual cord properties, and repeated CIP measurements affect the tension/CIP relationships. Spinal cord distraction is a known cause of spinal cord injury. Several articles published on the pathophysiology of the cord distraction injury suggest that the underlying mechanism of injury is a microvascular ischemic event. We have previously described an increase in CIP with spinal cord distraction, pressures average 23 mmHg at 1 kg loads. Six cord segments harvested from 2 pigs contained cervical, thoracic, and lumbar segments, and underwent distraction using a series of 7 calibrated weights from 0 to 1000 g weight. The cords were measured at each level of distraction. The cords were then frozen at -20 degrees C for a period of 2 weeks, and then thawed and retested. Multiple linear regression was then performed. There was no difference between the fresh and the frozen-thawed cords; there was statistical difference between the 2 pigs (18 mmHg) (P < 0.001). There are differences between the cervical and the thoracic cord segments (P < 0.001), and between cervical and lumbar cord segments (P = 0.056). There is a significant relation between the tension applied and CIP. Repeated trials showed no drift with repeated measures. Freezing and thawing spinal cords has no effect on the CIP/tension curves. Cord interstitial pressure developed is dependant on cord tension, cord level, individual cord properties, but not on the number of repetitions carried out while testing the spinal cord.