Effect of spinal cord stretching due to head flexion on intramedullary pressure.

The effect of the longitudinal stretching force of the spinal cord on intramedullary pressure was investigated using our method for measuring intramedullary pressure of the spinal cord with implanted balloons. The transverse compressive force against the posterior wall of the spinal column was excluded by measuring the intramedullary pressure during flexion of the head with the middle and lower cervical spine in the neutral position. The intramedullary pressure of the cervical spinal cord was measured simultaneously at the C-2, C-4, and C-6 levels in 10 mongrel dogs, in three head positions: neutral, and head extension and flexion. Head flexion caused significant increases in the intramedullary pressure at C-2, C-4, and C-6. The pressure increase in the middle to lower cervical cord must have been due to the transmission of the longitudinal stretching force of the cord itself, and may be a factor in the development of intramedullary disorders such as syringomyelia and intramedullary neoplasms.