Nucleus pulposus-induced nerve root injury: relationship between blood flow and motor nerve conduction velocity

It is well known that nucleus pulposus induces nerve root injury. The aim of this study was to assess the relationship between intraneural blood flow and motor nerve conduction velocity (NCV) after incision of the adjacent disc.

A total of 65 dogs were used. A left hemilaminotomy was performed, the annulus fibrosus of the L6-L7 intervertebral disc was incised, and nucleus pulposus was gently pushed into the epidural space by saline solution injection. A left hemilaminotomy without disc incision was used as the sham operation. Seven dogs were used for incision and five dogs for sham treatment for each of the following time points: 1 day, 3 days, 1 week, 1 month, and 2 months of exposure. Five additional dogs were used to establish baseline data. Blood flow in the nerve root was measured in the left L7 nerve root with a tissue blood flowmeter, using an electrolytic hydrogen clearance method. Motor NCV over the exposed area of the nerve root was measured using a neurophysiological technique.

There was a reduction in blood flow in the nerve root after disc incision that began after 1 day and was maximal after 1 week. This reduction had resolved by 1 month, however. The motor NCV showed a reduction pattern similar to that for blood flow in the nerve root, but reduction did not begin until 3 days after disc incision and was not fully resolved until 2 months.

This study demonstrates that the reduction and recovery of motor NCV are related to, and preceded by, a reduction in blood flow in the nerve root. The data might provide important information regarding the basic pathophysiological mechanisms of nucleus pulposus-induced nerve root injury.