Itaru Arai

Experimental disc herniation: evaluation of the natural course.

Study Design. Changes in L7 nerve root conduction velocity and changes in appearance on magnetic resonance study of the L6‐L7 intervertebral disc in the dog were assessed for 2‐6 months after an experimental disc herniation was performed. Objectives. To assess the time‐related changes of nerve conduction velocity and magnetic resonance changes of the invertebral discs. Summary of Background Data. It is known that nucleus pulposus may induce nerve root morphologic and functional changes when applied epidurally. However, it is not known whether such changes are reversible. Methods. The spinal canal was opened by laminotomy of the upper part of the L7 lamina and the lower part of the L6 lamina on the left side. The L7 nerve root was gently retracted (sham) or the disc was punctured and injected with saline to produce herniation of the nucleus pulposus during the retraction time (herniation). After 1 day to 2 months, nerve root conduction velocity was determined by local electrical stimulation. Six dogs had the herniation or the sham procedure, and the L6‐L7 disc was studied by magnetic resonance imaging at various times up to 6 months after the procedure. Results. Decrease in nerve conduction velocity reached a maximum after 7 days and recovered to baseline level fully within 2 months. Although there was a clear reduction‐recovery pattern, the difference in conduction velocity compared with that of the sham group was statistically significant after only 7 days. Disc degeneration started in the herniated discs within 7 days after the herniation procedure. However, none of the experimentally induced disc herniations were visualized by magnetic resonance imaging 7 days after the procedure. In no case was there subsequent nerve root compression. In one case, disc protrusion was visible 6 months after the herniation procedure. Conclusions. The results demonstrate for the first time that nucleus pulposus‐induced nerve root injury reverses in 2 months and that it may be present without simultaneous nerve root compression, as confirmed by findings in magnetic resonance imaging. The previously described nucleus pulposus‐induced nerve root changes may therefore be of clinical importance, and experimental studies of these mechanisms will probably be relevant for expanded understanding of the pathophysiologic mechanism behind sciatica that is caused by disc herniation.

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

OBJECTIVE 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. METHODS 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. RESULTS 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. CONCLUSION 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.

Chronic double-level cauda equina compression : An experimental study on the dog cauda equina with analyses of nerve conduction velocity

Study Design. Nerve conduction velocity was studied in the dog cauda equina subjected to chronic double‐level compression. Objectives. To analyze the effects of chronic double‐level cauda equina compression. Summary of Background Data. Double‐level cauda equina compression produces more symptoms in patients and more changes in acute experimental set‐ups than does single‐level compression. However, there have been no controlled, experimental studies on chronic double‐level compression. Methods. A total of 20 dogs were anesthetized. Two balloons were placed under the lamina of the seventh lumbar vertebra and the first sacral vertebra, respectively. One week (10 mm Hg, n = 5; 0 mm Hg, n = 5) and 1 month (10 mm Hg, n = 5; 0 mm Hg, n = 5) after inflation with a viscous substance, nerve conduction velocity was studied by local electrical stimulation and recording of muscle action potentials in the tail muscles. Results. Nerve conduction velocity was determined over the cranial balloon, the caudal balloon, and both balloons. The data were similar for all three recordings. After 1 week there was a significant reduction in nerve conduction velocity induced by 10 mm Hg, compared with that induced by 0 mm Hg, which showed normal conditions. However, after 1 month this initial reduction in nerve conduction velocity had recovered partially. The reduction was similar to that described for single‐level compression in a previous study in which the same compression model was used. Conclusions. Unlike the acute situation, chronic double‐level compression does not induce more changes than single‐level compression after 1 week, although the recovery after 1 month of compression is less complete after double‐level compression. This less complete recovery may be a result of an adaptation of the nerve tissue and the vascularization of the cauda equina nerve roots to the applied pressure.

Indomethacin blocks the nucleus pulposus-induced effects on nerve root function. An experimental study in dogs with assessment of nerve conduction and blood flow following experimental disc herniation.

Inflammatory mechanisms have been suggested to be involved in the basic pathophysiologic events leading to nerve root injury after local application of nucleus pulposus. To assess if these nucleus pulposus-induced effects could be blocked by anti-inflammatory treatment, 41 dogs were exposed to either incision of the L6-7 disc to induce experimental disc herniation with (n=12) or without (n=14) indomethacin treatment per os (5 mg/kg per day), and no incision with (n=5) or without (n=10) indomethacin. Intraneural blood flow and nerve conduction velocity were assessed after 7 days to evaluate the degree of nerve injury. Disc incision induced a reduction in nerve root and dorsal ganglion blood flow as well as nerve function, similarly to previous studies. However, simultaneous treatment with indomethacin efficiently blocked the negative effects on both blood flow and nerve conduction but had no effects per se. The present study thus indicates that inflammatory mechanisms may be of relevance in the pathophysiology of nucleus pulposus-induced nerve root injury and thereby also for sciatica.

Effects of beraprost sodium on canine cauda equina function and blood flow using a chronic spinal cord compression model.

Changes in blood flow after chronic compression were observed in 19 dogs after 10 mmHg compression for 1 week before and 1 hour after the intravenous administration of one of three doses of beraprost sodium (BPS; 30 ng x kg(-1) x min(-1), n = 7; 100 ng x kg(-1) x min(-1), n = 7; and 300 ng x kg(-1) x min(-1), n = 5). The speed of blood flow was calculated using a specially designed microscope equipped with a video camera. Dogs treated with BPS had lesser degrees of reduction in their nerve conduction velocity compared with controls. A vascular mechanism of injury likely explains why BPS-treated dogs had a lesser degree of reduction in their nerve conduction velocities compared with the control population.

FOUR-YEAR FOLLOW-UP OF PREGNANCY-ASSOCIATED OSTEOPOROSIS : A CASE REPORT

A 22-year-old woman presented with complaints of severe pain in a wide region of the thoracolumbar spine. She developed severe pain in the thoracolumbar spine region 2 months after her first delivery and was referred 1 month later. A lateral thoracic X-ray showed depressed degenerative vertebrae (T7, T9). One month after the initial examination, thoracic sagittal magnetic resonance imaging showed low intensity areas on T1-weighted imaging and iso-high intensity areas on T2-weighted imaging at T5, 7, 8, 9 and 11. Bone mineral density measured by ultrasound was low (%YAM 76%). The bone metabolic markers were high, suggesting accelerated osteoclast activity. These findings prompted a diagnosis of pregnancy-associated osteoporosis. She was asked to stop breastfeeding and to wear a lumbar brace, and treatment with nutritional calcium, activated vitamin D3, and risedronate sodium was started. Her low back pain almost disappeared after treatment. Bone metabolic markers showed normalization 8 months after the initial examination. Risedronate sodium was stopped 2 years and 2 months after the initial examination. Teriparatide treatment was started because her bone mineral density remained low; however, the osteoblast marker P1NP was not increased 5 months after the start of teriparatide treatment.