Satoru Kayama

Incision of the anulus fibrosus induces nerve root morphologic, vascular, and functional changes : An experimental study

Study Design The effects on nerve root structure, vasculature, and function after incision of the adjacent disc was studied in a dog model. Objectives To see if only incision of the disc per se is sufficient for inducing similar changes. Summary of Background Data It is well known that nucleus pulposus will induce nerve root structural and functional changes in experimental situations. In these previous studies, relatively large amounts of nucleus pulposus were applied. Methods The left L7 nerve root was exposed and mobilized in 10 dogs. In five dogs, the adjacent L6‐L7 disc was incised, and in five other dogs, the disc was not incised. After 7 days, nerve conduction velocity was recorded, and specimens were obtained for histologic evaluation. Results The nerve conduction velocity was significantly lower in the incision group (13 ± 14 m/sec) compared with the nonincision group (73 ± 5 m/sec). Structural changes of the axons were more pronounced in the incision group, however, the degree and distribution was too limited to fully account for the neurophysiologic reactions observed. There also were obvious signs of capillary stasis with an increased number and diameter of the intraneural capillaries in the incision group. Conclusions The present study indicated that incision of the anulus fibrosus is sufficient to induce significant morphologic and functional changes and that vascular mechanisms may be of importance for the observed changes. These experimental data suggest that leakage of nucleus pulposus material from anular tears, with injury to adjacent nerve roots, might be one pathophysiologic mechanism in patients with low back pain and sciatica but with no radiologic or surgical evidence of disc herniation.

Cultured, autologous nucleus pulposus cells induce functional changes in spinal nerve roots.

Study Design. Nerve conduction velocity in pig nerve roots was assessed after application of various preparations of nucleus pulposus and control. Objective. To study whether cultured nucleus pulposus cells could reduce nerve conduction velocity after epidural application. Summary of Background Data. It is known that nucleus pulposus applied epidurally may reduce the nerve conduction velocity of the adjacent nerve roots and that this reduction seems to be related to the cells of the nucleus pulposus. Methods. Nucleus pulposus cells and fibroblasts were cultured for 3 weeks, and various preparations were applied to the cauda equina in 29 pigs. The cells were always from the same animals from which they had been harvested. After 1 week, nerve conduction velocity was determined by local electrical stimulation. Results. Application of live fibroblasts and conditioned culture medium from the nucleus pulposus cell culture dishes did not induce significant reduction of conduction velocity, compared with application of dead fibroblasts, which served as control. However, application of live and dead nucleus pulposus cells induced significant reductions. Conclusions. Application of nucleus pulposus cells reproduced the previously seen reduction in nerve conduction velocity induced by nonmodified nucleus pulposus. Because membranes of the nucleus pulposus cells had similar effects, it can be assumed that the effects are related to membrane‐bound substances or structures.

Anatomic study of the axis for surgical planning of transarticular screw fixation

Transarticular screw fixation has shown increased stability compared with other posterior stabilization techniques. However, there have been few reports on vertebral artery injury related to the screw insertion. The current study measured the parameters of the pedicle and vertebral artery groove of the axis and clarified the accuracy and safety of the transarticular screw fixation. Direct measurements were taken from 98 dry axis vertebrae. The width and height of the pedicle were measured. The mediolateral and anteroposterior dimensions of the vertebral artery groove also were measured. Forty-one percent had asymmetry. In 20% of the specimens, the pedicle was smaller than the diameter of the screw (3.5 mm). The pedicle of the axis has large anatomic variability and asymmetry. Some pedicles were not suitable for atlantoaxial transarticular screw fixation. The risks associated with screw fixation should be prevented by preoperative computed tomography with three-dimensional reconstruction. Screw trajectory reconstruction with coronal and sagittal reconstruction is useful to evaluate the pedicle width and height.

Increased resistance to acute compression injury in chronically compressed spinal nerve roots : An experimental study

Study Design Nerve conduction velocity was studied in the dog cauda equina subjected to chronic and, 1 week later, additional acute compression. Objectives To model the situation of spinal stenosis by first inducing a controlled, chronic compression injury and then to add compression at various pressure levels to the already compressed cauda equina. Summary of Background Data Previous models on nerve root and cauda equina compression have analyzed the effects of compression only on noninjured nerves. Clinically, the nerves that are compressed in spinal stenosis already are exposed to chronic compression. Methods The cauda equina in the lumbar spine of 10 dogs was first compressed by inflating a plastic balloon, which was placed in the spinal canal, to 10 mm Hg with a viscous substance or leaving it noninflated for control. After 1 week, a second plastic balloon, which was welded together with the first balloon, which had been located in the spinal canal for 1 week, was inflated to 50 or 100 mm Hg for 2 hours with 1.5 hour of recovery, and changes in the nerve conduction velocity were analyzed. Before inflation, baseline data, reflecting the effects of the chronic compression per se, were obtained. Results After 1 week, the nerve conduction velocity was significantly lower in the compressed cauda equina than in the control series, as an effect of the chronic compression. Additional compression demonstrated that the chronically compressed cauda equina was less susceptible to the compression‐induced effects at 100 mm Hg compression. Conclusions The data of the present study indicate that chronically compressed nerve roots acquire a tolerance to acute compression, which may indicate that there has been adaptation processes present in the compressed nerve tissue.

Effects of OP-1206 (prostaglandin E1) on nerve-conduction velocity in the dog cauda equina subjected to acute experimental compression.

The effect of OP-1206, a prostaglandin E1 derivative, on cauda equina function was analyzed in a model for acute cauda equina compression in the dog. An inflatable balloon was placed under the lamina of the seventh lumbar vertebra in the dog and muscle action potential area (MAP area) and nerve-conduction velocity (NCV) were monitored during 2 h of compression and 1.5 h of recovery. OP-1206 was infused systemically at three concentrations. Only the highest concentration (30 ng/kg/min) of OP-1206 could prevent the reduction in NCV. However, this concentration had no similar effect on the MAP area. The data suggest the potential therapeutic use of prostaglandin E1 analogues for the future treatment of intermittent claudication.

Nucleus pulposus inhibits the axonal outgrowth of cultured dorsal root ganglion cells

Abstract Although it is well established that nucleus pulposus cells may induce structural and functional changes in adjacent nerve roots when placed epidurally, it is not known whether this is due to direct neurotoxic effects or whether the nerve roots are affected indirectly by reduction of nutrition and inflammatory/immunologic mechanisms. In the present study we assessed the effects of various tissues on cultured dorsal root ganglions from newborn rats. Nucleus pulposus was found to have a toxic effect on the axons by blocking axonal outgrowth, but no similar effects on the nerve cell bodies (extra-ganglionic nerve cell density, nerve cell arborisation) were found as compared to the series with only culture medium. Sterile water for 1 or 24 h (positive controls) induced significant effects by all four criteria, whereas medium without nerve growth factor, fat and frozen nucleus pulposus had no statistically significant effects. The study thus showed that there are direct axonotoxic effects induced by the nucleus pulposus, and since frozen nucleus pulposus did not have any effects, it may be assumed that the mechanisms are related to substances produced by the nucleus pulposus cells. The presented model allows for future studies on the neurotoxic properties of nucleus pulposus cell-derived candidate substances.

Intramedullary spinal cord sarcoidosis : report of two cases

Two cases of intramedullary spinal cord sarcoidosis are reported. These lesions could not be differentiated from neoplastic spinal cord tumors by clinical findings or imaging studies. In magnetic resonance imaging, the lesions were enhanced around the gray matter with gedlinium diethylene triamine pentaacetic acid (Gd-DTPA). The true diagnosis was established only by histologic examination of the surgical specimen. The possibility of intramedullary sarcoidosis presenting as a tumor should be included in the differential diagnosis of mass lesions of the spinal cord.

Tolerance to acute compression injury and recovery of nerve function in chronically compressed spinal nerve roots: Experimental study

Chronic compression (10 mm Hg for 1 week) of spinal nerve roots in a dog experimental model has been shown to reduce nerve conduction velocity. Although injured, the compressed nerve roots demonstrated increased resistance to acute compression applied in addition to the chronic compression after 1 week. In the present study reduction of nerve conduction velocity induced by chronic compression recovered when the duration of compression was extended to 1 month. However, the tolerance to additionally applied compression was still present. This study provides important base-line data for continued studies of the basic mechanisms of the development of tolerance to changes in compression pressure levels in chronically compressed nerve roots.

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.