Kjell Olmarker

Autologous nucleus pulposus induces neurophysiologic and histologic changes in porcine cauda equina nerve roots

Epidural application of autologous nucleus pulposus in pigs, without mechanical nerve root compression, induced a pronounced reduction in nerve conduction velocity in the cauda equina nerve roots after 1-7 days, compared to epidural application of retroperitoneal fat in control experiments. Histologically, the nerve fiber injury was more pronounced after application of nucleus pulposus than after control tissue application. The results demonstrate that nucleus pulposus may induce nerve tissue injury by mechanisms other than mechanical compression. Such mechanisms may be based on direct biochemical effects of nucleus pulposus components on nerve fiber structure and function and microvascular changes including inflammatory reactions in the nerve roots.

Inflammatogenic properties of nucleus pulposus

Study Design The inflammatogenic properties of nucleus pulposus were assessed in two experimental models previously used for screening of inflammatogenic properties of other substances. This study was performed to assess the inflammatogenic properties of nucleus pulposus in models previously screened for other substances. Summary of Background Data Previous experimental studies, as well as clinical observations, have indicated that inflammatory mechanisms may constitute an important pathogenetic component in sciatica due to herniation of the nucleus pulposus. Methods In the first experimental series, autologous nucleus pulposus and retroperitoneal fat were placed in perforated titanium chambers, which were placed subcutaneously in pigs, together with an empty chamber as sham. After 7 days, the number of leukocytes in the chambers was determined. In the second experimental series, the microvascular reactions were studied by vital microscopy of the hamster cheek-pouch after local injections of suspensions of homologous nucleus pulposus and homologous subcutaneous fat. Macromolecular extravascular leakage was studied by fluorescence microscopy using FITC-dextran as a tracer. Results The leukocyte ration between fact control and sham was 0.9 ± 0.6 and between nucleus pulposus and sham 2.4 ± 0.7. The nucleus pulposus thus attracted significantly more leukocytes than fat. Injection of nucleus pulposus suspension induced thrombosis formation and pronounced leakages of macromolecules in a majority of the injection sites. However, injection of vehicle and fat suspension in the cheek-pouch only resulted in minor vital microscopic changes. Conclusions Nucleus pulposus demonstrated inflammatogenic properties as indicated by leukotaxis and an increase of vascular permeability. It was not clear, however, if these reactions were induced by substances from the nucleus pulposus per se or from substances being liberated from other tissues as a response to an interaction with components of the nucleus pulposus.

Edema formation in spinal nerve roots induced by experimental, graded compression. An experimental study on the pig cauda equina with special reference to differences in effects between rapid and slow onset of compression.

Edema formation in spinal nerve roots of the pig cauda equina was studied following experimental compression at various pressure levels, durations, and rates of onset, using a fluorescence microscopic technique. The time–pressure thresholds for the occurrence of edema in the nerve roots were: following rapid onset of compression (0.05–0.1 seconds), 2 minutes at both 50 mm Hg and 200 mm Hg, and following slow onset of compression (the pressure was slowly increased during 15–20 seconds), 2 hours at 50 mm Hg and 2 minutes at 200 mm Hg. Generally, the edema formation was more pronounced after rapid than after slow onset of compression. The data in this study also indicate that intraneural edema might be more easily formed in nerve roots than in peripheral nerves after compression injury.

Ultrastructural changes in spinal nerve roots induced by autologous nucleus pulposus

Study Design Ultrastructural changes were analyzed by transmission electron microscopy in nerve roots exposed to autologous nucleus pulposus experimentally. Objectives To assess if ultrastructural changes were present in areas with no light microscopic changes in nerve roots exposed to autologous nucleus pulposus in a pig model. Summary of Background Data Previous analyses have shown that there is focal nerve fiber damage in nerve roots exposed to autologous nucleus pulposus in the pig. These changes could not fully explain the reduction in nerve conduction velocity seen in the same nerve roots. In the present study, the parts of the nerve roots that did not display breakdown of axons or myelin sheaths at the light microscopic level were analyzed regarding ultrastructural changes. Methods In a previous study, nucleus pulposus was harvested from a lumbar disc and placed epidurally onto the cauda equina at the sacrococcygeal level in pigs. Retroperitoneal fat was used as control. After 1, 3, and 7 days, the nerve roots were excised and processed for light microscopy. Parts of the nerve roots that appeared normal at the light microscopic level were further processed for the present electron microscopic examination. Results Significant ultrastructural changes, such as expansion of the Schwann cell cytoplasm and intracellular edema with vesicular swelling of the Schmidt‐Lanterman incisures, were observed in nerve fibers with normal axons. Although present after nucleus pulposus and control application, the changes were more pronounced after the application of nucleus pulposus. Conclusions Epidural application of autologous nucleus pulposus without any pressure may induce not only nerve function impairment but also axonal injury and significant primary Schwann cell damage with vesicular swelling of the Schmidt‐Lanterman incisures. However, because axonal and Schwann cell changes affected only part of the nerve fibers, further causes of the impaired nerve conduction need to be determined.

Effects of methylprednisolone on nucleus pulposus-induced nerve root injury

Study Design. The effects of intervention by intravenous injection of methylprednisolone to reduce the nerve root injury after epidural application of autologous nucleus pulposus was studied in an experimental model on the pig cauda equina in 20 animals. Methods. Nucleus pulposus was harvested from a lumbar disc. After lowering the pH of the nucleus pulposus to 3.5 it was placed onto the sacrococcygeal cauda equina. Fifteen of the pigs received a single intravenous injection of 30 mg/kg methylprednisolone, 5 minutes, 24 hours, or 48 hours, respectively, after the application. After 7 days, the nerve conduction velocity was determined, and biopsies of the cauda equina was examined by lightmicroscopy. Results. In the live pigs that did not receive any methylprednisolone treatment, nerve conduction velocity was reduced, whereas it was normal in the pigs treated 5 minutes and 24 hours after nucleus pulposus application. In pigs treated after 48 hours, nerve conduction velocity was reduced only slightly. At the light microscopic level, significant changes occurred in all series. Conclusions. This study indicates that the nucleus pulposus-induced effects on nerve function in an experimental pig model may be reduced dramatically by high-dose methylprednisolone administration within 24–48 hours after epidural application of autologous nucleus pulposus. The light microscopic changes were probably not significant for the nerve function. Instead, a morphologic explanation on a subcellular level should probably be sought.

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.

Proinflammatory cytokines in cerebrospinal fluid and serum in patients with disc herniation and sciatica.

Abstract. Proinflammatory cytokines have been identified in herniated intervertebral discs in humans, and such cytokines have experimentally been demonstrated to be important in the pathophysiological mechanisms of disc herniation. Cerebrospinal fluid (CSF) and serum concentrations of interleukin (IL)-1β, IL-6, IL-8, interferon (IFN)-γ and tumour necrosis factor (TNF)-α were investigated using the enzyme-linked immunosorbent assay (ELISA) technique in 39 patients with lumbar disc herniation and sciatica. Pain duration and pain intensity (visual analogue scale, VAS) were recorded at inclusion, and a clinical examination was performed evaluating neurological findings. The extent of disc herniation (protrusion or extrusion/sequestration) was evaluated perioperatively. Normal concentrations of IL-1β, IL-6, IFN-γ and TNF-α were present in CSF and serum in almost all patients with lumbar disc herniation. The concentrations of IL-8 in CSF were increased in 12 out of 39 patients, and these increased levels of IL-8 correlated to a short duration of pain and to more pronounced herniation (extrusion or sequestration). No relationship between IL-8 concentrations in CSF and pain intensity, positive neurological findings or a positive straight leg-raising (SLR) test was found. The observation of increased concentrations of IL-8 in CSF in patients with a short duration of symptoms supports the concept of the initial involvement of inflammatory mechanisms after a disc herniation. The finding that most of the patients with increased concentrations of IL-8 in CSF had an extrusion or a sequestration may suggest that the increase in IL-8 is related to mechanical nerve root compression, but may also indicate a biochemical effect exerted by the herniated disc on the surrounding tissue. Further studies on the potential role of IL-8 as a biomarker for disc herniation are warranted.

Back muscle injury after posterior lumbar spine surgery. Topographic evaluation of intramuscular pressure and blood flow in the porcine back muscle during surgery.

Study Design Intramuscular pressure and blood flow of the back muscles were evaluated topographically during posterior lumbar spine surgery. The topographic damage of the back muscle after surgery was studied. Objective To investigate the relationship between intramuscular pressure or blood flow during posterior lumbar surgery and the back muscle injury after surgery. Summary of Background Data Iatrogenic back muscle injury in an animal and human model has been reported previously. Changes of intramuscular pressure and blood flow during surgery might be related to the muscle injury. No previous study on this issue has been published. Methods The contact pressure between the retractor blade and muscle tissue was monitored in 10 pigs during posterior surgery of the lumbar spine. On one side, intramuscular pressure at 5, 10, and 20 mm lateral to the retractor and on the other side blood flow of the back muscle at 5 and 20 mm during surgery were measured. Histologic changes of the back muscle at 5, 10, and 20 mm to the midline were evaluated 3 hours after surgery. Results The contact pressure decreased exponentially with time. Intramuscular pressure 5 mm lateral to the retractor was 114 ± 31 mm Hg and was significantly higher than at 10 mm and 20 mm. Blood flow markedly decreased during surgery and recovered incompletely after releasing the retractor at 5 mm and 20 mm lateral to the retractor. Blood flow at 5 mm was significantly lower than at 20 mm throughout surgery. The muscle damage 3 hours after surgery was more severe near the retractor blade. Conclusions The back muscles were exposed to pathophysiologic condition by a retractor during posterior lumbar spine surgery. External compression by a retractor increases intramuscular pressure to levels that impede local muscle blood flow. The muscle degeneration after surgery could be explained by direct mechanical damage and by the increased intramuscular pressure of muscle tissue by the retractor.

Inflammatory cytokines released from the facet joint tissue in degenerative lumbar spinal disorders.

Study Design. A prospective study of surgical cases of degenerative lumbar spinal disorders demonstrated inflammatory cytokines in the facet joint tissue. Objective. To quantify various inflammatory cytokines released from the facet joint tissue in surgical cases of degenerative lumbar spinal disorders. Summary of Background Data. In degenerative lumbar spinal disorders, pain is often caused by osteoarthritis of a facet joint. There are inflammatory mediators such as prostaglandins and leukotrienes in facet joint tissue in lumbar spinal degeneration. However, no reports have studied if there are also inflammatory cytokines in the facet joint, which generated arthropathic changes in degenerative lumbar spinal disorder and if pain is caused by chemical factors associated with inflammation such as inflammatory cytokines. Methods. Forty patients with degenerative lumbar disorders who had undergone operative treatment were included in this study. Fifty-five joint cartilages and 67 synovia were harvested from the lumbar facet joints in responsible intervertebral levels of patients. There were 24 male and 16 female subjects with average ages of 50 and 67 years, respectively, in 11 cases of lumbar disc herniation and 29 cases of lumbar spinal canal stenosis. Using ELISA and CLEIA methods, joint cartilage and synovial tissues were harvested during surgery from the facet joint at the responsible upper levels to measure IL-1β, TNF-α, and IL-6 in individual tissues. Results. IL-1β was detected in joint cartilage and synovium in both groups and its positive reaction rate was higher in LSCS than in LDH. There was no difference in IL-1β concentration in cartilage tissue between the two groups. There was TNF-α in the synovium of LSCS. IL-6 was high in joint cartilage and synovium in both groups. The concentration was significantly higher in LSCS than in LDH. Conclusions. There are inflammatory cytokines in facet joint tissue at high levels in degenerative lumbar spinal disorders. Inflammatory cytokines have a higher concentration rate in lumbar spinal canal stenosis than in lumbar disc herniation. This finding suggests that inflammatory cytokines in degenerated facet joints may have some relation to the cause of pain in degenerative lumbar disorders.

Local application of disc-related cytokines on spinal nerve roots.

Study Design. To analyze the effects of tumor necrosis factor-&agr;, interleukin-1&bgr;, and interferon-&ggr; on cauda equina function and to define if any of these cytokines could induce nerve root dysfunction comparable with the situation with application of nucleus pulposus. Summary of Background Data. Proinflammatory cytokines derived from the intervertebral disc have been suggested to mediate the nucleus pulposus–induced nerve root injury following local application of nucleus pulposus. However, it is not known if such cytokines may induce similar injury if applied separately. Methods. A total of 29 pigs were used. Nucleus pulposus was harvested from lumbar discs and applied to the sacrococcygeal cauda equina following laminectomy of the first coccygeal vertebra in seven pigs. Five pigs received 1.66 &mgr;g of tumor necrosis factor-&agr;, five pigs received 0.85 &mgr;g of interleukin-1&bgr;, and five pigs received 1.66 &mgr;g of interferon-&ggr;. Seven pigs received autologous fat for control. Nerve conduction velocity was studied by local electrical stimulation and recordings in the tail muscles 7 days after the application. Results. Application of nucleus pulposus and fat induced similar effects as seen in previous studies, with normal nerve conduction velocity for fat and a significant reduction for nucleus pulposus. Application of both interleukin-1&bgr; and IFN-&ggr; induced slight reductions of nerve conduction velocity compared with fat, but they were not statistically significant. Tumor necrosis factor-&agr;, however, induced a reduction of the velocity that was even more pronounced than for nucleus pulposus. Conclusion. Based on previous observations and the data of the present study, one may conclude that tumor necrosis factor-&agr; from nucleus pulposus cells seems to be intimately involved with the basic pathophysiologic events leading to both nerve root dysfunction and pain after local, epidural application of nucleus pulposus. One may therefore also suspect that pharmacologic inhibition of tumor necrosis factor-&agr; may at least theoretically be considered in the clinical situation with disc herniation and sciatica.