Pathology of spinal cord lesions caused by ossification of the posterior longitudinal ligament, with special reference to reversibility of the spinal cord lesion

Compression analysis of the gray and white matter of the spinal cord

The spinal cord is composed of gray matter and white matter. It is well known that the properties of these two tissues differ considerably. Spinal diseases often present with symptoms that are caused by spinal cord compression. Understanding the mechanical properties of gray and white matter would allow us to gain a deep understanding of the injuries caused to the spinal cord and provide information on the pathological changes to these distinct tissues in several disorders. Previous studies have reported on the physical properties of gray and white matter, however, these were focused on longitudinal tension tests. Little is known about the differences between gray and white matter in terms of their response to compression. We therefore performed mechanical compression test of the gray and white matter of spinal cords harvested from cows and analyzed the differences between them in response to compression. We conducted compression testing of gray matter and white matter to detect possible differences in the collapse rate. We found that increased compression (especially more than 50% compression) resulted in more severe injuries to both the gray and white matter. The present results on the mechanical differences between gray and white matter in response to compression will be useful when interpreting findings from medical imaging in patients with spinal conditions.

Surgical management of ossification of the posterior longitudinal ligament in the cervical spine

OPLL is a progressive process that can result in spinal cord compression and myelopathy. Various surgical approaches for the management of OPLL in the cervical spine exist. Our goal is to present our institution's experience in the management of OPLL over the last 20 years. Sixty-eight patients underwent surgery for cervical OPLL. Mean age at surgery was 56.9 years. No differences between demographic characteristics and surgical approach were identified. There were no significant differences between the approaches regarding the mean estimated blood loss, occurrence of durotomy, reoperation rate, positive K-line and preoperative cervical spine sagittal balance. Number of levels operated on was significantly different (anterior approach 2 ± 0.8 levels, posterior approach 4.3 ± 1.3 levels, combined approach 3.3 ± 0.9 levels, p-value <0.01), but postoperative sagittal balance was not (anterior approach Cobb angle 11.9 ± 5.8 degrees, posterior approach Cobb angle 7 ± 3.5 degrees, combined approach Cobb angle 16.7 ± 7.3 degrees, p-value = 0.09). Functional outcomes were good for 70% of patients and did not significantly differ across approaches (anterior approach 28%, posterior approach 33%, combined approach 9%, p-value = 0.46). Good functional outcomes were more commonly observed in patients with a positive K-line (OR 0.2, 95% CI 0.04-0.9, p-value 0.05) while poor outcomes were most commonly observed in patients with an occupational ratio >0.6 (OR 6.9, 95% CI 1.35-42.7, p-value 0.02). OPLL is a rare disease for which prompt referral for surgical decompression may lead to good clinical outcomes.

Role of macrophages and activated microglia in neuropathic pain associated with chronic progressive spinal cord compression

Neuropathic pain (NeP) is commonly encountered in patients with diseases associated with spinal cord damage (e.g., spinal cord injury (SCI) and compressive myelopathy). Recent studies described persistent glial activation and neuronal hyperactivity in SCI, but the pathomechanisms of NeP in chronic compression of the spinal cord remains elusive. The purpose of the present study was to determine the roles of microglia and infiltrating macrophages in NeP. The study was conducted in chimeric spinal hyperostotic mice (ttw/ttw), characterized by chronic progressive compression of the spinal cord as a suitable model of human compressive myelopathy. The severity of spinal cord compression correlated with proportion of activated microglia and hematogenous macrophages. Spinal cord compression was associated with overexpression of mitogen-activated protein kinases (MAPKs) in infiltrating macrophages and reversible blood-spinal cord barrier (BSCB) disruption in the dorsal horns. Our results suggested that chronic neuropathic pain in long-term spinal cord compression correlates with infiltrating macrophages, activated microglial cells and the associated damage of BSCB, together with overexpression of p-38 MAPK and p-ERK1/2 in these cells. Our findings are potentially useful for the design of new therapies to alleviate chronic neuropathic pain associated with compressive myelopathy.

Intramedullary high signal intensity and neurological status as prognostic factors in cervical spondylotic myelopathy

PURPOSE

The neurological outcome of cervical spondylotic myelopathy (CSM) may depend on multiple factors, including age, symptom duration, cord compression ratio, cervical curvature, canal stenosis, and factors related to magnetic resonance (MR) signal intensity (SI). Each factor may act independently or interactively with others. To clarify the factors in prognosis, we prospectively analyzed the outcomes of patients with myelopathy caused by soft disc herniation in correlation with magnetic resonance imaging (MRI) findings and other clinical parameters.

MATERIALS AND METHODS

From June 2006 to July 2009, we performed surgical operations in 137 patients with CSM. Of these patients, 70 (51.1%), including 45 men and 25 women with ventral cord compression at one or two levels, underwent anterior cervical discectomy and fusion. The mean duration of follow-up was 32.7 months. We surveyed the cervical curvature index (CCI), canal stenosis (Torg-Pavlov ratio), cord compression ratio, the length of SI change on T2WI, and clinical outcome using the Japanese Orthopedic Association (JOA) score for cervical myelopathy. The MRI SI was evaluated by grade: grade 0, no change in signal intensity; grade 1, light signal change; and grade 2, bright signal change on the T2WI. Multifactorial effects were identified by regression analysis.

RESULTS

The mean preoperative and postoperative JOA scores were 10.5 ± 2.9 and 14.9 ± 2.1, respectively (p < 0.05). The mean recovery rate based on the JOA score was 70.0 ± 20.1%. The respective preoperative JOA scores and recovery ratios(%) were 11.6 ± 2.3 and 81.5 ± 17.0% in 20 patients with SI grade 0; 10.8 ± 2.3 and 70.1 ± 17.3% in 25 patients with grade 1; and 9.2 ± 3.6 and 60.7 ± 20.9% in 25 patients with grade 2, respectively. Post-surgical neurological outcome showed no significant relationship to age, symptom duration, cervical alignment, stenosis, or cord compression.

CONCLUSIONS

Among the variables tested, preoperative neurological status and intramedullary signal intensity were significantly related to neurological outcome. The better the preoperative neurological status was, the better the post-operative neurological outcome. The SI grade on the preoperative T2WI was negatively related to neurological outcome. Hence, the severity of SI change and preoperative neurological status emerged as significant prognostic factors in post-operative CSM.

Tumor necrosis factor-alpha and its receptors contribute to apoptosis of oligodendrocytes in the spinal cord of spinal hyperostotic mouse (twy/twy) sustaining chronic mechanical compression

STUDY DESIGN.: To examine the distribution of apoptotic cells and expression of tumor necrosis factor (TNF)-alpha and its receptors in the spinal hyperostotic mouse (twy/twy) with chronic cord compression using immunohistochemical methods. OBJECTIVE.: To study the mechanisms of apoptosis, particularly in oligodendrocytes, which could contribute to degenerative change and demyelination in chronic mechanical cord compression. SUMMARY OF BACKGROUND DATA.: TNF-alpha acts as an external signal initiating apoptosis in neurons and oligodendrocytes after spinal cord injury. Chronic spinal cord compression caused neuronal loss, myelin destruction, and axonal degeneration. However, the biologic mechanisms of apoptosis in chronically compressed spinal cord remain unclear. METHODS.: The cervical spinal cord of 34 twy mice aged 20 to 24 weeks and 11 control animals were examined. The apoptotic cells were detected by the terminal deoxynucleotidyl transferase (TdT)-mediated dUTP-biotin nick end labeling (TUNEL) staining. The expression and the localization of TNF-alpha, TNF receptor 1 (TNFR1), and TNF receptor 2 (TNFR2) were examined using immunoblot and immnohistochemical analysis. RESULTS.: The number of TUNEL-positive cells in the white matter increased with the severity of compression, which was further increased bilaterally in the white matter of twy/twy mice. Double immunofluorescence staining showed that the number of cells positive for TUNEL and RIP, a marker of oligodendrocytes, increased in the white matter with increased severity of cord compression. Immunoblot analysis demonstrated overexpression of TNF-alpha, TNFR1, and TNFR2 in severe compression. The expression of TNF-alpha appeared in local cells including microglia while that of TNFR1 and TNFR2 was noted in apoptotic oligodendrocytes. CONCLUSION.: Our results suggested that the proportion of apoptotic oligodendrocytes, causing spongy axonal degeneration and demyelination, correlated with the magnitude of cord compression and that overexpression of TNF-alpha, TNFR1, and TNFR2 seems to participate in apoptosis of such cells in the chronically compressed spinal cord.

Neuronal loss and expression of neurotrophic factors in a model of rat chronic compressive spinal cord injury

STUDY DESIGN

An experimental animal study about neuronal loss and the expression of neurotrophic factors in the chronic compressive spinal cords.

OBJECTIVES

To investigate neuronal loss and the expression of neurotrophic factors in the chronic compressive spinal cords of rats, and to evaluate effects of decompressive procedures for the neuronal loss.

SUMMARY OF BACKGROUND DATA

Chronic compression of spinal cords induces the loss of motor neurons in the anterior horn. However, the precise mechanism of this neuronal loss is not still understood completely. Furthermore, it is uncertain whether decompressive procedures prevent this neuronal loss or not.

METHODS

A thin expanding polymer sheet was implanted microsurgically underneath T7 laminae of rats. After 6, 9, 12, and 15 weeks, the thoracic spinal cord was harvested and examined histopathologically. The expression of neurotrophic factors, including NGF, BDNF, NT-3, GDNF, CNTF, and VEGF, was analyzed using semiquantitative RT-PCR, enzyme immunoassay, and immunohistochemistry. Decompressive surgery was performed through the removal of T7 laminae and the compression materials 6, 9, and 12 weeks after starting compression. Three weeks later, respectively, the neuronal loss in the anterior horn was estimated.

RESULTS

The spinal cords were progressively flattened by the expanding of the implanted polymer sheet, and the number of motor neurons in the anterior horn decreased, especially from 6 to 9 weeks after starting compression. Semiquantitative RT-PCR analysis showed that the expression of NGF and BDNF mRNAs was decreased significantly in the spinal cords of 12-week compression group compared with the 6-week compression group and that NGF mRNA expression was up-regulated significantly in the 6-week compression group relative to the 6-week control group. Any changes of expression of other neurotrophic factors were not significant. Since BDNF, not NGF, has been known to be one of the powerful survival factors for spinal motoneurons, we investigated the levels of BDNF protein in the compressive spinal cords using enzyme immunoassay and immunohistochemistry. We demonstrated the level of BDNF protein in the compressive spinal cords was increased 6 weeks after compression but declined after 12 weeks. The decompressive procedure in the 6 weeks after compression prevented neuronal loss, but the same procedure in the 9 or 12 weeks was ineffective.

CONCLUSIONS

From the point of view of neuronal loss, decompressive surgery at an earlier stage, when compensatory mechanisms including the up-regulation of BDNF might be still effective, could provide better therapeutic results against chronic mechanical compressive spinal cord lesions.

Multivariate analysis of the neurological outcome of surgery for cervical compressive myelopathy

BACKGROUND

The neurological outcome of decompressive surgery for cervical myelopathy is influenced by several factors. Although each factor may have an independent effect, it is more likely that the outcome is influenced by more than one factor. We examined the results of multivariate analysis and multiple regression analysis of the neurological outcome of patients treated by cervical cord decompression.

METHODS

A total of 77 patients with cervical spondylotic myelopathy (43 men, 34 women) and 58 with ossification of the posterior longitudinal ligament (OPLL) (39 men, 19 women) were studied with an average follow-up interval of 8.3 years. The clinical data, neurological and radiological findings, and results of spinal cord evoked potentials (SCEPs) were retrieved from the medical records and included in the analysis.

RESULTS

Multivariate analysis indicated that the outcome for patients with spondylosis was positively influenced, in order of importance, by increased transverse area of the cord >or=60%, presence of single-level anterior fusion, a high preoperative neurological score, normal epidural SCEPs, and clinical features of brachialgia and cord type. In patients with OPLL, multivariate analysis showed that the long-term outcome was positively influenced, in order of importance, by the presence of mixed or localized OPLL, normal epidural SCEPs, high preoperative neurological score, a single-vertebra spondylectomy with anterior fusion, laminoplasty, widening of the transverse area of the cord >or=40%, and an expansion rate of the spinal canal after laminoplasty >or=40%.

CONCLUSIONS

We suggest that multivariate analysis is useful for assessing the neurosurgical outcome in patients with cervical compressive myelopathy.

Increased expression of neurotrophins and their receptors in the mechanically compressed spinal cord of the spinal hyperostotic mouse (twy/twy)

The purpose of the present study was to identify any compensatory changes at the site of chronic compression of the spinal cord and neighboring segments. For this purpose, serial immunohistochemical and immunoblot analyses were performed for the expression levels of endogenous brain-derived neurotrophic factor (BDNF), neurotrophin (NT)-3, and their receptors, trkB and trkC in 24 tip-toe walking Yoshimura mice (twy/twy) aged 12-24 weeks. The twy mouse exhibits spontaneous calcified deposits posteriorly at the C1-C2 level, compressing the spinal cord. Immunoreactivities for BDNF, NT-3, trkB and trkC were preferentially localized in the gray matter, particularly in the anterior horn cells. In 24-week-old twy mice with severe compression, expression levels of these neurotrophins at the site of maximal compression were significantly lower than at the less- or non-compressed sites. In contrast, the expression levels of BDNF, NT-3, trkB and trkC were significantly higher at the rostral and caudal sites immediately adjacent to the maximal compression site. No such changes were noted in 12-week-old twy mice or in control Institute of Cancer Research mice. Our results suggest that overexpression of BDNF, NT-3, trkB and trkC in motoneuron areas neighboring the site of mechanical compression may represent compensatory changes in response to the compromised neuronal function at the level of compression, and that these proteins possibly contribute to neuronal survival and plasticity.

Progressive changes in neurofilament proteins and growth-associated protein-43 immunoreactivities at the site of cervical spinal cord compression in spinal hyperostotic mice

STUDY DESIGN

Immunohistochemical examination of the expression and localization of neurofilament (NF) proteins and growth-associated protein (GAP)-43 in spinal hyperostotic (twy/twy) mice with progressive compression of the cervical spinal cord.

OBJECTIVE

To determine the biologic functions of NF proteins and GAP-43 in the mouse cervical spinal cord during chronic mechanical compression.

SUMMARY OF BACKGROUND DATA

The pathologic and repair process in the chronically compressed spinal cord are understood poorly. The present authors hypothesized that there existed an increased expression of NF proteins and GAP-43 in twy/twy mice during the lengthy period of spinal cord compression, which resembles compressive myelopathy.

METHODS

The cervical spinal cords of 54 twy mice (aged 8 weeks [n = 18], 14 weeks [n = 18], and 20 weeks [n = 18]) and 18 control animals were examined histologically. Using appropriate antibodies, sections were also stained immunohistochemically for NF proteins and GAP-43.

RESULTS

Separation of the myelin sheath from the axon and axonal swelling with deformation were detected in the anterior and lateral funiculi of the spinalcords of 20-week-old twy/twy mice. No such changes were noted in 8-week-old twy mice. In twy/twy mice aged 8 and 14 weeks with mild-to-moderate compression, weak immunoreactivities (mainly in the white matter) for NF proteins and GAP-43 were noted; however, in 20-week-old twy/twy mice, these axons stained strongly positive and immunoreactive swollen axons were present. The relative area of GAP-43 immunoreactive axons gradually increased between 8 and 20 weeks in each column, particularly in the anterior and lateral funiculi in the contralateral side of compression.

CONCLUSIONS

The results showed that the expression of NF proteins and GAP-43 in the white matter increased proportionally with the magnitude of spinal cord compression, and indicated the possible involvement of GAP-43 in both axonal degeneration and repair processes in the chronically compressed spinal cord.

Three-dimensional topographic analysis of spinal accessory motoneurons under chronic mechanical compression: an experimental study in the mouse

We investigated the effect of chronic mechanical compression of the cervical spinal cord on the number of spinal accessory motoneurons in 25 tiptoe-walking Yoshimura mice. The animals had calcified deposits in the atlantoaxial membrane at the C1-C2 vertebral level, compressing the spinal cord posterolaterally. Motoneurons of the spinal accessory nerve between C1 and C5 segments were labelled using wheat germ agglutinin-horseradish peroxidase (WGA-HRP) injected into the sternocleidomastoid muscles. The counted cells were processed into a three-dimensional computer display to analyse the cytoarchitectonic changes caused by external cord compression. The number of WGA-HRP-labelled spinal accessory motoneurons was significantly reduced on the affected side. The number of motoneurons in compromised C2 and C3 cord segments correlated linearly with the extent of mechanical compression, but no such relationship was present on the contralateral side. There was an increase in the number of WGA-HRP-labelled spinal accessory motoneurons in the medial cell pools of the anterior grey horn at a level most rostral to the compression, and in the ventrolateral cell pools at levels immediately rostral to the compression. Our findings suggest that the spinal accessory motoneurons translocate rostral to the area of external compression in order to avoid mechanical injury.

Quantitative analysis of the spinal cord motoneuron under chronic compression: an experimental observation in the mouse

We investigated quantitative changes in spinal cord motoneurons following chronic compression using a mouse model of cervical cord compression. Twenty-five tip-toe-walking Yoshimura (twy) mice with calcified mass lesions compressing the spinal cord posterolaterally at the C1-C2 vertebral levels were compared with five Institute of Cancer Research (ICR) mice that served as controls. Spinal cord motoneurons in the anterior grey horn between the C1 and C3 spinal cord segments were Nissl-stained and counted topographically and then analysed in relation to the extent of spinal cord compression. The number of motoneurons in C1-C3 spinal cord segments decreased significantly with a linear correlation with the transverse area of the spinal cord when the cord was compressed to 50-70% of control values. A significant reduction in the number of motoneurons occurred at the C2-C3 spinal cord segment compressed at the C1-C2 vertebral level. In contrast, at the level rostral to the C1 vertebra, the number of motoneurons increased significantly in proportion to the magnitude of compression. The current study demonstrates that a number of neurons, morphologically consistent with anterior horn cells, were observed at a rostral site absolutely free of external compression where no such cells normally exist.