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PubMed1998

Magnetic resonance imaging of experimental subacute spinal cord compression.

STUDY DESIGN: Subacute compression of the spinal cord was applied to rats. The animals were chronologically observed using magnetic resonance imaging for more than 8 weeks after surgery and were killed for histopathologic examination. OBJECTIVES: To investigate the correlation of changes in signal intensity on magnetic resonance images with those observed in histopathologic study and with the degree of spinal cord compression and paralysis. SUMMARY OF BACKGROUND DATA: No consensus has been reached concerning the correlation of magnetic resonance images to clinical symptoms of compressive myelopathy. Few reports are available in which magnetic resonance imaging findings are compared with histopathologic features in chronic or subacute experiments. METHODS: In rats under general anesthesia, the T11 lamina was thinned and a slow increase in volume was applied. Hind limb paralysis appeared 1 week after the procedure and spontaneously subsided thereafter. The degree of spinal compression and signal intensity was observed chronologically using magnetic resonance imaging. The signal intensity on the final MR images was rated on a four-point scale and compared with histopathologic findings. RESULTS: As spinal compression increased, the incidence of high signal intensity on long spin-echo images became higher. Low signal intensities on short spin-echo images were visible in animals in which compression and paralysis were the most severe. In these animals, cavitation and a dilated central canal were visible. High signal intensities on long spin-echo images reflected various pathologic changes. CONCLUSIONS: Changes in signal intensity on MR images are visible after the induction of myelopathy by high-pressure compression. These signal intensities may be useful in predicting the outcome of compressive myelopathy.

Animals↗

PubMed1998

Quantitative analysis of edema in the dorsal nerve roots induced by acute mechanical compression.

STUDY DESIGN: Edema in the dorsal nerve roots caused by acute compression was assessed quantitatively in the lumbar spine of the adult dog. OBJECTIVE: To establish quantitative evaluation of edema in the dorsal nerve roots and to observe changes after acute compression with time. SUMMARY OF BACKGROUND DATA: Mechanical compression induces an increase in microvascular permeability of the endoneurial capillaries and results in intraneural edema. However, there are no quantitative studies on edema in the nerve roots. METHODS: The seventh lumbar nerve root was compressed with a 60-g force clip for 10 minutes. The nerve roots were removed immediately and at 24 hours, 1 week, and 3 weeks after compression. Nerve roots from the control and the sham groups were also obtained. Before removing the nerve roots, Evans blue albumin was injected intravenously. Changes in edema were examined using fluorescence microscopy. Evans blue albumin emits a bright red fluorescence. The relative red fluorescent area was calculated using computer image analysis, and the data were used to indicate the degree of edema. RESULTS: In the compressed segment, edema was most pronounced just after decompression and reduced in nerves removed at 24 hours. In nerves removed at 1 week, edema was pronounced but was reduced at 3 weeks. In the segments closest to the spinal cord, edema was seen after 1 week and was significant after 3 weeks. In the segments closest to the dorsal root ganglion, edema was not detected at any time. CONCLUSION: In the dorsal nerve roots the degree and the area of edema changed with time elapsed after acute compression. The degree of edema 24 hours after decompression was one third the degree immediately after decompression. These results show that edema induced by mechanical compression can recover after decompression.

Animals↗

PubMed1999

Behavioral and morphologic studies of the chronically compressed cauda equina. Experimental model of lumbar spinal stenosis in the rat.

STUDY DESIGN: An experimental model in rats of chronically compressed cauda equina was produced, and behavioral and morphologic changes were examined. OBJECTIVES: To provide a useful model for analyzing the pathophysiologic changes of the cauda equina by chronic compression and to examine behavioral and morphologic changes in this model. SUMMARY OF BACKGROUND DATA: Several animal models have been reported in which various materials were used to compress the cauda equina. However, the pathophysiology of the cauda equina by chronic compression is not yet well understood. Studies in which rats were used are scarce. METHODS: A silicone sheet was applied to the spinal canal at L4 in the rat. Walking durations on treadmill tests and paw-withdrawal latencies to thermal stimuli were measured before and after the operation for 24 weeks. Histologic changes also were examined. RESULTS: Walking durations decreased after chronic compression. However, paw-withdrawal latencies were not significantly changed. Histologically, the number of large-diameter myelinated axons decreased after compression, whereas the number of small-diameter myelinated axons increased. Electron microscopic observation indicated that the continuous degeneration and regeneration of axons occurred throughout the chronic compression experiment. CONCLUSIONS: The current model and behavioral assessments may be useful in analyzing the pathophysiology of chronically compressed cauda equina.

Animals↗

PubMed2000

Does long-term compressive loading on the intervertebral disc cause degeneration?

STUDY DESIGN: Coil springs were stretched and attached to produce a compressive force across the lumbar intervertebral discs of dogs for up to 53 weeks. OBJECTIVE: To test the hypothesis that compressive forces applied to the intervertebral disc for a long period of time cause disc degeneration in vivo in a dog model. SUMMARY OF BACKGROUND DATA: It is a commonly held belief that high forces applied to the intervertebral disc, and to joints in general, play a role in causing degeneration. METHODS: Coil springs were stretched and attached to produce a compressive force across the lumbar intervertebral discs (L3/L4) of 12 dogs. After up to a year, the dogs were killed, and their lumbar spines were removed and radiographed. The L3/L4 disc and the controls (T13/L1 and L4/L5) were excised and examined for visible signs of degeneration. The discs then were assessed using immunohistochemical analysis and enzyme-linked immunosorbent assay. Disc chondrocytes also were assayed for apoptosis. RESULTS: No obvious signs of degeneration in the discs (L3/L4) that had been under compression for up to a year could be observed. There was no disc bulging, anular fissures, or disc space narrowing. Some changes were observed at the microscopic level, although no thickening of the endplate was apparent. The enzyme-linked immunosorbent assay analysis provided significant data for all three regions of the disc (nucleus, inner anulus, and outer anulus). When comparing the compressed disc (L3/L4) with either of the control discs (T13/L1 and L4/L5), in the compressed disc: 1) the nucleus contained less proteoglycan and more collagen I and II; 2) the inner anulus contained less proteoglycan and collagen I; and 3) the outer anulus contained more proteoglycan and less collagen I. The collagen II differences for the inner and outer anulus were not significant. CONCLUSION: Compression applied to the lumbar intervertebral discs of dogs for up to a year does not produce degeneration in any visible form. It does produce microscopic changes and numerical changes, however, in the amounts of proteoglycan and collagen in the nucleus, inner anulus, and outer anulus. The present results add no credence to the commonly held belief that high compressive forces play a causative role in disc degeneration.

Animals↗

PubMed2002

Effects of disc height and distractive forces on graft compression in an anterior cervical discectomy model.

STUDY DESIGN: An in vitro biomechanical study using a calibrated distractor and a subminiature load cell in a cadaver anterior cervical discectomy construct was conducted. OBJECTIVE: To study the interrelations of preoperative disc height, graft height, and compressive and distractive forces in an anterior cervical discectomy model. SUMMARY OF BACKGROUND DATA: The effects of graft size on compressive and distractive forces in a discectomy model remain unknown. Larger grafts afford neural decompression through anterior column distraction. This distraction may subject the graft and vertebral bodies to excessive loads, increasing graft fracture, and subsidence risk. METHODS: Disc height was measured radiographically in 18 specimens. A Smith-Robinson discectomy was performed, and the superior and inferior ends of the specimens were embedded in polyester resin. Distraction was applied through a calibrated Caspar distractor to measure the distractive force applied while steel spacers rigidly fixed to a subminiature load cell were introduced. After distraction was removed, immediate compressive force was measured. RESULTS: Distractive forces of 112.4 N and 189.9 N were required to insert the 6-mm and 8-mm grafts, respectively. When this distractive force was removed, immediate compressive loads of 8.8 N and 21.5 N on the graft were noted. When a compressive load of 45 N was applied in a loading frame, measured graft loads of 16.2 N and 29.2 N also increased. No statistically significant relation was observed between preoperative disc height and distractive force or compression of the graft. Significantly lower distractive and compressive forces were associated with insertion of the 6-mm rather than 8-mm graft. CONCLUSIONS: Significantly higher distractive and compressive forces were recorded with larger grafts. Preoperative disc height was not an accurate predictor of graft loads.

Aged↗

PubMed2004

Flexion-extension response of the thoracolumbar spine under compressive follower preload.

STUDY DESIGN: The authors conducted an in vitro biomechanical flexibility study of T2-S1 specimens in flexion-extension under compressive follower preloads of physiological magnitudes. OBJECTIVES: The objectives of this study were to test the hypotheses that 1) the thoracolumbar spine will support compressive preloads of in vivo magnitudes and 2) allow physiological mobility under flexion-extension moments if the preload is applied along an optimized follower load path that approximates the kypholordotic curve of the thoracolumbar spine. SUMMARY OF BACKGROUND DATA: In the absence of muscle forces, the ligamentous thoracolumbar spine specimens cannot support the compressive loads expected in vivo. As a result, the flexibility of the thoracolumbar spine in flexion-extension has not been studied in vitro under physiological compressive preloads. METHODS: Seven human thoracolumbar spines (T2-sacrum) were subjected to flexion and extension moments (up to 8 and 6 Nm, respectively) under compressive preloads from 0 to 800 N applied along an optimized follower preload path. The experimental technique applied the compressive preload such that: 1) it minimized the internal shear forces and bending moments resulting from the preload application, 2) made the internal force resultant compressive, and 3) caused the preload path to approximate the tangent to the curve of the thoracolumbar spine. The range of motion was measured in the T2-sacrum, T2-T11, T11-L1, and L1-sacrum regions. RESULTS: All thoracolumbar specimens supported the compressive follower preload up to 800 N without damage or instability. At 800 N preload, the total flexion-extension range of motion of the T2-sacrum region decreased by 22%, from a mean of 73 degrees to 57 degrees (P < 0.05). The range of motion of the T2-T11 and L1-sacrum regions decreased from the baseline value by 23% and 30%, respectively, at a preload of 800 N. The sagittal mobility of the thoracolumbar junction (T11-L1) was not affected by the preload. The follower preload did not significantly affect the proportion of the total T2-sacrum flexion-extension range of motion contributed by the T2-T11 and L1-sacrum regions of the thoracolumbar spine. CONCLUSIONS: The optimized follower preload vector minimizes the effects of artifact moment and shear force on the range of motion of the thoracolumbar spine in flexion-extension. This model allows the entire thoracolumbar spine to be investigated under physiological loading for different clinical applications.

Aged↗

PubMed2005

Transient cervical nerve root compression in the rat induces bilateral forepaw allodynia and spinal glial activation: mechanical factors in painful neck injuries.

STUDY DESIGN: An in vivo rat model of transient cervical nerve root compression. OBJECTIVES: To investigate the potential for cervical nerve root compression to produce behavioral hypersensitivity and examine its dependence on compression. SUMMARY OF BACKGROUND DATA: Clinically, nerve root injury has been hypothesized as a potential source of neck pain, particularly because cervical nerve roots are at mechanical risk for injury during neck loading. Lumbar radiculopathy models of nerve root ligation show that mechanical allodynia and spinal glial changes depend on nerve root deformation magnitude. However, no investigation has been performed to examine cervical nerve root compression as a cause of pain. METHODS: Two compressive forces (10 and 60 grams force [gf]) were transiently applied to the C7 nerve roots unilaterally using microvascular clips in separate groups (n = 12 each). Sham procedures were also performed in a separate group of rats (n = 12). Bilateral forepaw mechanical allodynia was monitored after surgery for 7 days. On day 7, spinal glial activation was assessed using immunohistochemistry to investigate its dependence on nerve root compressive force, in the context of behavioral hypersensitivity. RESULTS: Bilateral allodynia was observed following injury, which was significantly (P < 0.042) increased over sham and baseline responses. No difference in allodynia was found between the 10 and 60 gf injuries. Astrocytic and microglial activation were observed in the ipsilateral dorsal horn following compression, with only astrocytic activation paralleling allodynia patterns. CONCLUSIONS: Results imply a force threshold exists less than 10 gf for persistent pain symptoms following transient cervical nerve root compression. Findings also suggest that spinal glial activation may be related to behavioral sensitivity and may modulate cervical nerve root mediated pain.

Animals↗

PubMed2006

Texture characterization for joint compression and classification based on human perception in the wavelet domain.

Today's multimedia applications demand sophisticated compression and classification techniques in order to store, transmit, and retrieve audio-visual information efficiently. Over the last decade, perceptually based image compression methods have been gaining importance. These methods take into account the abilities (and the limitations) of human visual perception (HVP) when performing compression. The upcoming MPEG 7 standard also addresses the need for succinct classification and indexing of visual content for efficient retrieval. However, there has been no research that has attempted to exploit the characteristics of the human visual system to perform both compression and classification jointly. One area of HVP that has unexplored potential for joint compression and classification is spatial frequency perception. Spatial frequency content that is perceived by humans can be characterized in terms of three parameters, which are: 1) magnitude; 2) phase; and 3) orientation. While the magnitude of spatial frequency content has been exploited in several existing image compression techniques, the novel contribution of this paper is its focus on the use of phase coherence for joint compression and classification in the wavelet domain. Specifically, this paper describes a human visual system-based method for measuring the degree to which an image contains coherent (perceptible) phase information, and then exploits that information to provide joint compression and classification. Simulation results that demonstrate the efficiency of this method are presented.

Algorithms↗

PubMed2004

Changes in expression of PACAP in rat sensory neurons in response to sciatic nerve compression.

In the present study, expression of pituitary adenylate cyclase-activating polypeptide (PACAP) in rat dorsal root ganglion (DRG) neurons and sciatic nerve following experimental sciatic nerve compression was studied with the use of quantitative immunohistochemistry and in situ hybridization. Previously, we have investigated changes in PACAP expression after nerve transection and, here, the far more frequently encountered condition of nerve compression injury is examined. Nerve compression was performed unilaterally on the rat sciatic nerve, at mid-thigh level, by application of a narrow silicone tube around the nerve for 3, 7, 14 or 28 days, respectively. We detect a statistically significant upregulation in the number and density of PACAP mRNA expression in both small and large DRG neurons in response to nerve compression. An increased number of PACAP-immunoreactive neurons is also found in the ipsilateral DRG. In addition, PACAP immunoreactivity is observed in the compressed sciatic nerve segment and adjacent nerve tissue after nerve compression. The present findings can be compared with previous studies where we have shown that PACAP expression is upregulated in DRG; in response to peripheral inflammation (primarily in small-medium neurons), and after axotomy (dramatic upregulation in medium-large neurons). In view of the recent findings of an increased PACAP expression in DRG after nerve compression, as well as the previous findings of a modulation of PACAP expression in response to axotomy and inflammation, it is likely that PACAP is also involved in the modulation of the response to peripheral nerve compression.

Animals↗

PubMed2006

Dynamic response of immature bovine articular cartilage in tension and compression, and nonlinear viscoelastic modeling of the tensile response.

Very limited information is currently available on the constitutive modeling of the tensile response of articular cartilage and its dynamic modulus at various loading frequencies. The objectives of this study were to (1) formulate and experimentally validate a constitutive model for the intrinsic viscoelasticity of cartilage in tension, (2) confirm the hypothesis that energy dissipation in tension is less than in compression at various loading frequencies, and (3) test the hypothesis that the dynamic modulus of cartilage in unconfined compression is dependent upon the dynamic tensile modulus. Experiment 1: Immature bovine articular cartilage samples were tested in tensile stress relaxation and cyclical loading. A proposed reduced relaxation function was fitted to the stress-relaxation response and the resulting material coefficients were used to predict the response to cyclical loading. Adjoining tissue samples were tested in unconfined compression stress relaxation and cyclical loading. Experiment 2: Tensile stress relaxation experiments were performed at varying strains to explore the strain-dependence of the viscoelastic response. The proposed relaxation function successfully fit the experimental tensile stress-relaxation response, with R2 = 0.970+/-0.019 at 1% strain and R2 = 0.992+/-0.007 at 2% strain. The predicted cyclical response agreed well with experimental measurements, particularly for the dynamic modulus at various frequencies. The relaxation function, measured from 2% to 10% strain, was found to be strain dependent, indicating that cartilage is nonlinearly viscoelastic in tension. Under dynamic loading, the tensile modulus at 10 Hz was approximately 2.3 times the value of the equilibrium modulus. In contrast, the dynamic stiffening ratio in unconfined compression was approximately 24. The energy dissipation in tension was found to be significantly smaller than in compression (dynamic phase angle of 16.7+/-7.4 deg versus 53.5+/-12.8 deg at 10(-3) Hz). A very strong linear correlation was observed between the dynamic tensile and dynamic compressive moduli at various frequencies (R2 = 0.908+/-0.100). The tensile response of cartilage is nonlinearly viscoelastic, with the relaxation response varying with strain. A proposed constitutive relation for the tensile response was successfully validated. The frequency response of the tensile modulus of cartilage was reported for the first time. Results emphasize that fluid-flow dependent viscoelasticity dominates the compressive response of cartilage, whereas intrinsic solid matrix viscoelasticity dominates the tensile response. Yet the dynamic compressive modulus of cartilage is critically dependent upon elevated values of the dynamic tensile modulus.

Animals↗

PubMed2006

Compression or tension? The stress distribution in the proximal femur.

BACKGROUND: Questions regarding the distribution of stress in the proximal human femur have never been adequately resolved. Traditionally, by considering the femur in isolation, it has been believed that the effect of body weight on the projecting neck and head places the superior aspect of the neck in tension. A minority view has proposed that this region is in compression because of muscular forces pulling the femur into the pelvis. Little has been done to study stress distributions in the proximal femur. We hypothesise that under physiological loading the majority of the proximal femur is in compression and that the internal trabecular structure functions as an arch, transferring compressive stresses to the femoral shaft. METHODS: To demonstrate the principle, we have developed a 2D finite element model of the femur in which body weight, a representation of the pelvis, and ligamentous forces were included. The regions of higher trabecular bone density in the proximal femur (the principal trabecular systems) were assigned a higher modulus than the surrounding trabecular bone. Two-legged and one-legged stances, the latter including an abductor force, were investigated. RESULTS: The inclusion of ligamentous forces in two-legged stance generated compressive stresses in the proximal femur. The increased modulus in areas of greater structural density focuses the stresses through the arch-like internal structure. Including an abductor muscle force in simulated one-legged stance also produced compression, but with a different distribution. CONCLUSION: This 2D model shows, in principle, that including ligamentous and muscular forces has the effect of generating compressive stresses across most of the proximal femur. The arch-like trabecular structure transmits the compressive loads to the shaft. The greater strength of bone in compression than in tension is then used to advantage. These results support the hypothesis presented. If correct, a better understanding of the stress distribution in the proximal femur may lead to improvements in prosthetic devices and an appreciation of the effects of various surgical procedures affecting load transmission across the hip.

Compressive Strength↗

PubMed2003

Compressive preload improves the stability of anterior lumbar interbody fusion cage constructs.

BACKGROUND: Insertion of an anterior lumbar interbody fusion cage has been shown to reduce motion in a human spine segment in all loading directions except extension. The "stand-alone" cages depend on compressive preload produced by anular pretensioning and muscle forces for initial stabilization. However, the effect that the in vivo compressive preload generated during activities of daily living has on the construct is not fully understood. This study tested the hypothesis that the ability of the cages to reduce the segmental motions in flexion and extension is significantly affected by the magnitude of the externally applied compressive preload. METHODS: Fourteen specimens from human lumbar spines were tested intact and after insertion of two threaded cylindrical cages at level L5-Sl. They were subjected to flexion and extension moments under progressively increasing magnitudes of externally applied compressive follower preload from 0 to 1200 N. The range of motion at level L5-S1 after cage insertion was compared with the value achieved in the intact specimens at each compressive preload magnitude. RESULTS: The cages significantly reduced the L5-S1 flexion motion at all preloads (p < 0.05). They decreased flexion motion by 29% to 43% of that of the intact specimens for low preloads (0 to 400 N) and by 69% to 79% of that of the intact specimens under preloads of 800 to 1200 N. In extension, in the absence of an externally applied preload, the cages permitted 24% more motion than the intact segment (p < 0.05). In contrast, they reduced the extension motion at preloads from 200 to 1200 N. Under preloads of 800 to 1200 N, the reduction in extension motion after cage placement was 42% to 48% of that of the intact segment (p < 0.05). The reduction of motion in both flexion and extension after cage placement was significantly greater at preloads of 800 to 1200 N compared with the motion reductions at preloads of < or =400 N (p < 0.05). CONCLUSIONS: In contrast to the observed extension instability under anular tension preload only, the two-cage construct exerted a stabilizing effect on the motion segment (a reduction in segmental motion) in flexion as well as extension under externally applied compressive preloads of physiologic magnitudes. The external compressive preload significantly affected the stabilization provided by the cages. The cages provided substantially more stabilization, both in flexion and in extension, at larger preloads than at smaller preloads. CLINICAL RELEVANCE: The study suggests that the segment treated with an anterior lumbar interbody fusion cage is relatively less stable under conditions of low external compressive preload. The magnitude of preload required to achieve stabilization with stand-alone cages may be only partially achieved by anular pretensioning. Since the magnitude of the preload across the disc space due to muscle activity can vary with activities of daily living, supplemental stabilization of the cage construct may provide a more predictably stable environment for lumbar spine fusion.

Aged↗

PubMed2005

Effects of mechanical compression of a fibrous tissue interface on bone with or without high-density polyethylene particles in a rabbit model of prosthetic loosening.

BACKGROUND: The mechanisms leading to aseptic loosening of a total hip replacement are not fully understood. A fibrous tissue interface can be present around the implant. Hypothetically, component micromovements can compress this interface and cause increased fluid pressure according to biphasic models. We tested the hypothesis that compression of a fibrous membrane with or without the presence of high-density polyethylene particles leads to bone degradation. METHODS: A titanium implant was inserted in forty-five rabbit tibiae, and, after osseous integration was achieved, a fibrous tissue interface was generated. The animals were randomized to undergo a sham operation, treatment with compression of the fibrous membrane, treatment with high-density polyethylene particles, or treatment with both compression and particles. Morphometric analysis of the surrounding bone was performed on cryostat sections after Giemsa staining and staining of tartrate-resistant acid phosphatase activity. RESULTS: Forty specimens were available for analysis; five tibiae with an infection were excluded. After nine weeks, the controls showed vital bone, whereas the specimens treated with compression showed necrosis of bone and replacement of bone by cartilage in a discontinuous layer (p < 0.05 for both) but not fibrous tissue. Treatment with high-density polyethylene particles caused replacement of bone by fibrous tissue (p < 0.05) but not necrosis or cartilage formation. Compression combined with the presence of high-density polyethylene particles caused bone necrosis and loss of bone with replacement by cartilage and fibrous tissue (p < 0.05). CONCLUSIONS: In this in vivo study in rabbits, fibrous membrane compression led to bone necrosis and cartilage formation, possibly because of fluid pressure or fluid flow, whereas the presence of high-density polyethylene particles led to the loss of bone with replacement of bone by fibrous tissue. Cartilage formation may be a protective response to fluid pressure and/or fluid flow. Fibrous membrane compression may play an important role in the early stages of loosening of a total hip replacement.

Animals↗

PubMed1975

Vasogenic edema following acute and chronic spinal cord compression in the dog.

The T-13 spinal cord segment of dogs was compressed both acutely and chronically by means of a balloon catheter. The vascular permeability to protein was assessed using Evans blue albumin (EBA), and the dorsal column evoked potential recorded to monitor conduction failure. With acute compression sufficient to cause conduction failure there was a marked leakage of EBA from the intermediate gray matter, which spread into the dorsolateral white matter. The degree of edema was similar whether the compression was maintained or released. Chronic compression maintained over 4 to 5 hours did not increase vascular permeability, but following release of compression leakage of EBA occurred in the same cord locations observed with leakage from acute compressions. This increased permeability following release of chronic compression may result from reactive hyperemia. Dorsal column conduction returned after the release of both acute and chronic compression. The extravasated EBA was present both in the extracellular space and within cells. The results and their clinical application are discussed.

Acute Disease↗

PubMed2003

Nonlinear and viscoelastic characteristics of skin under compression: experiment and analysis.

In physiological loading conditions, the soft tissues in the hands and fingers are predominantly in compression. The goal of the present study was to characterize the nonlinear and time-dependent behavior of skin in compression. The pigskin samples used in the study were collected from five different animals. The compression tests were performed in confined and unconfined loading configurations and at four different loading speeds (0.5, 1.0, 40, and 400 microm/s). A multi-axial material model was proposed to simulate the nonlinear and viscoelastic behavior of the skin in compression. The good agreement between the model predictions and experimental data suggests that the mechanical behavior of the skin in compression can be well characterized using the Ogden strain energy potential combined with a time-integration using a Prony series. Our results show that the stress/strain curve of the skin is much stiffer in confined compression compared to that in unconfined compression, indicating that the compressibility of the skin is small.

Animals↗

PubMed1991

[An experimental study on compression neuropathy--changes of the neurofilament and axonal tubulin content detected by enzymatic antibody technique].

Changes of axonal transport were investigated by enzymatic antibody technique in an experimental model of compression neuropathy. Neurofilament and tubulin were selected as marker protein and avidin-biotin-peroxidase complex method was used to stain specimens. Compression was applied on the sciatic nerves of the mongrel dogs by the KEIO compression clamps with compression force of 15, 30, and 50 grams. Staining was performed at 1, 2, 3, 4, 6, 8 weeks after the onset of the compression. Electrophysiologic and histologic examination were also studied. As a result, neurofilament and axonal tubulin content decreased in the site distal to the compression clamps. The degree of the changes was correlated with the duration and force of the compression. The decrease of axonal tubulin content closely corresponded with the decrease of neurofilament content. In conclusion, axonal transport was impaired in the peripheral nerve even under a low compression force.

Animals↗

PubMed1983

[Experimental study on compression neuropathy--determination of blood flow by a hydrogen washout technic].

The role of ischemia in the pathophysiology of compression neuropathy is still a subject of debate. Nor is the effect on blood supply induced by neurolysis for this lesion so clearly elucidated. In order to shed some light on these problems, two series of experiments were undertaken. In the first series of experiments, the changes in intrafascicular blood flow and nerve function when acute, graded compression was applied to a dog's sciatic nerve by a specially designed compression device were investigated by means of the hydrogen washout technique, electrophysiological study and histological observation. In the second series, Type II injury according to the classification of Sunderland was experimentally caused by embedding a compression device for three weeks, and the intrafascicular blood flow of this model was measured by using the embedded electrode for the hydrogen clearance method. Furthermore, the blood flow before and after neurolysis for this lesion was compared, and cases in which internal neurolysis had been performed were observed after one and three weeks. The intrafascicular blood flow was decreased at 47.2 +/- 3.7 (mean +/- S.D.) mmHg, with increasing pressure, blood flow gradually declined and a statistically significant correlation was shown between the values (r=-0.77, p less than 0.01). This completely stopped at 118.6 +/- 5.9 mmHg (p less than 0.001). The effect of compression on intrafascicular blood flow was immediately observed and disappeared at once after release of the compression. An actual pressure of 118.6 mmHg maintained for 75 minutes produced complete conduction block, which was immediately recovered after release of the compression, though more slowly than the blood flow. When the compression device was applied, the intrafascicular blood flow was reduced to about 80% of the precompression level (p less than 0.05) and this reduction remained unchanged after three weeks (p less than 0.01), at which time the nerve had sustained the Type II injury. After the removal of the device, the blood flow was restored to more than the precompression level (p less than 0.01). Following this, when external neurolysis was performed, a slight reduction of blood flow was observed. After internal neurolysis, however, a remarkable reduction was noticed, the blood flow decreasing to about 20% of the precompression value (p less than 0.01). The blood flow after internal neurolysis was restored to about 70% of the precompression level after one week and, three weeks later, remained about the same.

Animals↗

PubMed1978

Effect of duration of acute spinal cord compression in a new acute cord injury model in the rat.

The effect of duration of acute compression of the spinal cord was assessed in a new model in the rat. The spinal cord was acutely compressed for varying times by a modified aneurysm clip which produced a compression force of 180 grams. The effect of duration of compression was measured by the inclined plane method of assessing the animals' clinical performance. The results showed a linear relationship between log compression time and clinical performance. Thus, the clinical effect of acute compression of the spinal cord injury is inversely related to duration of compression time and the relationship has been precisely quantified. These results suggest that persisting compression should be relieved as soon as possible in order to improve recovery.

Acute Disease↗