[Rete compensation in agenesis of the internal carotid artery]

The term carotid rete mirabile refers to an anatomic structure common in several lower mammals (e.g., swine). The blood supply for the intracranial arteries originates from branches of the external carotid artery, predominantly the ascending pharyngeal and internal maxillary arteries. In these animals the intracranial internal carotid artery forms from a dense network of numerous converging, small-caliber vessels. An analogous structure is rarely found in humans. Associated with segmental agenesis of the internal carotid artery, so-called carotid rete mirabile can be observed. In it numerous tortuous vessels with a diameter of 1-2 mm are found along the expected course of the internal carotid artery and coming from branches of the external carotid artery. These vessels converge to the intradural paraclinoid segment of the internal carotid artery, which shows a normal diameter. This rare pattern of collateral supply to the brain is illustrated here on the basis of two clinical case histories. Both patients presented with aneurysmal subarachnoid hemorrhage. In one, histological examination of a vessel biopsy revealed medial fibromuscular dysplasia. In both patients the rete mirabile was found in only one carotid system. The affected carotid canal in the skull base was hypoplastic. Human carotid rete mirabile probably has no inherent pathologic significance, but its frequent association with other intra- and extracranial vascular pathologies should be kept in mind.

Endovascular treatment of small intracranial aneurysms: three alternatives to coil occlusion

INTRODUCTION

Small intracranial aneurysms with a fundus diameter of 2 - 3 mm may rupture and are therefore potential targets for an endovascular approach in treatment. Currently available coil technology is less than optimal for the treatment of aneurysms within this size range. Even the smallest coils are sometimes too large. If such a minute coil can be introduced into a small aneurysm, the hemodynamic effect and the induced thrombosis are frequently inadequate to occlude the aneurysm sufficiently from the parent artery circulation.

METHODS

Three technical alternatives for the endovascular treatment of small intracranial aneurysms not suitable for coil occlusion are illustrated with the following three case descriptions.

RESULTS

Stent grafts are usable for the intracranial internal carotid artery and for the V4 segment. The stiffness of the stent and the high expansion pressures are the two major drawbacks. Coaxial deployment of two or more self-expanding porous stents can result in sufficient redirection of the blood flow to induce aneurysmal thrombosis. Deployment of multiple stents, however, may require several treatment sessions in order to allow for the integration of the stents into the vessel wall from session to session. A regular microcatheter can block aneurysmal inflow in aneurysms with a very narrow neck. This allows the occlusion of the aneurysm with an appropriate amount of highly concentrated, rapidly polymerizing glue. Polymer emboli may result from excessive or rapid glue injection.

CONCLUSION

The available coil technology has inherent limitations in the treatment of very small intracranial aneurysms. Liquid embolic agents and stent-based extrasaccular treatment strategies may provide solutions for these challenging lesions.

Anästhesiologisches Management bei neuroendovaskulären Eingriffen

The endovascular treatment of diseases of intracranial and spinal vessels has become widely accepted in recent years. The patient is usually treated under general anesthesia and in choosing an appropriate anesthesia regimen and an optimized pre-interventional preparation, the anesthesiologist can influence the postinterventional result. The working environment in the angiography suite should address the requirements of a routine procedure and the necessities of complication management. Application of short-acting narcotics and relaxation of the patient if required, facilitate the intervention for both the neuroradiologist and the anesthesiologist. The patient should be supplied with everything needed before the intervention to avoid any waste of time in the case of an emergency (e.g., haemorrhage or fibrinolytic treatment). After the procedure the patient has to be monitored for at least 24 h. Peri-interventional and postinterventional complications, such as thrombo-embolism or hemorrhage, must be managed aggressively and consequently by the anesthesist to improve the postinterventional outcome. Therefore a close collaboration between the anesthesiologist and the neuroradiologist is essential.

Endovaskulärer Verschluss der A. basilaris zur Behandlung dissektionsbedingter und dysplastischer fusiformer Aneurysmen

Dissecting aneurysms of the basilar artery trunk frequently affect young adults. Fusiform shape and narrowing of the proximal parent artery are typical features. Changes in aneurysm size and geometry may be observed more rapidly than in atherosclerotic or dysplastic aneurysms. Dissecting aneurysms carry a significant risk of rupture. Thrombotic or embolic occlusion of small pontine branches may cause ischemic symptoms. Sufficiently large aneurysms compress the adjacent brainstem. The operative treatment of these aneurysms is associated with unacceptable risks. At least one posterior communicating artery with normal calibre together with the ipsilateral P1 segment needs to provide adequate collateral flow to the upper basilar artery to allow endovascular coil occlusion of the segment that is affected by the dissection and/or fusiform aneurysmal dilatation. Four illustrative cases of endovascular coil occlusion of the basilar artery for the treatment of fusiform aneurysms are presented and discussed.

A new device for endovascular coil retrieval from intracranial vessels: alligator retrieval device

The clinical use of a new device (Alligator Retrieval Device) designed specifically for endovascular foreign body (eg, coils) retrieval from intracranial vessels is reported. The Alligator has intrinsic advantages compared with microsnares for the endovascular catheter-based removal of coils.

Treatment of intracranial atherosclerotic stenoses with balloon dilatation and self-expanding stent deployment (WingSpan)

The endovascular treatment of atherosclerotic intracranial arterial stenoses has previously been based on balloon dilatation or the deployment of a balloon expandable stent. Both methods have advantages (balloon: flexibility; balloon expandable stent: high radial force) and drawbacks (balloon: risk of elastic recoil and dissection; balloon expandable stent: limited flexibility, risk of injury to the vessel due to excessive straightening, overexpansion at ends of stent). A new combination of balloon dilatation, followed by the deployment of a self-expanding microstent has been applied in 15 patients with atherosclerotic arterial stenoses, symptomatic despite medical treatment. An anatomically and clinically adequate result was achieved in all patients. The initial degree of stenosis was 72% (mean). Balloon dilatation resulted in an average residual stenosis of 54% (mean), reduced further to a mean of 38% after stent deployment. Arterial dissection, occlusion of the target artery or symptomatic distal emboli was not encountered. In one patient, a side branch occlusion occurred after dilatation of a M1 stenosis, with complete neurological recovery. All patients were either stable or improved 4 weeks after the treatment. Recurrent TIA did not occur in any patient. Balloon dilatation and subsequent deployment of a self-expandable stent for the treatment of symptomatic intracranial arterial stenoses combines the advantages of both techniques and allows a rapid, clinically effective and technically safe treatment of these frequently challenging lesions.

Molecular and functional characterization of the four-transmembrane molecule l6 in epidermal keratinocytes

In normal human epidermal keratinocytes (NHEK) proteolytic detachment from the substrate induces a complex activation cascade including expression of new proteins, morphological alterations, and the onset of migration for epidermal regeneration. By subtractive cloning we have shown that L6, a four-transmembrane protein, is newly expressed after proteolytic keratinocyte detachment. In this study, we have generated a novel anti-L6 antibody (clone HD-pKe#104-1.1) and investigated L6 expression regulation in vitro and in vivo as well as L6 function in keratinocyte migration. Dispase-mediated detachment induced L6 expression in NHEK at the mRNA and protein level. Immunohistology of skin biopsies displayed a strong expression of L6 in follicular epidermis and epidermolytic lesions of autoimmune bullous dermatoses (bullous pemphigoid, pemphigus vulgaris), but not in normal interfollicular epidermis. In contrast to normal keratinocytes, HaCaT cells showed constitutive L6 expression, indicating a constitutively active phenotype. After artificial wounding of confluent HaCaT cultures, anti-L6 antibody strongly impaired cell migration velocity and migratory reepithelization of the defect, indicating L6 involvement in keratinocyte migration. These findings suggest that L6 is an important activation-dependent regulator of keratinocyte function and epidermal tissue regeneration.

Immunohistochemical and molecular characterization of cultured keratinocytes after dispase-mediated detachment from the growth substratum

Keratinocyte activation comprises changes in protein and gene expression pattern resulting in phenotypic and functional changes necessary for re-epithelialization such as the expression of urokinase-type plasminogen activator (uPA) and its cell surface receptor (uPA-R; CD87). As uPA and uPA-R are rapidly induced after dispase-mediated detachment of cultured normal human epidermal keratinocytes (NHEK) we hypothesized that dispase-mediated detachment may cause a similar "activation" of keratinocytes with uPA and uPA-R being only one aspect of a complex "activation reaction". To test this hypothesis we have comparatively analysed adherent versus detached keratinocyte sheets for selected indicators of keratinocyte activation by immunohistochemistry. Furthermore we have identified genes via subtraction cloning which are up-regulated upon dispase-induced detachment. The analyses provided evidence for an increased transcriptional and translational activity in detached keratinocytes, as indicated by over-expression of several ribosomal components (L3 and S10 ribosomal protein) and transcription factors (initiation factor 4A, elongation factor 1alpha). Increased proliferative activity was indicated by increased expression of the proliferation markers Ki67, keratin 6 and keratin 17. Finally, several markers of keratinocyte activation such as the integrin chain alpha(v), psoriasin, glutathion-S-transferase and heparin-binding epidermal growth factor-like growth factor were up-regulated. Furthermore mevalonate kinase, a molecule as yet unknown to be expressed in keratinocytes, was identified. The findings provide evidence that dispase-mediated detachment in cultured keratinocytes induces a reaction, which comprises the up-regulation of a complex array of proliferation- and migration-related molecules. The pattern of which resembles the activation reaction observed in the re-epithelializing keratinocytes in vivo.

Tumor necrosis factor-alpha-induced apoptosis in a human keratinocyte cell line (HaCaT) is counteracted by transforming growth factor-alpha

The integrity of the human epidermis is guaranteed by a regulated balance of proliferation, differentiation, and physiologic cell death of its main cellular constituent, the epidermal keratinocyte. Physiologic cell death is known as apoptosis and has been recognized as an active regulatory mechanism, complementary to, but functionally opposite of, proliferation. The regulators of the delicate balance between cell death and proliferation are only partially understood in human keratinocytes. Transforming growth factor-alpha (TGF-alpha) has been identified as a positive regulator of proliferation and growth, while tumor necrosis factor-alpha (TNF-alpha) induces apoptosis. Both mediators are thought to influence epidermal keratinocytes under various physiological and pathophysiological conditions. In the current study we have begun to investigate potential regulatory interactions between these two mediators in the human keratinocyte cell line HaCaT. We have found that, when the HaCaT cells were sensitized by the translation inhibitor cycloheximide, TNF-alpha induced apoptosis, as evidenced by nuclear disintegration, DNA fragmentation ("DNA laddering"), and the appearance of soluble DNA/histone complexes. Moreover, we found that the induction of apoptosis was reduced by preincubation of the cells with TGF-alpha. The protective effect of TGF-alpha was abrogated by translation inhibition, indicating that it depended on de novo protein synthesis. Moreover, the protective effect was not accompanied by a reduced surface expression of TNF receptor molecules. We postulate that TNF-alpha-induced apoptosis in HaCaT cells is counteracted by constitutively produced suppressors of apoptosis, the synthesis of which can be downregulated by inhibition of translation and upregulated by the cytokine TGF-alpha.

Dispase-mediated basal detachment of cultured keratinocytes induces urokinase-type plasminogen activator (uPA) and its receptor (uPA-R, CD87)

Keratinocytes synthesize and secrete urokinase-type plasminogen activator (uPA), which is bound in an autocrine manner to a specific receptor (uPA-R, CD87) at their surface. Plasminogen, which is also bound to membrane binding sites, is readily activated by uPA-R-bound uPA. Thus, plasmin for proteolysis of pericullular glycoproteins is provided. While uPA-R and uPA are at low to undetectable levels in keratinocytes of the normal epidermis, both compounds are upregulated in migrating keratinocytes during reepithelialization of epidermal defects and in affected keratinocytes of various epidermal disorders, including bullous dermatoses. We have hypothesized that the disturbance of cell/matrix interactions--a common feature of these diverse pathological situations--induces uPA/uPA-R. Accordingly, we explored whether the dispase-mediated detachment of cultured keratinocytes, which have formed a multilayered epidermis-like structure in vitro, induced uPA and uPA-R. We found increases in uPA secretion, cell-associated uPA activity, and uPA- and uPA-R-antigen in keratinocytes upon dispase-mediated detachment from their growth substratum. The increase was preceded by an increase in uPA-R- and uPA-specific mRNA, which was not observed when the proteinase inhibitor phosphoramidon was added together with dispase. In conclusion, we present evidence that experimental detachment with dispase provides signals for the concomitant upregulation of uPA-R and uPA. The findings support the hypothesis that cell/matrix interactions may influence the expression of the cell surface-associated PA system in human keratinocytes.

Interleukin-1 beta upregulates tissue-type plasminogen activator in a keratinocyte cell line (HaCaT)

Human keratinocytes synthesize and secrete tissue-type plasminogen activator (tPA). tPA converts the inactive precursor enzyme plasminogen into the trypsin-like proteinase plasmin. tPA is not found in normal epidermis, but in lesional epidermis from patients with a variety of cutaneous diseases, including psoriasis, pemphigus and pemphigoid. The presence of tPA is probably a reaction to the disease process rather than the initiating event in these etiologically and histopathologically diverse lesions. However, the factor(s) that upregulate tPA expression and secretion in keratinocytes have remained largely elusive. We sought to determine whether the inflammatory cytokine interleukin-1 beta (IL-1 beta), which is commonly present in diverse epidermal lesions, influences tPA production. Accordingly, we studied the influence of IL-1 beta on secretion of tPA by cells of the human keratinocyte cell line HaCaT. We found that IL-1 beta increased tPA secretion in these cells. Given the observation that IL-1 beta is a common proinflammatory mediator in cutaneous diseases, our findings may explain the increase in tPA in clinically and etiologically diverse inflammatory epidermal lesions.

Upregulation of cell-surface-associated plasminogen activation in cultured keratinocytes by interleukin-1 beta and tumor necrosis factor-alpha

Keratinocytes synthesize and secrete urokinase-type plasminogen activator (uPA) which is bound in an autocrine manner to a specific receptor (uPA-R) at the keratinocyte surface. Plasminogen that is also bound to specific membrane binding sites is readily activated by uPA-R-bound uPA. Thus, plasmin is provided for proteolysis of pericellular glycoproteins. The expression of uPA and the uPA-R is confined to migrating keratinocytes during epidermal wound healing, rather than to keratinocytes of the normal epidermis. The regulatory factors of uPA/uPA-R expression in keratinocytes remained largely elusive. Proinflammatory cytokines, such as tumor necrosis factor-alpha (TNF-alpha) or interleukin-1 beta (IL-1 beta), are present in epidermal wounds. We have therefore tested IL-1 beta and TNF-alpha for their influence on surface-associated plasminogen activation in a human keratinocyte cell line (HaCaT) as well as in primary cultures of normal human epidermal keratinocytes. Both cytokines induced the secretion of uPA into the culture supernatants and a concomitant increase in uPA activity as well as in uPA and uPA-R antigen at the cell surface. The increase was preceded by an increase in specific mRNA. The induction was accompanied by an accelerated uPA-dependent and plasmin-mediated detachment of HaCaT cells from the culture substratum. Taken together, the proinflammatory cytokines IL-1 beta and TNF-alpha induced a coordinated increase in uPA and uPA-R as well as increased pericellular plasmin-mediated proteolysis in human epidermal keratinocytes. This function might be an element of the molecular cell biological events during epidermal wound healing.

Plasminogen activator inhibitor type-2 (PAI-2) in human keratinocytes regulates pericellular urokinase-type plasminogen activator

Plasminogen activation is observed in the human epidermis during reepithelialization of epidermal defects and under certain pathological conditions. The activation reaction depends on keratinocyte-associated plasminogen activators (PAs), which convert the ubiquitous proenzyme plasminogen into the active trypsin-like serine proteinase plasmin. The PAs are controlled by PA inhibitors (PAIs), of which two major types are known: PAI-1 and PAI-2. In vitro and in vivo keratinocytes express both PAIs. In the current study, we have addressed the possible function of PAI-2 in regulating extracellular PA activity in cultured normal human epidermal keratinocytes (NHEK), the human keratinocyte cell line (HaCaT), and a Ha-ras transfected HaCaT variant (HaRas). PAI-2 was detected intracellularly in all three cell types. Whereas only the NHEK and the HaCaT cells secreted detectable levels of PAI-2 into the culture medium, all three cell types released urokinase-type PA (uPA) into the supernatants. When comparing HaCaT and HaRas cells, we found that the cell lines secreted comparable levels of uPA antigen, whereas the levels of uPA activity were low in the presence of PAI-2, indicating that PAI-2 serves to regulate uPA activity. This assumption was supported by the findings that PAI-2 formed complexes with secreted uPA and that uPA/PAI-2 complexes were present at the surface of the PAI-2-secreting HaCaT cells but not at the surface of PAI-2 nonsecreting HaRas cells. Finally, PAI-2 was found to counteract the uPA-dependent and plasmin-mediated detachment of cultured HaCaT cells. Taken together, our findings indicate that secreted PAI-2 serves to regulate the activity of extracellular uPA in keratinocytes.

tPA of human keratinocytes: contribution to cell surface-associated plasminogen activation and upregulation by retinoic acid

We tested distinct variants of a human keratinocyte line (HaCaT) for the expression of tissue-type plasminogen activator (tPA)-specific mRNA, as well as cell surface-associated and secreted tPA. Cells of early passages (passage no. 22) only expressed urokinase plasminogen activator (uPA)- but not tPA-specific mRNA. Cells after prolonged culture (passage no. 44) expressed uPA- and tPA-specific mRNA, but did not release tPA in the extracellular space and did not display surface-associated tPA. HaCaT cells transformed with the c-Ha-ras oncogene (HaCaTras) showed both secreted and surface-associated tPA antigen. The secreted and the surface-associated plasminogen activator (PA)-activity of HaCaTras cells were in part inhibitable by anticatalytic anti-tPA antibodies, thus indicating that tPA contributes to extracellular and surface-associated plasminogen activation. Finally, we demonstrate that tPA secretion of HaCaT 44 cells can be induced by retinoic acid, most likely via interaction of retinoic acid with nuclear-associated retinoic acid-receptor(s).

Cervical vertebral strain measurements under axial and eccentric loading

The mid to lower cervical spine is a common site for compression related injury. In the present study, we determined the patterns of localized strain distribution in the anterior aspect of the vertebral body and in the lateral masses of lower cervical three-segment units. Miniature strain gages were mounted to human cadaveric vertebrae. Each preparation was line-loaded using a knife-edge oriented in the coronal plane that was moved incrementally from anterior to posterior to induce compression-flexion or compression-extension loading. Uniform compressive loading and failure runs were also conducted. Failure tests indicated strain shifting to "restabilize" the preparation after failure of a component. Under these various compressive loading vectors, the location which resulted in the least amount of deformation for a given force application (i.e., stiffest axis) was quantified to be in the region between 0.5- 1.0 cm anterior to the posterior longitudinal ligament. The location in which line-loading produced no rotation (i.e., balance point) was in this region; it was also close to where the vertebral body strains change from compressive to tensile. Strain values from line loading in this region produced similar strains as recorded under uniform compressive loading, and this was also the region of minimum strain. The region of minimum strain was also more pronounced under higher magnitudes of loading, suggesting that as the maximum load carrying capacity is reached the stiffest axis becomes more well defined.

Plasmin abrogates alpha v beta 5-mediated adhesion of a human keratinocyte cell line (HaCaT) to vitronectin

At cellular surfaces, urokinase-type plasminogen activator (uPA) is bound to a specific receptor (uPA-R). When bound to this receptor, uPA activates plasminogen, which is derived from plasma or the interstitial fluids. Thus, plasmin is provided for proteolysis of pericellular proteinaceous substrates. Here we demonstrate by immunocytology and laser scan microscopy that in the human keratinocyte cell line HaCaT uPA-R and uPA are localized together with the integrin alpha v beta 5 in focal contacts. Via the integrin alpha v beta 5, HaCaT cells adhere to vitronectin in a RGD-dependent manner. Plasmin interfered with the alpha v beta 5-mediated keratinocyte adhesion to vitronectin, most likely via cleavage of vitronectin and destruction of its cell binding function. Our findings demonstrate that plasmin, when generated by the uPA-dependent cell surface-associated pathway of plasminogen activation, can abrogate the cell-binding function of vitronectin and can thus disturb the adhesive interaction with this matrix molecule. In focal contacts molecules are assembled that are crucial for adhesion to vitronectin (i.e., the integrin alpha v beta 5), as well as for the generation of plasmin (i.e., uPA-R and uPA), which can negatively influence the binding interaction. We suggest that the plasmin-mediated abrogation of the interaction between the integrin alpha v beta 5 and vitronectin is a pathway of negative regulation; the codistribution of uPA-R/uPA and alpha v beta 5 in focal contacts may restrict this process to areas of cell/matrix contact.

Plasminogen activation by human keratinocytes: molecular pathways and cell-biological consequences

Keratinocytes are the major cellular constituent of stratified epithelia. Defects in these epithelia are re-epithelialized by keratinocytes migrating from the edge of the defect into the wound. The cells form a monolayer with subsequent differentiation into a multilayered epithelium. It is thought that plasminogen activation by migrating keratinocytes is an important event during re-epithelialization. In the present report we summarize the studies on plasminogen activation by human keratinocytes in vitro and in vivo. Under the aspect of pericellular proteolysis the discussion is focused on the molecular mechanisms of plasminogen activation at the keratinocyte surface and on the cell-biological consequences of pericellular plasmin formation. We describe a cell surface-associated pathway of plasminogen activation which crucially depends on cell surface receptors for (pro)-uPA and plasmin(ogen). uPA bound to its receptor converts cell-bound plasminogen into the active protease plasmin. Compared to plasminogen activation in solution, activation at the keratinocyte cell surface is accelerated by a factor of approx. 7-10, and the plasmin generated and bound at the cell surface is protected against its specific inhibitor alpha 2-antiplasmin. Plasmin thus provided in the pericellular space leads to detachment of cultured keratinocytes from the growth substratum. Plasmin interferes with the adhesion of keratinocytes to fibrin, but not with the adhesion to collagen type I. By demonstrating that keratinocytes of the epithelial outgrowth in healing skin wounds express uPA and the uPA-R and that plasmin(ogen) is colocalized with uPA and/or uPA-R, indirect evidence is provided that this pathway may be operative in vivo. In view of previous findings that plasminogen activation is also observed under certain pathologic conditions in the epidermis, we conclude that plasminogen activation by keratinocytes is rather related to tissue damage and subsequent repair mechanisms than to a specific pathologic situation.

Complement component C7 is a plasminogen-binding protein

Ab deposition, whether by reaction with the specific Ag or by preformed immune complexes, is followed by activation and deposition of complement components. Tissue destruction is observed in the Ab- and complement-induced lesions. The proteolytic enzyme plasmin is thought to participate in the Ab- and complement-mediated organ pathology. Plasmin is generated from plasma-derived plasminogen by cell-derived plasminogen activators (PAs). Two types of PAs are known, urokinase-type PA (uPA) and tissue-type PA (tPA). We investigated whether the PA system and the complement system can interact to promote local plasmin generation. Among the terminal complement components C5b6, C7, C8, and C9, the nonenzymatic component C7 is a plasminogen-binding protein. Radioligand binding studies revealed that the isolated component, as well as C7 after its incorporation into the terminal complement complex C5b-9, can bind plasminogen. Binding was inhibited by the lysine analogues 6-aminohexanoic acid and tranexamic acid, implicating the lysine binding sites of plasminogen into the binding interaction. tPA-mediated plasminogen activation was enhanced in the presence of C7. Based on these findings, an interaction is proposed between the complement system and the plasminogen activator system; a mechanism that may focus plasmin activity to structures that have been tagged by Ab and complement deposition.

Complement component C7 is a plasminogen-binding protein

Ab deposition, whether by reaction with the specific Ag or by preformed immune complexes, is followed by activation and deposition of complement components. Tissue destruction is observed in the Ab- and complement-induced lesions. The proteolytic enzyme plasmin is thought to participate in the Ab- and complement-mediated organ pathology. Plasmin is generated from plasma-derived plasminogen by cell-derived plasminogen activators (PAs). Two types of PAs are known, urokinase-type PA (uPA) and tissue-type PA (tPA). We investigated whether the PA system and the complement system can interact to promote local plasmin generation. Among the terminal complement components C5b6, C7, C8, and C9, the nonenzymatic component C7 is a plasminogen-binding protein. Radioligand binding studies revealed that the isolated component, as well as C7 after its incorporation into the terminal complement complex C5b-9, can bind plasminogen. Binding was inhibited by the lysine analogues 6-aminohexanoic acid and tranexamic acid, implicating the lysine binding sites of plasminogen into the binding interaction. tPA-mediated plasminogen activation was enhanced in the presence of C7. Based on these findings, an interaction is proposed between the complement system and the plasminogen activator system; a mechanism that may focus plasmin activity to structures that have been tagged by Ab and complement deposition.

Continuous motion analysis of the head-neck complex under impact

The objective of the present study was to analyze the localized kinematic biodynamics of the human head-neck complex under impact loading. Unembalmed human cadaveric head-neck complexes were subjected to axial compressive forces delivered using an electrohydraulic testing device. The head-neck complex was aligned along the stiffest-axis; musculature was simulated using preloaded springs and cables; and retroreflective targets were inserted into the vertebral body, the facet joint articulation, and the spinous process at every level of the cervical column. At dynamic loading rates (1.8-5.1 m/min), mid to lower cervical spine injuries consistently occurred in these preparations. Continuous motion analysis of the components (vertebral body, intervertebral disk, facet joint, and the spinous process) at all levels of the cervical spine showed the temporal order of the transfer of the external load. Injuries documented by computed tomography and cryomicrotomy techniques correlated with the kinematics of the structure. The application of dynamic loading to the head-neck complex coupled with high-speed, continuous-motion analysis of the intervertebral components of the entire cervical column makes possible the definition of the temporal kinematic mechanics that are fundamental to the understanding of the biodynamics of cervical spine trauma. Using these procedures, we have correlated the kinematics with the onset and pattern of neck injury secondary to impact forces.

The receptor for urokinase-type plasminogen activator of a human keratinocyte line (HaCaT)

It is assumed that plasmin participates in pericellular proteolysis in the epidermis. Plasmin is generated by keratinocyte-associated plasminogen activators from the proenzyme plasminogen; plasminogen activation can proceed at the keratinocyte surface. The resultant plasmin interferes with cell to matrix adhesion and does possibly contribute to keratinocyte migration during reepithelialization. Here we describe the receptor for urokinase-type plasminogen activator (uPA-R) in the human keratinocyte cell line HaCaT, which serves to direct plasminogen activation to the cell surface; we relate the receptor to the uPA-R previously described in human myelo-/monocytes. Binding of uPA to the receptor accelerated plasminogen activation by a factor of approximately 10, compared to uPA in solution. Receptor-bound uPA was susceptible to inhibition by the plasminogen activator inhibitors 1 and 2. uPA and uPA-R antigen, as well as uPA activity, were localized to the leading front of expanding sheets of HaCaT cells. Exposure of HaCaT cells to plasminogen was followed by detachment of the cells. Detachment was prevented by an anticatalytic anti-uPA antibody, by the plasmin-specific inhibitor aprotinin, and by the lysine analogue tranexamic acid, the latter of which prevents plasmin(ogen) binding to the cell surface. Our findings support the hypothesis that uPA-mediated plasminogen activation is characteristic of mobile rather than sessile keratinocytes. Moreover, the uPA-R seems to focalize plasminogen activation to the surface of cells at the site of keratinocyte migration.

Intravertebral pressure changes caused by spinal microtrauma

Clinical studies indicate variations in intravertebral pressures in patients with and without low back pain. It is known that not all patients with back pain have abnormal lumbar radiographs and, furthermore, microfractures of the endplate may be one of the causes in the origin of low back pain. Consequently, this study was conducted to determine the interrelationship between microtrauma and intraosseous pressures in the lumbar spine. Miniature pressure transducers were inserted into the vertebral bodies and spinous processes of human cadaver spinal units. Radio-opaque medium was injected into the nucleus to fluoroscopically monitor the movement of the fluid from the disc as the preparation was loaded up to the initiation of microtrauma (before reaching the ultimate load-carrying capacity). The onset of injury was evidenced by the microfracture of one of the two endplates and impregnation of the contrast medium into the spongiosa. After relaxation, another cycle of loading was applied by limiting the deflections to the maximum compression sustained under the intact configuration. The load, stiffness, and energy-absorbing capacities were lower (P < 0.05) for the injured specimen compared with the intact configuration. The intraosseous pressures were higher (P < 0.05) in the vertebral body and the spinous process of the vertebra where the endplate exhibited microtrauma in the injured cycle compared with the intact cycle. In contrast, the intraosseous pressures in the vertebral body and the spinous process at the level where the endplate remained intact were not significantly different between the two cycles of loading.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of nuclear magnetic resonance spectroscopy with dual-photon absorptiometry and dual-energy X-ray absorptiometry in the measurement of thoracic vertebral bone mineral density: compressive force versus bone mineral

31P nuclear magnetic resonance spectroscopy (NMRS) measurements were made on human T2 and T3 vertebral bodies. The bone mineral content (BMC) of isolated vertebral bodies minus the posterior elements and disks was measured using (1) NMRS on a 3.5 T, 85 mm bore GE Medical Systems NT-150 superconducting spectrometer, (2) a Lunar Corporation DPX-L dual-energy X-ray absorptiometry (DXA) scanner in an anterior-posterior (AP) orientation, (3) a Norland Corporation XR26 DXA scanner, also in an AP direction, and (4) a Norland Corporation model 2600 dual-photon absorptiometry (DPA) densitometer in both the AP and superior-inferior (SI) directions. Vertebral body volumes were measured using a water displacement technique to determine volume bone mineral densities (VBMD). They were then compressed to failure using an electrohydraulic testing device, followed by ashing in a muffle furnace at 700 degrees C for 18 h. Correlations of BMC between NMRS and DPA, DXA and ashing were excellent (0.96 < or = r < or = 0.99); in a one-way analysis of variance (ANOVA) test, means were not statistically different at a p level of 0.757. The correlations of VBMD between NMRS and the other methods were not as good (0.83 < or = r < or = 0.95); in a one-way ANOVA test, means were not statistically different at a p level of 0.089. BMC was a better predictor of ultimate compressive failure than VBMD for all six methods. For NMRS, the regression coefficient for BMC was r2 = 0.806, compared with r2 = 0.505 for VBMD. NMRS may prove an alternative to present methods of determining bone mineral.

Failure of synthes anterior cervical fixation device by fracture of Morscher screws: a biomechanical study

Anterior cervical fixation using the Synthes system has become increasingly popular. Two screw types for anchoring the plates include a "solid" titanium expansion screw and a plasma-sprayed fenestrated expansion screw that permits bony ingrowth. These screws were compared clinically and in the laboratory. In our first 20 cases using Synthes plates secured by Morscher fenestrated screws, 3 failures were observed, unilaterally in 1 patient and bilaterally in 2 others. In the unilateral screw failure, the contralateral screw was "solid" and did not fail. In the mechanical studies, screws were secured in the Synthes plate and embedded into methylmethacrylate and subjected to a sinusoidal bending moment to the mid-shaft of the screw. Load deflection data and cycles to failure were recorded. Fenestrated screws were found to demonstrate nearly twice as much deformation at failure and tolerated significantly fewer cycles to failure than did "solid" screws (p < 0.05). Because benefits of bony ingrowth into the screw are not well identified, the risks of fenestrated screw failure should preclude their routine use.

Cyclic compression-flexion loading of the human lumbar spine

STUDY DESIGN

The present study was designed to investigate the biomechanical behavior of the lumbar spine under controlled complex physiologic situations with chronic input.

OBJECTIVE

The objective was to determine the response of the human cadaver lumbar spinal column under repetitive compression-flexion forces.

SUMMARY OF BACKGROUND DATA

Studies have been conducted in the past to determine the biomechanical response of the spine under uniaxial or pure forces. There is no methodology that can be used to apply and continuously quantify the fatigue response of the lumbar spinal column under controlled combined complex loading vectors (e.g., compression flexion).

METHODS

Intact cadaver lumbar columns (L1-L5) were mounted with the superior end in contact with a ball-transfer mount, inducing a flexion load to the spine while allowing multiple degrees of freedom. The distal portion of the specimen was attached to a six-axis load cell to quantify the force sustained by the specimen during the entire loading cycle. The applied load and piston deformation and the generalized six-axis force histories were gathered as a function of time using a digital data acquisition system.

RESULTS

The stiffness versus number of cycles (K-N) response exhibited nonlinear characteristics. The stiffness increased initially and then stabilized after 1,000-2,000 cycles of loading, delineating the viscoelastic characteristics of the spine. The initial stiffness increase before stabilization was found to be significantly different (P < 0.025) compared to the stiffness beyond 2,000 cycles.

CONCLUSIONS

The data suggest that the fatigue response can be understood by cyclically loading the ligamentous lumbar spine preparation to approximately 2,000 cycles.

Correlation of microtrauma in the lumbar spine with intraosseous pressures

This study was conducted to determine the relationship between intraosseous pressure and vertebral microtrauma in the lumbar spine. Functional spinal units were excised from human cadavers. Radio-opaque dye was injected into the nucleus. Miniature transducers were inserted into the vertebrae to record intraosseous pressures. Compressive loading was applied quasistatically (2 mm/sec) until injury occurred. Movement of the contrast medium was monitored under fluoroscopy. The subchondral endplate was the most vulnerable component for initiation of injury to the lumbar spine segment. In the initial stages of loading, the vertebral endplates gradually bulged outward, with the contrast medium staying within the nucleus. However, at higher physiologic load levels, before reaching the limiting load, the deformations increased, resulting in buckling of one of the endplates. This was followed by the contrast medium impregnating the spongiosa. Microlevel trauma was not observed radiographically after load removal, indicating that one cannot always equate a normal radiograph with normal spinal anatomy. Mean forces, deformations, stiffnesses, energies, and strains were 7.8 kN (+/- 1.4), 5.23 mm (+/- 0.78), 1940 N/mm (+/- 226), 18.7 J (+/- 4.4), and 35.5% (+/- 3.7), respectively. Pressure in the vertebral body containing the injured endplate before the onset of microtrauma was different (P < 0.05) from the pressure after injury; the pressures in the body containing the intact endplate, however, were not statistically different. Significant differences (P < 0.05) in the intraosseous pressures occurred between the two spinal levels at low-level physiologic loads before the onset of microtrauma.(ABSTRACT TRUNCATED AT 250 WORDS)

[The autoimmune dermatosis bullous pemphigoid: deposition and activation of plasminogen in affected epidermis]

Autoimmune dermatoses are associated with antibody deposition, complement activation and subsequent tissue destruction. Plasmin-mediated proteolysis is thought to be one element of tissue destruction in autoimmune bullous dermatoses such as bullous pemphigoid. Biochemical and immunological studies on bullous pemphigoid skin blister fluid disclosed plasmin/alpha 2-antiplasmin and putative plasmin/alpha 2-macroglobulin complexes. Since the formation of plasmin/inhibitor complexes requires active plasmin, our findings indicate previous activation of plasminogen to plasmin in skin lesions.

Effects of anterior vertebral grafting on the traumatized lumbar spine after pedicle screw-plate fixation

This study was conducted to determine the effects of corpectomy and anterior strut grafting on the biomechanics of traumatized lumbar spine after pedicle screw-plate fixation. Eight lumbar spines were loaded until fracture (initial cycle) and then reloaded to the same deformation (injury cycle). After transpedicular fixation, spines were again loaded (fixation cycle). Partial corpectomy of the fractured body and anterior strut grafting were accomplished; the spine reloaded (strut cycle). Spine angles were measured and biomechanical strength and kinematic parameters analyzed. Load-deformation relationships were similar for fixation and strut cycles until maximum load; at failure, loads were higher for the former (P < 0.05), however. Alignment was improved by stabilization or stabilization plus anterior grafting (P < 0.05). Vertebral height was best maintained by grafting as an adjunct to pedicle fixation (P < 0.05). Kinematics were largely unaffected by grafting, except for reduced motion at the posterior vertebral targets between the fixated levels (P < 0.05). The strength of the fixated spine is relatively unchanged by corpectomy and anterior grafting; alignment may be improved in the latter group.

Biomechanical evaluation of Caspar cervical screws: comparative stability under cyclical loading

Anterior cervical instrumentation is used as an adjunct to bone fusion; however, definitive biomechanical data to support some applications and techniques are lacking. In the absence of supportive experimental data, posterior cortical penetration has been recommended with the Caspar system. Previously, we compared the axial pull-out strength of Caspar screws with and without posterior cortical penetration. This study compares the stability of unicortical versus bicortical screw penetration groups under cyclical loading simulating physiological flexion-extension. Caspar screws were placed in human cadaveric vertebrae with or without posterior cortical purchase. Each screw was separately tested, simulating flexion-extension to 200 cycles. Deformation time data allowed a direct comparison of screw "wobble" with and without posterior cortical purchase. The mean deformation differences between subcortical and bicortical groups were statistically significant and increased over time within both groups. Enhanced stability was noted with bicortical purchase throughout most of the examined range, becoming more pronounced over longer periods of cyclical loading. Significant (P < 0.05) increases in deformation over time were noted for both groups, suggesting potentially significant deterioration at the screw-bone interface, despite bicortical purchase. Such deterioration with repeated flexion-extension loading may be of concern in the use of Caspar plates in the presence of multicolumn instability.

Binding and activation of plasminogen at the surface of human keratinocytes

Plasmin is thought to be involved in the pericellular proteolysis of the human epidermis under physiological and pathological conditions. Plasmin is provided by activation of the proenzyme plasminogen. We have explored in vitro whether plasminogen is bound and activated at the keratinocyte surface, a possible mechanism for providing plasmin in the pericellular space. Plasminogen and plasmin could be eluted from the surface of keratinocytes grown in serum-containing medium. When plasminogen was added to cultured keratinocytes it was activated by cell-associated urokinase-type plasminogen activator. The activation required plasminogen binding to the cell surface. Plasminogen binding by keratinocytes was saturable and proceeded in a time- and concentration-dependent manner. Surface-bound plasmin was rapidly displaced from the surface into the culture supernatant. When compared to plasmin in solution surface-bound plasmin was relatively protected from interaction with the specific inhibitor alpha 2-antiplasmin. Addition of exogenous plasmin or plasmin generation by the keratinocyte-associated plasminogen activators was ensued by the detachment of adherent keratinocytes in culture. Along the same line, plasmin counteracted keratinocyte adhesion to fibrin-coated but not to collagen-coated culture plates. The findings indicate that plasmin may be generated in the pericellular space of keratinocytes and may interfere with the adhesion to particular extracellular substrates.

The autoimmune blistering skin disease bullous pemphigoid. The presence of plasmin/alpha 2-antiplasmin complexes in skin blister fluid indicates plasmin generation in lesional skin

Plasminogen activators produced locally in the skin have been implicated in blistering skin diseases. To explore whether plasminogen activators convert their substrate plasminogen into plasmin locally in the lesional skin we have analyzed the autoimmune blistering skin disease bullous pemphigoid. Enzyme activity was detected in bullous pemphigoid skin blister fluid by using a low molecular weight chromogenic substrate for plasmin. Enzyme activity was detected neither in suction blister fluid raised on normal skin nor in normal plasma. Immunoprecipitation or fractionation by molecular sieve chromatography of bullous pemphigoid skin blister fluid followed by testing in immunoassays disclosed putative plasmin/alpha 2-macroglobulin complexes and plasmin/alpha 2-antiplasmin complexes. Enzyme activity detected in bullous pemphigoid skin blister fluid by the low molecular weight chromogenic peptide assay was ascribed to the putative plasmin pha 2-macroglobulin complexes. Because formation of plasmin-inhibitor complexes requires the active plasmin, our findings indicate previous activation of plasminogen to plasmin in skin lesions. There was no evidence for free plasmin (i.e., plasmin not complexed to inhibitors) in bullous pemphigoid blister fluid, suction blister fluid, or plasma.

Enzyme-linked immunosorbent assays for plasminogen activators

ELISA procedures are described for the quantitative analysis of the urokinase-type plasminogen activator (uPA) and of the tissue type PA (tPA). The assays were developed to detect the respective type of PA in cell culture supernatants. TPA can be present as a single-chain or a two-chain protein; uPA as pro-uPA, high or low molecular weight uPA, respectively. In addition, both PAs can be complexed with the plasminogen activator inhibitors PAI-I or PAI-2. Monoclonal antibodies specific for uPA or tPA were selected that recognized the distinct molecular forms of the PAs, even in the presence of fetal calf serum, which is a common--relatively ill-defined--ingredient of cell culture media. The test systems were found to be reliable, easy to perform, and to permit the detection of both types of PA in serum-free and serum-containing cell culture supernatants. Finally, the ELISA--in combination with functional tests--were used to analyse the different PA components in culture supernatants of uPA- or tPA-producing cell lines.

Kinematics of the lumbar spine following pedicle screw plate fixation

This investigation was conducted to determine the kinematic response of the lumbar spine instrumented with transpedicular screws and plates. Seven unembalmed human cadaveric lumbar spines were used. Retroreflective targets were inserted into the bony landmarks of each vertebral body, facet column, and spinous process. The specimen was quasistatically loaded until failure (initial cycle) using an electrohydraulic testing device at a rate of 2.5 mm/sec. After radiography, the specimen was again loaded (injury cycle) to the failure compression determined in the previous cycle. Transpedicular screws then were inserted bilaterally at one level proximal and distal to injury. The stabilized cycle of loading was conducted using the procedure adopted in the injury cycle. Comparative analysis of the localized kinematic data between the stabilized and injured columns indicated a reduction in motion between fixated levels, increasing the rigidity of the column. At levels proximal and distal to fixation, however, motion increased, indicating added flexibility. These alterations in the motion, observed during single-cycle loading, may be further accentuated in vivo, leading to hypermobility and degeneration of the spine.

A biomechanical impact test system for head and facial injury assessment and model development

A biomechanical test system has been developed and validated to conduct controlled uniaxial impact experiments of head and facial trauma. The design reduces off-axis accelerations which are not in the direction of impact and allows accurate positioning of test specimens. Impact forces, displacement histories, impulses at impact and spectral responses are compared to free-fall test results at contact velocities representative of facial injuries (2.5, 3.1 and 3.8 m s-1). Models based on the experimental results are developed to reveal stiffness and inertial properties of impact for use in the design of biomechanically protective steering wheels, air bags and other potential impact structures. The results indicate that the system provides a flexible yet controllable method for positioning and testing impact structures reliably.

Plasminogen activation in lesional skin of Pemphigus vulgaris type Neumann

Zymographic and immunological studies revealed that primarily tissue-type plasminogen activator and to a lesser extent urokinase-type plasminogen activator were present in fluids of pemphigus vulgaris (type Neumann) skin blisters. Furthermore, plasmin activity was detected in pemphigus blister fluids using chromogenic peptide substrate assays. In pemphigus, but not in control, suction blister fluids plasmin/alpha 2-antiplasmin and plasmin/alpha 2-macroglobulin complexes were found by immunoprecipitation or by testing in immunoassays after fractionation by molecular-sieve chromatography. Plasmin activity, detected by a low molecular weight chromogenic peptide assay, was ascribed to plasmin/alpha 2-macroglobulin complexes. Since formation of plasmin/inhibitor complexes requires active plasmin, the finding indicates previous activation of plasminogen in pemphigus lesions.

Pull-out strength of Caspar cervical screws

Anterior cervical instrumentation as an adjunct to bone fusion has an important role in cervical spine surgery. Posterior vertebral body cortex purchase is strongly recommended in the use of the Caspar system, although few biomechanical data exist to validate this requirement. In this study, Caspar screws were placed in 43 human cadaveric cervical vertebral bodies, either putting them into the posterior vertebral cortex as identified radiographically or penetrating it by 2 mm as recommended in the literature. Pull-out tests were conducted with tension applied to a connected plate at 0.25 mm/s, and force-deformation data were obtained. Failure typically occurred with clean pull-out; in most instances, cancellous bone remained attached to screw threads. Mean load without posterior cortical purchase was 375 +/- 53 N; with penetration it was 411 +/- 70 N. These differences were nonsignificant. Average deformation to failure was 1.41 +/- 0.10 mm in the group without posterior cortical penetration. In the posterior penetration group, mean deformation was 1.56 +/- 0.16 mm. Again, differences were not significant. Posterior cortical penetration does not improve the pull-out strength of Caspar screws in an isolated vertebral body model, but other biomechanical studies need to be done before insertion methods are altered.

The biomechanics of lumbar facetectomy under compression-flexion

Alterations of posterior spinal elements including the facet joints are commonly associated with a variety of lumbar operative procedures. Under continuous physiologic compression-flexion load application L2-L3 and L4-L5 functional units were tested as intact preparations and then sequentially altered with unilateral facetectomy, bilateral facetectomy, posterior ligament transection, and partial discectomy. Using a method of continuous motion analysis, the movement of the individual spinal components (disc, facet joint, interspinous process distance) were statistically compared between the various surgical alterations. Higher physiologic loads produced significant increases in overall deflection from BF to BFL alterations indicating a preference to preserve the posterior ligaments for this surgical approach. Although insignificant changes in the force-deflection response from one surgical alteration to the next sequential alteration were noted, statistically significant increases in localized facet joint motion may suggest the potential for acceleration of segmental degenerative changes.

Strength and kinematic response of dynamic cervical spine injuries

This study was conducted to evaluate the biodynamic strength and localized kinematic response of the human cervical spine under axial loading applied to the head. Intact ligamentous fresh human cadaveric head-neck complexes were subjected to dynamic compressive forces with a custom-designed electrohydraulic testing device at varying rates. The structure included the effects of anterior and posterior cervical spine muscles with a system of pulleys, dead weights, and spring tension. Localized kinematic data were obtained from retroreflective targets placed on the bony landmarks of the specimen at every level of the spinal column. Input forces, accelerations, displacement, and output generalized force histories were recorded as a function of time with a digital data acquisition system at dynamic sampling rates in excess of 8,000 Hz. High-speed photography at 1,000-1,200 frames/sec also was used. Pathologic alterations to the head-neck complex were evaluated with conventional radiography, computed tomography, and cryomicrotomy. In all specimens, cervical spine injuries occurred as a result of impact. Compressive forces recorded at the distal end of the preparation indicated large-duration, short-magnitude pulses in contrast to short-duration, high-amplitude input waveforms at the head, suggesting decoupling characteristics of the head-neck system. Cervical vertebral body accelerations were consistently smaller than the accelerations recorded on the head. Kinematic data demonstrated temporal deformation characteristics as well as a plausible sequence of spinal deformations leading to injury, which were correlated with the pathoanatomic alterations documented with the post-test computed tomographic and sequential cryomicrotome sections.

Biomechanics of lumbar pedicle screw/plate fixation in trauma

This investigation was conducted to determine alterations in the biomechanical strength and stiffness characteristics of the lumbar spine fixated with Steffee instrumentation. Comparative studies of these parameters were conducted using seven lumbar columns from fresh human cadavers. Three runs were conducted on each T12-L5 column: control, injured, and fixated. The specimens were loaded under the compression-flexion mode until failure (control run) and then reloaded (injury run) to the failure deformation determined in the control run. Screw/plates were then inserted one level proximal and distal to injury, and the specimens were reloaded (fixation run). Radiographs were taken before and after each trial. Data on deformation and force histories were gathered. The load-deflection response of the injured and fixated specimens were bimodal with two representative stiffnesses. Control failure loads and stiffnesses were higher than those for the injured (P less than 0.001) or fixated (P less than 0.01) spine. Initial stiffness was significantly higher for the fixated than for injured columns (P less than 0.001), but the final stiffnesses were similar. The increase in the initial stiffness in the fixated specimen compared to the injured specimen indicates the strength added to the posterior region of the spine. The relatively smaller alteration in the final stiffness between the fixated and the injured columns, corresponding to the load shared by the anterior column, may suggest that, above a critical strain level, the anterior column absorbs a higher portion of the external load and posterior fixation may be inadequate as sole treatment in trauma.

Injury biomechanics of the human cervical column

In this study, the authors have developed a technique to replicate clinically relevant traumatic cervical spine injuries and determined the injury biomechanics. Because of the importance of compressive forces in neck injuries, this research was conducted using compression as the primary load vector. Six fresh human cadaveric head-neck complexes were prepared by fixing the distal end in methylmethacrylate. Tests were done with varying loading rates to include quasistatic and dynamic conditions. For quasistatic experiments, the proximal end was fixed to the piston of the testing device. In dynamic tests, the cranium was unconstrained, and to maintain stability, the effects of the spinal musculature were simulated by means of pulleys, deadweights, and springs in the anterior and posterior parts of the head-neck complex. Quasistatic tests conducted at a rate of 2.0 mm/sec produced cervical spine trauma at forces ranging from 1.7 to 2.3 kN, with deformations ranging from 2.2 to 3.7 cm. The specimens were deep-frozen at the level of injury, preserving the local deformation of the tissues to enable a detailed evaluation immediately after the injury. Dynamic tests conducted at velocities of 3.2 to 5.7 m/sec resulted in impact injuries at one level of the head-neck complex. The applied forces at the vertex were considerably higher than those recorded at the distal end. The failure deformations for both the quasistatic (2.2-3.7 cm) and dynamic (1.7-3.2 cm) tests, however, were found to be similar, suggesting that the human head-neck complex is a deformation-sensitive structure.

Effect of axial loading on neural foramina and nerve roots in the lumbar spine

The hypothesis that the neural foramina in some patients are critically narrowed by axial compression of the spine has not been studied with direct imaging techniques. Frozen cadaveric motion segments of the lumbar spine (intervertebral disk and contiguous vertebrae) were imaged with computed tomography (CT). The segments were thawed and compressed in a hydrostatic press to simulate axial loading, and then the segments were frozen and imaged again. The motion segments were subsequently sectioned with a cryomicrotome, and the chronic degenerative changes present in the disks were classified. Pre- and post-compression CT images were compared, and anatomic relationships were studied. In 41 randomly selected segments (some with preexisting radial, transverse, and concentric annular tears), compression diminished the diameters and cross-sectional areas of the spinal canal and neural foramina. In no cases were nerve roots displaced, distorted, or compressed by axial loading. This study suggests that axial loading, such as that produced by ordinary weight bearing, does not critically compromise the neural foramina even in the presence of chronic degenerative disk changes.

Dynamic response of human cervical spine ligaments

This study was undertaken to investigate the dynamic response of human cervical spine ligaments. Uniaxial tensile failure tests were conducted on anterior longitudinal ligament (AL) and ligamentum flavum (LF) structures. These ligaments were tested under in situ conditions by transecting all the elements except the one (AL or LF) under study. A fixture was designed to properly align the specimen to induce a uniaxial mode of loading. A six-axis load cell was placed at the distal end of the specimen. The proximal end of the specimen was attached to the piston of a specially designed electrohydraulic testing device. The biomechanical properties of the ligaments were determined at four different loading rates of 8.89, 25.0, 250.0 and 2500 mm/sec. The mechanical response indicated nonlinear and sigmoidal characteristics. The ultimate tensile failure load, stiffness, and energy-absorbing capacity at failure were found to increase with increasing loading rates for both the AL and LF. However, the distractions at failure did not indicate this tendency. While the ultimate tensile force and ultimate energy-absorbing capacity varied nonlinearly with the logarithm of the loading rate, the stiffness varied linearly.