DEVICES AND METHODS FOR TREATING SPINAL CORD TISSUE Louis C. Argenta David L. Carroll Nicole H. Levi Jie Liu Michael J. Morykwas Stephen Tatter William D. Wagner Field of the Invention [0001] The present invention relates generally to devices and methods for treating damaged or compromised spinal cord tissue using sub-atmospheric pressure and more particularly, but not exclusively, to devices and methods for treating spinal cord tissue that have experienced a recoverable or non-recoverable injury. Background of the Invention [0002] The anatomy, physiology, and pathologic processes that involve the spinal cord pose special concerns for the treatment of damaged or compromised spinal cord tissue. The preservation of both the three-dimensional structural anatomy and the microanatomical relationships of neurons (whose function depends on specific spacial relationships with other neurons and other supporting cells), as well as the maintenance of properly oxygenated blood flow and the homogeneous ground substance matrix in which the neurons survive, are vital to the survival and function of spinal cord tissues. Moreover, the inability of spinal cord cells to regenerate emphasizes the need to maximize survival of every possible neuron. For reasons such as these, treatment of both open and closed space pathology in the spinal cord poses special concerns. [0003] Among the clinical problems that threaten survival of spinal cord tissue, the control of spinal cord edema, infection, and blood supply are central. The spinal cord responds to trauma and injury by collecting a significant amount of interstitial edema. Because the spinal cord is enclosed in a closed space (dura and the spinal canal), edema
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results in compression and compromise of the blood flow and nutritional performance of the spinal cord, which greatly impairs physiological recovery of the spinal cord and often of itself results in progression of compromise and death of the spinal cord. Currently available treatments for reducing edema include pharmacologic agents, such as glucocorticoids (Dexamethasone, Prednisone, Methyl Prednisolone), diuretics, and extensive surgical decompression. However, disadvantagesto these treatments include irregular and unpredictable results, complications of the drugs, infection, and surgical complications. [0004] The need for rapid and effective treatment is also vital due to the disastrous consequences and high likelihood of rapid propagation of infection and edema in the spinal cord. At present there are few successful methods available to treat pathologies affecting the intraspinal space, spinal cord parenchyma, and the surrounding structures. Where tissues elsewhere in the body can be treated with dressing changes, the spinal cord is not amenable to this type of treatment because of its precarious strcture, propensity for infection, and potential for progression of injury. There is evidence that inflammation and immunological response to spinal cord trauma and other pathology are of equal or greater long term consequences than the initial trauma or insult. The response of the spinal cord to decreased blood flow secondary to edema results in hypoxia and ischemia/ reperfusion-mediated injury. These injuries contribute to the neuropathological sequella, which greatly contribute to the adverse outcome of spinal injury. [00051 In addition, the spinal cord requires a continuous supply of oxygenated blood to function and survive. Within a few minutes of complete interruption of blood flow to the spinal cord, irreversible spinal cord damage results. The spinal cord can, however, remain viable and recover from reduced blood flow for more prolonged periods. There is evidence that focal areas of the spinal cord can remain ischemic and relatively functionless for days and still recover. This finding has led to the concept of an ischemic zone, termed the penumbra or halo zone, that surrounds an area of irreversible injury. A secondary phenomena in the ischemic zone is the release of excitotoxins that are released locally by injured neurons, alterations in focal blood flow, and edema. -2- [0006] Vascular pathology of the spine may be a result of: inadequate blood flow to the spinal cord cells from decreased perfusion pressure, rapture of a blood vessel resulting in direct injury to the local spinal cord area, or by compression of adjacent tissue; intrinsic disease of the spinal cord blood vessels such as atherosclerosis, aneurysm, inflammation, etc.; or a remote thrombus that lodges in the spinal cord blood vessels from elsewhere such as the heart. [00071 In cases of intraspinal hemorrhage, the hemorrhage usually begins as a small mass that grows in volume by pressure dissection and results in displacement and compression of adjacent spinal cord tissue. Edema in the adjacent compressed tissue around the hemorrhage may lead to a mass effect and a worsening of the clinical condition by compromising a larger area of spinal cord tissue. Edema in the adjacent spinal cord may cause progressive deterioration usually seen over 12 to 72 hours. The occurrence of edema in the week following the intraspinal hemorrhage often worsens the prognosis, particularly in the elderly. The tissue surrounding the hematoma is displaced and compressed but is not necessarily fatally compromised. Improvement can result as the hematoma is resorbed, adjacent edema decreased, and the involved tissue regains function. [0008] Treatment ofthese conditions has been disappointing. Surgical decompression of the spinal cord can be helpful in some cases to prevent irreversible compression. Agents such as mannitol and some other osmotic agents can reduce intraspinal pressure causedbyedema. Steroids are ofuncertain value in these cases, andrecently hyperbaric oxygen has been proposed. [0009] Thus, though the application of negative (or sub-atmospheric) pressure therapy to wounded cutaneous and subcutaneous tissue demonstrates an increased rate of healing compared to traditional methods (as set forth in US Patent Nos. 5645081, 5636643, 7198046, and 7216651, as well as US Published Application Nos. 2003/0225347, 2004/0039391, and 2004/0122434, the contents of which are incorporated herein by reference), there remains a need for devices and methods specifically suited for use with the specialized tissues of the spinal cord. -3- Summary of the Invention [0010] The present invention provides devices and methods that use sub-atmospheric (or negative) pressure to treat damaged spinal cord tissue, such as spinal tissue damaged by disease, infection, or trauma, for example, which may lead to the presence of swelling, compression, and compromised blood flow secondary to interstitial edema. For instance, the spinal cord may be damaged by blunttrauma resulting in a recoverable or non-recoverable injury. [00111 In one of its aspects the present invention provides a method for treating damaged spinal cord tissue using sub-atmospheric pressure. The method.comprises locating a porous material proximate the damaged spinal cord tissue to provide gaseous communication between one or more pores of the porous material and the damaged spinal cord tissue. The porous material may be sealed in situ, proximate the damaged spinal cord tissue to provide a region about the damaged spinal cord tissue for maintaining sub-atmospheric pressure at the damaged spinal cord tissue. The porous material may be operably connected with a vacuum system for producing sub atmospheric pressure at the damaged spinal cord tissue, and the vacuum system activated to provide sub-atmospheric pressure at the damaged spinal cord tissue. The sub-atmospheric pressure may be maintained at the damaged spinal cord tissue for a time sufficient to decrease edema at the spinal cord. For example, the sub-atmospheric pressure may be maintained at about 25 mm Hg below atmospheric pressure. The method may also include locating a cover over damaged spinal cord tissue and sealing the cover to tissue proximate the damaged spinal cord tissue for maintaining sub-atmospheric pressure at the damaged spinal cord tissue. The covermay be provided in the form of a self-adhesive sheet which may be located over the damaged spinal cord tissue. In such a case, the step of sealing the cover may include adhesively sealing and adhering the self-adhesive sheet to tissue surrounding the damaged spinal cord tissue to form a seal between the sheet and tissue surrounding the damaged spinal cord tissue. [00121 In another ofits aspects the present inventionprovides an apparatus for treating damaged spinal cord tissue. The apparatus may include a porous bio-incorporable material, such as an open-cell collagen, having pore structure configured to permit gaseous communication between one or more pores of the porous material and the -4- H:\ z \lerwovn RPod\DCC\KZR\6253073 - do -5/05/201 -5 spinal cord tissue to be treated. The bio-incorporable nature of the porous material can obviate the need for a second procedure to remove the porous material. (As used herein the term "bio incorporable" is defined to describe a material that may be left in the patient indefinitely and is capable of being remodeled, resorbed, dissolved, and/or otherwise assimilated or modified.) The apparatus also includes a vacuum source for producing sub-atmospheric pressure; the vacuum source may be disposed in gaseous communication with the porous material for distributing the sub-atmospheric pressure to the spinal cord tissue. The porous material may have, at least at a selected surface of the porous material, pores sufficiently small to prevent the growth of tissue therein. In addition, the porous material may have, at least at a selected surface of the porous material, a pore size smaller than the size of fibroblasts and spinal cord cells, and may have a pore size at a location other than the selected surface that is larger than that of fibroblasts and spinal cord cells. The pore size of the porous material may be large enough to allow movement of proteins the size of albumin therethrough. Also, the porous bio incorporable material may include at least one surface that is sealed to prevent the transmission of sub-atmospheric pressure therethrough. The apparatus may also include a cover configured to cover the damaged spinal cord tissue to maintain subatmospheric pressure under the cover at the damaged spinal cord tissue. [0012A] According to one aspect, the present invention provides an apparatus for treating damaged spinal cord tissue, including: a porous bio-incorporable material having pore structure configured to permit gaseous communication between one or more pores of the porous bio-incorporable material and the spinal cord tissue to be treated, the porous bio-incorporable material having, at least at a selected surface of the porous bio-incorporable material for placement proximate the damaged spinal cord tissue, pores sufficiently small to prevent the growth of tissue therein; and a vacuum source for producing sub-atmospheric pressure disposed in gaseous communication with the porous bio-incorporable material for distributing the sub atmospheric pressure to the spinal cord tissue to be treated. [00131 Thus, the present invention provides devices and methods for minimizing the progression of pathologic processes, minimizing the disruption of physiological spinal cord integrity, and minimizing the interference with spinal cord blood flow and nutrition. By decreasing spinal cord edema and intraspinal pressure the risk of spinal cord herniation and compromise may be minimized. In addition, the present invention facilitates the removal of H:\ z \lerwovn RPod\DCC\KZR\6253073 - dc- -5/05/201 - 5A mediators, degradation products, and toxins that enhance the inflammatory and neuropathological response of tissues in the spinal cord. Brief Descriition of the Drawings 100141 The foregoing summary and the following detailed description of the preferred embodiments of the present invention will be best understood when read in conjunction with the appended drawings, in which: [0015] Figure1 schematically illustrates a partial cross-sectional viewofan exemplary configuration of an apparatus of the present invention in situ prior to the application of sub-atmospheric pressure; [0016] Figure 2 schematically illustrates the partial cross-sectional view of Fig. 1 as a sub-atmospheric pressure is being applied; [00171 Figure 3 schematically illustrates the partial cross-sectional view of Figs. 1 and 2 showing the effect of the applied sub-atmospheric pressure on the tissues surrounding the spinal cord; [00181 Figure 4 schematically illustrates a partial cross-sectional view of a second exemplary configuration of the present invention in situ comprising arigidor semi-rigid cover disposed subcutaneously over the spinal cord; [00191 Figure 5 schematically illustrates a partial cross-sectional view of a third exemplary configuration of the present invention in situ comprising a flexible cover disposed subcutaneously over the spinal cord; [00201 Figure 6 illustrates the BBB score as a function of time for control animals exposed to recoverable blunt trauma of the spinal cord; [0021] Figure 7 illustrates the BBB score as a function of time for animals exposed to recoverable blunt trauma of the spinal cord and treated with sub-atmospheric pressure; [00221 Figure 8 illustrates the cross-sectional area of the spinal cord as a function of time for control animals exposed to non-recoverable blunt trauma of the spinal cord; 10023] Figure 9 illustrates the cross-sectional area of the spinal cord as a function of time for animals exposed Io non-recoverable blunt trauma ofthe spinal cord and treated with sub-atmospheric pressure; and [00241 Figure 10 schematically illustrates a porous material having a multi-layer structure for use in a sub-atmospheric pressure apparatus of the present invention. Detailed Description of the Invention [00251 Referring now to the figures, wherein like elements are numbered alike throughout, the present invention relates to devices and methods that use sub atmospheric (or negative) pressure for treating damaged spinal cord tissue, where -6- "damaged" tissue is defined to include tissue that is injured, compromised, or in any other way impaired, such as damage due to trauma, disease, infection, surgical complication, or other pathologic process, for example. More specifically, the devices and methods of the present invention can effect treatment of edema of the spinal cord parenchyma secondary to any cause, such as the aforementioned causes; treatment of any of the spaces surrounding the spinal cord, including the subdural/epidural spaces; and, treatment of elevated intraspinal pressure due to any cause, such as the aforementioned causes. [0026J An exemplary configuration of a sub-atmospheric spinal cord treatment device 100 of the present invention may include a vacuum source 30 for supplying sub atmospheric pressure via a tube 20 to a porous material 10 disposed proximate the spinal cord 7, Figs. 1-3. In this regard, the porous material 10 may be structured to deliver and distribute sub-atmospheric pressure to the spinal cord 7. The spinal cord treatment device 100 may be applied to a patient by locating a porous material 10 proximate the damaged spinal cord tissue 7 to provide gaseous communication between one or more pores of the porous material 10 and the damaged spinal cord tissue 7. A tube 20 may be connected to the porous material 10 at a distal end 22 of the tube 20, and the porous material 10 may be sealed in situ by sutures 8 in the skin and subcutaneous tissues 2 to provide a region about the damaged spinal cord tissue 7 for maintaining sub atmospheric pressure. The proximal end 24 ofthe tube 20 may be attached to a vacuum source 30 to operably connect the porous material 10 to the vacuum system 30 for producing sub-atmospheric pressure at the damaged spinal cord tissue 7 upon activation of the vacuum system 30. [0027J Turning to Fig. 1 in greater detail, an exemplary configuration of a sub atmospheric spinal cord treatment device 100 of the present invention is illustrated in situ in a patient with surrounding tissues shown in partial cross-section. The tissues illustrated include the skin and subcutaneous tissue 2, muscle tissue, such as the trapezius 3 and erector spinae 4, vertebrae 5, transverse process 6, and the spinal cord 7. To provide access to the spinal cord 7, a portion of the vertebrae 5 may be missing. For instance, the spinous process may be absent due to surgical dissection, disease, or injury. A porous material 10, such as an open-cell collagen material, may be placed in the subcutaneous space proximate the spinal cord tissue 7 to be treated with sub -7atmospheric pressure to decrease edema in the parenchymal tissues and improve physiologic function, for example. In addition to. an open-cell collagen material, the porous material 10 may also include a polyglycolic and/or polylactic acid material, a synthetic polymer, a flexible sheet-like mesh, an open-cell polymer foam, a foam section, a porous sheet, a polyvinyl alcohol foam, a polyethylene and/or polyester material, elastin, hyaluronic acid, alginates, polydiolcitrates, polyhyrdoxybutyrate, polyhyrdoxyfumarate, polytrimethylenecarbonate, polyglycerolsebecate, aliphatic/aromatic polyanhydride, or other suitable materials, and combinations of the foregoing any of which may be fabricated by electrospinning, casting, or printing, for example. Such materials include a solution of chitosan (1.33% weight/volume in 2% acetic acid, 20 ml total volume) which may be poured into an appropriately sized mold. The solution is then frozen for 2 hours at -70*C, and then transferred to the lyophylizer with a vacuum applied for 24 hours. The material may be cross-linked by 2.5% - 5% glutaraldehyde vapor for 12 - 24 hours (or by ultraviolet radiation for 8 hours) to provide a cast porous material 10. [0028] Additionally, the porous material 10 may be made by casting polycaprolactone (PCL). Polycaprolactone may be mixed with sodium chloride (1 part caprolactone to 10 parts sodium chloride) and placed in a sufficient volume of chloroform to dissolve the components. For example, 8 ml ofthe solution may be poured into an appropriately sized and shaped contained and allowed to dry for twelve hours. The sodium chloride may then be leached out in water for 24 hours. [0029] It is also possible to use electrospun materials for the porous material 10. One exemplary of a formulation and method for making an electrospun porous material 10 was made using a combination of collagen Type Lchondroitin-6-sulfate (CS): poly 1,8 octanediol citrate (POC) in a ratio of 76%:4%:20%: by weight. Two solvents were utilized for the collagen/CS/POC. The CS was dissolved in water and the collagen and POC were dissolved in 2,2,2-trifluoroethanol (TFE). A 20% water/80% TFE solution (volume/volume) solution was then used. For electrospinning, the solution containing the collagen:CS:POC mixture was placed in a 3 ml syringe fitted to an 18 Ga needle. A syringe pump (New Era Pump Systems, Wantaugh, NY) was used to feed the solution into the needle tip at a rate of 2.0 ml/hr. A voltage of 10-20 kV was provided by a high voltage power supply (HV Power Supply, Gamma High Voltage Research, Ormond -8- Beach. FL) and was applied between the needle (anode) and the grounded collector (cathode) with a distance of 15-25 cm. The material was then cross-linked with glutaraldehyde (Grade II, 25% solution) and heat polymerized (80"C) for 48 hours. It is also possible to electrospin collagen Type I porous materials 10 starting with an initial concentrationof80 mg/ml ofcollagen in 1,1,1,3,3,3-hexafluoro-2-propanol (HFP), then use the same electrospinning conditions as the collagen:CS:POC combination. [0030] An additional method for creating porous materials 10 is to use thermal inkjet printing technologies. Bio-incorporable materials such as collagen, elastic, hyaluronic acid, alginates, and polylactic/polyglycolic acid co-polymers may be printed. As examples, Type I collagen (Elastin Products Co., Owensville, MO) dissolved in 0.05% acetic acid, then diluted to 1mg/ml in water can be printed, as can sodium alginate (Dharma Trading Co., San Raphael, CA) 1 mg/ml in water. A mixture of Type I collagen (2.86 mg/ml in 0.05% acetic acid) and polylactic/polyglycolic acid (PURAC America, Blair, NE) (14.29 mg/ml in tetraglycol (Sigma Aldrich, St. Louis MO)) can also be printed. Hardware from a Hewlett Packard 660c printer, including the stepper motors and carriage for the cartridges, can be mounted to a platform. The height ofthe hardware above the platform can then be adjusted for printing in layers. [0031] The porous material 10 may comprise pores sufficiently small at the interface between the porous material 10 and the spinal cord 7 to prevent the growth of tissue therein, e.g., a pore size smaller than the size of fibroblasts and spinal cord cells; otherwise the porous material 10 may stick to the spinal cord 7 and cause bleeding or trauma when the porous material 10 is removed. In addition, the pore size at the interface between the porous material 10 and the spinal cord 7 may be sufficiently small so as to avoid the excessive production of granulation or scar tissue at the spinal cord 7 which may interfere with the physiologic function of the spinal cord 7. At the same time, the pore size of the porous material 10 may be large enough to allow movement of proteins the size of albumin therethrough to permit undesirable compounds to be removed, such as mediators, degradation products, and toxins. [00321 The porous material 10 may, however, have a larger pore size (e.g., larger than that offibroblasts and spinal cord cells) interior to the porous material 10 or at any other location of the porous material 10 that is not in contact with spinal cord tissue 7. For -9example, the porous material 110 may comprise a multi-layer structure with a non ingrowth layer 112 having a sufficiently small pore size to prevent the growth of tissue therein for placement at the spinal cord, and may have an additional layer 114 of a different material that has a relatively larger pore size in contact with the non-ingrowth layer 112. [00331 Altematively, the porous material 10 may be homogeneous in composition and/or morphology. At a location away from the interface with the spinal cord 7, the porous material 10 may have a pore size sufficiently large to promote the formation of granulation tissue at other tissues in the spaces surrounding the spinal cord 7, such as promotion of granulation tissue in areas where spinal cord disruption has occurred. In addition, the porous material 10 may have a configuration in which one or more sides or surfaces of the porous material 10 are sealed to prevent the transmission of sub atmospheric pressure through such a sealed surface, while at the same time having at least one surface through which sub-atmospheric pressure may be transmitted. Such a configuration of the porous material 10 can present preferential treatment of tissue on one side of the porous material 10 while not treating the other side. For instance, the parenchyma of the spinal cord 7 could be treated with the non-sealed interface on one side of the porous material 10. [00341 The porous material 10 may be comprised of a material that needs to be removed after sub-atmospheric therapy is given, which could require a second surgery. Alternatively, the porous material 10 may be comprised of a material that is bioabsorbable or degrades harmlessly over time to avoid a second surgery, such as collagen. In addition, the porous material 10 may comprise a non-metallic material so that an MRI can be performed while the porous material 10 is in situ. The porous material 10 may also comprise a material that is sufficiently compliant so that if it presses against the spinal cord 7 the porous material 10 does not interfere with spinal cord function. At the same time, the porous material 10 may comprise a material that is sufficiently firm so that the porous material 10 does not collapsed so much as to create a pull on, or distortion of, the "normal spinal cord"that might interfere with spinal cord function. -10- [0035] To deliver sub-atmospheric pressure to the pomus material 10 for distribution to the spinal cord 7, a tube 20 may be connected directly or indirectly in gaseous communication with the porous material 10 at the distal end 22 of the tube 20. For example, the distal end 22 of the tube 20 may be embedded in the porous material 10 or may be placed over the porous material 10. The distal end 22 ofthe tube 20 may also include one or more fenestrations to assist in delivering the sub-atmospheric pressure to the porous material 10 and the spinal cord 7. The tube 20 may extend through an opening in the skin and subcutaneous tissue 2 which may be secured about the tube 20 with a suture 8 to assist in providing a seat about the tube 20. The proximal end 24 of the tube 20 may be operably connected to a vacuum source 30, such as a vacuum pump, to provide sub-atmospheric pressure that is transmitted via the tube 20 to the porous material 10 and the spinal cord 7. [0036] The vacuum source 30 may include a controller 32 to regulate the production of sub-atmospheric pressure. For instance, the vacuum source 30 may be configured to produce sub-atmospheric pressure continuously or intermittently; e.g. the vacuum source 30 may cycle on and off to provide alternating periods of production and non production of sub-atmospheric pressure. The duty cycle between production and non production may be between I to 10 (on/off) and 10 to 1 (on/off). In addition, intermittent sub-atmospheric pressure may be applied by a periodic or cyclical waveform, such as a sine wave. The vacuum source 30 may be cycled after initial treatment to mimic a more physiologic state, such as several times per minute. The sub-atmospheric pressure may be cycled on-off as-needed as determined by monitoring of the pressure in the spinal cord 7. In general, the vacuum source 30 may be configured to deliver sub-atmospheric pressure between atmospheric pressure and 75mm Hg below atmospheric pressure to minimize the chance thatthe sub-atmospheric pressure may result in bleeding into the spinal cord 7 or otherwise be deleterious to the spinal cord 7. The application of such a sub-atmospheric pressure can operate to remove edema from the spinal cord 7, thus preserving neurologic function to increase the probability of recovery and survival in a more physiologically preserved state. [00371 To assist in maintaining the sub-atmospheric pressure at the spinal cord 7, a flexible cover/sheet 50 or rigid (or semi-rigid) cover 40 may be provided proximate the -11spinal cord 7 to provide a region about the spinal cord 7 where sub-atmospheric pressure may be maintained, Figs. 4, 5. Specifically, with reference t Figs.4 and 5, a cover40, 50 may be provided overthe spinal cord 7 and porous material 10 by adhering the cover 40, 50 to tissues proximate the spinal cord 7 to define an enclosed region 48, 58 about the spinal cord 7 and porous material 10. For instance, the cover 40, 50 may be glued to the vertebrate 5, muscle tissue 4, and/or other appropriate tissues using an adhesive 42, such as a fibrin glue. The adhesive 42 may comprise an auto-polymerizing glue and/or may desirably include a filler to provide the adhesive 42 with sufficient bulk to permit the adhesive 42 to conform to the shapes of the potentially irregular surfaces which the adhesive 42 contacts. The adhesive 42 may be provided as a separate component or as a portion of the cover 40, 50 to provide a self-adhesive cover 40, 50. For instance, the cover 50 may comprise a flexible self-adhesive sheet which includes a suitable adhesive on one or more of its surfaces. [00381 For the flexible cover 50, an outside edge or border ofthe flexible cover 50 may be rolled under (or toward) the spinal cord 7. Alternatively, the flexible cover 50 may be curled out away from the spinal cord 7 so that the underside ofthe cover 50 (that side facing with the porous material 10) may then contact with the vertebrae 5 and surrounding muscles and soft tissue, Fig. 5. If the flexible cover 50 is rolled under the spinal cord 7, an adhesive 52 may then be applied to the outside ofthe cover50 between the cover 50 and the vertebrae 5, surrounding muscle and soft tissues to help promote an airtight seal. If the flexible cover 50 is curled away from the spinal cord 7, an adhesive may be applied to the underside of the cover 50, between the cover 50 and the vertebrae 5 and surrounding muscle and soft tissue to create an airtight seal. [0039] Sub-atmospheric pressure may be delivered under the cover 40, 50 by cooperation between the cover 40, 50 and the tube 20. Specifically, the cover 40 (or flexible cover 50) may include a vacuum port 43 to which the distal end 22 of the tube 20 connects to provide gaseous communication between the tube 20 and the space 48 under the cover 40 over the spinal cord 7, Fig. 4. Alternatively, the cover 50 (or cover 40) may include a pass-through 52 through which the tube 20 passes so that the distal end 22 of the tube 20 is disposed interior to, and in gaseous communication with, the space 58 under the cover 50 over the spinal cord 7, Fig. 5. -12- [00401 The cover 40, 50 may serve to further confine the subcutaneous region about the spinal cord 7 at which sub-atmospheric pressure is maintained. That is, as illustrated in Figs. 4 and 5, the cover 40, 50 provides an enclosed space/region 48, 58 about spinal cord 7 under the cover 40, 50, which can serve to isolate the tissues exterior to the cover 40, 50 from exposure to the sub-atmospheric pressure applied to the spinal cord 7. In contrast, as illustrated in Figs. 2 and 3, in the absence of a cover, sub-atmospheric pressure deliveredto theporous material 10 and spinal cord 7may draw the surrounding tissues, such as muscles 3, 4, inward towards the tube 20 and porous material 10 along the directions of the arrows shown in Fig. 2 resulting in the configuration of tissues illustrated in Fig. 3. In this regard the stretched and/or moved tissues, such as muscles 3, 4, can help to confine the applied sub-atmospheric pressure to a region between the muscles 4 and the spinal cord 7. In addition the covers 40, 50 may further protect the spinal cord7 from exogenous infection and contaminationbeyondthe protection already afforded by the porous material 10 and sutured skin 2. Likewise, the covers 40, 50 may further protect surrounding tissues from the spread of infection from the spinal cord 7 such as spinal cord abscesses, meningitis, and spinal tissue infection. [00411 In another of its aspects, the present invention also provides a method for treating damaged spinal cord tissue using sub-atmospheric pressure with, by way of example, the devices illustrated in Figs. 1-5. In particular, the method may comprise locating a porous material 10 proximate the damaged spinal cord tissue 7 to provide gaseous communication between one or more pores of the porous material 10 and the damaged spinal cord tissue 7. The porous material 10 may be sealed in situ proximate the damaged spinal cord tissue 7 to provide a region about the damaged spinal cord tissue 7 for maintaining sub-atmospheric pressure at the damaged spinal cord tissue 7. In this regard, the muscles 3,4 and subcutaneous tissues may be loosely re-approximated over top of the porous material 10 with the tube 20 exiting through the skin 2 and the skin 2 sutured closed. A further airtight dressing may optionally be placed over the suture site to promote an airtight seal. The porous material 10 may be operably connected with a vacuum system 30 for producing sub-atmospheric pressure at the damaged spinal cord tissue 7, and the vacuum system 30 activated to provide sub atmospheric pressure at the damaged spinal cord tissue 7. For example, the sub-atmospheric pressure may be maintained at about 25 to 75 mm Hg below -13atmospheric pressure. The sub-atmospheric pressure may be maintained at the damaged spinal cord tissue 7 for a time sufficient to decrease edema at the spinal cord 7 or to control spinal fluid leaks. In addition, the sub-atmospheric pressure may be maintained at the damaged spinal cord tissue 7 for a time sufficient to prepare the spinal cord tissue 7 to achieve a stage of healing and diminution of bacterial counts such that acceptance of secondary treatments (e.g., flaps, skin grafts) can be successful. The method may be used for at least 4 hours, or can be used for many days. At the end of the vacuum treatment, the sutures 8 may be removed and the skin 2 re-opened. The porous material 10 may then be removed and the skin 2 re-sutured closed. [00421 The method may also include locating a cover 40, 50 over the damaged spinal cord tissue 7 and sealing the cover 40, 50 to tissue proximate the damaged spinal cord tissue 7 for maintaining sub-atmospheric pressure at the damaged spinal cord tissue 7. The step of sealing the cover 40,50 to tissue surroundingthe damaged spinal cord tissue 7 may comprise adhesively sealing and adhering the cover 40, 50 to tissue surrounding the damaged spinal cord tissue 7. The cover 50 may be provided in the form of a self-adhesive sheet 50 which may be located over the damaged spinal cord tissue 7. In such a case, the step of sealing the cover 50 may include adhesively sealing and adhering the self-adhesive sheet 50 to tissue surrounding the damaged spinal cord tissue 7 to form a seal between the sheet 50 and tissue surrounding the damaged spinal cord tissue 7. In addition, the step of operably connecting a vacuum system 30 in gaseous communication with the porous material 10 may comprise connecting the vacuum system 30 with the vacuum port 42 of the cover 40. [0043] Examples [00441 Rat Spinal Cord Injuries and Sub-atmospheric Pressure Exposure [0045] Experiment 1 [00461 A series of experiments were conducted to determine the effects of sub atmospheric pressure on the spinal cord in rats post contusion injury. In a first animal protocol, 250-300 gram Sprague Dawley rats were obtained and the model of spinal contusion developed and verified. The procedure for creating the injury and assessing recovery was based upon the description of spinal cord contusion injury in Wrathall, et al., Spinal Cord Contusion in the Rat: Production of Graded, Reproducible, Injury -14- Groups, Experimental Neurology 88, 108-122 (1985). The surgical technique was developed for exposing the spinal cord in the anesthetizedrats and consistent production of a contusion injury by dropping a cylindrical 10 gram weight through a glass tube from a height of 5 cm. Half of the rats were untreated controls while the other half had the area of contusion exposed to 4 hours ofsub-atmospheric pressure (25 mm Hg below atmospheric). However, the degree of injury did not produce a significant injury in the control animals (they recovered quickly), and thus it was not possible to compare the treated animals to the control animals. [00471 Experiment 2 [00481 A second protocol was developed in which a more severe injury was inflicted on the spinal cord (a 10 gram weight was dropped from a higher height - 7.5 cm). Twenty-eight large (300 gram) Sprague Dawley rats were procured over time and allowed to acclimate to housing conditions. On the day of surgery, the animals were sedated and the back shaved and scrubbed for surgery. A midline incision made over the spine was made extending through the skin and subcutaneous tissue and the cutaneous maximus muscle and fascia exposing the deeper back muscles. The paired muscles that meet at the midline (trapezius and potentially latisimus dorsi) were separated at the midline and retracted laterally. The deep 'postural' muscles such as the spinotrapezius and/or the sacrospinal muscles that are attached to the bony structures ofthe spine itselfwere also divided on the midline and retracted laterally. This exposed the spinous process and potentially some ofthe transverse processes. At the levelof T7 T9, the spinous processes and the small transversospinal muscles that extend between two consecutive vertebra were removed, exposing the surface (dura) ofthe spinal cord. A laninectomy was performed at T-8. The spine was stabilized at T-7 and T-9 and a 10 gram weight was dropped from a height of 7.5 cmto produce a moderate degree of spinal cord injury based on the procedure of Wrathall, et al. Five animals died on their respective day of initial surgery (three in the control group and two in the vacuum treated group), and early in the experiment one animal in the control group died two days into the experiment, leaving 22 animals. By the end of the experiment, eleven animals had been assigned randomly to each of the control group and the 25 mm Hg vacuum group. -15- [00491 For the control rats, no treatment was provided, and the injury was sutured closed. For the vacuum treated rats, a polyvinyl alcohol vacuum dressing (Vacuseal Plus, Polymedics, Belgium) was placed on the cordandthe skin sutured closed, withthe vacuum tube extending through the incision. After 1 hour delay, a vacuum (sub atmospheric pressure) of25 mm Hg below atmospheric pressure was applied for 4 hours to each animal in the vacuum treatment group. At the end ofthis time, the animals were re-sedated, the vacuum dressings removed, and the skin incision re-sutured with monofilament suture. [0050] The incision sites were inspected daily. The animals were examined for signs of ability to self void their bladders. Any animal unable to void received manual assistance three times per day at 8 hour intervals. The animals were examined daily for signs of auto-cannibalism, pressure sores, and for degree of hydration (pinch test). The animals were housed in soft shavings to minimize potential for pressure sore development. Food was placed on the bottom of cages to facilitate eating. Animals were examined daily for recovery of motor function of hind limbs using a modified Tarlov scoring system for each hind limb. (0 = no movement, no weight bearing; 1 = slight movement, no weight bearing; 2== frequent movement, no weight bearing; 3 = weight bearing, 1-2 steps; 4 = walking with deficit; 5= walking with no deficit.) The animals were tested daily on an inclined plane (angle at which they can no longer hold on and slide off the plane), and for hind limb grip strength. The animals were euthanized 14 days post surgery, and the spines removed and examined histologically. [0051] Theresults ofthe experiment are provided in Tables I and 2, with day "0" being the day of surgery. Several animals exhibited minimal injury/deficit and may not have had an adequate injury during weight drop. (Control animals 1,2,11 andtreated animals 3, 9, 10. See Tables I and 2.) Two animals exhibited a severe/total injury and did not recover. (Control animal 5 and treated animal 2. See Tables 1 and 2.) This left a total of seven control and seven treated animals believed to have an adequate injury but not a severe/total injury. [0052] For purposes of analysis, an animal was considered "recovered" as of the day on which it achieved a score of at least "4/4." Of the seven control animals, three had not recovered to at least a score of 4/4 (right leg/left leg - walking with deficit) by day -16eight post surgery. (Animals 3, 6, 7. Table 1.) Of the remaining four control animals (animals 4, 8, 9, 10), three animals reached a score of 4/4 on days 4, 6, and 13, and one reached a score of 4/5 on day 7. Thus, the four control animals reached a score of at least 4/4 in a mean of 7.5 +/- 3.35 days. For the treated animals, all seven (animals 1, 4, 5, 6, 7,8, 11) reached a score of at least 4/4 in a mean of 5.14 +/- 1.24 days. Thus it is evident that application of25mn Hg vacuum to the injured spine was able to increase the rate of functional recovery (p=0.059). Time Post Surgery (days) 0 1 2 3 4 5 6 7 8 13 Animal 1 /5 5/5 5/5 5/5 5/5 5/5 5/5 5/5 5/5 /4 5/4 5/4 5/4 5/4 5/4 5/4 5/4 5/4 /0 0/0 1/1 1/1 2/1 2/1 2/2 3/2 3/2 2 2/2 3/3 3/3 4/4 4/4 4/4 5/4 5/4 51/0 1/0 1/0 1/0 1/1 1/1 1/1 1/1 1/1 /0 0/0 1/0 1/0 1/1 2/1 2/2 3/2 3/2 /1 0/1 1/1 1/2 1/2 2/2 2/3 3/3 3/3 /0 0/0 1/1 1/1 2/2 2/2 3/3 3/3 3/3 4/4 0/0 0/0 0/1 0/1 1/2 2/2 3/4 4/5 10 /0 0/0 1/1 1/1 1/1 1/1 414 4/4 11 4/4 4/4 5/4 5/5 5/5 Table 1. Control Time Post Surgery (days) 0 1 2 3 4 5 6 7 8 13 Animal 1 1/1 1/2 1/2 2/2 3/4 4/4 4/4 4/4 4/4 2/0 0/0 0/0 1/0 1/0 1/0 1/1 1/1 1/1 3 /4 4/5 5/5 5/5 5/5 5/5 5/5 5/5 5/5 4 /0 2/0 2/1 3/2 3/3 4/3 4/4 5/4 5/5 5 2/1 2/1 3/2 3/3 4/4 5/5 5/5 5/5 5/5 2/3 3/3 3/4 4/4 5/5 5/5 5/5 5/5 5/5 1/0 1/0 1/1 2/3 3/4 4/5 5/5 5/5 5/5 1/0 1/0 2/1 3/2 3/2 3/2 4/3 5/4 5/4 5/4 3/4 5/5 4/4 5/5 5/5 10 /4 4/4 4/4 5/5 5/5 11 /0 0/0 1/1 2/2 3/3 3/3 4/4 4/4 Table 2. Vacuum Treated -17- [0053] Experiment 3 [0054] An additional protocol was developed in which a still more severe injury was created that would result in a non-recoverable (permanent) functional deficit. The contusion paradigm was based upon techniques developed at the W.M. Keck Center for Collaborative Neuroscience - The Spinal Cord Injury Project using the NYU spinal cord contusion system. These systems (currently named "MASCIS") are custom built and are available commercially through the Biology Department at Rutgers University (W. M. Keck Center for Collaborative Neuroscience, Piscataway, New Jersey). [0055] Inthe preceding experiments, animals were operated on depending on weight, but in this experiment the animals were operated on depending on age. Long Evans hooded 0 rats were operated on at 77 days of age to standardize the severity of injury. Between one and six days before surgery, some ofthe animals were sedated and transported to the Small Animal MRI Imaging Facility of Wake Forest University School of Medicine, and the spinal cord was scanned at the level of T9-T1O using a Bruker Biospin Horizontal Bore 7 Tesla small animal scanner (Ettlingen, Germany). The animals which were scanned were then allowed to recover from anesthesia in a heated cage. On the day of surgery the animals were anesthetized, and the backs of the animals were shaved and a depilatory creamused. Using aseptic technique, alaminectomywas performed at the levelofT9-T10. The NYU spinal cord contusion system impactor was used, and the cord was impacted at T9-T1O with a10 gram rod dropped from heightof25 mm. Animals inthe control group had the incision sutured closed, and the animals were allowed to recover in a heated cage. For treated animals, a polyvinyl alcohol vacuum dressing (VersaFoam, Kinetic Concepts, Inc., San Antonio, TX) was placed over the cord, the incision sutured closed, and 25 mm Hg vacuum, i.e. 25 mm Hg below atmospheric pressure, applied for 8 hours. After this time the treated animals were re-sedated, the incision opened, the vacuum dressing removed, and the incision re-sutured closed. If the animals received a post-surgery MRI, the animal was scanned 8 hours post impaction. [00561 Functional recovery was assessed with the BBB scale, a 22 point scale from the W.M. Keck Center for Collaborative Neuroscience. (Table 3). The animals were monitored for 21 days, then euthanized by lethal CO 2 exposure. Bladders were expressed -18daily, and the animals were monitored for signs of auto-caunibalism, pressure sores, skin lesions, etc. Any animal exhibiting signs of auto-cannibalization were removed from the study and euthanized. Pressure sores and skin lesions were treated as appropriate and with consultation of ARP veterinary staff Despite this care, in the course of this experiment some animals died, while others were excluded for other problems. Value Condition 0 No observable hind limb (HL) movement I Slight Movement of one or two joints, usually the hip &/or knee 2 Extensive movement of one joint or Extensive movement of one joint and slight movement of one other joint 3 Extensive movement of two joints 4 Slight movement of all three joints ofthe HL 5 Slight movement of two joints and extensive movement of the third 6 Extensive movement of two joints and slight movement of the third 7 Extensive movement of all three joints of the HL 8 Sweeping with no weight support or Plantar placement of the paw with no weight support 9 Plantar placement of the paw with weight support in stance only (i.e. when stationary) or Occasional, Frequent or Consistent weight supported dorsal stepping and no plantar stepping 10 Occasional weight supported plantar; no front limb (FL)-HL coordination 11 Frequent to consistent weight supported plantar steps and no FL-HL coordination 12 Frequent to consistent weight supported plantar steps and occasional FL-HL coordination 13 Frequent to consistent weight supported plantar steps and frequent FL-HL coordination 14 Consistent weight supported plantar steps, consistent FL-HL coordination and Predominant paw position during locomotion is rotated (internally or externally) when it makes initial contact with the surface as well as just before it is lifted off at the end of stance or Frequent plantar stepping; consistent FL-HL coordination; and occasional dorsal stepping -19- 15 Consistent plantar stepping and Consistent FL-HL coordination; and No toe clearance or occasional toe clearance during forward limb advancement Predominant paw position is parallel to the body at initial contact 16 Consistent plantar stepping and Consistent FL-HL coordination during gait; and Toe clearance occurs frequently during forward limb advancement; Predominant paw position is parallel at initial contact and rotated at lift off 17 Consistent plantar stepping and Consistent FL-HL coordination during gait; and Toe clearance occurs frequently during forward limb advancement; Predominant paw position is parallel at initial contact and lift off 18 Consistent plantar stepping and Consistent FL-HL coordination during gait; and Toe clearance occurs consistently during forward limb advancement; Predominant paw position is parallel at initial contact and rotated at lift off 19 Consistent plantar stepping and Consistent FL-IL coordination during gait; and Toe clearance occurs consistently during forward limb advancement; Predominant paw position is parallel at initial contact and lift off; and tail is down part or all of the time 20 Consistent plantar stepping and Consistent coordinated gait; consistent toe clearance' Predominant paw position is parallel at initial contact and lift off; and Trunk instability; Tail consistently up 21 Consistent plantar stepping and Consistent coordinated gait; consistent toe clearance; predominant paw position is parallel throughout stance; consistent trunk stability; tail consistently up Table 3. BBB Locomotor Rating Scale [00571 For these studies of a permanent injury, 36 rats with the dura intact completed the study and were analyzed. Eleven (11) vacuum treated animals started the study, with one animal removed at five weeks and one at eight weeks due to urinary tact infections and kidney failure. Thus, 9 vacuum treated animals completed the 12 week study. Twenty seven control animals started and completed the study. The vacuum treated animals exhibited a greater functional recovery (p<0.072 ) at 3 weeks post injury: BBB Score = 12.818 +/- 1.401 (n=11) vacuum treated versus 11.704 +/- 2.391 (n=27) control. The vacuum treated animals exhibited a significantly greater functional recovery (p<0.001) at 4 weeks post injury: BBB Score= 13.625 +/- 1.303 (n=11) vacuum treated versus 11.500 +/- 0.707 control (n=27). Figs. 6 and 7. The recovery of the vacuum treated animals plateaued, and the recovery levels ofthe control animals gradually approached the level of the vacuum treated animals. Figs. 6 and 7. (Note, some animals were studied for three -20weeks (generally earlier in the study) while some were observed for 12 weeks for functional recovery.) [0058] In additionto the BBB assessments, two animals withintact duxawere analyzed for a change in the cross sectional area (e.g., in mm 2 ) of the spinal cord by pre- and post injury MRI scans (with the post-injury scan performed post-treatment for the vacuum treated animals) using the procedures listed above for this experiment. Of the four animals produced for this analysis, only one vacuum treated animal did not have any technical or impaction error and could be used. Ofthe control animals, one had a minor height eror which occurred when the release pin of the spinal cord contusion system was pulled from its housing; all other control animals had significant impaction errors which precluded analysis of the cross sectional area of the spinal cord. The machine recorded height from which the weight was dropped for the vacuum treated rat was 24.8 mm and for the control rat was 25.782 mm. [0059] Turning to Fig. 8, the control animal showed a slight increase in cross sectional area as the scans went down (tail-ward) the spine. This was evident for both the pre-impaction scan and the post-impaction scan. At both the above-injury and below injury sites, the cross sectional area was not significantly different between the pre-impaction scan and the post-impaction scan. The above-injury pre-impaction mean was 5.49 mm 2 +/- 0.2 (n=5) versus a post impaction mean of 5.32 mm 2 +/- 0.23 (n=4): p < 0.211) (The below-injury pre-impaction mean was 6.81 mm 2 +/- 0.25 (n=3) versus a post-impaction mean of 6.46 mm +/- 0.78 (n=4): p < 0.464) However, at the site of impaction, the post-impaction cross sectional area for the control animal was significantly larger (p<0.001) than the pre-impaction cross sectional area: mean of pre-impaction area of 5.63 mm 2 +/- 0.24 (n=5 scans) versus mean post-impaction area of 6.43 mm 2 +/- 0.32 (n=4 scans). This was most likely due to swelling of the cord due to the limits of the dura, as the bone which would be the limiting factor on diameter of the cord had been removed. [00601 Unlike the control animal, the vacuum treated animal did not show an increase in mean diameter ofthe cord at the site ofthe injury after vacuum treatment, Fig. 9. The mean pre-impaction area at the level of the injury was 7.28 mm 2 +/- 0.73 (n= 4 scans) versus a mean post-treatment area of 7.03 mm 2 +/- 0.99 (n =4 scans) (p <0.73). The -21- H:\ z \lerwovn RPod\DCC\KZR\6253073 - do -5/05/201 -22 similarity in the size of the spinal cord pre-impaction and post-treatment at the site of the injury was most likely due to removal of fluid from within the dura, thus maintaining the initial diameter of the cord. 100611 The pre-impaction and post-treatment scans at the above-injury area were similar (not significantly different). The pre-impaction above-injury area was 7.79 +/0.64 (n= 3 scans) versus post-treatment of 8.33 +/- 1.11 (n =5 scans) (p < 0.48). For the scans of the vacuum treated animal below-injury, the post-treatment cross sectional area of the cord was significantly larger than the pre-impaction cross sectional area: Pre-impaction area of 7.61 +/- 0.43 ( = 4 scans) versus post treatment area of 10.76+/-0.35 (n = 4 scans), p < 0.001. A possible explanation for the increase in below-injury cross sectional area of the cord maybe attributable to venous congestion. Alternatively, the applied vacuum may have actively withdrawn cerebrospinal fluid from around the cord, allowing the cord to expand to fill the area of the spinal canal within the vertebral bodies. This expansion would act to minimize the intra-dura pressure and help to preserve cell viability. [0062] These and other advantages of the present invention will be apparent to those skilled in the art from the foregoing specification. Accordingly, it will be recognized by those skilled in the art that changes or modifications may be made to the above-described embodiments without departing from the broad inventive concepts of the invention. It should therefore be understood that this invention is not limited to the particular embodiments described herein, but is intended to include all changes and modifications that are within the scope and spirit of the invention as set forth in the claims. [0063] Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps. [0064] The reference in this specification to any prior publication (or infonnation derived from it), or to any matter which is known, is not, and should not be taken as, an acknowledgement or admission or any form of suggestion that that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.