FIELD OF THE INVENTION 
       [0001]    This invention relates to wound therapy. In particular, it provides a device and method for applying vacuum-assisted wound therapy. 
       BACKGROUND OF THE INVENTION 
       [0002]    There are many orthopedic procedures that involve placing pins or screws into bone. External skeletal fixation involves stabilization of fractured bone segment by pins or screws which protrude through the overlying skin. The pins or screws may be connected to an external frame for stabilization. These external skeletal fixation appliances comprise swivel joints, connecting bars, sliding bars, articulations, and anchorage clamps intended to hold and position transcutaneous pins. For example, when a patient suffers a severe bone injury or undergoes limb-lengthening surgery, it is often necessary to stabilize the fracture area with an external fixation device. 
         [0003]    Often, the transcutaneous pins or screws of an external fixation device must remain in place for an extended period. These appliances create a breach in the skin. Because of this breach, the resulting pin-site wound provides a path along which microorganisms present on the skin surface may move into deeper tissues. In addition, inflammation and localized edema at the wound site may lead to a loss of blood flow to the surrounding tissue, decreasing the tissue&#39;s ability to fend off infection and slowing the healing process. 
         [0004]    The antiseptic effect of vacuum therapy is well-known. Maintaining vacuum pressure on the area around a wound site not only inhibits microbe migration to the wound, it also quickly reduces bacteria population and reproduction in the wound area. Vacuum-assisted wound dressings may comprise a thin film semi-permeable cover containing a perimeter adhesive for creating an air tight seal with the skin. A vacuum tube penetrates the cover. Such dressings are difficult to apply however, where a bone stabilization pin or screw extends through the skin. The vacuum supplied under the cover tends to collapse the thin film cover onto the skin. If used with a protruding pin, the film would tend to tent around the top of pin, and apply an unwanted destabilizing force to the pin. 
         [0005]    An alternative vacuum device is disclosed in Argenta et al. (U.S. Pat. No. 5,636,643). Argenta discloses a wound cover that is either rigid or semi-rigid and which has a port for attachment to a vacuum source. The cover fits over the wound and is sealed against the surrounding skin to maintain the vacuum. The device is adapted for use over large open wounds such as burns, pressure sores, and wounds requiring skin grafts or flaps. While a protruding stabilization pin could conceivably be entirely captured within the dome of the rigid cover, the cover is a rather large and unwieldy device and may not be suitable for covering the small wound surrounding a pin. Similarly, such a device would not be suitable for situations in which several pins are used and connected to a common rack or brace, such as in the case of a badly shattered bone. There is also the risk that an external force could cause the pin to rupture the cover. 
         [0006]    Yamamoto et al. (U.S. Pat. Nos. 4,856,504 and 4,915,694) disclose antimicrobial wound dressings and skin fixators suitable for use with orthopedic pins and percutaneous conduits (such as catheters), respectively. These devices comprise antimicrobial pads adapted to fit closely to the skin around a pin or conduit. The pad is then covered by a flange with an orthogonally projecting collar which fits around the pin and fits flush with and covers the antimicrobial pad. These devices are aimed at preventing infection around the wound in the patient&#39;s skin through use of traditional antiseptic medications and do not contemplate the use of vacuum-assisted healing techniques. 
         [0007]    It is therefore apparent that a need exists for a device that can conveniently apply vacuum-assisted treatment to pin-site wounds. 
       SUMMARY OF THE INVENTION 
       [0008]    In accordance with the present invention, a device is provided for applying therapeutic vacuum to a wound surrounding the shaft of a bone stabilization device that extends through the skin of a patient. By “bone stabilization device” is meant a transcutaneous element, such as a pin or screw, which is adapted for embedding in the bone of the patient and extending through the skin. The device of the invention comprises a hollow generally conical member defining an enclosed space through which the stabilization device may pass. The conical member has at a first end a first opening adapted to conform to the bone stabilization shaft. At an opposite second end, the device has a second opening adapted to enclose a wound in the skin surrounding the bone stabilization device shaft. The openings are dimensioned, respectively, for conforming to the bone stabilization device shaft, and for enclosing the wound surrounding the bone stabilization device shaft. The opening for enclosing the wound will typically be larger than the opening conforming to the bone stabilization device. The conical member has, preferably at a point intermediate the ends thereof, a port for connecting a suction tube to the conical member, to communicate a negative pressure from a vacuum source to a space defined by the conical member. The conical member has sufficient flexibility at the first end to contract against the bone stabilization device shaft to form an airtight seal therewith. 
         [0009]    In one embodiment, the conical member has sufficient rigidity to generally maintain its conical shape and resist collapsing on to the wound during use. In another embodiment, an antimicrobial sponge or other soft object is placed between the conical member and the wound, and the conical member has sufficient flexibility to partially collapse onto the antimicrobial sponge. 
         [0010]    One embodiment the device of the invention includes a sealable slit in the conical member extending from the conical member first and second openings. The slit facilitates placement of the device around a pin and wound site. A sealing device, such as a flexible adhesive tape, is used to close the slit. While use of a flexible adhesive for sealing the slit is contemplated, the slit may be closed and sealed by any means that will serve to maintain the integrity of the seal created by the mating of the structure to the skin and the stabilization device. 
         [0011]    A method for applying a vacuum to a wound surrounding the shaft of a bone stabilization device that extends through he skin is provided, comprising, placing the device of the invention over a wound and a protruding bone stabilization device shaft such that the shaft passes through both openings of the conical member to enclose the wound, connecting the device to a vacuum source, and applying vacuum pressure to the device. 
     
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0012]      FIG. 1  shows a perspective view of a wound treatment device for applying therapeutic vacuum to a wound surrounding the shaft of a bone stabilization device that extends through a patient&#39;s skin. 
           [0013]      FIG. 2  shows a perspective view of an alternative embodiment of a wound treatment device for applying therapeutic vacuum to a wound surrounding the shaft of a bone stabilization device that extends through a patient&#39;s skin. 
           [0014]      FIGS. 3A-3C  show an enlarged perspective view of an alternate port design in three stages of operation—before insertion of the tube, with the tube inserted and withdrawing air, and after sealing. 
           [0015]      FIG. 4  shows a perspective view of a further alternative embodiment of a wound treatment device for applying therapeutic vacuum to a wound surrounding the shaft of a bone stabilization device that extends through a patient&#39;s skin. 
       
    
    
       [0016]    Although these Figures depict an embodiment of the contemplated invention, they should not be construed as foreclosing alternative or equivalent embodiments readily apparent to those of ordinary skill in the subject art. 
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0017]    As shown in  FIG. 1 , a wound treatment device  10  is provided for applying a therapeutic vacuum for treating a wound  15  caused by a bone stabilization device  11  that protrudes through a patient&#39;s skin  13 . In the embodiment shown in  FIG. 1 , the device  10  includes a hollow, preferably generally conical member  12 . At one end, the conical member  12  has a small opening conforming to the shaft of the bone stabilization device  11 . At the other and opposite end, the conical structure  12  has a larger opening that is dimensioned to enclose the wound  15  surrounding the bone stabilization device  11 . While the openings in the generally conical member  12  will typically be circular, it is noted that other shape openings are possible. For example, the body of the conical member may be oval in cross-section, and the opening contacting the skin will be oval. Likewise, the shape of the opening for engaging the shaft of the bone stabilization device is advantageously selected to conform to the cross-sectional shape of the shaft, if other than circular. 
         [0018]    It is also contemplated that the openings may not be predetermined, instead being defined by the attachment of the member  12  to the bone stabilization device  11 . Thus, in the event that the stabilization device is rectangular, the upper opening would conform to the shape of the device upon application of negative pressure, as will become more apparent below. 
         [0019]    Preferably, the conical member is comprised of a flexible, semi-rigid, airtight material so that when reduced pressure is applied, the walls of the conical member are drawn inwards toward the skin and stabilization device. In a preferred embodiment, the conical member is comprised of a flexible, semi-rigid polymer such as silicone or low linear density polyethylene. Ideally, the cone geometry is such that while the ends of the cone conform to the stabilization device and the skin respectively, the middle section of the cone is drawn inwards under the applied negative pressure. Use of a flexible but semi-rigid polymer in the conical member allows the structure to conform roughly to the surfaces of the stabilization device shaft and the patient&#39;s skin while also retaining its shape when the vacuum is applied. Whatever material is used, the conical member preferably has sufficient flexibility at the end having the smaller opening to contract against the stabilization device and form an air tight seal, but preferably has sufficient rigidity to generally maintain its conical shape and prevent the structure from collapsing onto the wound, as well as the ability to securely support the vacuum port and tube. The conical member should also have sufficient flexibility at the opposite end to form an airtight seal with the skin. The conical member  12  can be optionally secured to the stabilization device  11  and to the skin  13  by adhesive  14 . Any suitable adhesive which can adhere to the skin can be used. 
         [0020]    As shown in  FIG. 1 , the wound  15  is completely enclosed within the conical member  12 . Negative pressure is supplied to the interior of the enclosure formed by the member through a tube  16 . The tube  16  connects to the conical member  12  through a port  18  formed in the conical member  12 , preferably at a location that is between the ends of the conical member. Tube  16  connects the port  18  to a vacuum source (not shown) which supplies a negative pressure (vacuum) to the space inside the conical member  12 . The tube  16  may be either integrally connected to port  18 , or it may be capable of attachment by any commonly understood or suitable means. In a preferred embodiment, the tube measures ¼ inch in diameter and is comprised of a flexible polymer such as polycarbonate, e.g. LEXAN® brand polycarbonate. 
         [0021]    While the port  18  and tube  16  are both shown as cylindrical in shape, it is also contemplated that either or both can be formed in a variety of shapes. For example, referring to  FIGS. 3A-3C , the port  18  can be formed from two flaps of material that extend from the member  12  and which flaps are attached at their upper and lower ends, thereby defining a narrow slit. The tube  18  can be easily inserted into the slit when a vacuum is needed. After sufficient negative pressure is applied to the enclosure, the flaps can then be closed, such as by clipping or taping, and the tube  18  removed. 
         [0022]    The level and duration vacuum pressure necessary to achieve a suitable antiseptic effect is well understood in the art. In a preferred embodiment, the vacuum pressure applied is  5  in Hg below atmospheric pressure until the bacterial count is reduced to a desired level. Although not shown, a sensing device can be located along the tube for monitoring bacterial count. Alternately, when substantially all the air is withdrawn from the enclosure, the enclosure could be sealed. 
         [0023]    As shown in  FIG. 2 , an alternative form of the device of the invention includes a slit  20  in the member which extends from one end to the other. This allows the device to be opened to fit around the shaft of a bone stabilization device which has already been inserted into the body of the patient, where access to the end of the stabilization device is blocked, for example, by a bar, rack, brace or frame or other structure, as shown in  FIG. 2 . The slit is then sealed, preferably by means of flexible adhesive material, such as adhesive tape or glue  14 . This method of attachment enables the device to be used when the stabilization device is itself attached to a larger apparatus, such as in the case of a badly shattered bone where a series of pins or screws may be attached to a rack or brace  21 . It should be readily apparent that the shape of the member  12  in this embodiment need not be conical before application of pressure. Instead, the member  12  may be formed from flexible material that has a flat sheet with a square, trapezoidal, or other shape. The sheet is wrapped around the pin and sealed to the pin and the skin, thus defining the conical shape. 
         [0024]    The embodiment of the device of the invention shown in  FIG. 1  may be fitted to the patient by passing the bone stabilization device shaft axially through the openings in the conical member until the larger opening contacts the patient&#39;s skin. Where the protruding end of the bone stabilization device is connected to a rack or frame, the alternative embodiment of the device of the invention, as shown in  FIG. 2 , is preferably employed. The stabilization device shaft passes through the slit in the conical member until the shaft extends through each opening in the conical member. The vacuum pressure is applied at either a constant or cyclical rate and for a time period sufficient to achieve the desired antiseptic effect as understood by those of ordinary skill in the art. 
         [0025]    As shown in  FIG. 4 , an alternative form of the device of the invention includes a conical member  12  that is sufficiently flexible to collapse under the pressure difference between external ambient pressure and the negative pressure inside the conical member. To protect the wound  15 , a soft element  22 , which may be a sponge, is placed between the conical member  12  and the wound. The soft element  22  may be treated with an antimicrobial substance. The antimicrobial sponge may be supplied in a package with the conical member  12  when the wound treatment device is supplied, or may be provided separately and combined with the conical member only when the wound treatment device  10  is applied to a patient. In some circumstances, the mechanical contact between the soft element  22  and the wound  15 , where gentle mechanical forces are transmitted to the wound from the conical member  12  through the soft element  22 , may mechanically stimulate the wound in such a manner as to promote healing. The use of the flexible conical member  12  without the soft element  22  is possible but in most circumstances less preferred. 
         [0026]    All references cited herein are incorporated by reference. The present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. 
         [0027]    For example, although distinct embodiments have been described and shown in the several drawings, features from the different embodiments may be combined in a single embodiment. For example, the treatment device  10  shown in  FIG. 4  may have either the connector  18  shown in  FIG. 1  or the connector shown in  FIGS. 3A to 3C . For example, the treatment device  10  shown in  FIG. 4  may have a conical shape similar to that shown in  FIG. 1  or may have the slit  20  shown in  FIG. 2 . 
         [0028]    Accordingly, reference should be made to the appended claims, rather than to the foregoing specification, as indication the scope of the invention.
A vacuum-assisted wound healing device is provided comprising an airtight hollow conical member surrounding a skin-breaching bone stabilization device, and a port for attaching a suction tube. The conical member has an opening at one end conforming to the circumference of the shaft of a bone stabilization device, and a opening at the other end to enclose a wound in a patient's skin surrounding the bone stabilization device. The device may be used to provide controlled reduced pressure to the wound site, reducing healing time and risk of infection.