Abstract:
An acetabular cup and sheath assembly comprises a sheath and an acetabular cup. The sheath is configured to receive the acetabular cup within the sheath. The sheath and acetabular cup together are configured to pass through a surgical wound toward an implantation site. The sheath further comprises a penetration structure for passing the acetabular cup through the sheath when the acetabular cup is proximately close to an implantation site.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a United States National Phase filing of International Application No. PCT/US2009/045314 filed on May 27, 2009 which claims the benefit of U.S. Provisional Application No. 61/056,321 filed May 27, 2008, both of which are is herein incorporated by reference. 
    
    
     RELATED FIELD 
     The present devices relate generally to improving fixation of acetabular cups, and more particularly to preventing bio matter (such as soft tissue and fatty deposits) from contacting an acetabular shell during delivery through a wound until just prior to impaction. 
     BACKGROUND 
     In surgery, it is possible to contaminate an acetabular shell with bio matter, soft tissue, and fatty deposits prior to and during impaction. Each time an acetabular cup is inserted into a body cavity, soft tissues and bio matter can build up on portions of the acetabular cup and become stuck. If these materials gather onto or bind to a porous outer coating of the cup, it could adversely affect bone in-growth and initial “bite” and “fixation”. If these materials gather on a smooth inner surface of the cup, it could adversely affect subsequent taper-locking between the cup and a liner. Connections between acetabular cups and liners are generally designed with tight tolerances to form a tight fit. Bio-matter can compromise such a tight fit. The devices aim to provide a novel and unique apparatus and method of preserving the porosity of an acetabular cup during insertion into a body cavity. 
     US 2007/100464 AA titled “Orthopaedic implant sleeve and method” and assigned to Zimmer discloses a debris-preventing device for use with modular-style necks and femoral stems. This is shown in  FIG. 1 . This reference does not disclose use with acetabular cups, and the sheaths shown in this reference teach away from providing a means for acetabular cup penetration as the disclosure is used to protect surfaces proximal to the wound. 
     Other related art teaches soft tissue protection devices which may be placed over a wound or within a wound. These devices are placed onto or into the wound prior to advancement of a medical device. Such a device only protects the soft tissue covered by the device from damage. 
     SUMMARY 
     The aforementioned needs are satisfied by several aspects of the devices. 
     According to one aspect, there is provided a method of providing a debris-preventing sheath for an acetabular cup. The method includes the steps of: creating a cup-shaped sheath for an acetabular cup which is preferably disposable and somewhat flexible, said sheath having at one end, a means for insertion of the acetabular cup. The means for insertion of the acetabular cup may comprise an open end. At another end opposite said one end, the cup is provided with a means for passage of the acetabular cup. The means for passage may be for instance, a slit, slot, hole, aperture, flap, accordion sleeve, a reduction in diameter, a perforation, a series of perforations, a perforation pattern, a perforation shape, a perforation window, and/or combinations thereof. The means for passage may comprise any shape such as a star, circle, square, pizza slice, etc. 
     According to another aspect, there is provided a method of using a cup-shaped sheath with an acetabular cup. The method includes the steps of: providing a cup-shaped sheath for an acetabular cup; positioning the cup within the cup-shaped sheath; inserting both of the acetabular cup and cup-shaped sheath into a body cavity; allowing the sheath to shield the acetabular cup from bio-matter (e.g., fatty and soft tissues); allowing the acetabular cup to protrude from or penetrate through said cup-shaped sheath and become affixed to a body portion (e.g., acetabulum); removing the cup-shaped sheath from the acetabular cup and from the body cavity; and, disposing of said cup-shaped sheath. The debris-preventing sheath acts as a shield for a scratchy porous acetabular shell during insertion into a body cavity. Therefore, no biomatter becomes lodged in the porous structure and porosity of the acetabular cup is retained. 
     Another aspect of the invention provides an acetabular cup and sheath assembly comprising a sheath and an acetabular cup. The sheath is configured to receive the acetabular cup within the sheath. The sheath and acetabular cup together are configured to pass through a surgical wound toward an implantation site. The sheath further comprises a penetration structure for passing the acetabular cup through the sheath when the acetabular cup is proximately close to an implantation site. 
     According to yet another aspect, there is provided a sterile-packaged implant assembly. The packaged implant assembly comprises: a cup-shaped sheath for an acetabular cup, and an acetabular cup disposed within said cup-shaped sheath; wherein the cup-shaped sheath is provided with a means for passing an acetabular cup through itself; wherein, in use, the cup-shaped sheath allows an acetabular cup to protrude or penetrate through said cup-shaped sheath and become affixed to a body portion; and wherein said cup-shaped sheath prevents build-up and/or generation of debris onto portions of the acetabular cup when the acetabular cup is placed inside a body cavity. 
     Another aspect of the invention provides a method of implanting an acetabular cup. The method includes forming a sheath for an acetabular cup having at one end, a penetration structure for passage of the acetabular cup through the sheath. A step receives the acetabular cup in the sheath through an end opposite the end having the penetration structure. Another step guides the sheath and the cup through a surgical wound such that the sheath is in front of the cup. Another step removes the sheath from the cup when the cup is proximately near the implantation site. 
     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating certain embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and form a part of the specification, illustrate the embodiments of the present invention and together with the written description serve to explain the principles, characteristics, and features of the invention. In the drawings: 
         FIGS. 1   a - 1   c  illustrate prior art sheaths for use with femoral stems and modular-style necks; 
         FIG. 1   d  illustrates the problems associated with the prior art methods; 
         FIG. 2  illustrates one embodiment; 
         FIG. 3  illustrates another embodiment; 
         FIG. 4  illustrates yet another embodiment; 
         FIG. 5  illustrates yet even another embodiment; 
         FIG. 6  illustrates another embodiment; 
         FIG. 7  illustrates yet another embodiment; 
         FIG. 8  illustrates yet even another embodiment; 
         FIG. 9  illustrates another embodiment; 
         FIG. 10  illustrates yet another embodiment; 
         FIGS. 11   a - 11   c  illustrate a method of packaging an embodiment; and 
         FIGS. 12   a - 12   e  illustrate a method of using an embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. 
     The device provides, in part, an improved method of inserting an acetabular cup (i.e., shell) into a body cavity. The method utilizes a sheath that temporarily encloses the acetabular cup during insertion into a body cavity. The sheath protects the cup from bio-matter which could compromise a good taper lock with a liner, or a good initial scratch-fit with bone. 
     It is preferred that the sheath be sterile-packed with the acetabular cup. The sheath may be incorporated as an integral or separate part of the acetabular cup packaging, or may have a separate part number and used as a disposable instrument. Furthermore, the sheath may be provided as a non-disposable instrument which is configured for multiple sterilizations. The sheath should be somewhat flexible at portions to allow an acetabular cup to penetrate or protrude from one end; however, the sheath may also incorporate more rigid portions at other areas for strength, conformity, and to better push surrounding soft tissues radially-outward away from the acetabular cup. Sheaths may be made so as to be capable of universal use across a variety of differently-sized acetabular cups. 
     The usefulness of the sheath and methods associated therewith is not limited to acetabular cups. The present device may also be advantageously used with acetabular liners, cages, and/or augments alike such that a surface away from the wound must be passed through the sheath. 
       FIGS. 1   a - 1   c  illustrate sheaths used in the prior art for hip applications. The sheath is disposed on a proximal end of an implant and is used to protect a taper lock. The sheath is not penetrable by the implant, and is meant to roll off the implant. The embodiments of the present invention, however, include a port through which the implant must pass in order to properly position the implant in the bone. 
       FIG. 1   d  illustrates the problems associated with prior art methods. Conventionally, acetabular cups  10  are inserted using a positioner/impactor  12  into a body cavity wound  20  without any protective sheath. The cup  10  is passed through the wound  20  across fatty tissue and soft tissue  22  until the cup  10  is positioned over the prepared acetabulum  24 . As the cup  10  is passed, the fatty tissue and soft tissue  22  may brush against the porous surface of the implant. Consequently, fatty tissues and soft tissues  30  cling to the rough, porous, or frictional surfaces of the acetabular cup  10 , which are purposely designed for bony ingrowth and initial fixation. With portions or all of the rough, porous, or frictional surfaces “gummed up” by bio-matter, bone ingrowth and the initial fixation “bite” of the acetabular cup  10  is compromised. 
       FIG. 2  illustrates one embodiment of a cup-shaped sheath  30  for an acetabular cup  10 . The sheath incorporates a means for acetabular cup penetration comprising a single slot  32 . The slot  32  is sized such that the cup  10  is retained within the sheath  30  as the shell  10  and sheath  30  are passed through the wound. Once the cup  10  reaches the implant site, then the cup  10  may be pushed through the slot  32  by deformation or tearing of the slot  32  and sheath  30 . 
       FIG. 3  illustrates another embodiment of a cup-shaped sheath  40  for an acetabular cup  10 . The sheath incorporates a means for acetabular cup penetration comprising two generally orthogonal slots  42 . While the slots are generally orthogonal, the slots may otherwise by oriented relative to each other such that the give an appropriate amount of clearance to the cup  10  as it passes through the sheath  40 . By using multiple slots crossing each other, it may be possible to have thinner or shorter slots than a single slot orientation. 
       FIG. 4  illustrates another embodiment of a cup-shaped sheath  50  for an acetabular cup  10 . The sheath incorporates a means for acetabular cup penetration comprising at least one aperture  52 . While the aperture  52  is generally oval, other aperture shapes for passing the shell through the sheath may be used such as a round, square or triangular apertures. The size of the aperture should be smaller than the shell but large enough so that the cup may pass through the aperture. Smaller aperture sizes may minimize the contact between the cup and the soft tissue and thus minimize the amount of bio-matter on the porous surface. 
       FIG. 5  illustrates another embodiment of a cup-shaped sheath  60  for an acetabular cup  10 . The sheath  60  incorporates a means for acetabular cup penetration comprising several circumferentially-spaced, radially-extending slits  62 . The slits may be simple cuts through the sheath  60 . Such a sheath  60  may preferably be made of a less flexible material so that the triangular wedges made between the slits may retain the shape of the bottom of the sheath  60  and may better retain the cup  10  from passing through the sheath  60  prematurely. 
       FIG. 6  illustrates another embodiment of a cup-shaped sheath  70  for an acetabular cup  10 . The sheath  70  incorporates a means for acetabular cup penetration comprising a reduced diameter end  72 . The end  72  may be extruded, but again the size of the opening should be less than the size of the cup  10  so that the cup  10  cannot pass through the sheath  70  without some amount of force between the sheath  70  and the cup  10 . 
       FIG. 7  illustrates another embodiment of a cup-shaped sheath  80  for an acetabular cup  10 . The sheath  80  incorporates a means for acetabular cup penetration comprising at least one flap  82 . The flap may have a reduced width connection portion to facilitate movement and passage of the acetabular cup  10 . The flap  82  may be preformed with the sheath using perforations that can be severed after the acetabular cup has passed through the body cavity and is ready for bony contact. The tab  82  may also be cut through the bottom of the sheath  80  and made from a less flexible material such as the sheath  60  of  FIG. 5 . 
       FIG. 8  illustrates another embodiment of a cup-shaped sheath  90  for an acetabular cup  10  having a slot  92  for passing the cup  10 . The sheath incorporates at least one removal structure  94  of the sheath  90  from a body cavity. The removal structure  94  may comprise a tab, a hole, an engagement lip, or any other structure which can be engaged to easily remove the sheath  90  from a body cavity. The removal structure  94  may be engaged by the surgeon&#39;s fingers, or may be part of a mechanism attached to the impactor which would pull the sheath  90  away from the porous surface of the cup  10 . 
       FIG. 9  illustrates another embodiment of a cup-shaped sheath  100  for an acetabular cup  10 . The sheath  100  incorporates a means for acetabular cup penetration comprising a perforation pattern  102 . The pattern may be in a pizza-slice configuration as shown, in a simple line configuration, or in a flap configuration as shown in  FIG. 7 . The perforations  102  may allow better isolation of the porous surface from the soft tissue than the embodiments of slots or shapes, but may require more force to push the cup  10  through the sheath  100 . Also, complete removal of the sheath  100  (including the tabs at the perforations) may require additional visual acuity during the replacement surgery. 
       FIG. 10  illustrates another embodiment of a cup-shaped sheath  110  for an acetabular cup  10 . The sheath  110  incorporates a means for acetabular cup penetration comprising a perforation shape  112 . The shape may be in any form and not to be limited to what is shown. For instance, a perforation shape may be comprised of one or more of a triangle, oval, star, polygon, or other multi-sided geometric shape having spline curves. 
     While the embodiments described above have disclosed many individual forms for the penetration means, it is possible to combine these forms into a single form. For example, a shape similar to the example shown in  FIG. 4  may also have a slot or slit extending through remaining portions of the sheath. Such embodiments may allow additional flexibility in the type of material used and the amount of force necessary to push the cup through the sheath. 
       FIGS. 11   a - 11   c  illustrate a method of packaging one embodiment. A sheath  100  is packaged with an acetabular cup  10 . The assembly is packaged (e.g., using a box or container  120  shown in  FIG. 11   c ) and then sterilized according to conventional methods. The perforation pattern  102  may be any of the penetration means disclosed herein. 
       FIGS. 12   a - 12   e  illustrate a method of using an embodiment. A packaged sheath  100  and acetabular cup  10  assembly is removed from a container  120  ( FIG. 12   a ). An inserter instrument  12  is inserted into the acetabular cup  10  ( FIG. 12   b ). The inserter  12  inserts the acetabular cup  10  through a body cavity  20  ( FIGS. 12   c - 12   d ) to a prepared acetabulum  24  such that the sheath  100  shields the acetabular cup from contact with “gummy” bio-matter  22  which can clog the outer porous structure of the acetabular cup  10 . At the bottom of the body cavity, the acetabular cup  10  protrudes from or penetrates through a means for acetabular cup penetration ( FIG. 12   d ). Flaps  130  on the sheath  100  part to allow the cup to pass through the sheath  100 . Finally, the sheath  100  is removed or otherwise generally displaced from the acetabular cup  10 , the cup  10  is impacted, and both the sheath  100  and the inserter instrument  12  are removed from the body cavity  20 . 
     In some embodiments, it may be necessary to change the sizes, shapes, lengths, and widths of the slits, slots, flaps, shoulders, etc. to accommodate various shapes and sizes of acetabular cups, shells, augments, cages, etc. and to allow easy penetration of the acetabular cup through the sheath during impaction. 
     The sheath may be disposable, flexible, colored, non-colored, opaque, transparent, translucent, lubricated, non-lubricated, anatomically-shaped, non-anatomically shaped, cylindrical, implant conforming or cup-shaped, and may have various cross-sectional types. The sheath may be flanged at the open end and configured to rest on bony portions of the acetabular rim, or may be un-flanged to facilitate insertion and withdrawal. The thickness of the sheath may vary. Means provided to the sheath to allow cup penetration can be configured in different ways as would be expected by one having an ordinary skill in the art. Indicia may be provided on the sheath, such as arrows, trademarks, instructions (e.g., for insertion, disposal, orientation, patient or physician info, model number, product number, identification, etc.), or other forms of indicia. Indicia may be moulded in or provided through the usage of inks or dyes. Sheaths may be incorporated with other instruments as an integral unit, or sheaths may be provided with means for effectively facilitating removal from a body cavity—such means may amount to apertures, locking mechanisms, tangs, shelves or ledges for engagement by a tool, etc. In some instances, it may be desirable to incorporate the sheath with a liner inserter guide as one integral unit such as the inserter guide disclosed in co-pending application “Acetabular Liner Inserter Guide” PCT US2008/055323. 
     While the sheath has been described as having a formed bottom portion, the top portion may also be similarly formed as opposed to open. This may help to further protect the cup from bio-matter and may further allow the surgeon to reposition the sheath and cup by moving the sheath and cup out of the wound. In packaging the cup, the cup would then pass through one side of the sheath in order to get the cup within the sheath and then be passed through the other side during implantation. 
     As various modifications could be made to the exemplary embodiments, as described above with reference to the corresponding illustrations, without departing from the scope of the invention, it is intended that all matter contained in the foregoing description and shown in the accompanying drawings shall be interpreted as illustrative rather than limiting. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims appended hereto and their equivalents. 
     The embodiments may improve initial bony fixation by preventing clogging of porous or frictional surfaces on an acetabular cup during insertion into a body cavity. The embodiments may further reduce the risk of liner mal-alignment by keeping most of the inside of the acetabular cup free from debris and soft tissue. The embodiments may even further decrease the risk of an acetabular liner dislodging from its acetabular shell by ensuring that all mating portions between a liner and shell are free from bio-matter.