Abstract:
A bone cement collector includes a body having a structure that is permeable to bone cement and has opening for trapping bone cement. The body is releasably attached to an orthopaedic implant component at a location on the implant at which bone cement is likely to escape during positioning of the orthopaedic implant.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a national stage application under 35 U.S.C. 371 of International Patent Application PCT/GB2009/000903 filed Apr. 7, 2009. 
     The present invention relates generally to the field of bone cement and in particular to methods and apparatus for handling excess bone cement during an orthopaedic arthroplasty procedure. 
     BACKGROUND OF THE INVENTION 
     Bone cement is used during many orthopaedic arthroplasty procedures in order to securely attach the arthroplasty implant to the patient&#39;s bone. It is of vital importance to ensure that sufficient cement is applied to ensure good interlock. The amount of interlock depends on a number of factors such as pressurisation, bone density and any cavities present. These factors currently require the surgeon to apply more cement than is actually required. If too little cement is used, then the implant may fail by becoming partially or wholly detached from the bone. This may require revision surgery, if there is sufficient remaining bone stock, or some other remedial procedure. 
     It can also be important to ensure that the bone cement is used when it is at the correct consistency as it cures. If the cement is used too soon during its cure, then the cement can be too runny and may leak off the bone. If the cement is used too late during its cure, then its adhesive properties in securing the implant to the bone may be impaired and an insufficiently strong fixation may occur. Hence, there is also a window of time during which cement should be used. However, there is great demand for orthopaedic surgery procedures and surgeons do not have time to wait during the procedure to ensure that the cement is at the perfect point in its cure either in terms of its ease of handling or its adhesive properties for application to the bone. 
     If too much cement is placed on the bone then when the implant is placed, the implant often squeezes cement away from the bone at the edges and the cement tends to become trapped in and around the patient&#39;s joint. Similarly if the cement is too runny, the cement can run off the bone and accumulate in and around the patient&#39;s joint. Hence, the surgeon often has to spend considerable time and skill trying to clean excess cement from on and around the implant and joint using curettes, scalpels or by hand. Otherwise, the cement, when dried, will harm the patient and may require surgical intervention to remove. It can be particularly difficult to ensure that all cement is removed as often there is very limited access to the joint. For example if may be necessary to try and remove cement from behind a knee joint and access to that space may be very limited. This is particularly the case during minimally invasive surgical procedures. Therefore, both the risk of leaving cement pieces in the joint and also scratching the implant surface is high. 
     Hence, apparatus and methods for improving the handling of bone cement during placement of an orthopaedic implant would be beneficial. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention provides apparatus and a method for quickly removing excess cement around an implant where the excess cement forms. 
     A first aspect of the invention provides a bone cement collector, comprising a body and a releasable attachment mechanism by which the body can be releasably attached to an orthopaedic implant component. The body can be attached at a location on the implant at which bone cement is caused or likely to be caused to escape during placement of the orthopaedic implant. 
     Hence, the body can act to collect excess cement displaced by the implant and can then be removed from the implant, taking the excess bone cement with it, thereby reducing or eliminating the need to remove excess cement after the implant has been placed. 
     The body can have a structure which is configured to be permeable to bone cement and/or to trap bone cement. The structure can be a foam or mesh or similar. The structure can be a support or substrate bearing a plurality of formations. The structure can be a single part or can comprise a plurality of parts. The structure can have a plurality of voids or apertures. The voids or apertures can present a tortuous fluid flow path. The structure can present a plurality of different and/or separate surfaces to which bone cement can adhere. 
     The releasable attachment mechanism can comprises an adhesive. 
     The releasable attachment mechanism can be a mechanical coupling. For example, the mechanical coupling can include a push-fit or snap-fit coupling or a plurality of push-fit or snap-fit couplings. 
     The releasable attachment mechanism comprises a suction coupling. The suction coupling can comprise a plurality of suction pads or cups disposed on a rear side of the collector. This provides a particularly suitable mechanism for attaching to the smooth surface of many implants. 
     The bone cement collector comprises a substrate bearing at least one formation or a plurality of formations defining a plurality of voids through which bone cement can pass. 
     The bone cement collector can comprise a substrate bearing at least one formation, or a plurality of formations, defining a plurality of separate or different surfaces or parts to which bone cement can adhere. This can help to retain the bone cement on the collector when removing the collector after the bone cement has been allowed to continue curing. 
     The bone cement collector can include at least one handle by which a user can pull to remove the bone cement collector. The handle can be attached to a free end of the collector. A handle can be provided at each free end of the or each collector. 
     A second aspect of the invention provides a bone cement controlling orthopaedic implant comprising: an orthopaedic implant component; and a bone cement collector according to any of the first aspects of the invention. The cement collector can be releasably attached to the orthopaedic implant component by the releasable attachment mechanism at a location on the implant at which bone cement is caused to escape during placement of the orthopaedic implant. 
     The bone cement collector can extend at least partially about an end or part of the component. The end of part of the component can be an end or part intended to face rearward when the component is implanted. This helps with removing excess cement from particularly inaccessible parts of a surgical site. 
     The bone cement collector can extend substantially entirely around the periphery of the component. This helps to collect all excess cement that might escape. 
     The implant can include a plurality of cement collectors releasably attached to the orthopaedic implant. Different types of cement collectors can be attached at different positions. This allows the implant to be customised for specific uses. 
     The implant can be any orthopaedic implant secured by bone cement, such as a knee implant, a hip implant or a shoulder implant. In particular, the implant can be a tibial implant, a femoral implant, a femoral stem or an acetabular cup. 
     A third aspect of the invention provides a method for handling bone cement during an orthopaedic arthroplasty procedure, comprising: applying bone cement to a prepared surface of a bone; placing an implant component having a bone cement collector releasably attached thereto on the bone cement; and removing the bone cement collector, and any or at least some cement attached thereto, from the implant component. 
     Removing the bone cement collector from the implant component can includes removing at least a portion of the bone cement collector from a rearward facing portion of the implant component. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the invention will now be described in detail, by way of example only, and with reference to the accompanying drawings, in which: 
         FIG. 1  shows a perspective view of an implant and cement collector according to the invention; 
         FIG. 2  shows a side view of the implant and cement collector of  FIG. 1 ; 
         FIG. 3  shows a magnified view of a part of the implant and cement collector shown in  FIG. 2 ; 
         FIG. 4  shows a perspective view of a further implant and cement collector according to the invention; 
         FIG. 5  shows a schematic perspective view of a cement collector according to the invention; 
         FIG. 6  shows a schematic perspective view of a further cement collector according to the invention; 
         FIG. 7  shows a schematic perspective view of a further cement collector according to the invention; 
         FIG. 8  shows a perspective view of a further implant and cement collector according to the invention; 
         FIG. 9  shows a perspective view of a femoral part of the implant shown in  FIG. 8 ; and 
         FIG. 10  shows a perspective view of a tibial part of the implant shown in  FIG. 8 . 
     
    
    
     Similar items in different Figures share common reference signs unless indicated otherwise. 
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to  FIG. 1 , there is shown a schematic perspective view of an implant  100  according to the invention and bearing a bone cement collector  150  also according to the invention.  FIG. 2  shows a cross section through implant  100  when placed on a resected proximal end  110  of a femur. The implant  100  is a generally conventional femoral implant except that it has been adapted to have the bone cement collector  150  releasably attached thereto as will be described in greater detail below. 
     The bone cement collector  150  has a generally elongate body made of a plastic mesh  152  and having a flange or lip member  154  extending from the mesh. The flange or lip  154  is snugly received in a narrow channel  102  which extends around the periphery of the implant  150 . The channel  102  and flange  154  are dimensioned so that the cement collector can be released from the implant in a tearing motion which extracts the flange from the channel. Hence, the channel and flange provide between them a releasable attachment mechanism by which the cement collector can be removed from the implant. 
     The mesh has a complex and convoluted structure which provides a plurality of voids. The mesh structure is chosen so that the voids are sufficiently large and common to allow bone cement to pass into or at least partially through the cement collector. That is the cement collector is at least partially permeable to bone cement. Further, the material of the mesh giving rise to its structure presents a plurality of members which help to trap bone cement within or on the cement collector and which also provide a plurality or surfaces to which the bone cement can at least partially adhere in use. 
       FIG. 3  shows a view of an enlarged condylar portion of the implant and bone shown in  FIG. 2 . The condylar portion of the implant  104  is located toward the rear of the patient&#39;s knee joint. A portion  154  of the cement collector located on the rear facing part of the implant is positioned so that in use, when the implant is pressurised against bone cement, bone cement squeezed out from between the implant and bone is collected by the mesh. 
     In use, the bone is resected and otherwise generally prepared in a conventional manner. Bone cement is applied to the resected bone surface and then the implant  100  bearing the bone cement collector  150  is place on the bone and pressurised. Pressurisation of the implant causes the egress of bone cement at a number of locations around the periphery of the implant. However, the bone collector allows the excess bone cement to escape from the gap between the implant and the bone surface and pass into the mesh. The mesh also acts to trap and hence collect the excess bone cement owing to the tortuous paths through the voids in the mesh and the large surface area presented by the material of the mesh both restricts movement of cement through the mesh and also provides a large surface area to which the bone cement can begin at least partially to adhere. After a short wait of a few minutes, to allow the bone cement to continue curing, the surgeon can pull on a free end of the bone cement collector and release the cement collector from the implant using a tearing motion. The bone cement trapped in and by the mesh breaks away cleanly from the cement mantel between the implant and bone and is retained in and on the mesh thereby preventing or reducing the amount of bone cement left on the implant or bone or in the joint space. 
       FIG. 4  shows a further implant  120  bearing a further embodiment of a bone cement collector  160 . The implant  120  is in the form of a tibial tray  122  and includes a plurality of holes  124  in a side wall and arranged around its periphery. The cement collector  160  is similar to that shown in  FIGS. 1 to 3  in that it has a mesh body  162 , but differs in that it has a plurality of male formations or pegs  164  positioned and dimensioned so as to mate with holes  124  in a push fit manner and provide a releasable attachment mechanism. By pulling on the cement collector  160  in the direction generally indicated by arrow  168 , the cement collector can be removed from the implant in a generally tearing motion thereby removing any excess cement trapped on or in the mesh during use. 
     It will be appreciated that the cement collector can have a wide variety of form and can be releasably attached to a wide variety of implants using a wide variety of releasable attachment mechanisms. 
     For example,  FIG. 5  shows a schematic perspective view of a further embodiment of a bone cement collector  170  also according to the invention and similar to that shown in  FIG. 4 . The bone cement collector has a body  172  made from a mesh or foam material, which is permeable to bone cement, and includes a peg  174 ,  176  at each end by which the bone collector  170  can be releasably attached to an implant via matching, mating holes. 
       FIG. 6  shows a schematic perspective view of a further embodiment of a bone cement collector  180  also according to the invention. The bone cement collector has a central support or substrate  184  from which a plurality of members or fingers  186  extend in a variety of different directions and in a generally cucumiform manner. The fingers and substrate provide a body which is generally permeable to bone cement, as it can pass between the fingers, but the fingers also act to trap bone cement and also provide a plurality of different or separate surfaces to which bone cement can adhere. A peg  188 ,  189  is provided toward each end by which the bone collector  180  can be releasably attached to an implant via matching, mating holes. 
       FIG. 7  shows a schematic perspective view of a further embodiment of a bone cement collector  190  also according to the invention. The bone cement has a body  192  in a generally spiral or coiled form. The coiled form of the body provides a body which is generally permeable to bone cement, as it can pass between the loops of the coil, but the loops of the coil can also act to trap bone cement and also provide a plurality of different or separate surfaces to which bone cement can adhere. A peg  194 ,  196  is provided toward each end by which the bone collector  190  can be releasably attached to an implant via matching, mating holes. 
     The cement collector can have a length selected to correspond to a region of the periphery of the implant at which cement egress is commonly experience in use. 
       FIG. 8  shows a further embodiment of implants  200 ,  210  and bone cement collectors  220 ,  230  according to the invention. A first implant  200  is a femoral implant and a second implant  210  is a tibial tray implant.  FIG. 9  shows an enlarged view of a part  202  of the femoral implant  200  and  FIG. 10  shows an expanded view of the tibial implant  210  in use. Each implant  200 ,  210  has a bone cement collector  220 ,  230  releasably attached to it. The bone cement collectors  220 ,  230  have a generally similar construction and are made from a suitable silicone material. The bone cement collectors each have a main support or substrate  222 ,  232  in the form or a ribbon or a band, with a plurality of suction cups (not shown) on a rear implant facing side. A cement permeable structure  224 ,  234  in the form of a concertina or folded strip is mounted on the substrate and defines a plurality of apertures, e.g.  226 , toward a lower end thereof. The apertures defined by folded strip  224 ,  234  are positioned below the support  222 ,  232 , so as to be located adjacent a region of the periphery of the implant from which bone cement  240  is likely to escape during use, as illustrated in  FIG. 9 . 
     The plurality of apertures provided by the folded strip make the bone cement collector permeable as bone cement can pass through it and the constriction caused by the material of the folded strip helps to trap bone cement within the collector and the walls of the folded strip provide a plurality of separate surface regions to which the bone cement can adhere. The suction cups provided on the rear surface of the collector co-operate with the shiny surface of the implant to provide a releasable attachment mechanism by the which collectors can be ‘torn’ from the implants to remove the excess bone cement captured therein in use, as illustrated by the arrows in  FIG. 8 . 
     It will be appreciated that there are a wide variety of modifications and changes and combinations of features which can be used in various embodiments of the invention beyond those described in detail above. 
     A wide variety of different releasable attachment mechanisms can be used. For example, various different types of mechanical mechanisms can be used, such as push-fit and snap fit mechanisms, such as snap in clips. None-mechanical mechanisms can also be used, such as various medical adhesives  221 , including, for example, pressure sensitive adhesives, such as the ARcare  7261  adhesive as provide by Adhesives Research Inc. 
     A wide variety of different permeable body forms can be used to trap the cement. As well as the meshes and foams, nets, webs and other interlaced structures which define a plurality of voids having tortuous flow paths can be used. Various types of materials can be used, such as fabrics, gauzes, metals, alloys, plastics (including resorbable plastics such as PLA), silicones and similar. 
     The collector can have a one piece constructions and can extend around substantially the whole of the periphery of the implant of just around a part or parts of the periphery of the implant. The collector can be made up from multiple pieces which can extend around substantially the whole of the periphery of the implant of just around a part or parts of the periphery of the implant. 
     The collector can have handles in the form of strings or tabs extending from one or both the free ends of the collector and which a surgeon can grab and pull on in order to remove the collector from the implant. This is particularly helpful if the free ends of the collector are located toward a rearward facing part of the implant, in which case the handles can be located toward the front of the implant to help tear the collector from the implant by pulling on the handles.