referring to the drawings , fig1 shows a femur 2 which has been resected at its upper end . cancellous bone has been removed from the centre of the femur at the upper end to form a cavity 4 in which a prosthesis 6 is to be located . the prosthesis comprises a stem which is received in the cavity and a head which engages an acetabular cup component , as is known . the stem of the prosthesis is bonded to the bone of the cavity by means of bone cement injected into the cavity under pressure . pressure in the cement injected into the cavity is maintained during and after injection ( while the cement hardens ) by means of a sealing gasket positioned over the end of the bone . the gasket comprises a sealing plate 10 having an opening 12 in it , and a plug 14 located in the opening in which the nozzle 16 of bone cement delivery apparatus can be received . force can be applied to the gasket against the bone directly , or by means of a u - shaped tool 19 which can be located around the opening 12 in the sealing plate . referring to fig2 and 3 , the sealing plate is formed from a resiliently deformable material such as a silicone by moulding . it has a thin central portion 18 surrounding the opening 12 and a relatively thick edge portion 20 defining a lip . the lip has an inclined under - surface for engaging the upper edge of the resected bone in line contact . for example , the thickness of the plate in the portion surrounding the opening might be about 7 mm and the thickness at the edge might be about 12 mm . the width of the edge portion is about 10 mm at its widest along the long edges of the sealing plate and about 5 mm at its narrowest along the short edges of the sealing plate . the dimensions of the sealing plate will be selected according to the bone against which it is to be used and the prosthesis which is to be inserted into the bone cavity . for example , a sealing plate to be used against the femur of an adult human might have dimensions 60 mm by 55 mm . the opening in the plate has dimensions 20 mm by 11 mm . the opening 12 in the sealing plate is generally oval , having semi - circular portions at each end joined by straight portions . referring to fig4 and 5 , the plug 14 is formed from a resiliently deformable material by moulding . it can be formed from the same material as that of the sealing plate , although a material that is more rigid than that of the sealing plate can be preferred for some applications . it comprises a neck portion 22 which is generally oval in cross - section with a shape corresponding substantially to that of the opening 12 in the sealing plate 10 . there is a back plate 24 on the neck , by which the plug can be gripped and manipulated , in particular during insertion into and removal from the opening 12 in the sealing plate . the back plate can be curved upwardly as shown in fig5 to facilitate manipulation of the plug . an injection port 26 extends through the plug , in which the nozzle of bone cement delivery apparatus can be received . a laterally extending lug 28 in the manner of a flange depends from the lower end of the neck portion 22 , which can engage the lower face of the sealing plate when the plug is located in the opening 12 , restricting inadvertent removal of the plug from the opening . the lug has a profiled lower edge to facilitate insertion into the opening in the sealing plate . fig6 shows a plug 30 for use in the sealing plate of a sealing gasket , such as described above with reference to fig2 and 3 . the plug has a neck portion 36 and a flange - like lug 38 which extends around its periphery . an injection port 32 extends through the plug , in which the nozzle of bone cement delivery apparatus can be received . the plug 30 is made from a relatively rigid material so that , on insertion into the opening in a sealing plate , the material of the sealing plate is deformed by the lug 38 . the plug has a back plate 34 which is flat . a plug with a flat back plate formed from a rigid material can be used to apply pressure to the sealing plate , to form the seal between the plate and the bone . fig7 shows the plug 30 located in the opening 12 in the sealing plate 10 with the neck portion of the plug engaging the edges of the opening . the lug 38 extends laterally in contact with the lower face 30 of the sealing plate , restricting removal of the plug from the opening . the nozzle 16 of bone cement delivery apparatus is received in the injection port 32 which extends through the plug , for delivery of cement through the sealing gasket into the cavity of a bone against which the gasket is positioned in use . in use , after injection of bone cement into the bone cavity , the plug 30 is removed from the opening 12 in the sealing plate 10 . the plug can be removed soon after injection of the cement . however , it can be preferred for its removal to be deferred until the cement has partially hardened , for example , until it has hardened sufficiently for insertion into the cavity of the prosthesis . the prosthesis to be located in the bone cavity can be inserted in the cavity through the opening 12 after removal of the plug . once the bone cement has hardened sufficiently to bond the prosthesis to the bone , the sealing plate can be removed from the bone . preferably , the sealing plate is severed before removal , for example by tearing or more preferably by cutting , from the opening 12 to an edge of the plate , so that it can be removed by lateral movement rather than having to be passed over the end of the prosthesis . fig8 shows a sealing gasket in which the sealing plate 40 has an opening 42 in it to accommodate a plug 44 , generally as described above in relation to other embodiments . the sealing plate also has a flap portion 46 extending from the portion with the opening 42 in it , which can be used to pressurise and to control flow of bone cement from an opening into the bone cavity other than the opening into which cement is to be injected through the opening in the sealing plate and the plug inserted therein . for example , it can be used to extend over the resected trochanter on a femur , and to control egress of bone cement from the trochanter region and to apply pressure to that cement . the sealing gasket of the invention has the advantage that the component by which cement is retained in place in the bone cavity does not need to be moved from the end of the bone throughout the period from injection of bone cement to hardening of the cement to form the bond between the bone and the prosthesis located in the cement in the cavity . this allows pressure to be maintained on the cement throughout the period in which it hardens , as preferred for secure bonding of the cement to the bone . while the invention has been described with reference to the drawings as applied to a hip joint , it will be understood that the invention is applicable to other joints .
a bone cavity sealing gasket which can be fitted over the resected end of a bone to be provided with bone cement in its axial cavity , includes a sealing plate which has a quantity of a resiliently deformable material on its lower face to enable a seal to be created between the plate and the upper edge of the bone , and an opening extending through it . a plug can be received in the opening in the sealing plate . the plug has an injection port extending through it aligned with the opening in the sealing plate in which the injection nozzle of bone cement delivery apparatus can be received .