Abstract:
An apparatus and a method for removing a hip socket liner from surface attachment to a socket, that includes providing a carrier and multiple penetrators carried to be displaced relative to the carrier, inserting the carrier in the liner so that the penetrators project toward a liner cup-shaped surface, effecting controlling limited forceful displacement of tips defined by the penetrators toward and into said liner cup-shaped surface, and transmitting pushing force acting between the carrier and hip socket whereby the liner is suddenly freed from attachment to the socket.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates generally to hip joints and freeing of attachment elements thereof, and more particularly concerns freeing of hip joint liners from sockets to which they have become attached, over time. 
     There is need for a safe, easily and quickly performed method of freeing a hip joint liner from a socket to which it has become attached. This is particularly needed where metallic surfaces of the liner and socket have become attached, as for example after extensive rubbing or frictional contact. There is particular need for the method and apparatus as defined herein. 
     SUMMARY OF THE INVENTION 
     It is a major object of the invention to provide improved method and apparatus meeting the above needs. Basically, the method of the invention for removing a hip socket liner from surface attachments to a socket, includes: 
     a) providing a carrier and multiple indentors or penetrators carried to be displaced relative to the carrier, 
     b) applying the carrier to the liner so that the penetrators project toward a liner cup-shaped inner surface, 
     c) effecting controlled and limited forceful displacement of the indentors or penetrators so that tips defined by the indentors or penetrators penetrate said liner cup-shaped surface, 
     d) and transmitting jarring force to one of the liner and carrier whereby the liner is suddenly freed from said attachment to the socket. The freed liner is then withdrawn relative to the socket. 
     The cup-shaped interior surface is metallic, and outer surface attachment is spaced from said cup-shaped surface. At least three tips are typically employed (to penetrate directionally substantially normal to the cup-shaped liner surface. 
     A further object is to provide means to pull the carrier away from the liner to drag the liner, via the tips, free of engagement with the socket. 
     A further object is to provide axial force, and/or prying force, and/or vibration to assist liner extraction. 
     These and other objects and advantages of the invention, as well as the details of an illustrative embodiment, will be more fully understood from the following specification and drawings, in which: 
    
    
     
       DRAWING DESCRIPTION 
         FIG. 1  is a section taken through a cup-shaped acetabulum having a liner to be detached from the cup socket, and a carrier for penetration, received in the cup; 
         FIG. 2  is a view like  FIG. 1 , showing forcible displacement of the indentors or penetrators to push the tips into the liner inner surface; 
         FIG. 3  is a view like  FIG. 2 , but showing axial forcible detachment of the liner by axial displacement of the carrier and tips, directionally away from the acetabulum socket; and 
         FIG. 4  is a section showing position of penetrator tip penetration into the liner. 
         FIG. 5  is a view like  FIG. 3 , but showing provision and use of means to push the liner free of the socket; 
         FIG. 6  is a plan view of a bracket useful in such pushing; 
         FIG. 7  is a view taken on lines  7 - 7  of  FIG. 6 ; and 
         FIG. 8  is an edge view of under-cut structure facilitating prying and pushing apart of the liner and socket. 
     
    
    
     DETAILED DESCRIPTION 
     In  FIG. 1 , a generally hemispherical acetabulum  10  has an inner cup-shaped surface  10   a . A liner  11  fits in the acetabulum, and has an outer convex ball shaped surface  11   a  that becomes attached, over time, to the surface  10   a . During hip replacement surgery, it becomes necessary to remove liner  11 , which is difficult and prevents many problems. 
     In accordance with the invention, a carrier  13  is provided and sized to be axially received or inserted closely within the space surrounded by the liner interior cup-shaped surface  11   b . The common axis shown at  14 . Multiple penetrators  15  (at least three, but up to six) are carried by  13 , within generally radial through openings  16  in the carrier. Those penetrators have shafts  15   a  movable endwise in the openings  16 , and shaped tips  15   b  which are sharp, and presented toward the liner interior surface  11   b , at spaced locations about axis  14 . Those locations are preferably equally spaced about axis  14 . At that time, the carrier may endwise engage the liner, as at axial location  17 . 
     Means is provided for effecting controlled limited forceful outward displacement of the indentors, so that their sharp tips are displaced toward and into the material of the liner cup-shaped surface  11   b . The tips typically consist of non-bending material such as hard metal or diamond, and harder than the liner material, which may also be metallic, or consist of polyethylene or ceramic material to enable limited tip penetration or indentation into the liner. This condition is shown in  FIG. 2  and also  FIG. 4 . Such displacement is typically effected by penetrator shaft end engagement with the outer tapered surface  26   a  of a cam  26 , that surface being tapered conical, as shown. The cam is carried by a threaded shaft  43  to be rotated as indicated by arrow  30 . The shaft threading  43   a  may engage the bore threads at  31  of a carrier wall  32 . That wall may also engage the rim  33  of the acetabulum shell part, as shown at  32   a , to position the cam. 
     As the penetrators are forced outward, they penetrate the liner as at grip locations  34 , see in  FIG. 4 , which are located at equal spacing  35   a  about axis  14 . Typically penetration is between 1/64 and ⅛ inch. 
     Thereafter, the carrier is forcibly pulled or displaced to the left, as in  FIG. 3 , which effects simultaneous leftward bodily displacement of the penetrators, their tapered tips, and the liner  11  gripped by the tips. Subsequently the shaft  43  is rotated in the opposite direction, to allow inward bodily displacement of the penetrators and tips, freeing the liner from the carrier. The acetabulum may be held in position, as by a holder  60 , during such extraction of the liner. The penetrator tips are tapered so as to release from the liner as the cam  26  is displaced by shaft  43  rotation, as referred to. If desired, the assembly can be vibrated, as by tuning fork high frequency vibrator means so to assist jarring loose of the liner. 
       FIG. 1  also shows a puller hook  70  attached to the shaft  43 , to be pulled to assist forcible extraction of the liner from the acetabulum. Alternatively, a prying tool or blade  71  may be inserted into a notch  72  between the acetabulum and carrier, and twisted, to assist liner extraction. 
     Referring to  FIG. 5 , it shows provision of means for transmitting pushing force acting between the carrier  13  and the hip socket  10  whereby the liner  11  is suddenly and/or forcibly freed from attachment to the socket. As shown, a pusher  80 , when rotated pushes the carrier to the left, in the direction of arrow  81 , whereby the pusher has operative connection to the carrier. Such a connection is shown in the form of a threaded connection  82 , typically made up after the carrier has been connected to the liner by rotation of screw  43  to effect carrier displacement of the penetrators  15  into the liner, at the tips of the penetrators. 
     A nut  84  has external thread  85  that is made up into internal thread  86  on the carrier annular part  87 , to make up connector  82 . This causes the pusher to initially move to the right until it is stopped by engagement with the end  88   a  of spacer  88  engaging the socket, as at  89 . Alternatively a bracket  90  may be assembled against the socket end  89 , in position to block rightward travel of the nut. Continued rotation of the nut then causes the internal thread  86  on the carrier, and the carrier itself, to move bodily leftwardly, pushing the liner free of the socket, or free of an insert liner  92  carried by the socket, as in the case of a metal-to-metal ball joint where the liners  92  and  11  are “frozen” together. 
     Note that the nut  84  may have an end opening at  84   a , providing access to the turning knob  70   a  on the stem carrying the cam  26 . 
     It will therefore be seen that the invention provides means for readily removing a liner “frozen” in position in a socket, obviating need for the surgeon to repeatedly hammer a tool against the liner in an attempt to free it. Such hammer impacts can cause severe damage to the socket structure, and the present invention precludes risk of such potential damage. 
       FIG. 6  shows bracket  90  having turned ends or fittings  91  at opposite sides of axis  93  to fit against the socket ends, when the bracket interior annulus  90  is assembled over the carrier part  87 . The bracket then transmits pressure from nut  84  to the socket end  89 . 
       FIG. 8  shows provision of multiple (typically six) under cut openings  96  formed in the periphery of spacer  88 , or in the bracket loop  99 , adjacent end  89 , to enable insert of the tip  100   a  of a pry tool or bar  100 . Pivoting of bar  100  then enables tip  100   a  to pry or push the spacer  88  and liner free of the socket. A vibrating tuning fork may be used in place of bar  100 . 
     Multiple under cuts enable selective and successive insertion of tip  100   a  in two or more under cuts, and prying at such multiple locations, to ensure liner release.