Femoral component hip joint prosthesis extractor
The present invention relates to the surgical procedures involved in the removal of a femoral component of a total or partial hip joint reconstruction and, in particular, to extractors for the removal of a prosthesis which has been cemented with polymethylmethacrylate or the like into the proximal medullary cavity of the femur. 
     Current methods used to remove femoral components include that of grasping the neck of the prosthesis with pliers or a similar instrument and striking the side of the instrument with a hammer. Such primitive methods require the surgeon&#39;s hands as part of the system and are ineffective in that the hands absorb a high shock load of the impact of the hammer, and so transmit a very small part of the shock to the implanted prosthesis. Removal of an implant in polymethylmethacrylate requires a shock load to shear the cement at the interface between the implant prosthesis and the cement. Since the surgeons hands absorb much of the shock, less is transmitted to the cement, and removal is difficult. This also causes pain in the surgeon&#39;s hands. 
     It is the object of the invention to provide an effective mechanism for removal of a prosthesis previously implanted. Another object is to provide an effective mechanism such that the extraction requires a minimum of effort, can be performed quickly and is not painful to the operator. 
     These and still further objects are addressed hereinafter. 
     The foregoing objects are achieved, generally, in a prosthesis extractor for removing the femoral component of a hip-joint prosthesis having a head, a shoulder, with a neck therebetween, and a stem, which stem is elongate and shaped to the conform to the proximal medullary cavity of the femur within which the prosthesis is implanted; the prosthesis extractor has a base portion and a pair of spaced jaws, the jaws converging toward each other from a widely spaced region to a closely spaced region to form an opening sufficiently large to receive the head of the prosthesis and tapering so as to grasp the neck of the prosthesis therein, said jaws being angled with respect to said base portion to permit substantial alignment of forces applied by the extractor with the stem of the prosthesis. The prosthesis extractor, in an operative system, has attached to it an impact device which, typically, consists of a hammer or weight slidably disposed upon a shaft which has a stop at the end thereof to receive impact forces from the hammer. The shaft is attached to the extractor by a pivot joint that permits compensation for small amounts of misalignment between the shaft and the stem of the prosthesis--for forces to be proper, the two should be in alignment. 
    
    
     The invention is hereinafter described with reference to the accompanying drawing in which: 
     FIG. 1 is an isometric view of an assembly that includes a prosthesis extractor of the present invention in an assembly with other elements that interact therewith and a prosthesis; 
     FIGS. 2 and 3 are respectively a top isometric view and a side isometric view of a prosthesis extractor, like the prosthesis extractor in FIG. 1; 
     FIG. 4 is an elevation view of an assembly like the assembly of FIG. 1 and a prosthesis; and 
     FIG. 5 is an isometric view showing the prosthesis extractor shown in FIGS. 2 and 3 and a prosthesis. 
    
    
     Turning now to FIG. 1 there is shown at 101 an assembly or system for removing the femoral component labeled 100 of a total or partial hip reconstruction. The typical prosthesis 100 is cemented in a cavity in the femur, as is well known, and the function of the system 101 is to remove that prosthesis should trouble arise from the installation. To break the cement bond, it is necessary that a substantial outward impact shock be applied to the prosthesis and that shock, to be effective, it has been found for present purposes, must be one that is substantially aligned with the stem of the prosthesis. 
     The system 101 includes a prosthesis extractor 1 which, as best shown in FIGS. 2 and 5 has a base portion 9 and a pair of spaced jaws 10 and 11 that converge toward each other from a widely-spaced region 12 to a closely-spaced region 13 to form an aperture 14 sufficiently large to receive the head labeled 99 of the prosthesis 100 in FIG. 5 and tapering, as shown, to grasp the neck shown at 98 of the prosthesis securely therein, the jaws 10 and 11 being angled (at an angle θ in FIG. 4) to the base portion to permit alignment of the stem designated 97 of the prosthesis with the elements of an impact device to apply the outward impact force properly. 
     The impact forces are applied by moving a sliding weight 2 that moves along a shaft or elongate portion 4 of the impact device up and down in FIG. 1 in the direction of the arrow marked A. Impact is thus effected between the sliding weight 2 and an end stop or anvil portion 3 of the impact device secured to the top of the shaft 4. The shaft 4 is attached to the extractor 1 by a pivotable joint 16 (see the pin labeled 15 in FIG. 1 which permits pivoting of the joint 16) that permits, upon impact, adjustment of alignment between the shaft 4 and the stem 97 to compensate for small misalignment therebetween to assure that the impact forces applied to the prosthesis 100 are properly directed. It has been found by the inventors that the angle θ is in the range from about 30° to 60°; in the actual extractor shown in FIGS. 2-5, the angle θ is 45°. The jaws 10 and 11 converge in the actual device at an angle of 25°, but a range from about 10° to about 30° is acceptable. The closely-spaced region 13 terminates in a curved end 17A in FIG. 5 having a small (0.2 inch) inner radius. The outside of the jaws or legs 10 and 11 converge in a radius that is small enough not to interfere with access to the prosthesis head 99, in vivo. In this same matter, the legs and the region of convergence thereof (i.e., the curved portion 18 between 17A and 17B in FIG. 5) must be sufficiently thin enough (˜3/8 inch) that neither interferes with extraction. The joint 16 is threaded to accept a threaded shaft 4. The extractor 1 is formed of stainless steel or some other material which can be sterilized and which can withstand the large impact forces. 
     Removal procedure is depicted in FIG. 4 which shows two hands of an operator who secures the neck of the prosthesis in the tapered portion of the device and applies the necessary movement of the hammer or weight 2. 
     The prosthesis extractor 1 eliminates many of the problems of the previously used mechanisms for removing the femoral component of a hip-joint prosthesis and provides a relatively simple system, yet one that applies the necessary shock forces to dislodge such prosthesis. It is a relatively uncomplicated design, offers easy manipulation, sterlization, and so forth, and is adapted for use with existing impact-providing devices. 
     Further modifications of the invention herein disclosed will occur to persons skilled in the art and all such modifications are deemed to be within the spirit and scope of the invention as defined by the appended claims.