Patent Publication Number: US-11020243-B2

Title: Tool and method for removing an acetabular ball from an acetabular cup in a hip replacement prosthesis

Description:
This is an application filed as a continuation application of U.S. Ser. No. 15/742,208, which in turn was an application filed under 35 USC 371 based on PCT/US2016/042430 filed 15 Jul. 2016, which in turn claims priority to U.S. Serial No. 62/197,200 filed 27 Jul. 2015. The present application claims the full priority benefit of these prior applications and herein incorporates by reference the full disclosures of these prior applications as if set forth herein. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to surgical tools used in connection with a reverse hip prosthesis. More particularly, the invention has to do with a surgical tool for extracting an acetabular ball from an acetabular cup. 
     The Related Art 
     A reverse hip prosthesis is described in U.S. Pat. Nos. 8,313,531 B2 and 8,540,779 B2. The prosthesis and a revision surgery method also are described in U.S. Pat. No. 8,992,627 B2. The disclosures of these three patents are incorporated herein in their entireties by reference. 
     SUMMARY OF THE INVENTION 
     As described in the patents referenced above, the acetabular ball is affixed by means of a Morse taper to an acetabular cup stem. The stem extends from the bottom of a concave surface of the acetabular cup. The surgical tool of the invention enables a surgeon to remove the acetabular ball from an implanted prosthesis without pulling on the acetabular cup and without disrupting any bone ingrowth. In the present disclosure, we use the term “acetabular ball extractor” from time to time to describe the tool of the invention and the term “tool” or “instrument” is sometimes used to refer to either or both of the first and second embodiments of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a first embodiment of the surgical tool of the invention. 
         FIG. 2  is an elevation view of a second embodiment of the tool. 
         FIG. 3  is a section view of the tool in a first step illustrating the jaws positioned over an acetabular ball which has been affixed in an acetabular cup. 
         FIG. 4  is an elevation view of the tool in a second step fully engaged with the acetabular ball and cup. 
         FIG. 5  is a section view of  FIG. 4  taken along section line A-A. 
         FIG. 6  is a section view of the tool in a third step illustrating an acetabular ball separated from the stem of the acetabular cup. 
         FIG. 7  is an elevation view of a handle or outer shaft for the acetabular ball extractor. 
         FIG. 8  is an elevation view of a jaw assembly of the acetabular ball extractor. 
         FIG. 9  is an elevation view of a block bar of the acetabular ball extractor. 
         FIG. 10  is an elevation view of the handle bell of the acetabular ball extractor. 
         FIG. 11  is an elevation view of a shaft nut of the second embodiment of the acetabular ball extractor. 
         FIG. 12  is a partially exploded view of the second embodiment of the tool of the invention. 
         FIG. 12A  is a magnified view of the proximal end of  FIG. 12 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The tool  1  is the first embodiment of the tool of the invention and is illustrated in perspective in  FIG. 1 . The tool  1   a  is the second embodiment of the tool of the invention and is illustrated in a partially exploded view in  FIG. 12  and in elevation in  FIG. 2 . 
     Referring to  FIGS. 1-6 , the tool  1  comprises a jaw shaft  10  having two or more than two jaws  2  disposed at the distal end thereof. Each jaw  2  is pivotable about a pin  12  having an axis perpendicular to a central axis of jaw shaft  10 . And jaw shaft  10  has a threaded proximal end  11 . (See  FIGS. 8, 12 and 12A .) The jaw shaft  10  is disposed concentrically in outer shaft  4 . A bell shaped element, referred to herein as handle bell  3 , is affixed to the distal end of outer shaft  4 . The handle bell  3  is internally sized to cause jaws  2  to close as the jaws  2  are drawn into the handle bell  3  by proximal movement of jaw shaft  10  toward the proximal end of the tool  1  as explained in more detail below. The handle bell  3  has a circumferential bell edge  33  at its distal end sized to engage a circumferential cup edge  23  of an acetabular cup. Outer shaft  4  has an optional knurled portion  5 . 
     A jaw shaft nut  9  or  9   a  is threaded onto the proximal end of jaw shaft  10  and an outer shaft nut  6  or  6   a  is affixed to the proximal end of outer shaft  4 . When the jaw shaft nut abuts the outer shaft nut and the threads at the proximal end of shaft  4  are right handed, tightening jaw shaft nut  9  or  9   a  by turning it in a clockwise (or right-handed) direction will exert a distal force on nut  6  or  6   a  causing the jaw shaft  10  to move in a proximal direction relative to the outer shaft  4 . By way of further explanation, the nuts are disposed adjacent to one another with the jaw shaft nut  9  or  9   a  being disposed proximally to the outer shaft nut  6  or  6   a . Jaw shaft  10  is illustrated in section in  FIGS. 3, 5 and 6 , and in elevation in  FIG. 8 .  FIGS. 12 and 12A  illustrate the threaded proximal end  11  of jaw shaft  10 ;  FIG. 12A  being a magnified view of the proximal end A of the tool illustrated in  FIG. 12 .  FIG. 7  is an elevation view of outer shaft  4  with an outer shaft nut  6   a  thereon. The jaw shaft  10  is illustrated in elevation in  FIG. 8  with jaws  2  thereon and a block bar  8  is illustrated in elevation in  FIG. 9 .  FIGS. 10 and 11  are elevations of handle bell  3  and jaw shaft nut  9   a , respectively. 
     The difference between tools  1  and  1   a  has to do with differences in outer shaft nuts  6  and  6   a  and jaw shaft nuts  9  and  9   a . Nuts  6  and  9  are knurled and holes  7  are provided in the knurled portions to receive block bars  8  which are used to provide leverage in the operation of the tool. Nuts  6   a  and  9   a  are also knurled but they are additionally provided with hex portions  14  and  15 , respectively. Holes  7   a  are provided for block bars  8  in hex portions  14  and  15 . The hex portions allow the surgeon to use a wrench or wrenches (not shown) instead of some or all of the block bars in order to obtain increased leverage during operation of the tool. Of course, flattened portions on the outer surface of the nuts having shapes other than a hex can be used to permit use of a wrench or other tool in order to obtain increased leverage as will be apparent to those having ordinary skill in the art. 
     The operation of the tool is illustrated in  FIGS. 3-6 . The jaws  2  are allowed to open when jaw shaft  10  is pushed in a distal direction while holding shaft  4  so that the jaws move out of handle bell  3 . The jaws  2  are hinged by pins  12 . In  FIG. 3  the jaws  2  are shown in section after they have been pushed out of handle bell  3  and pushed over acetabular ball  20 . Two or more than two jaws may be used as will be apparent to those having skill in the art. Acetabular ball  20  is securely affixed by means of a Morse taper on stem  21 . Stem  21  is affixed to and extends from the concave surface off acetabular cup  22 . 
     In  FIGS. 4 and 5  the circumferential bell edge  33  at the distal end of handle bell  3  has been pushed into engagement with the circumferential cup edge  23  of acetabular cup  22 . When the tool has been engaged with the ball and cup in this manner, the next step is to grip shaft  4  while turning jaw shaft nut  9  or  9   a  causing the jaw shaft to move in a proximal direction so that jaws  2  pull on acetabular ball  20  while handle bell  3  exerts an opposing force on the circumferential cup edge  23  of acetabular cup  22 . The opposing force prevents pulling on acetabular cup  22  so that the cup is not pulled out of the acetabulum. A rod or block bar  8  is placed in a hole  7  or  7   a  of outer shaft nut  6  or  6   a  and another rod or block bar  8  is placed in a hole  7  or  7   a  of jaw shaft nut  9  or  9   a  when additional leverage is needed to exert a pulling force on acetabular ball  20  and an opposing pushing force on acetabular cup  22 . The holes  7  and  7   a  are perpendicular to the central axes of the nuts. If more leverage is needed, the block bars  8  are removed from one or both of shaft nuts  6   a  or  9   a  and a wrench is used on either or both shaft nuts by placing the open end of the wrench(es) (not shown) over one or both hex portions  14  or  15 . When sufficient force is exerted, the ball separates from stem  21  as illustrated by space  30  in  FIG. 6 .