Abstract:
Disclosed herein is an implant assembly including an alignment guide for aligning the engagement between a glenosphere and baseplate via a central screw engaged to the baseplate. The glenosphere includes first and second recess portions. The first recess portion of the glenosphere is configured to engage a tapered side surface of the baseplate and the second recess portion of the glenosphere is configured to engage a portion of a head of the central screw projecting outwardly from a top surface of the baseplate when engaged thereto. The portion of the head of the central screw projecting outwardly from the baseplate is slip-fit into the second recess of the glenosphere. This engagement aids the alignment of the glenosphere and the baseplate and helps to ensure the accurate alignment of the tapered engagement of the side surface of the baseplate and the first recess of the glenosphere.

Description:
FIELD OF THE TECHNOLOGY 
     The present invention relates to an alignment guide for reverse shoulder arthroplasty (RSA), and in particular it relates to such a guide for aligning the engagement between a glenosphere and baseplate via a central screw engaged to the baseplate. 
     BACKGROUND OF THE INVENTION 
     Many existing reverse shoulder systems (RSA) require a baseplate and a glenosphere. These systems generally differ from one another in how the baseplate is fastened to the glenoid cavity and how the glenosphere becomes engaged to the baseplate. In some systems, the baseplate may be fastened to the glenoid cavity of the scapula by a plurality of screws and a glenosphere having a convex joint surface may be screwed into the baseplate using an axial threaded feature and/or taper locked to a periphery of the baseplate. In other systems, the glenosphere may engage the baseplate solely via a taper connection. Generally, a compression fit is not preferable between the glenosphere and baseplate due to the potential need for separating the two components once engaged to one another. 
     In cases where the glenosphere becomes engaged to the baseplate through either a threaded or taper connection, the glenosphere and baseplate may become separated after a certain length of time. This may cause the glenosphere to tilt with respect to the baseplate or in some cases even completely separate therefrom. In either situation, the baseplate and glenosphere become misaligned. 
     Some systems include first fastening a central screw to a glenosphere and then guiding the connection between the baseplate and glenosphere via the central screw. Guiding the connection between the baseplate and glenosphere is generally an important consideration due to minimal access and visibility that the surgeon may have during a RSA procedure. Access to the baseplate is generally narrow making it relatively difficult for the surgeon to have the visibility needed to correctly align the engagement between a baseplate and glenosphere. 
     BRIEF SUMMARY OF THE INVENTION 
     One embodiment in accordance with a first aspect of the present invention is an implant assembly including first, second and third components. The first component is preferably a baseplate, the second component is preferably a glenosphere, and the third component is preferably a central screw. First component of the implant assembly preferably includes a top surface, a bottom surface, a side surface connecting the top and bottom surfaces, and at least one borehole extending through the top and bottom surfaces. Second component of the implant assembly preferably includes first and second circumferential recesses, the first circumferential recess defining a tapered wall having a minimum diameter at a base of the tapered wall, the second circumferential recess defining a circumferential wall having a constant diameter, the constant diameter of the circumferential wall being less than the minimum diameter of the tapered wall, the first and second circumferential recesses being in communication with one another. Third component of the implant assembly preferably includes a head portion and a body portion, the third component configured to be received at least partially within the at least one borehole of the first component. At least a portion of the head portion of the third component extends outwardly from the top surface of the first component when the third component is engaged to the at least one borehole of the first component such that the head portion can be slip-fit into the second circumferential recess of the second component and into engagement with the circumferential wall thereof, thereby guiding the engagement of the side surface of the first component into the first circumferential recess and into engagement with the tapered wall of the second component. 
     In another embodiment of the first aspect of the present invention the top surface of the second component is substantially flat and the bottom surface is convex. The side surface of the first component is preferably tapered and forms a circumferential perimeter of the first component, the side surface having a central longitudinal axis. In some embodiments, the implant assembly includes a plurality of baseplates having variable thicknesses connecting the top and bottom surfaces thereof. 
     In yet another embodiment of the first aspect of the present invention the at least one borehole of the first component has a central axis that is coaxial with the central longitudinal axis of the side surface of the first component. 
     In yet still another embodiment of the first aspect of the present invention the implant assembly further comprises a plurality of boreholes extending through the top and bottom surfaces of the first component that are equally spaced around a perimeter of the top and bottom surfaces, the boreholes adapted to receive screws for fixing the first component to a glenoid cavity of a patient. Each of the plurality of boreholes preferably includes a ramp portion adapted to receive and engage a head of a fixation screw. Each of the plurality of boreholes can either be straight or angled from the top surface of the baseplate. 
     In still yet another embodiment of the first aspect of the present invention the third component further includes a neck portion that is tapered and at least partially threaded, and the at least one borehole includes a threaded portion adapted to engage the at least partially threaded portion of the third component. Preferably, the head portion of the third component has a circumferential side surface and at least a portion of the body portion of the third component is threaded. 
     In still yet another embodiment of the first aspect of the present invention the second component has a semispherical convex outer surface and the second component has a bore hole through an apex portion thereof. The borehole through the apex portion of the second component is preferably at least partially threaded. 
     In still yet another embodiment of the first aspect of the present invention the tapered wall and the circumferential wall of the second component each have a longitudinal axis therethrough, the longitudinal axes being coaxial. Preferably, when the first component is engaged to the second component, the central axis of the at least one borehole is coaxial with the longitudinal axes of the tapered wall and the circumferential wall. 
     One embodiment in accordance with a second aspect of the present invention is an implant assembly including first, second and third components. The first component preferably has a top surface, a bottom surface, a side surface connecting the top and bottom surfaces, and at least one borehole extending through the top and bottom surfaces, the distance between the top surface and bottom surface defining a first height. The second component preferably has first and second circumferential recesses, the first circumferential recess defining a tapered wall having a second height substantially equal to the first height, the second circumferential recess defining a circumferential wall having a third height greater than the second height of the tapered wall, the first and second circumferential recesses being in communication with one another. The third component has a head portion and a body portion, the third component configured to be received at least partially within the at least one borehole of the first component. The third component when engaged to the at least one borehole of the first component the head portion thereof extends outwardly from the top surface of the first component in an amount substantially equal to the third height, and at least a portion of the head portion of the third component is located within the second circumferential recess of the second component and is in engagement with the circumferential wall when at least a portion of the side surface of the first component is located within the first circumferential recess and is in engagement with the tapered wall of the second component. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete appreciation of the subject matter of the present invention and the various advantages thereof can be realized by reference to the following detailed description in which reference is made to the accompanying drawings in which: 
         FIG. 1  is an exploded view of an implant system showing a two-piece construct prior to assembly with a glenosphere. 
         FIG. 2A  is a front view of one embodiment of a baseplate of the present invention. 
         FIG. 2B  is a cross-sectional side view taken along line A-A of the baseplate shown in  FIG. 2A . 
         FIG. 2C  is an alternate side view of the baseplate shown in  FIG. 2A . 
         FIG. 3A  is a back view of one embodiment of a glenosphere of the present invention. 
         FIG. 3B  is a cross-sectional side view taken along line B-B of the glenosphere shown in  FIG. 3A . 
         FIG. 3C  is an alternate side view of the glenosphere shown in  FIG. 3A . 
         FIG. 4A  is a perspective view of an alternate embodiment of a glenosphere of the present invention. 
         FIG. 4B  is a front view of the glenosphere shown in  FIG. 4A . 
         FIG. 4C  is a cross-sectional side view taken along line C-C of the glenosphere shown in  FIG. 4B . 
         FIG. 5A  is a perspective view of one embodiment of a central screw of the present invention. 
         FIG. 5B  is a side plan view of the central screw shown in  FIG. 5A . 
         FIG. 5C  is a cross-sectional side view taken along line D-D of the central screw shown in  FIG. 5B . 
         FIG. 6A  is a perspective view of one embodiment of a two-piece construct of the present invention including an assembled baseplate and central screw. 
         FIG. 6B  is a top view of the two-piece construct shown in  FIG. 6A . 
         FIG. 6C  is a side view of the two-piece construct shown in  FIG. 6A . 
         FIG. 7A  is a perspective view of one embodiment of an implant assembly of the present invention showing a two-piece construct assembled to a glenosphere. 
         FIG. 7B  is a bottom view of the implant assembly shown in  FIG. 7A . 
         FIG. 7C  is a side view of the implant assembly shown in  FIG. 7A . 
         FIG. 7D  is a cross-sectional view taken along line E-E of the implant assembly shown in  FIG. 7C . 
         FIG. 8A  is a cross-sectional view of a two-piece construct being assembled to a glenosphere. 
         FIG. 8B  is a cross-sectional view of the two-piece construct and glenosphere shown in  FIG. 8A  in an almost fully assembled position. 
     
    
    
     DETAILED DESCRIPTION 
     As used herein, when referring to bones or other parts of the body, the term “proximal” means closer to the heart and the term “distal” means more distant from the heart. The term “inferior” means lower or bottom and the term “superior” means upper or top. The term “anterior” means towards the front part of the body or the face and the term “posterior” means toward the back of the body. The term “medial” means toward the midline of the body and the term “lateral” means away from the midline of the body. 
     Referring to  FIG. 1 , there is shown an exploded view of an embodiment of an implant assembly of the present invention designated generally by reference numeral  10 . As shown in this figure, implant assembly  10  includes a first component or baseplate  20 , a second component or glenosphere  50 , and a third component or central screw  80 . 
     Referring to  FIGS. 2A-2C , there is shown one embodiment of baseplate  20  of the present invention. Baseplate  20  includes a bottom surface  22 , a top surface  24 , and a tapered side surface  26  connecting the bottom and top surfaces, the side surface  26  defining a height H 1  and a having a minimum diameter D 1  defined by a perimeter of top surface  24 . A central bore hole  28  extends through bottom and top surfaces  22 ,  24 , the central bore hole  28  having a longitudinal axis  30 . 
     As shown in  FIG. 2B , bore hole  28  preferably includes a first diameter  32  and a second diameter  34  with the first diameter being larger than the second diameter. An intermediate portion  36  preferably separates first and second diameters  32 ,  34 , the intermediate portion formed preferably as a singular thread projecting outwardly from a wall  38  of first diameter  32  of central bore hole  28 . 
     Bottom surface  22  of baseplate  20  is generally convex, while top surface  24  is generally flat. Disposed around and adjacent a perimeter or circumference  40  formed by side surface  26  of baseplate  20  are a plurality of screw receiving apertures  42 . While baseplate  20  as shown in  FIG. 2A , includes four screw receiving apertures  42 , baseplate  20  may include less or more than four screw receiving apertures  42 . As shown in  FIG. 2A , apertures  42  moving in a clockwise direction include a longitudinal axis  41 ,  43 ,  45 , or  47 , respectively. Longitudinal axes  41 ,  43 ,  45  and  47  are preferably angled from longitudinal axis  30  between 15° and 75° as shown in  FIG. 2C , for example. Longitudinal axes  41 ,  43 ,  45  and  47  may each be angled from longitudinal axis  30  that same amount of degrees or each may be angled from longitudinal axis  30  a different amount of degrees. In some embodiments, longitudinal axes  41 ,  43 ,  45  and  47  may be parallel to longitudinal axis  30  of bore hole  28 . 
     Referring to  FIGS. 3A-3C , there is shown one embodiment of a second component or glenosphere  50  of the present invention. Glenosphere  50  includes a hemispherical or semispherical outer surface  52  having a perimeter  54  forming an outer diameter of a bottom surface  56 . Starting at bottom surface  56  and projecting inwardly therefrom is a first circumferential recess  58  having a depth DP 1  slightly larger than height H 1  of baseplate  20 . In one embodiment, depth DP 1  may be substantially equivalent to height H 1 . First circumferential recess  58  defines a tapered wall  59  having a maximum diameter defining an outer perimeter  57  and a minimum diameter defining a first base portion  60  of the tapered wall. First circumferential recess  58  terminates at first base portion  60  of tapered wall  59 . 
     Starting at first base portion  60  and projecting inwardly therefrom is a second circumferential recess  62  having a depth DP 2 . Second circumferential recess  62  defines a circumferential wall  61  having a constant diameter. Second circumferential recess  62  terminates at a base portion of circumferential wall  61  at a second base portion  64 . The constant diameter of the circumferential wall  61  is preferably less than the minimum diameter of tapered wall  59 . The first and second circumferential recesses  58  and  62  are in communication with one another. First circumferential recess includes a longitudinal axis  63  and second circumferential recess includes a longitudinal axis  65 , the longitudinal axes  63 ,  65  of first and second circumferential recesses are coaxial. In other embodiments, longitudinal axes  63  and  65  may be offset from one another. 
     As shown in  FIGS. 3A-3C , located at a polar or apex portion of glenosphere  50  is a threaded bore  70 . Threaded bore  70  is in communication with first and second circumferential recesses  58  and  62 . In other embodiments, threaded bore  70  is a recess formed in outer surface  52  and is not in communication with either first or second circumferential recess  58  and  62 . In other embodiments, bore  70  is only partially threaded about a length thereof. 
     Referring to  FIGS. 4A-4C , there is shown another embodiment of glenosphere  50  of the present invention denoted as  50 ′. Glenosphere  50 ′ includes all of the same features as glenosphere  50  except that the first and second circumferential recesses  58 ′,  62 ′ are offset from threaded bore  70 ′ of glenosphere  50 ′. First circumferential recess  58 ′ includes a longitudinal axis  63 ′ and second circumferential recess  62 ′ includes a longitudinal axis  65 ′, the longitudinal axes  63 ′,  65 ′ of first and second circumferential recesses are coaxial. Glenosphere  50 ′ includes a hemispherical or semispherical outer surface  52 ′ having a perimeter  54 ′ forming an outer diameter of a bottom surface  56 ′. Perimeter  54 ′ includes a longitudinal axis  67 ′ that is offset from longitudinal axes  63 ′,  65 ′ of first and second circumferential recesses  58 ′,  62 ′. 
     Referring to  FIGS. 5A-5C , there is shown one embodiment of a third component or central screw  80  of the present invention. Central screw  80  includes a head portion  82 , a body portion  84 , a neck portion  86  and a longitudinal axis  90 . Head portion  82  includes a circumferential side surface  83  defining a perimeter with a diameter D 4 . Body portion  84  of central screw  80  is preferably threaded. Neck portion  86  is preferably tapered and threaded. Central screw  80  further includes an engagement portion  88  for receiving an adjustment tool such as a screwdriver, for example. 
     In reference to  FIGS. 6A-6C  there is shown one embodiment of a two-piece construct  100  including an assembled baseplate  20  and central screw  80 . When assembled, a portion of head portion  82  of central screw  80  projects outwardly from outer surface  24  of baseplate  20  a height H 2 . Depending on the configuration of first and second circumferential recesses and  62  of glenosphere  50 , namely depths DP 1  and DP 2 , respectively, the height H 2  may vary. 
     In reference to  FIGS. 7A-7D  there is shown implant assembly  10  with baseplate  20 , glenosphere  50 , and central screw  80  all being assembled together. The alignment guide of implant assembly  10  serves to enable a more efficient and reproducible alignment between glenosphere  50  and baseplate  20  during RSA. In one method of the invention, after baseplate is secured to a patient&#39;s scapula by fixation screws, glenosphere  50  may be coupled thereto. It is important for the alignment of glenosphere  50  to be accurate on the baseplate  20 . In other words longitudinal axis  30  of baseplate  20  and longitudinal axis  63  of glenosphere should be coaxial when implant assembly  10  is in an assembled position. 
     The diameter D 4  of head portion  82  of central screw  80  is preferably 8 mm, but may be as little as 2 mm and as much as 14 mm, for example. When central screw  80  is assembled to baseplate  20 , head portion  82  of central  80  preferably protrudes from top surface  24  of baseplate  20  approximately 5 mm. Second circumferential recess  62  of glenosphere  50  has a diameter of approximately 9 mm (just slightly more than the diameter of head portion  82  of central screw  80 ) and a depth of 5.4 mm (just slightly more than the amount head portion  82  of central screw  80  protrudes from top surface  24  of baseplate  20 ). 
     Implant assembly  10  provides a surgeon or other operating room personnel with improved tactile feel and axial alignment when introducing glenosphere  50  onto baseplate  20  during final implantation. Reduction of surgery time is preferably a benefit attributable to implant assembly  10 , which also has the potential to reduce the amount of time a surgeon needs to implant this device with a one step procedure strategy. 
     One aspect of the present invention is the assembly of glenosphere  50  with a two-piece construct  100 , namely assembled central screw  80  and baseplate  20 . A holding instrument (not shown) can be secured to bore  70  in order to aid the assembly of glenosphere  50  with two-piece construct  100 . Alignment between baseplate  20  of two-piece construct  100  and glenosphere  50  is first introduced by the peripheral external taper of perimeter  26  of baseplate  20  and first internal bore  58  of glenosphere  50  as shown in  FIG. 8A . At least a portion of head portion  82  of central screw  80  is located within pilot bore  62  prior to engagement between external taper  26  of baseplate  20  and tapered wall  59  of glenosphere  50  as shown in  FIG. 8B . Pilot diameter D 4  of head  82  of central screw  80  is configured to be accepted by pilot bore  62  with diameter D 3  of glenosphere  50  in a slip-fit manner. The dimensions of head portion  82  of central screw and pilot bore  62  of glenosphere  50  aids in preventing glenosphere  50  from cantilevering out of its intended assembled position when external taper  26  of baseplate  20  is engaged to tapered wall  59  of glenosphere  50 . 
     Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.