Abstract:
Humeral prosthesis having a rod for anchoring into a humeral canal of a humerus. The prosthesis has a hemispherical cup adapted to engage a shoulder socket and a connection which connects the rod to the hemispherical cup. The connection includes a spherical portion and the spherical portion includes a spherical engaging surface having at least one recess. At least one reference mark is disposed on at least one of the rod, the hemispherical cup, and the connection. The at least one reference mark corresponds to the at least one recess. The prosthesis also has a binding mechanism for engaging the at least one recess. The hemispherical cup is pivotal about the spherical portion and fixable in a finite number of combined angular positions which correspond to a number of recesses.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority under 35 U.S.C. § 119 of French Patent Application No. FR 97 11603, filed on Sep. 12, 1997. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to improvements made to sphere-type shoulder prostheses of the kind which comprise a rod which is anchored into the humeral canal and a hemispherical cup which can interact with the shoulder socket. 
     The prosthesis according to the invention, which may or may not be associated with a prosthetic socket, allows for the surgical treatment of degenerative afflictions of gleno-humeral arthrosis, and also of other afflictions. Furthermore, the prosthesis according to the invention is also intended for cephalo-tuberosital fractures which are not accessible to conservative surgery, and also to any painful syndrome of the shoulder. 
     2. Description of Background and Relevant Information 
     French patent application No. 2 727 002 of which the present applicant is proprietor discloses a humeral prosthesis with a sphere comprising, in the metaphyseal region of the humeral rod, a cylindrical housing with a spherical end into which a sphere designed to receive a hemispherical cup is inserted, while binding means allow these to be immobilized in a determined position with respect to the axis of the rod. 
     Also, French patent application No. 2 685 633 of which the applicant is proprietor discloses a modular humeral prosthesis made up of three elements one of which is an anchoring rod provided with a metaphyseal region formed of an oblique bearing face. The second element is a distance piece in the form of a wedge, one of the end faces of which fits on the bearing face of the rod. The third element of the prosthesis is a hemispherical cup, the base of which is fixed with respect to the second end face of the distance piece. This attachment, which is offcentered with respect to the geometric axis of the cup, allows for angular adjustment of the latter with respect to the distance piece. 
     Such prostheses have certain drawbacks regarding the systems for immobilizing the spheres, which are inaccessible once the prostheses have been inserted into the humeral canal, because the binding screws are located inside the bone cavity. 
     Furthermore, it can be observed that, because a sphere is being used, there are an infinite number of relative positions between rod and sphere, and this makes reproducing on the implant the geometry measured using the test piece impossible. 
     SUMMARY OF THE INVENTION 
     The improvements which are the subject of the present invention aim to allow a humeral prosthesis to be produced which overcomes the above drawbacks. 
     The humeral prosthesis with a sphere, comprising a rod which can be anchored into the humeral canal, a hemispherical cup which can interact with the shoulder socket and a sphere providing the connection between the rod and the cup, and provides for indexing the sphere and/or the cup with respect to the rod in a finite number of combined angular positions α and β of the cup with respect to the rod, which positions are obtained from measurements read off from a test piece or some other method in order, using binding mechanisms, to immobilize the sphere and/or the cup on the rod before it is fitted in the humeral canal, the angles α and β respectively representing the angle of inclination in the frontal plane, and the anteversion or retroversion angle of inclination with respect to the frontal plane about the axis of the rod. [sic] 
     The humeral prosthesis comprises a combination of a fixed pointer with a reference mark and a recess opposite the axis of the hole which allows the angles α and β to be reproduced. 
     The humeral prosthesis comprises a hole that receives the binding mechanisms which is located along an axis that does not run through the center of the sphere and/or the cup so as to prevent any relative movement between the sphere and/or the cup with respect to the rod. 
     The humeral prosthesis comprises a rod which in its metaphyseal region comprises a cavity capable of accommodating a sphere interacting with the cup, while binding mechanisms provided on the rod allow the sphere and the cup to be immobilized. 
     The humeral prosthesis comprises a rod which in its metaphyseal region is secured to a sphere which interacts with a housing formed in the cup, while binding mechanisms provided on the cup allow it to be immobilized on the sphere. 
     The humeral prosthesis comprises a rod which in its metaphyseal region comprises a housing in the middle of which there is drilled a hole with a tapering profile receiving a peg of the same profile extending from a flange placed in the housing, the flange being secured, on the opposite side from the peg, to a sphere which interacts with the housing provided in the cup. 
     The humeral prosthesis comprises an axis of the sphere which is laterally offset by a distance with respect to the axis of the flange, so as to allow the cup to be offcentered. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The description which will follow with reference to the appended drawings, given by way of nonlimiting examples, will allow a better understanding of the invention, its features and the advantages it is able to afford: 
     FIG. 1 is a frontal view depicting the humeral prosthesis according to the present invention in a first angular position α of the cup with respect to the rod of the prosthesis. 
     FIG. 2 is a view from above showing the humeral prosthesis in its angular position of FIG.  1 . 
     FIG. 3 is a frontal view illustrating the humeral prosthesis in a second angular position α of the cup with a different value than the one provided in FIG. 1, of the cup with respect to the rod of the prosthesis. 
     FIG. 4 is a view from above showing the humeral prosthesis according to the present invention, in its angular position of FIG. 2 [sic]. 
     FIG. 5 is a frontal view depicting the humeral prosthesis in a third angular position. 
     FIG. 6 is a view from above illustrating the humeral prosthesis in its angular position of FIG. 5, at an angle β with respect to the frontal plane of the rod of the prosthesis. 
     FIG. 7 is a view showing a first alternative form of the humeral prosthesis according to the present invention. 
     FIG. 8 is a view depicting a second alternative form of the humeral prosthesis according to the present invention. 
     FIG. 9 is a view illustrating a third alternative form of the humeral prosthesis according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Depicted in FIGS. 1 to  6  are the three elements of the humeral prosthesis according to the invention, namely a rod  1  that can be anchored into the humeral canal, a hemispherical cup  2  capable of interacting with the shoulder socket and a sphere  3  providing the mechanical link between the rod  1  and the cup  2 . 
     The rod  1  is of cylindrical section comprising a metaphyseal region  10 , with a flared profile, which has a cavity  11  in which the sphere  3  engages. In the sagittal plane, the metaphyseal region  10  has straight and parallel panels  12  and  13  defining its thickness. Note that the thickness of the metaphyseal region  10  is smaller than the diameter of the sphere  3 . This is because the panels  12  and  13  can each be pierced with a hole or cut-out  14  opening into the cavity  11  and allowing the poles of the sphere  3  to protrude outward. 
     The metaphyseal region  10  has one or more fins  15  which are arranged on the external and/or lateral face of the rod  1 , while perforations  16  are formed in the fins  15  to allow the upper end of the humerus to be reconstructed around the prosthesis in the event of fracture. 
     The rod  10  terminates in a face  17  which is inclined with respect to the longitudinal axis of the rod. The rod  10  comprises a fixed pointer  18  which may, for example, be embodied by the fin  15  or any other mechanisms. 
     The exterior profile of the cup  2  has graduations or reference marks  20  which correspond to recesses  30  formed on the surface of the sphere  3  so that the latter can be perfectly positioned with respect to the rod  1  according to the measurements taken from a test piece. 
     Between the fin  15  and the inclined face  17 , the metaphyseal region  10  is pierced with a tapped hole  19  which opens into the cavity  11  to allow the sphere  3  to be immobilized, using a screw  4 , in a position that is determined using the pointer  18  and the reference marks  20 . 
     The binding screw  4  interacting with the hole  19  enters the sphere  3  along an axis that does not run through the center of the sphere, and this prevents any relative movement of the sphere  3  with respect to the rod  1 . 
     It can be seen that the axis of the hole  19  is slightly inclined with respect to the vertical axis of the rod  1  so as to allow the screw  4  always to be accessible when the prosthesis is introduced into the humeral canal. 
     Note that the combination of a pointer  18  with a reference mark  20  and a recess  30  facing the axis of the hole  19  reproduces a previously measured combined angular position of the angles α and β, measured for example from the test piece. 
     The sphere  3  is intended to be solid and connected directly to the cup  2  by a pin  21 , the length of which can vary depending on the pathological case. This structure entails having in stock a certain number of spheres  3  secured to their cup  2  in order to be able to cater for all operating scenarios. 
     A first alternative form depicted in FIG. 7 consists in the fact that the cavity  11  of the rod  1  receives a sphere  5  which is secured to a circular flange  51 , from the center of which there emerges a tapering peg  52 . The latter interacts with a hemispherical cup  2 ′ which is similar to those described in patent application No. 2 685 633 of which the applicant is proprietor. 
     The cup  2 ′ has a base  20 ′ in which there is formed an off-centered circular cavity  21 ′ the diameter of which corresponds, give or take the clearance, to that of the flange  51 . 
     Formed at the center of the cavity  21 ′ is a tapering bore  22 ′ capable of receiving the peg  52 . The way in which the cup  2 ′ is mounted and immobilized is identical to the way described in patent application No. 2 685 633. 
     The screw  4  placed in the hole  19  interacts with recesses  50  made on the surface of the sphere  5  allows it to be immobilized in a determined position. [sic] 
     Note that the rod  1  comprises the pointer  18  as was described earlier, while the flange  51  comprises reference marks  53 . 
     The combination of a pointer  18  with a reference mark  53  and a recess  50  opposite the axis of the hole  19  reproduces a previously measured combined angular position of the angles α and β measured from the test piece. 
     A second alternative form shown in FIG. 8 consists in the rod  1  being secured at its metaphyseal region  10  to a sphere  6  which extends at right angles to the inclined face  17 . The sphere  6  interacts with a cup  2 ″ which has a housing  20 ″ in the shape of a portion of a sphere. A tapped hole  21 ″ passes through the cup  2 ″ to emerge in the housing  20 ″ so that a press screw  4 , identical to the one described in FIG. 1, can immobilize the cup on the sphere  6 . 
     The axis of the hole  21 ″ is intended not to run through the center of the housing  20 ″ and/or the sphere  6 , so as to allow the latter to be perfectly immobilized in the said housing. 
     The position of the cup  2 ″ with respect to the rod  1  is determined by the reference marks  22 ″ provided either on the base  23 ″ or on the exterior profile  24 ″ of the cup, of the fixed pointer  18  provided on the rod  1  and of the recesses  60  formed on the surface of the sphere  6 . 
     Note that the combination of a pointer  18  with a reference mark  22 ″ and a recess  60  opposite the axis of the hole  21 ″ reproduces a previously measured combined angular position of the angles α and β measured from the test piece. 
     A third alternative form illustrated in FIG. 9 consists in the metaphyseal region  10  of the rod  1  comprising on its inclined face  17  a housing  7  in the middle of which there is drilled a non-emerging hole  70  of tapering profile. The housing  7  is intended to receive a flange  81  secured to a tapering peg  82  which interacts with the hole  70  to immobilize the flange  81  on the rod  1  by wedging. The flange  81  has, on the opposite side from the tapering peg  82 , a sphere  8  which interacts with the housing  20 ″ of the cup  2 ″ described previously in FIG.  8 . 
     Note that the axis S of the sphere  8  is offset by a distance d with respect to the axis C of the flange  81  fitted without play into the housing  7  of the rod  1  to allow the cup  2 ″ to be offcentered. 
     The position of the cup  2 ″ with respect to the rod  1  is determined by the reference marks  22 ″ provided either on the base  23 ″ or on the exterior profile  24 ″ of the said cup, of the fixed pointer  18  provided either on the rod  1  or on the flange  81  and of the recesses  80  formed on the surface of the sphere  8 . 
     Note that the combination of a pointer  18  with a reference mark  22 ″ and a recess  80  facing the axis of the hole  21 ″ reproduces a previously measured combined angular position of the angles α and β measured from the test piece. 
     A fourth alternative form according to the invention, depicted in FIG. 10, consists in the rod  1  being identical to the one described previously in FIG. 1 so that its cavity  11  interacts with a sphere  9  similar to the one described in patent application FR 2 727 002 of which the applicant is proprietor. 
     The sphere  9  comprises at its middle, a bore  91  into which there opens a radial slot  92 . The bore  91  is intended to receive a rod  21 ′″ secured to and laterally offset by a distance d with respect to the middle of the cup  2 ′″, to allow the latter to be offcentered. 
     The fact that the cup  2 ′″ is independent of the sphere  9  allows heightwise adjustment of the latter with respect to the metaphyseal region  10  of the rod  1 . 
     Note that in this embodiment, the screw  4  interacting with the hole  19  on the one hand allows the sphere  9  to be immobilized in the cavity  11  and on the other hand allows the rod  21 ′″ to be fixed into the bore  91 . 
     Attachment may be supplemented by another binding screw to improve the fixing of the rod  21 ′″ into the bore  91 . 
     The position of the cup  2 ′″ with respect to the rod  1  is determined by the reference marks  93  provided on the truncated poles  94  of the sphere  9 , of the fixed pointer  18  provided either on the rod  1  and of the recesses  90  formed on the surface of the sphere  9 . [sic] 
     Note that the combination of a pointer  18  with a reference mark  93  and a recess  90  opposite the axis of the hole  19  reproduces a previously measured combined angular position of the angles α and β measured from the test piece. 
     The humeral prostheses described hereinabove are set up using a test piece or identical model of the prosthesis to be fitted. This test piece thus allows the surgeon to measure perfectly the relative position of cup/sphere with respect to the rod  1  as a function of two angles α and β. To each combination of its two angles there corresponds a reference mark  20 ,  53 ,  22 ″,  93  to be used on the prostheses to be implanted. The angles α and β are defined with respect to the reference axis which is the axis of the rod or of the humeral canal. 
     Thus, the angle α is the angle of inclination in the frontal plane, while the angle β is the anteversion or retroversion angle of inclination with respect to the frontal plane about the axis of the rod. 
     The surgeon transfers the measurements, as far as the tolerances will allow, read off from the test piece onto the humeral prosthesis to be implanted, using the fixed pointer  18 , the graduations or reference marks  20 ,  53 ,  22 ″,  93  and the recesses  30 ,  50 ,  60 ,  80 ,  90  so that the sphere  3 ,  5 ,  6 ,  8 ,  9  and/or the cup  2 ,  2 ′,  2 ″,  2 ′″ will, with respect to the rod  1 , be positioned in accordance with the combination of angles α and β. 
     The surgeon immobilizes the sphere  3 ,  5 ,  6 ,  8 ,  9  and/or the cup  2 ,  2 ′,  2 ″,  2 ′″ in the determined position by means of the binding screw  4  before implanting the prosthesis in the patient&#39;s humeral canal.