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Home | Alpha Telephone | Domain Names | Web Hosting | Get Traffic | xrEvidence | xrSoccer United States Patent
SURGICALLY IMPLANTABLE JOINT PROSTHESIS Surgically implantable shoulder joint prosthesis comprising a gimbal supported joint attached by cushioned rotating pin connections to an intramedullary pin in the humerus and a cruciform shaped perforated connector in the glenoid cavity. Perforations allow for bone ingrowth to secure the glenoid connection. Gimbal joint is preferably covered with a sheath to prevent tissue ingrowth.
Primary Examiner: Gaudet; Richard A. Assistant Examiner: Frinks; Ronald L. Attorney, Agent or Firm: That which is claimed is: 1. A surgically implantable joint prosthesis comprising a gimbal housing, a gimbal ring pinned at first axially opposite points to said housing, an inner body pinned to said ring at opposite sides thereof on an axis perpendicular to said first axially opposite points, first bone securing means rotatably attached to said housing, and second bone securing means rotatably attached to said inner body. 2. A surgically implantable joint prosthesis as defined in claim 1 wherein cushioning means are provided between said housing and said bone securing means. 3. A surgically implantable joint prosthesis as defined in claim 1 wherein cushioning means are provided between said inner body and said bone securing means. 4. A surgically implantable joint prosthesis in claim 1 wherein said gimbal ring is a self lubricating polymeric material. 5. A surgically implantable joint prosthesis as defined in claim 4 wherein at least one of said first and second bone securing means comprises a backing disc and a perforated plate structure extending from said backing disc and adapted to be driven into bone adjacent said joint. 6. A surgically implantable joint prosthesis as defined in claim 5 wherein said perforated plate structure has a tapered edge along its extremity on the side opposite said disc. 7. A surgically implantable joint prosthesis as defined in claim 5 wherein said perforated plate structure is of generally cruciform configuration. 8. A surgically implantable joint prosthesis as defined in claim 5 wherein the other of said first and second bone securing means is an elongated stem adapted to be driven into the intramedullary canal of adjacent bone, said stem having flat face portions on the surface thereof. 9. A surgically implantable joint prosthesis as defined in claim 8 wherein cushioning means are provided in the rotatable attachment between said gimbal housing and said first bone securing means and also between said inner body and said second bone securing means. 10. A surgically implantable joint prosthesis as defined in claim 9 wherein a flexible sheath covers relatively moveable parts thereof to prevent tissue ingrowth from interfering with movement thereof. BACKGROUND OF THE INVENTION The present invention relates to surgically implantable prosthetic joints and more particularly to devices for replacing the shoulder joint. Surgery involving excision and removal of damaged or diseased bone tissue and replacement with various types of prosthetic devices is now relatively common. In such operations prosthetic devices of various designs and materials are employed. Materials which are substantially inert within the living body are required but several suitable materials such as stainless steel alloys, cobalt-chromium base alloys, silicone rubber, high molecular weight polyethylene, and polytetrafluoroethylene have been successfully used for such purposes. One of the most difficult joints for satisfactory prosthetic correction is the shoulder because of the relatively great freedom of motion normal to the natural shoulder joint. To date no wholly satisfactory prosthesis has been available for replacement of this joint. SUMMARY OF THE INVENTION Accordingly it is a primary object of the present invention to provide a satisfactory surgically implantable shoulder joint prosthesis. This is accomplished in accordance with the present invention by the provision of a gimbal supported joint which is semirigidly and rotatably attached to connection means for securing the joint to the humerus and the glenoid cavity of the clavicle. Preferably the arm securing means is an intramedullary pin having planar surfaces to prevent rotation in the intramedullary canal. The glenoid securing means is preferably a perforated generally cruciform device designed to be driven into the glenoid and eventually secured by ingrowth of bone through the perforations. Further, preferably a flexible sheath of silicone rubber, for example, is fitted over the exposed portions of the joint to prevent tissue ingrowth from interfering with the freedom of movement of the joint . BRIEF DESCRIPTION OF THE DRAWINGS Other objects and the attendant advantages of the invention will become obvious and the invention will become better understood by reference to the following detailed description of an embodiment of the invention when read in conjunction with the accompanying drawings wherein: FIG. 1 is a front view in elevation of an embodiment of the invention; FIG. 2 is a vertical cross-sectional view of the embodiment shown in FIG. 1; FIG. 3 is a horizontal cross-sectional view of the embodiments shown in FIGS. 1 and 2 with the intramedullary stem removed; FIG. 4 is a view in perspective of the glenoid securing means; and FIG. 5 is a cross-sectional view of the intramedullary stem taken along the line 5--5 of FIG. 2. DESCRIPTION OF PREFERRED EMBODIMENTS Referring now to the drawings wherein like reference characters designate like parts throughout the figures thereof there is shown in FIG. 1 an elevational view of a shoulder joint prosthesis. A joint shown generally by the numeral 11 has its exposed portions encased in a flexible sheath 12 which may be of silicone rubber, for example. A glenoid securing device 13 is secured to one end of the joint by means of a pin 14. Similarly, a humerus securing means 16 which is shaped to be driven into the intramedullary canal is secured to the joint by means of a pin 17. Referring now to FIGS. 2-5 greater detail of the construction of the prosthesis can be observed in the various cross-sectional views. The joint 11 is in effect a simple gimbal supported universal joint comprising an outer metallic housing 18 having a truncated spherical opening in one end thereof to act as a socket. Inside the opening and in slideable relationship therewith is a gimbal ring 19 in the form of a truncated hollow sphere which is preferably made of high molecular weight polyethylene because of the rigidity and strength of that material coupled with its inherent lubricity against stainless steel and similar steel alloys. A first pair of axially aligned gimbal pins 21, 22 (FIG. 3) interconnect the gimbal ring 19 and the housing 18 allowing pivotal action about the pin axis. The pins 21, 22 are an interference fit in the metal holes and are chilled prior to insertion. This assures their remaining in place in use. Inside the gimbal ring 19 is a metallic sphere 23 pinned by a second pair of axially aligned gimbal pins 24, 26 having an axis perpendicular to the axis of the first pair of gimbal pins 21, 22, thereby allowing pivotal movement in a plane perpendicular to the plane of movement about the axis of the first pair. The sphere 23 has a diameter substantially equal to the inner diameter of the spherical gimbal ring 19 so that it can slide freely therein but tends to discourage migration of body fluids therethrough. The sphere 23 is connected to flanged pin 27 preferably by means of screw threads or alternatively by means such as press fitting or making the parts integral. The flange 28 of the pin 27 is confined between a pair of slightly compressible cushioning rings 29, 31 in a closed compartment formed by an attachment member 32 which in turn is affixed to the proximal end of the glenoid securing device 13 by means of a pin 14. The cushioning rings 29, 31 which may be, for example, polyethylene, serve to make the connections semirigid rather than rigid and thereby provide some inherent insurance against breakage of the metal parts in the event of shocks. Further the flange is free to rotate between the cushioning rings 29, 31. The glenoid securing device 13 (FIGS. 2, 3, and 4) comprises a generally disc shaped plate or proximal end 33 having a circumferential extension mating with the attachment member 32 for coupling thereto. The pin 14 passes through the extension and through the mating portion of the attachment member 32 to secure the parts together when desired. The distal portions of the securing device 13 as may be seen most clearly from FIG. 4 are a generally cruciform arrangement of plates 34 tapered to a knife edge at their extremities. The plates 34 have a plurality of holes 36 therethrough for bone ingrowth after implantation. The disc shaped portion 33 also has a plurality of holes 37 through it and also has a ring shaped offset 39 in its circumference. The purposes of these features will become more apparent hereinafter. The housing 18 at the opposite side of the gimbal joint from the glenoid securing device 13 is similarly semirigidly attached to the humerus securing means by means of a rotatable flanged pin 41 which is in axial alignment with the pin 27 to form the third axis of rotation of the joint. The flange of the pin 41 is similarly confined between a pair of slightly compressible cushioning rings 42, 43 confined in a hollow in the housing 11. A loose fitting metallic guide ring 44 and a cushioning washer 46 are also interposed along the length of the flanged pin 41. The pin in turn is rigidly secured to the flange 47 of the intramedullary pin 16 by means of the securing pin 17 passing through the flange and the flanged pin 41. The intramedullary securing pin 16, as may be seen from FIG. 5, is preferably hexagonal in cross-section along the major portion of its length. The flat portions allow for the introduction of bone adhesive more easily than would a round cross-section as the device is being inserted into the intramedullary canal. Further, the flat portions tend somewhat to prevent rotation of the stem within the intramedullary canal after implantation. In use, the pins 14 and 17 are initially removed and the device disassembled into three major pieces. These are the glenoid securing device, the joint with its connecting pins and the humerus securing device. After surgery to remove the end of the arm bone and shape the bone end, the glenoid securing device is driven into the glenoid cavity of the clavicle until the holes 36 are covered. Bone cement is squeezed under the disc 33 and the securing device is then driven in until the disc abuts the bone. The knife edges on the cruciform distal structure provide for relatively easy bone penetration without serious degradation of adjacent structure. A fillet of bone cement is applied to the ring shaped offset 39 and bone cement is also used to fill the holes 37 of the disc. The humerus securing means is likewise driven into the intramedullary canal of the humerus which is first preferably coated with bone cement. After it is in place the pins 14 and 17 are used to connect the joint to the bone securing means at the ends of the device and bone cement is applied to the pins as a precaution against their becoming dislodged. The operation is then completed and the patient immobilized for several days until partial healing takes place. In the embodiment described, No. 316L stainless steel was used for all metallic parts, high molecular weight polyethylene was used for all cushion parts, and a silicone rubber of 25 Durometer was used for the protective sleeve 12. Obviously, other materials known in the art can be substituted for these. Obviously, from a reading of the foregoing, variations of the design will also become obvious to those skilled in the art. The cruciform shaped securing means could also be used to secure the prosthesis to the humerus, for example. The direction of the connections to the gimbal arrangement could be reversed if desired. The sheath 12 and the cushioning devices could be omitted or changed in shape. Features of the prosthesis herein claimed can be used in prostheses for joints other than the shoulder. Certainly still other modifications and variations of the invention will become obvious to those skilled in the art. Therefore, it is to be understood that within the scope of the appended claims the invention may be practiced other than as specifically described. For U.S. patent law, rules, and procedures see MPEP. Disclaimer. Information presented on this page while believed to be reliable, is provided "as is" with no warranties of its accuracy or timeliness. 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