This invention relates to the medical field of orthopaedics and joint replacement. More specifically, the instant invention is directed to a modular shoulder prosthesis which provides the ability to custom fit an artificial joint to a patient's anatomy, and most specifically to the connection between the prosthesis components which secures the components together in a manner which prevents relative movement between the components after assembly.
Artificial joints or prosthesis have now been constructed for almost every natural joint in the living body. As the medical field gains more understanding of the problems involved in mating inanimate constructions with animate tissue and designing mechanical devices that can duplicate natural movement, the number of implantations will continue to increase. Better engineering, accompanied with miniaturization, permits reconstruction of the major joints, such as the hip, knee, shoulder, elbow, wrist and ankle with increased reliability and range of movement. The prosthesis construction of the instant invention may be utilized in all major joints.
The natural tubercle is the broadened area offset from the end of the humerus. The natural tubercle and humeral head may be at any radial angle about the axis of the humerus. This natural angular relationship must be reproduced by the intramedullary rod and the artificial tubercle. The artificial tubercle is seated in the end of the patient's humerus and is the main load bearing element of the prosthesis. It is important that this load, which is mostly compression, is transmitted along the axis of the humerus. A spherically shaped head element is attached to the tubercle element at a fixed angle. The angle between the tubercle and the humeral head should be variable to reproduce the retroversion angle of the patient's natural joint. The humeral head carries cantilevered forces in torque and compression between the glenoid surface and the tubercle. It is important that these forces do not result in relative movement between the tubercle and the humeral head or between the tubercle and the stem.
Shoulder implant prostheses generally consist of a humeral “head” portion of the implant which articulates with the natural or artificial glenoid surface, and a “stem” portion of the implant which provides fixation within the humeral canal. In replacing a shoulder joint, the head of the humerus is removed. The end portion of the humerus is then shaped and prepared for receiving the prosthesis so that the artificial joint will closely approximate the natural shoulder. Early shoulder implants were unitary structures which combined the stem and the head. This construction required large inventories of prostheses to accommodate various sized and shaped anatomies.
Later shoulder implant designs become modular. These modular implants were characterized in that the head independently mated via “taper-lock” connection to the humeral stem. This modularity increased the options for the surgeon by offering significantly more sizes of heads, e.g. ten to twenty heads instead of the three to six heads available in earlier non-modular prostheses and more stems, e.g. five to ten instead of the two to four sizes of stems available in non-modular prostheses. By manufacturing these components with interchangeable connections but different external sizes, inventories may be smaller because of the ability to mix and match components. Also, the modular prosthesis provides more flexibility in customizing the various components of a joint to the various parts of a patient's natural joint.
In a three piece artificial shoulder joint, the stem is further broken into an intermedullary “rod” element and a “body” element. In addition to the head, these components are available in various sizes for customization by the surgeon. The rod is inserted into the end of the humerus. The rod acts as a stabilizer in maintaining the artificial joint in the axis of the humerus. The upper portion of the rod which extends out of the humerus is fitted into a body element which is shaped like the removed broad head of the humerus which it replaces. This element, along with the rod, is used to adjust the length of the prosthesis to approximate the natural length of the humerus. All these elements have a central bore and are permanently secured together by a bolt which is inserted into the body element and is threaded into the upper end of the rod.
With the advantage of flexibility gained by modular prostheses, there comes the requirement that there be no movement between the several parts or elements after implantation. These movements may cause misalignment of the joint resulting in increased pain, trauma to the joint, and even dislocation of the joint. In some cases, the intramedullary rod may be attached to the bone with bone cement while, in other cases the cement is omitted. When the cement is omitted, the placement and fixation of the intramedullary rod becomes more critical to pain free usage of the prosthesis. Further, it is most important that the intramedullary rod not be disturbed after insertion since this would corrupt the union between the rod and the interior of the humerus. In order to maintain the original union between the humerus and the intramedullary rod, modular prosthesis have been developed to allow rotational adjustment of the several parts or elements about the emplaced rod during the placement of the prosthesis to more closely reproduce the natural structure of the shoulder. It has been found that, in some cases, as the intramedullary rod is inserted into the bone canal, there is rotational movement of the rod. In order to preserve the union between the rod and the bone, there must be a mechanism to accommodate the changed angular orientation of the proximal end of the intramedullary rod so that the prosthesis closely approximates the natural tubercle and humeral head.
While the above description refers to a modular shoulder prostheses, substantially the same considerations must be given to other modular prosthesis, such as a knee prosthesis in which an intramedullary rod is placed in the lower end of the femur and in the upper end of the tibia, or the elbow in which an intramedullary rod is placed in the lower end of the humerus and the upper end of the radius or ulna, or a hip prosthesis in which an intermedullary rod is placed in to the upper end of the femur. Because of individual physical anomalies, the functional prosthesis must be capable of angular adjustment to conform to the natural physique.
While the foregoing described prior art devices have improved the art and in some instances enjoyed commercial success, there remains nonetheless a need in the art for a prosthesis that provides rotation for adjustment between the rod and body elements and a fixed connection between the body and neck elements. Such a prosthesis should include juxtapositioned surfaces between the neck and body elements for load support and transfer of load to the rod element. The prosthesis should also include a fixed connection between the neck element and the body element to eliminate rotation therebetween while still providing interchangeability of components for close approximations of various anatomies.
In a particularly preferred embodiment of the instant invention, a modular prosthesis is taught which has an intramedullary rod element which is to be inserted in a bone. The rod has a frustoconically shaped proximal portion which is telescoped into one end of a bore in the prosthesis body element. The distal end of the rod is constructed for insertion into the intermedullary canal of the humerus. The mating surfaces of the proximal portion of the rod and the prosthesis body bore form a rotationally movable connection. A neck element having a tubular protuberance with a contoured perimeter is telescoped into the other end of the body element bore having a conjugately shaped bore until two load-bearing surfaces come into juxtaposed contact. The contoured protuberance extends outwardly from one of the load-bearing surfaces to interlock with a socket formed into the adjacent load-bearing surface to form a rotatably fixed connection. All three elements are locked together by a bolt extending through the neck and engaging the rod, forming a locked integral prosthesis. A head preferrably having a frustoconical bore for telescoping attachment to a second protuberance on the neck forms a rotationally adjustable connection. The head bore may be offset from the center portion of the head and the necks second protuberance may be supplied with various inclinations and/or offsets to facilitate interchangeability for various anatomies.
Accordingly, it is an objective of the instant invention to provide a shoulder joint with an intramedullary rod element which is connected with the body element in such a manner as to allow rotational movement between the elements after insertion of the rod. Rotational movement, in this context, refers to the turning of either element in a plane normal to the common longitudinal axis of the elements.
It is a further objective of the instant invention to provide a connection between the neck and body elements that prevents rotational movement between the elements.
It is a further objective of the instant invention to provide the intramedullary rod with a fluted exterior surface for increasing the surface area of the junction between the rod and the intramedullary canal of the humerus.
It is yet another objective of the instant invention to provide a connection between the body element and the intermedullary rod that includes locking tapers to provide a lockable connection between the elements.
It is a further objective of the invention to provide a connection between the body element and the intramedullary rod that provides a pre-set limit to the combined length of the elements.
It is a still further objective of the instant invention to provide an array of neck elements which allow for adjustment of inclination angle, height and offset.
It is an even further objective of the instant invention to provide a four piece modular shoulder joint prosthesis to provide intra-operative fit selection to build a best-fit shoulder joint.
It is still yet a further objective of the instant invention to provide a connection between the neck and body elements that includes a load-bearing surface to provide load transfer between the elements.
Still a further objective of the instant invention is to provide a neck element having a shaped tubular protuberance sized for telescoping engagement into a conjugately shaped bore formed in the proximal end of the body element bore to form a non-rotatable connection
Other objectives and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying drawings wherein are set forth, by way of illustration and example, certain embodiments of this invention. The drawings constitute a part of this specification and include exemplary embodiments of the present invention and illustrate various objects and features thereof.
While the present invention is susceptible of embodiment in various forms, there is shown in the drawings and will hereinafter be described a presently preferred embodiment with the understanding that the present disclosure is to be considered an exemplification of the invention and is not intended to limit the invention to the specific embodiments illustrated.
Referring to the Figures, various embodiments of the modular shoulder prosthesis 10 are illustrated. The modular prosthesis includes an intramedullary rod 12 which provides stability, a body element 18 which provides load transfer and rigidity, and a neck element 48 which provides a protuberance for mounting the head element 68. The rod has a distal end 12 and a proximal end 14 (
The body element 18 is mounted on the proximal end of the intramedullary rod. The body element has a through bore portion 20, through which the proximal end 14 of the intramedullary rod is inserted. As shown in
In a most preferred embodiment the self-holding taper is a morse type taper, however it should be noted that other self-holding tapers well known in the art such as the American National, Jacobs, Jarno, Brown and Sharp, British Standard and suitable combinations thereof may be utilized without departing from the scope of the invention.
Once inserted, the intramedullary rod 12 provides stability and the body 18 acts as the load bearing element for the articular head 68. The body 18 is shaped like the natural humerus head and has an outer diameter that is preferably larger than the intramedullary rod 12 at the distal end. The distal end 38 of the body 18 is inserted into the intramedullary canal. This junction of the body and the shaft of the femur is the primary load carrying connection between the prosthesis and the patient's body. The body flares to a larger diameter proximal end 40 which has a substantially planar load-bearing surface 42 containing a contoured interlocking socket 44 that is constructed and arranged to cooperate with the neck element 48. As shown in
Referring generally to the Figs., the neck 48 has a partially cylindrical body 64 with a laterally extending second protrusion 66 having a self-holding tapered shape for fixable engagement with a head element 68. This protrusion 66 carries the head element for an artificial shoulder and can be specifically set at different inclination and retroversion angles, as shown in
One embodiment of the prosthesis is assembled by turning the threads of the bolt 36 into the threads of the intramedullary rod 12. As these cooperating screw threads tighten, the elements of the prosthesis are drawn together forcing the load bearing surfaces into intimate contact and forcing the tapered proximal end of the rod into a friction fit with the tapered bore of the body and the body to a stop limit on the intramedullary rod. In the final disposition, the body and the intramedullary rod are locked together over a major part of the length of each and the neck is locked to the rotationally immovable body at a specific retroversion angle by the first protrusion and socket arrangement.
Referring to
All patents and publications mentioned in this specification are indicative of the levels of those skilled in the art to which the invention pertains. All patents and publications are herein incorporated by reference to the same extent as if each individual publication was specifically and individually indicated to be incorporated by reference.
It is to be understood that while a certain form of the invention is illustrated, it is not to be limited to the specific form or arrangement herein described and shown. It will be apparent to those skilled in the art that various changes may be made without departing from the scope of the invention and the invention is not to be considered limited to what is shown and described in the specification and any drawings/figures included herein.
One skilled in the art will readily appreciate that the present invention is well adapted to carry out the objectives and obtain the ends and advantages mentioned, as well as those inherent therein. The embodiments, methods, procedures and techniques described herein are presently representative of the preferred embodiments, are intended to be exemplary and are not intended as limitations on the scope. Changes therein and other uses will occur to those skilled in the art which are encompassed within the spirit of the invention and are defined by the scope of the appended claims. Although the invention has been described in connection with specific preferred embodiments, it should be understood that the invention as claimed should not be unduly limited to such specific embodiments. Indeed, various modifications of the described modes for carrying out the invention which are obvious to those skilled in the art are intended to be within the scope of the following claims.
The instant invention is related to U.S. Pat. No. 6,299,648 entitled Locking Hip Prosthesis, U.S. Pat. No. 6,355,068 entitled Sight Gauge Modular Joint and Method, U.S. Pat. No. 6,440,171 entitled Double D Locking Prosthesis, U.S. Pat. No. 6,692,530 entitled Split Sleeve Modular Joint and U.S. Pat. No. 7,033,399 entitled Welded Hip Prosthesis, the contents of which are incorporated herein by reference.