Modular Components for Prosthetic Implants

The present invention relates generally to prosthetic implants and pertains, more specifically, to prosthetic implants of the type in which at least one component of the implant is assembled from selected parts to construct a component fitted essentially to the needs of a particular recipient.

More recent developments in the implant of prostheses have shown that it is desirable to have available prosthetic implant components constructed of individual alternate parts so that a surgeon may select certain parts for assembly into a component fitted more closely to the requirements of a particular recipient of the prosthetic implant. Thus, for example, tibial components for prosthetic knee implants have been proposed in which the tibial tray member and the tibial stem member are constructed as separate parts selectively joined together to assemble a complete tibial component. In this manner, one of several alternate tibial tray members may be selected for assembly with one of several alternate stem members to provide an essentially custom fitted tibial component.

Since the performance and effectiveness of a prosthetic implant relies to a considerable extent upon the stability of the components in the implanted prosthesis, it is essential that, once assembled, the parts of each component be joined in an assembly so integrated as to preclude instability among the assembled parts. Thus, it becomes essential that the mechanism which joins together the members of a component, such as the tibial tray member and the stem member of a prosthetic knee implant, does so in a manner which assures the stable integrity of the assembly and maintains that stable integrity throughout the service life of the prosthesis. Further, the joining mechanism must be relatively easy to use, both for assembly at the time of implant and for subsequent disassembly, should it become necessary later to dismantle the component for replacement.

The present invention provides an improvement in a modular component for a prosthetic implant in which the mechanism for joining together the members selected for assembly into an integrated implant component attains improved stability between the assembled members. As such, the present invention attains several objects and advantages, some of which are summarized as follows: Provides improved integrity in the connection between the members selected for assembly into an integrated component of a prosthetic implant so as to provide enhanced stability in the completed assembly; enables ease of assembly for facilitating the joining together of selected parts into an integrated component fitted more closely to the requirements of a particular recipient, without sacrificing the stability provided previously only in unitary, one-piece components; employs a minimum number of individual parts of relatively simple construction for relatively economical manufacture and use; promotes reliability for exemplary performance throughout an extended service life.

The above objects and advantages, as well as further objects and advantages, are attained by the present invention, which may be described briefly as an improvement in a modular component for a prosthetic implant, in which modular component a first member and a second member are joined to establish an integrated implant component, the improvement comprising: a post on one of the members, the post extending longitudinally between a first end and a second end spaced away from the first end in a longitudinal direction, the post including an outer surface having a longitudinally tapered surface portion at least adjacent one of the ends of the post and a further surface portion adjacent the other of the ends of the post; a receptacle in the other one of the members for reception of the post when the members are joined, the receptacle extending between a first end and a second end spaced away from the first end in the longitudinal direction, the receptacle including an inner surface having a first surface portion adjacent one of the ends of the receptacle and generally complementary to the tapered surface portion of the outer surface of the post, and a second surface portion adjacent the other of the ends of the receptacle and for juxtaposition with the further surface portion of the outer surface of the post when the first surface portion of the inner surface of the receptacle is seated against the tapered surface portion of the outer surface of the post; laterally deflectable elements for placement adjacent the further portion of the outer surface of the post and the second surface portion of the inner surface of the receptacle when the first surface portion of the inner surface is seated against the tapered surface portion of the outer surface of the post; and operator means for urging the laterally deflectable elements laterally toward engagement-of the further surface portion of the outer surface of the post with the second surface portion of the inner surface of the receptacle, when the first surface portion of the inner surface is seated against the tapered surface portion of the outer surface, to preclude relative movement between the second surface portion and the further surface portion and thereby stabilize the connection between the first member and the second member in the integrated implant component.

The invention will be understood more fully, while still further objects and advantages will become apparent, in the following detailed description of preferred embodiments of the invention illustrated in the accompanying drawing, in which:

FIG. 1 is an exploded front elevational view of an implant component in the form of a tibial component employing the improvement of the present invention;

FIG. 2 is a front elevational view of the tibial component assembled;

FIG. 3 is a front elevational view of an alternate stem member capable of being selected for assembly as a part of the tibial component;

FIG. 4 is an enlarged, fragmentary cross-sectional view showing a portion of the assembled tibial component;

FIGS. 5 and 6 are further enlarged, diagrammatic views of parts of the implant component, exaggerated to show the mechanism by which the parts are assembled;

FIG. 7 is a top plan view of one of the parts, taken in the direction of the arrow in FIG. 5; and

FIG. 8 is a still further enlarged fragmentary view of a portion of FIG. 6, modified to illustrate an alternate embodiment of the invention.

Referring now to the drawing, and especially to FIGS. 1 and 2 thereof, a modular implant component constructed in accordance with the invention is illustrated in the form of a tibial component 10 for use in a prosthetic knee implant and is seen to include a first member in the form of a tibial tray member 12 and a second member in the form of a stem member 14. The tray member 12 includes a laterally extending tibial tray 16 and the stem member 14 includes a longitudinally extending stem 18. When assembled into an integrated tibial component 10, as seen in FIG. 2, the stem 18 is received within the tibia of a recipient and the tibial tray 16 provides a platform for a tibial bearing member 20, all as is now well known in prosthetic knee implants. Since requirements differ among different recipients, the modular tibial component 10 allows a more accurate fit by enabling the selection of one of several alternate combinations of tibial tray members, stem members and tibial bearing members, as dictated by the requirements of a particular recipient. Thus, for example, the tibial tray member 12 may be assembled with either the stem member 14 or an alternate stem member 22, illustrated in FIG. 3, having a stem 24 of dimensions different from the corresponding dimensions of stem 18. To that end, tibial tray member 12 includes a receptacle 26 and each stem member 14 and 22 includes a post 28 which is received within receptacle 26 for assembly of a selected stem member 14 or 22 with the tibial tray member 12. As seen in FIG. 2, the selected stem member 14 has been assembled with tibial tray member 12 to establish an integrated tibial component 10 for a prosthetic knee implant. The preferred material for the tibial tray member 12 and for the stem member 14 is a biocompatible metal alloy, such as a cobalt-chrome alloy now in common use. The tibial bearing member 20 preferably is constructed of a biocompatible material having appropriate lubricity characteristics, such as a high density polyethylene. An operator member 30 is employed to attain stability in the connection between the tibial tray member 12 and the selected stem member 14, as will be described in detail below.

Turning now to FIG. 4, as well as to FIGS. 1 and 2, receptacle 26 extends longitudinally into the tibial tray member 12 between an open end 32 and a remote end 34 spaced longitudinally away from the open end 32. A longitudinally tapered inner surface 36 extends along the receptacle 26 and includes a first, tapered inner surface portion 38 located adjacent the open end 32 and a second, further inner surface portion 40 located adjacent the remote end 34 of the receptacle 26. Post 28 extends longitudinally from the stem 18 of the stem member 14, between a first, or near end 42 at the stem 18 and a second, or far end 44 spaced longitudinally away from the near end 42. A longitudinally tapered outer surface 46 extends along the post 28 and includes a tapered outer surface portion 48 adjacent the near end 42 and a further outer surface portion 50 adjacent the far end 44 of the post 28. Both the tapered inner surface 36 and the tapered outer surface 46 preferably have a frusto-conical configuration. Upon assembly of the tibial tray member 12 with the stem member 14, the post 28 is received and fitted within the receptacle 26 to effect a secure connection between the tibial tray member 12 and the stem member 14.

In order to attain stability in the connection between the tibial tray member 12 and the stem member 14 in the assembled tibial component 10, a stabilizing mechanism 60 is provided in the connection effected between the post 28 and the receptacle 26. As best illustrated diagrammatically in FIGS. 5 and 6, and in FIG. 7, tapered inner surface 36 of the receptacle 26 is provided with a taper angle R, at least along the inner surface portion 38, while tapered outer surface 46 is provided with a taper angle P, at least along the outer surface portion 48. Taper angle R is no greater than, and preferably is slightly less than, taper angle P so that upon insertion of the post 28 into the receptacle 26, at least the inner surface portion 38, adjacent the open end 32 of the receptacle 28, will engage against and will be seated upon the outer surface portion 48, adjacent the near end 42 of the post 28, as seen in FIG. 5. For example, taper angle R may be about 2.8 degrees while taper angle P is between about 2.8 degrees and about 2.9 degrees, and the relative dimensions of the post 28 and the receptacle 26 are such that the post 28 is fitted into the receptacle 26 with inner surface portion 38 seated against outer surface portion 48. In this manner, reception of the greater length of post 28 fully into receptacle 26 is assured.

A generally cylindrical hole 62 extends longitudinally into post 28 from the far end 44 of the post 28 and a lateral slot 64 intersects the hole 62 to establish laterally deflectable portions of the post 28 comprising elements in the form of annular segments 66 spaced circumferentially around the perimeter of the hole 62 at the far end 44. Operator means include the operator member 30 which has a head 70 and an elongate longitudinal operator portion in the form of a shank 72. Deflector means include a helical thread 74 on the shank 72 for engaging a complementary helical thread 76 in the hole 62, along the annular segments 66. A lateral shoulder 80 extends into receptacle 26 adjacent remote end 34 and confronts a seating face 82 on the underside of the head 70 of the operator member 30.

Upon insertion of the post 28 into the receptacle 26 and seating of the inner surface portion 38 on the outer surface portion 48, as seen in FIG. 5, the operator member 30 is advanced longitudinally into the hole 62 by threading the shank 72 into the hole 62, until the seating face 82 on the head 70 of the operator member 30 engages the lateral shoulder 80. As seen in FIG. 6, further operation of the operating member 30 by continued torque on the operating member 30 will establish an upward longitudinal force UF on the post 28, which upward longitudinal force UF, by virtue of the engagement between the helical threads 74 and 76, will result in laterally outward forces OF on the annular segments 66. These laterally outward forces OF will urge the annular segments 66 in laterally outward directions toward engagement with the inner surface 36 at further inner surface portions 40 and, as illustrated in FIG. 6, will deflect the annular segments 66 laterally outwardly into such engagement. At the same time, the inner surface portion 38 is seated firmly against outer surface portion 48. In order to facilitate the laterally outward forces and deflection of the annular segments 66, the longitudinal extent of the annular segments 66, as established by the depth of slot 64, is greater than the longitudinal extent of helical thread 74 into helical thread 76 when the seating face 82 is seated on lateral shoulder 80 and the annular segments 66 are urged into engagement with inner surface 36. In this manner, any lateral movements, such as rocking or toggling movements, of the tibial tray member 12 relative to the stem member 14 are precluded and stability of the connection between the tibial tray member 12 and the stem member 14 in the integrated tibial component 10 is assured.

Referring now to FIG. 8, an alternate construction is illustrated for further enhancing the mechanism which attains deflection of the annular segments 66. In the embodiment of FIG. 8, the helical thread 76 which extends along the annular segments 66 is modified to include a supplemental wedge ramp 90, similar to that employed in connection with a thread form available commercially under the trademark SPIRALOCK. The employment of the supplemental wedge ramp 90 not only enhances the laterally outward forces on the annular segments 66, thus enhancing the stability provided by engagement of the laterally outwardly deflected annular segments 66 with the inner surface portion 40, but provides a self-locking mechanism for retaining the operator member 30 in place subsequent to completion of the connection between the tibial tray member 12 and the stem member 14.

It will be apparent that the present invention, as described in detail above, attains the several objects and advantages summarized above, namely: Provides improved integrity in the connection between the members selected for assembly into an integrated component of a prosthetic implant so as to provide enhanced stability in the completed assembly; enables ease of assembly for facilitating the joining together of selected parts into an integrated implant component fitted more closely to the requirements of a particular recipient, without sacrificing the stability provided previously only in unitary, one-piece components; employs a minimum number of individual parts of relatively simple construction for relatively economical manufacture and use; promotes reliability for exemplary performance throughout an extended service life.

It is to be understood that the above detailed description of preferred embodiments of the invention are provided by way of example only. Various details of design and construction may be modified without departing from the true spirit and scope of the invention, as set forth in the appended claims.