TIBIAL PROSTHESIS

Abstract: A tibial prosthesis (10) includes a tibial tray (11) and a stem (25). The stem (25) has a cylindrical section (39) and a tapering section (40). Fins (41) extend longitudinally from the proximal end to the distal end of the stem (25), tracking both the cylindrical and tapering portions (39, 40) thereof so that each of the fins (41) tracks a uniform diameter section of the stem (25) for a majority of its length. The tapering section (40) of the stem (25) is equal to about one third of its overall length, and defines the distal end of the stem. The fins (41) are longitudinally placed about the stem exterior surface, and are generally parallel. Between the fins are U-shaped channels (42) that are similarly longitudinally extending and generally parallel. The stem (25) provides a central longitudinal axis. The fins (41) and channels (42) are parallel to the central longitudinal axis of the stem (25).

Description: TIBIAL PROSTHESIS The present invention relates to orthopedic prosthetic devices and more particularly to an improved prosthesis for replacing a portion of a patient's knee joint. Even more particularly, the present invention relates to an improved tibial prosthesis that is modular, having a removable metaphyseal stem portion that includes a cylindrical section and a tapering section, and wherein parallel fins extend continuously from the proximal to the distal end of the metaphyseal stem, tracking first the cylindrically shaped section and then the tapering section. A number of tibial components have been patented that relate to tibial components having a tray, and a stem portion that provides initial fixation when the prosthesis is implanted. An example of a modular tibial support is seen in the Elias Patent 5,246,459 entitled "Modular Tibial Support Pegs for the Tibial Component of a Prosthetic Knee Replacement System". The Elias Patent discloses a modular tibial support peg operable to secure a tibial component of a knee joint prothesis to a tibia having a groove. The modular tibial support peg includes a cylindrical body with a ridged outer surface operable to engage the groove in the tibia. The modular tibial support peg further includes a plurality of spikes extending inferiorly from the cylindrical body. The spikes are operable to engage the tibia at the inferior end of the groove. U.S. Patent 5,137,536 issued to Tomihisa Koshino describes a tibial component for an artificial knee joint. The tibial component includes a plate section having an upper surface and a pair of bearing surfaces parts that are adapted to be in sliding contact with a femoral component. A stem portion extends downwardly from a lower surface of the plate section. A pair of blade like members extend obliquely and posteriorly from the stem. The plate section has a lower surface with a plurality of elongated grooves for improving affinity with respect to the surrounding bone, the grooves including a first group of grooves and a second set of group of grooves extending perpendicularly to the first group of grooves. A British Patent 2,192,543A discloses a peg for use in prosthetic devices. A peg of metal or ceramics is defined as being suitable for use as a fixator and/or a bone strengthener in connection with a prosthetic device. The peg has a portion of generally tapered form that increases in cross section from an insertion end. The surface of the tapering end portion has alternating ridges along its length extending therearound, each successive ridge as one moves away from the insertion end having an outer surface spaced by a comparatively small amount at a greater distance from the axis of the peg then the outer surface of the preceding ridge. The peg may be discrete or form a part of a prosthetic device. U.S. Patent 4,938,769 issued to James Shaw discloses an end bone anchorage assembly for a tibial prosthesis that includes an axially elongated central stem and a plurality of elongated fixation pegs spaced from the stem. The stem and the pegs have proximal and distal ends. The proximal ends of the stem define an attachment table. A plurality of structural links interconnect the pegs and the stem. Means is provided for removably attaching a tibial tray to the assembly wherein each of the pegs is connected to the stem by the structural link. The Bolesky et al. patent 4,479,271 entitled "Prosthetic Device Adapted to Promote Bone/Tissue Ingrowth" discloses a tibial component that includes a table and at least one porous metal stem protruding from the lower base surface of the bottom base layer of the table wherein the outer surface of the protruding stem is adapted to be in direct contact with the prepared bone surface to promote the ingrowth of bone and/or tissue and wherein each of the protruding porous metal stems includes a bore therethrough which extends from the distal end of the stem through the upper surface of the bottom base layer of the table. The Murray patent 4,016,606 discloses a knee prosthesis that includes a tibial component with a tray and with a stem adapted to be received in a longitudinal bore in the patient's femur. The stem has one end that is integral with a depending generally spheroidal surface having generally the same radius as the radius of the spheroidal depression in the insert. When implanting a tibial tray (eg. porous or cemented), it is extremely important to get excellent initial fixation. The implant must be able to resist forces that rotate, shear, or tilt the component. The present invention provides an improved stem, for use with a tibial component and which provides the ability to resist the forces of rotation, shear, and tilt. According to the invention, a tibial prosthetic knee component comprises a tibial tray for replacing a portion of the patient's proximal tibia; a stem portion having proximal and distal end portions, the stem defining a projection from the tray, forming an angle therewith, for anchoring the tibial tray to the proximal tibia; the stem comprising a generally cylindrically shaped proximal portion, a tapered distal portion and a plurality of generally parallel circumferentially spaced fins extending substantially the length of the stem. Thus, the present invention provides an improved tibial prosthesis with excellent initial fixation. The metaphyseal tibial stem of the present invention provides rotational, shear and tilting resistance for an implanted tibial component. The apparatus of the present invention includes a tibial tray for replacing a portion of the patient's proximal tibia. The stem has proximal and distal end portions and defines a projection from the under surface of the tray, forming an angle therewith. The stem is provided for anchoring the tibial tray to the proximal tibia. The stem may include a connection for attaching the stem to the tray in modular fashion. This allows multiple stems of differing size to form a kit that allows the surgeon to select a particular sized stem for connection to the tibial tray that fits the patient best. The stem includes a generally cylindrically shaped proximal portion and a gradually tapering distal portion. A plurality of longitudinally extending, generally parallel and circumferentially spaced fins extend along the stem and substantially the full length of the stem. Thus, each of the fins tracks the cylindrically shaped proximal portion and then angles to track the gradually tapering portion. In a preferred embodiment, the gradually tapering distal portion of the stem is conically shaped. The stem may have a hollow cylindrical portion with a generally tubular inner bore. The proximal and distal sections of the stem are integrally joined at a transition portion of the stem in the preferred embodiment. Each of the fins then has an outer edge that includes first and second linear sections that define an obtuse angle therebetween. In the preferred embodiment, this angle is greater than 90 and less than 180 degrees. The stem preferably provides a generally flat distal tip that defines the lower end of the stem and the end of the conically shaped portion. The fins are preferably equally spaced apart around the circumference of the stem. The fins may be separated by a longitudinal, generally U- shaped channel. Each of the fins preferably includes a pair of surfaces extending longitudinally between the proximal and distal ends. The fins are preferably generally triangularly shaped in transverse cross section. As each fin extends along the tapered section, the pair of surfaces of each fin preferably become narrower, resulting in a sharp edge prior to reaching the flat distal tip of the stem which edge may be less sharp proximally than distaily. At least one circumferential portion of the stem may be without fins. The tibial prosthesis is preferably supplied in modular form so that a suitable prosthesis may be assembled to suit an individual patient. Thus, in this form, the tibial tray and stem portion may be supplied separately and the stem is provided with a means for removably attaching it to the tibial tray. Such means may comprise a taper locking arrangement. For a further understanding of the nature and objects of the present invention, reference should be had to the following detailed description, which is given only as an example of the present invention, taken in conjunction with the accompanying drawings, in which like parts are given like reference numerals, and wherein: FIGURE 1 is a perspective exploded view of the preferred embodiment of the apparatus of the present invention; FIGURE 2 is a fragmentary end view of the stem portion of the preferred embodiment of the apparatus of the present invention; FIGURE 2A is a cross section through the conical section of the stem portion taken along lines 2A-2A of Figure 1 ; FIGURE 2B is a cross section taken along lines 2B-2B of Figure 1 and including an overlay of Figure 2A, thus illustrating the tapering of the stem and the changing thickness of the fins; FIGURE 3 is fragmentary sectional view of the preferred embodiment of the apparatus of the present invention illustrating the stem portion thereof; FIGURE 4 is a perspective view of the preferred embodiment of the apparatus of the present invention; FIGURE 5 is a perspective view of the preferred embodiment of the apparatus of the present invention; FIGURE 6 is a sectional view taken along lines 6-6 of Figure 5; FIGURE 7 is a partial perspective cutaway view of the preferred embodiment of the apparatus of the present invention illustrating the stem portion thereof; FIGURE 8 is another partial perspective cutaway view of the preferred embodiment of the apparatus of the present invention illustrating the stem portion thereof; FIGURE 9 is a partial elevational view of the preferred embodiment of the apparatus of the present invention illustrating various sized and shaped stem portions thereof; and FIGURES 10-12 are schematic elevational views that demonstrate the surgical method of implanting the preferred embodiment of the apparatus of the present invention. FIGURES 1 -6 illustrate the preferred embodiment of the apparatus of the present invention designated generally by the numeral 10. Tibial prosthesis 10 includes a transversely extending tibial tray 11 having a proximal surface 12 and a distal surface 13. As is known in the art, the distal surface 13 faces the proximal end of the patient's tibia after the proximal end of the patient's tibia has been surgically prepared with a transverse cut. The tibial tray 11 provides a peripheral surface 14 that is shaped to conform to the prepared surface of the proximal tibia. A plurality of openings 15 can be placed through the tray 11 , communicating with both the proximal 12 and distal 13 surfaces. Openings 15 are receptive of one or more bone screws for attaching the prosthesis 10 to the patient's proximal tibia. A plurality of bone spikes 16 extend from distal surface 13 forming an angle therewith, preferably about ninety degrees (90°). Distal surface 13 can provide a bone attachment surface 17 such as for example a beaded surface. At the central portion of distal surface 13, post 18 extends therefrom at an angle of about ninety degrees (90°). Post 18 includes a larger diameter section 19 and a smaller diameter section 20 that has a taper. An annular conical shoulder 21 defines a transition between larger diameter section 19 and smaller diameter tapered section 20. Post 18 has a flat surface 22 portion on the outer surface of larger diameter section 19, and extending to annular shoulder 21 as shown in Figure 1. As will be described more fully hereinafter, flat surface 22 cooperates with a similar flat surface of a modular metaphyseal stem 25 to prevent incorrect assembly of the metaphyseal stem 25 relative to post 18. Post 18 has a flat circular end portion 23 that defines the distal end of post 18. Post 18 attaches to tibial tray 11 at joint 24 that can be welded for example or post 18 and tray 11 can be machined as one piece. The bone attachment surface 17 can extend over joint 24, and partially to larger diameter section 19. Metaphyseal stem 25 (Figures 1 , 2, 2A-2B, 3, 4 and 7-9) provides a proximal end 26 and a distal end 27. Stem 25 has a closed end bore 28. Bore 28 has a closed end portion 29 and an open portion 30. Bore 28 is similarly sized and shaped to post 18 for receiving post 18 upon assembly of metaphyseal stem 25 thereto. Thus, bore 28 provides a larger diameter section 31 , an annular shoulder 35 defining a transition section, a small tapered diameter section 32, an annular shoulder 32A defining a transition section, and a conical end portion 33. Internal threads can be provided to closed end portion 29. The corresponding flat surfaces 22, 34 ensure proper assembly of stem 25 relative to post 18. The corresponding smaller diameter sections 20 and 32 are annular wedge shaped sections that engage upon assembly so that a wedge lock or morse taper lock fit is achieved between stem 25 and post 18 when stem 25 is „„ . ,„ 96/23459 9 placed over post 18 and loaded onto post 18 with an impact driver for example. In use, the impact driver would be used to transfer load to metaphyseal stem 25 at flat distal surface 36. In the preferred embodiment, there can be multiple metaphyseal stems 25A-25C of differing size as shown in Figure 9. The flat distal surface 36 of the metaphyseal stems 25A-25B shown in Figure 9 are of a larger diameter than the flat distal surface 36A for the metaphyseal stem 25C shown in Figure 9. Each of the flat metaphyseal stems 25 have a longitudinally extending flat surface 37 that begins at proximal end 26 of metaphyseal stem 25 and extends to an annular transition portion 38 of stem 25 as shown in Figures 5-6. The annular transition portion 38 is positioned between a generally cylindrical section 39 of metaphyseal stem 25 and a tapering section 40 of metaphyseal stem 25. The tapering section 40 can be frustroconically shaped as shown in Figures 1 , 3-9. By providing a cylindrical section 39 of generally constant diameter, the surgeon can drill a cylindrically shaped opening in the patient's cancellous bone tissue to receive stem 25 that is smaller in diameter than the outer diameter of cylindrical section 39. The tapering section 40 first enters the surgically formed opening, registering the metaphyseal stem 25 in the proper location. Thereafter, continued driving of the prosthesis 10 into the patient's tibia causes the plurality of fins 41 to cut into the cancellous bone. A plurality of channels 42 (Figures 2, 2A, 2B, 5, 7 and 8) are defined between the plurality of fins 41. Fins 41 are circumferentially spaced and generally parallel to one another. In the preferred embodiment the channels are generally U-shaped, extend longitudinally, and are generally parallel to one another. The fins 41 and channels 42 are circumferentially spaced about the central longitudinal axis 43 of metaphyseal stem 25. In Figures 2A- 2B fins 41 can be seen as having sharp edges 44 at frustroconical tapering section 40 and blunt edges 45 at cylindrical section 39. The bone is prepared to receive the metaphyseal stem by punching a plug into the bone (perpendicular to the plane of the cut) that creates a hole 46 that is for example 12-14 mm in diameter and 40-50 mm deep. The device is then driven into this hole as shown in Figures 10-12. Notice in Figure 11 that the hole 46 has a diameter smaller than the diameter of stem cylindrical section 39. This allows the fins 41 to bite into surrounding bone tissue that is adjacent hole 46. The following table lists the parts numbers and parts descriptions as used herein and in the drawings attached hereto. PARTS LIST Part Number Description 10 tibial prosthesis 11 tibial tray 12 proximal surface 13 distal surface 14 peripheral surface 15 openings 16 bone spikes 17 bone attachment surface 18 post 19 larger diameter section 20 smaller diameter tapered section 21 annular shoulder 22 flat surface 23 circular end 24 joint 25 metaphyseal stem 25A metaphyseal stem 25B metaphyseal stem 25C metaphyseal stem 26 proximal end 27 distal end 28 bore 29 closed end of bore 30 open end of bore 31 larger diameter section 32 smaller diameter tapered section 32A flat annular surface 33 conical section 34 flat surface 35 flat annular surface 36 flat distal surface 36A flat distal surface 37 flat longitudinal surface 38 annular transition portion 39 cylindrical section 40 tapering section 41 fins 42 channels 43 central longitudinal axis 44 sharp edges 45 blunt edges 46 surgically formed opening T tibia

Claims: CLAIMS 1. A tibial prosthetic knee component comprising: a) a tibial tray for replacing a portion of the patient's proximal tibia; b) a stem portion having proximal and distal end portions, the stem defining a projection from the tray, forming an angle therewith, for anchoring the tibial tray to the proximal tibia; c) the stem comprising a generally cylindrically shaped proximal portion and a tapered distal portion; and characterised in that a plurality of generally parallel circumferentially spaced fins extend substantially the length of the stem. 2. A tibial prosthetic knee component as claimed in claim 1 wherein the fins have tips that are sharp at the distal portion of the stem to cut the bone. 3. A tibial prosthetic knee component as claimed in claim 2 wherein the fin tips become less sharp proximally. 4. A prosthesis as claimed in any of the preceding claims wherein the fins are equally spaced apart. 5. A prosthesis as claimed in any of the preceding claims wherein the fins extend from a hollow cylindrical portion of the stem having a generally tubular inner bore. 6. A prosthesis as claimed in any of the preceding claims wherein the fins are generally triangularly shaped in transverse cross section. 7. A prosthesis as claimed in any of the preceding claims wherein the stem is removably attached to the tray. 8. A prosthesis as claimed in claim 7 further comprising taper locking means for removably attaching the stem to the tray. 9. A prosthesis as claimed in either claim 7 or claim 8 wherein said tibial tray and said stem portion are supplied as parts of a modular tibial prosthetic knee component. 10. A prosthesis as claimed in claim 9 wherein a plurality of said tibial trays and said stems are supplied together as a kit for assembling a modular tibial prosthetic knee component. 11. A prosthesis as claimed in any of claims 1-6 wherein the stem and tray are integral. 12. A prosthesis as claimed in any of the preceding claims wherein there are at least 3 fins. 13. A prosthesis as claimed in any of the preceding claims wherein the proximal section and distal sections are integrally joined at a transition portion. 14. A prosthesis as claimed in any of the preceding claims wherein each fin has an outer edge that includes proximal and distal linear sections that define an obtuse angle therebetween. 15. A prosthesis as claimed in claim 14 wherein the angle is greater than 90 and less than 180 degrees. 16. A prosthesis as claimed in any of the preceding claims wherein each fin is separated by a longitudinal channel. 17. A prosthesis according to claim 16 wherein the channels are equally spaced apart. 18. A prosthesis as claimed in any of the preceding claims wherein the stem further comprises a flat surface extending longitudinally along at least a part of the length of the stem. 19. A prosthesis as claimed in claim 18 wherein the longitudinal flat surface is between about 0 and 40 mm wide. 20. A prosthesis as claimed in claim 18 or 19 wherein the flat surface is generally parallel to the fins. 21. A prosthesis as claimed in any of the preceding claims wherein the stem has a flat distal tip. 22. A prosthesis as claimed in any of the preceding claims, wherein the fins are spaced circumferentially apart about 3 to 180° (3-180 degrees). 23. A prosthesis as claimed in any of the preceding claims, wherein the fin height measured from the core diameter of the cylindrical section to the outer edge portion of the fin is 2 mm to 40 mm.

Inventors: CARLS THOMAS A, EVANS DAVID L, JOHNSON CHRIS E, CARLS, THOMAS, A., EVANS, DAVID, L., JOHNSON, CHRIS, E.
Applicants: SMITH & NEPHEW RICHARDS INC, SMITH & NEPHEW RICHARDS INC.
Application year: 1996
Main classification: A61F2
IPC codes: A61F2