Prosthetic implant locking assembly

Abstract: The invention relates to a prosthetic implant assembly (10) comprising a base component (12) secured to a bone. Base component (12) includes a generally planar surface (16) having a recessed portion (28) formed therein. A spring clip (30) is situated in the recessed portion (28) of the base component (12). Spring clip (30) includes a tab (34) extending away from the spring clip (30). A bearing component (20) slidably engages the base component (12) to couple the bearing component (20) to the base component (12). The bearing component (12) is formed to include a groove (50) for receiving the tab (34) of the spring clip (30) therein to lock the bearing component (20) in a fixed position relative to the base component (12).

Description: Background and Summary of the Invention The present invention relates to a prosthetic implant assembly as specified in the preamble of claim 1 for attachement to a bone inside the body for replacing a bearing surface. Such an implant assembly is known from US-A-4,257,129. More particularly, the present invention relates to a locking assembly for rigidly attaching a bearing component to a base component which has been attached to a bone. Various methods are known in the art for securing a bearing component to a base component. One such method is disclosed in U.S. Patent No. 4,257,129. In this device, a pin is inserted through a hole in the bearing component and into a base component. A clip member is then inserted into a slot formed in the bearing component. The clip member engages the pin to hold the bearing component in place on the base component. US-Patent No. 4,944,757 shows a design in which a bearing component is fixed to a base component by a rigid boss member protruding from the surface of the base component and a lock key element which is inserted into corresponding groves of the boss member and the bearing component. U.S. Patent No. 4,795,468 discloses another known method for locking a bearing insert to a base support of a prosthetic implant. The implant includes a resilient locking clip which is positioned in a cavity formed on one side of the base support such that when the bearing insert and the base support are assembled together, the clip extends from the cavity to lie within a groove formed on an edge of the bearing insert to secure the two components together. Yet another method of attaching a bearing component to a base component is to compression mold the bearing component onto the base component. The bearing component cannot be removed from the base component without destruction of the bearing component. Therefore, the bearing component cannot be changed without also changing the base component. According to the present invention, a prosthetic implant assembly is provided. The assembly includes a base component including means for securing the base component to a bone and a generally planar surface having a recessed portion formed therein. The assembly also includes spring means situated in the recessed portion of the base component. The spring means includes a tab extending away from the spring means. The assembly further includes a bearing component including means for slidably engaging the base component to couple the bearing component to the base component and means for receiving the tab of the spring means therein to lock the bearing component in a fixed position relative to the base component. The following preferred embodiments may be present individually or in combination. The recessed portion of the implant assembly includes a first section having a predetermined, substantially uniform depth and a second section having a depth greater than the depth of the first section. The spring means includes a spring clip having a thickness substantially equal to the predetermined depth of the first section to provide a cantilevered spring within the recessed portion. The tab extends away from an end portion of the spring clip located within the second section of the recessed portion and the means for receiving the tab includes a groove formed in a bottom surface of the bearing component for receiving the tab therein. The assembly further includes a ramp surface formed along a side of the bearing component in close proximity to the means for receiving the tab. The ramp surface is configured to engage the tab of the spring clip and to force the tab along with a portion of the spring clip downwardly into the second section of the recessed portion as the bearing component slides relative to the base component during installation of the bearing component. The tab and the portion of the spring clip move upwardly toward the bearing component after the receiving means is situated over the tab so that the tab enters the receiving means and locks the bearing component in a predetermined position relative the base component. A hole is provided in the bearing component at a position over the spring clip to provide an access opening to permit the tab to be disengaged from the receiving means to permit removal of the bearing component from the base component. The present invention advantageously provides an assembly for locking a bearing component to a base component which uses few parts and is easy to construct. The bearing component can be rigidly fixed to the base component, but can be easily removed. Therefore, the variety of sizes or styles of bearing components can be inserted onto the base component and inspected to determine which bearing component best fits a patient's particular needs after the base component is implanted in a bone. Brief Description of the Drawings The invention may be best understood by referring to the following detailed description and drawings which illustrate the invention. The detailed description particularly refers to the accompanying figures in which: Fig. 1 is an exploded front elevational view of a preferred embodiment of the present invention illustrating a spring clip situated between a base component and a bearing component; Fig. 2 is a plan view illustrating a top surface of the base component; Fig. 3 is a plan view illustrating a bottom surface of the bearing component; Fig. 4 is a perspective view illustrating the spring clip; Fig. 5 is a sectional view taken through the assembly of the present invention illustrating operation of the locking assembly as the bearing component is being inserted onto the base component; and Fig. 6 is a sectional view similar to Fig. 5 illustrating the bearing component installed on the base component with the tab of the spring clip engaging a groove in the bearing component to lock the bearing component in a fixed position relative to the base component. Detailed Description of the Drawings Referring now to the drawings, Fig. 1 illustrates the assembly 10 of the present invention. The assembly 10 includes a base component 12 for attachment to a bone (not shown). Base component 12 is illustratively a tibial tray for insertion into a tibia bone. Base component 12 includes a tray 14 having a generally planar upper surface 16 and an anchoring stem 18. Base component 12 is configured to receive a bearing component 20 thereon. Base component 12 includes a pair of spaced-apart slide members 22 which are slidably received within a pair of spaced-apart grooves 24 formed in a bottom surface 26 of bearing component 20. Base component 12 is preferably made from a metal alloy such as cobalt-chrome or titanium. Bearing component 20 is preferably made from a polymeric material such as ultra high molecular weight polyethylene (UHMWPE). Base component 12 is formed to include a rectangularly-shaped countersink or recessed portion 28 therein between the slide members 22. Recessed portion 28 is configured to receive a spring clip 30 for locking the bearing component 20 in a fixed position relative to the base component 12. As shown in Fig. 4, spring clip 30 includes a generally planar rectangular body portion 32 and an elongated tab portion or tab 34 extending away from one end of the rectangular body portion 32 of spring clip 30. Tab 34 has a rounded upper surface 35. Spring clip 30 may be made from a variety of implantable materials. These materials include metal alloys or polymeric materials such as UHMWPE. Fig. 2 illustrates the top surface 16 of base component 12. Base component 12 includes an anterior side 36 and a posterior side 38. Slide members 22 extend from the anterior side 36 to the posterior side 38 of base component 12. Recessed portion 28 includes an anterior first section 40 extending from a middle portion of base component 12 illustrated by dotted line 42 toward the anterior side 36 of base component 12. First section 40 has a substantially uniform predetermined depth. Recessed portion 28 also includes a posterior second section 44 extending from line 42 toward the posterior side 38 of base component 12. Second section 44 has a depth greater than the depth of the first section 40. The predetermined depth of the first section is preferably about 0.030 inch (0.762 mm). At the middle portion 42, the depth of recessed portion 28 begins to increase to a maximum depth of about 0.100 inch (2.54 mm) at the extreme posterior end of recessed portion 28. The depths of first and second sections are best illustrated in Figs. 5 and 6. Spring clip 30 is positioned within recessed portion 28 so that the tab 34 is situated in the second section 44 near posterior side 38 of base component 12. Tab 34 extends in a direction opposite the second section 44 of recessed portion 28 and transversal to the main plane of body portion 32. The tab 34 of spring clip 30 is configured to engage a groove 50 formed in bearing component 20 to lock the bearing component 20 in a fixed position relative to base component 12. Therefore, groove 50 provides the means for receiving the tab 34 of the spring means therein. As illustrated in Fig. 3, bearing component 20 includes an anterior side 46 and a posterior side 48. The groove 50 extends in a medial/lateral direction along bearing component 20 at a location near posterior side 48. Grooves 24 for engaging slide members 22 of base component 12 extend from the anterior side 46 to the posterior side 48 of bearing component 20. It will be seen that slide members 22 and grooves 24 are shaped at an angle, inclined, or dovetailed such that, when the slide members are fully engaged in the grooves, the bearing component 20 is held downwardly on the base component 12. Operation of the assembly 10 of the present invention is best illustrated in Figs. 5 and 6. After stem 18 has been inserted into a bone (not shown) to secure base component 12 to the bone, bearing component 20 is inserted onto base component 12 by sliding the grooves 24 of bearing component 20 over the slide members 22 of base component 12. The posterior side 48 of grooves 24 of bearing component 20 are inserted onto the slide members 22 near the anterior side 36 of base component 12. The bearing component 20 slides relative to the base component 12 over slide members 22 in a direction of arrow 52 (Fig. 5). The rectangular body portion 32 of spring clip 30 has a thickness illustrated by dimension 54 in Fig. 4. Thickness 54 is substantially equal to the predetermined depth of the first section 40 of recessed portion 28. Therefore, thickness 54 is preferably about 0.030 inch (0.762 mm). Because spring clip 32 has about the same thickness as the depth of the first section 40 of recessed portion 28, the top surface of the rectangular portion 32 lies generally within the plane of the upper surface 16 of base component 12 and the surface of first section 40 supports the spring clip 30. Spring clip 30 provides a cantilevered spring member inside recessed portion 28 because the second section 44 of recessed portion 28 is deeper than the first section 40 and therefore does not contact the spring clip 30. Spring clip 30 can be secured within the first section 40 of recessed portion 28 if desired by welding, brazing, riveting, or sintering the spring clip within the first section at a position near anterior side 36 of base component 12. Otherwise, the spring clip 30 can simply be placed within the recessed portion 28 without any permanent attachment. Bearing component 20 includes a tapered or ramp-shaped surface 56 extending between the posterior end 48 of bearing component 20 and the groove 50. As bearing component 20 moves in the direction of arrow 52 shown in Fig. 5, ramp surface 56 engages the tab 34 of spring clip and forces the tab 34 in the direction of arrow 58 into the second section 44 of recessed portion 28. Second section 44 is deep enough that tab 34 can be forced in the direction of arrow 58 until the top of tab 34 is in a position even with the planar surface 16. After bearing component 20 is fully inserted onto base component 12 as illustrated in Fig. 6, tab 34 of spring clip 30 springs upwardly in the direction of arrow 60 as spring body 32 returns to its generally planar orientation so that the tab 34 enters groove 50 formed in bearing component 20. Slide members 22 on base component 12 and grooves 24 on bearing component 20 prevent movement of bearing component 20 relative to base component 12 along a medial/lateral axis 62 shown in Figs. 2 and 3 and along a vertical axis because of their inclination discussed above. Spring clip 30 is trapped in recessed portion by bottom surface 26 of bearing component 20 so that spring clip 30 cannot move relative to the base component 12 or bearing component 20. Therefore, by entering and engaging groove 50 in bearing component 20, tab 34 prevents movement of bearing component 20 relative to base component 12 along an anterior/posterior axis 64. A hole or access opening 66 is provided in bearing component 20 near groove 50 at a location situated over spring clip 30. Opening 66 permits a tool (not shown) to be inserted through opening 66 to engage spring clip 30 and press spring clip 30 downwardly into second section 44 of recessed portion 28 to disengage tab 34 from groove 50. This permits removal of bearing component 20 from base component 12. Therefore, bearing component 20 can be exchanged or replaced after it has been installed onto base component 12.

Claims: A prosthetic implant assembly (10) comprising a base component (12) including means (18) for securing the base component (12) to a bone and a generally planar surface (16), a spring clip (30) and a bearing component (20) including means (24) for slidably engaging the base component (12) to couple the bearing component (20) to the base component (12) and means (50) cooperating with the spring clip (30) to lock the bearing component (20) in a fixed position relative to the base component (12), characterised in that said surface (16) has a recessed portion (28) formed therein, said spring clip (30) is situated in the recessed portion (28) of the base component (12), the spring clip (30) including a tab (34) extending away from the spring clip (30) and in that said means cooperating with the spring clip is a means (50) for receiving the tab (34) of the spring clip (30) therein to lock the bearing component (20) in a fixed position relative to the base component (12). The assembly of claim 1, wherein the recessed portion (28) includes a first section (40) having a predetermined, substantially uniform depth and a second section (44) having a depth greater than the depth of the first section (40), the spring clip (30) having a thickness (54) substantially equal to the predetermined depth of the first section (40) to provide a cantilevered spring in the recessed portion (28). The assembly of claim 2, wherein the predetermined depth of the first section (40) is about 0.030 inch (0.762 mm) and the maximum depth of the second section (44) is about 0.100 inch (2.54 mm). The assembly of claim 2, wherein the tab (34) extends away from an end portion of the spring clip (30) located within the second section (44) of the recessed portion (28) and the means (50) for receiving the tab includes a groove (50) formed in a bottom surface (26) of the bearing component (20) for receiving the tab (34) therein. The assembly of claim 4, wherein the spring clip (30) includes a rectangularly shaped body portion (32). The assembly of claim 2, wherein the spring clip (30) is rigidly fixed to the first section (40) of the recessed portion (28). The assembly of claim 2, further comprising means (56) for deflecting the tab (34) of the spring clip (30) into the recessed portion (28) as the bearing component (20) is inserted onto the base component (12). The assembly of claim 7, wherein the deflecting means (56) includes a ramp surface (56) formed along a side of the bearing component (20) in close proximity to the means (50) for receiving the tab (34), the ramp surface (56) being configured to engage the tab (34) of the spring clip (30) to force the tab (34) and a portion of the spring clip (30) into the second section (44) of the recessed portion (28) as the bearing component (20) slides relative to the base component (12) during installation, the tab (34) and the portion of the spring clip (30) moving toward the bearing component (20) after the receiving means (50) is situated over the tab (34) so that the tab (34) enters the receiving means (50) to lock the bearing component (20) in a fixed position relative to the base component (12). The assembly of claim 1, further comprising a hole (66) formed in the bearing component (20) at a position situated over the spring clip (30), the hole (66) providing an access opening to permit the tab (34) to be disengaged from the receiving means (50) of the bearing component (20) so that the bearing component (20) may be removed from the base component (12). The assembly of claim 1, wherein the means (24) for slidably engaging the base component (12) includes first and second spaced-apart grooves (24) formed in a bottom surface (26) of the bearing component (20) for receiving first and second slide members (22), respectively, formed on the base component (12).

Inventors: SMITH TODD S, SMITH, TODD S.
Applicants: DEPUY INC, DEPUY INC.
Application year: 1992
Main classification: A61F2
IPC codes: A61F2