Alignment guide for insertion of fluted or keyed orthopedic components

Abstract: An alignment guide (10) and method is provided for assisting the insertion of a stem (30) of a prosthetic orthopedic implant (50) into a prepared bone cavity (21). A preferred embodiment provides an alignment guide (10) for aligning a fluted (31) stem (30) of a femoral hip stem (30) of a hip joint prosthesis (50) to be inserted into a prepared femoral canal (22). Other keyed features on an implant (50) may also be used for alignment of the implant (50) insertion.

Description: FIELD OF THE INVENTION The present invention relates to a device for assisting the insertion of a prosthetic implant into a bone in a proper alignment. BACKGROUND OF THE INVENTION Stems are used in prosthetic joint implants to anchor the implant in a bone cavity. The bone for receiving the stem is typically prepared by drilling a hole in the bone and creating an opening sized and contoured to receive the stem of the implant. The stem is inserted into a prepared cavity of a bone and a joint bearing surface attached or coupled to the stem, extends out to the cavity. Many stems are fluted, i.e., they have distally extending longitudinal grooves in the stems that provide greater stability and anchoring of the stem once it is inserted into the prepared cavity. A distally extending longitudinal portion between two such grooves is a rib. Typically, once a fluted stem is inserted into a prepared cavity, it is extremely difficult to rotate the stem to properly reorient it. In order to do so the stem must be removed and reinstated which can damage bone and increase operative time. Typically, the stem is aligned by marking the bone and the stem and using the marks to align the stem with respect to the bone. The drawback to this method is the potential imprecision in the alignment. Because the landmark on the stem and bone are not in close proximity to each other, parallax and other problems associated with alignment by eye may result. Also, the stem may move from its aligned position as it is inserted. Accordingly, it is an object of the present invention to provide a means for aligning a fluted stem of an orthopedic implant prior to and as it is being inserted into a prepared bone cavity. In EP-A-0342014, and in W088/01854, there is shown a sleeve which is inserted into a prepared bone cavity for guiding insertion of a femoral implant. The sleeve permits axial insertion whilst restricting rotational movement. When the implant is inserted, the sleeve is retained within the bone cavity. SUMMARY OF THE INVENTION According to the invention, there is provided a removable alignment guide adapted to guidingly insert a keyed component of an orthopedic prosthesis into a prepared bone cavity, as set forth in claim 1 of the accompanying claims. Further aspects of the invention are set forth in claims 2 to 13 of the accompanying claims. The bone may be prepared by removing bone material from the bone canal and by machining an opening of a predetermined shape in the bone cavity. Preferably, the key element of the alignment guide corresponds to the keyed component in a manner which provides contact with a small area of the stem. The alignment guide may be formed generally in a broken circle or circumference to allow flexibility in removing the alignment guide. The means for removing the alignment guide from the stem may, for example, be a tab or protrusion or an opening for inserting a tool to pry out the guide DETAILED DESCRIPTION OF THE DRAWINGS Figure 1 illustrates an exploded perspective view of a bone with a partial break away of a prepared cavity, an alignment guide and an implant inserted through the alignment guide; Figure 2 illustrates a perspective view of the bone, alignment guide and implant of Figure 1 with the alignment guide in place and the implant inserted partially into the bone through the alignment guide; and Figure 3 illustrates a perspective view of the alignment guide of the present invention. DETAILED DESCRIPTION OF THE INVENTION The following is a description of a preferred embodiment of the present invention in use with a hip stem implant. Referring now to Figures 1 through 4 an alignment guide 10 is illustrated. The alignment guide 10 comprises a body, a guide portion 12, and an opening 14. The body and guide portion 12 form an outer shape that will correspond to at least a portion of a machined cavity 21 in the bone 20. The guide portion 12 has an inner circumference 15 having grooves or notches 16 for receiving ribs 31 of the stem 30 of an implant 50. Protrusions 13 in the guide portion 12 may contact the stem 30 of the implant 50. In this embodiment, the grooves 16 and the protrusions 13 form a key for guiding insertion of the stem 30 into the bone cavity. In variations of this embodiment grooves 16, protrusions 13 or the like may be used alone or together to key insertion of the keyed stem 30. Figure 1 illustrates a prepared bone 20 having a machined cavity 21 and a longitudinal cavity 22 formed in the canal of the bone. At least a portion of the machined cavity 21 has a shape corresponding to the shape of the alignment guide 10. Figure 1 further illustrates an implant 50 comprising a stem 30 having ribs 31 distally extending along the length of the stem 30; a protrusion or proximal geometry 35 shaped to fit within the machined cavity 21 of the bone; and a neck 33 extending from the proximal end of the implant for receiving a ball portion of a ball and socket joint. The notches 16 in the inner circumference 15 of the guide are placed so that when the stem 30 is inserted into the alignment guide 10, the ribs 31 of the stem 30 fit within the notches 16 in the alignment guide 10 to hold or guide the stem 30 in an appropriate or aligned position within the bone cavity. In this embodiment the shape of the machined bone cavity 21 is generally tapered to form an elliptical end portion 23. The alignment guide 10 is similarly shaped with the body forming an elliptical end portion 18 on the proximal end of the body. The implant 50 as well includes a similarly shaped proximal section with an elliptical end portion 34. The bone cavity 21, further comprises a cut 24 corresponding to tapers 19, 35 on the alignment guide 10 and the implant 50 respectively. The cut 24 of the bone cavity 21 and the taper 19 of the alignment guide 10 prevent the alignment guide 10 from being inserted too far into the bone cavities 21, 22. The cut 24 of the bone cavity 21 and the taper 35 of the implant 50 similarly prevent the implant 50 from being inserted too far into the bone cavities, 21, 22 and thus prevent the neck 33 from being in an improper position. In use, the alignment guide 10 is inserted into the machined bone cavity 21 with the elliptical end portion 18 of the alignment guide 10 in alignment with the elliptical end portion 23 of the machined cavity 21. The stem 30 of the implant 50 is placed in the inner circumference 15 of the guide portion 12 of the alignment guide 10 with the elliptical end portion 34 of the implant 50 generally in line with a groove 9 across the elliptical end portion 18 of the alignment guide 10. In order to insert the implant 50 properly aligned, the proximal geometry 32 is generally aligned so that it will fit within the machined bone cavity 21. The ribs 31 are placed within the notches 16 of the guide portion 12 and the implant 50 is driven into the bone cavity 22 guided by the alignment guide 10. Once the stem 30 is inserted in the guide 10, the position or orientation is held true until the stem 30 is seated into the bone cavity 22. As the stem 30 is inserted, the ribs 31 form a path within the bone cavity 22 that the stem 30 will generally follow during the insertion of the final segment of the stem 30. When the implant 50 is generally in the bone cavities 21, 22 but prior to complete insertion, as illustrated in Figure 2, the alignment guide 10 is removed, for example, by inserting a device into the opening 14 in the guide 10 or by pulling the tab or protrusion to remove the guide from the bone cavity 21 and from the stem 30 of the implant 50. The implant 50 is then further driven into place with the elliptical end portion 34 fitting within the elliptical end portion 23 of the bone and the taper 35 abutting adjacent a cut 24 of the bone cavity 21. Although the alignment guide of the present invention is described with respect to a particular embodiment, i.e., in use with a fluted hip stem using the ribs of the stem as a key or reference, it will be apparent to those skilled in the art that various modifications may be made without departing from the character and scope of the invention as defined by the appended claims. For example, the insertion guide may be used to assist the insertion of any stem like component having a keyed feature on the outer surface of the stem to key the insertion of the stem in a properly selected aligned position. The alignment guide may have any number of indentations or protrusions to key in the proper insertion of the stem of the implant

Claims: A removable alignment guide (10) adapted to guidingly insert a keyed component (30) of an orthopedic prosthesis (50) into a prepared bone cavity (21,22), the alignment guide being removable when the prosthesis (50) is inserted in the bone cavity (21, 22) and comprising: a body having an outer shape corresponding to at least a portion (21) of the prepared cavity; an inner portion (12) of said body for receiving said keyed component (30), said inner portion (12) comprising a key element (13;16) formed therein for engageably receiving said keyed component (30). The alignment guide of claim 1 adapted to receive a keyed stem (30) of a prosthetic joint (50). The alignment guide of claim 2 wherein said key element comprises at least one groove (16). The alignment guide of claim 2 or claim 3 wherein said key element comprises at least one protrusion ( 13). The alignment guide of claim 3 wherein said keyed component (30) comprises at least one rib (31) extending longitudinally on said stem (30). The alignment guide of any one of claims 2 to 5 wherein said stem (30) is fluted, and said key element (13;16) of said inner portion (12) comprises an inner wall (15) adapted to engageably receive at least one rib (31) of said fluted stem component (30). The alignment guide of claim 6 wherein said key element comprises a plurality of grooves (16) formed in said inner wall (15) for receiving a plurality of ribs (31) of said fluted stem component (30). The alignment guide of claim 6 wherein said key element comprises a protrusion (13) for engaging said stem component (30) in a predetermined position. The alignment guide of any preceding claim wherein said alignment guide further comprises means (14) for removing said guide (10) from said stem (30). The alignment guide of any preceding claim wherein said alignment guide further comprises means (14) for removing said guide (10) from the proximal cavity (21) of the bone (20). An alignable prosthetic orthopedic implant system comprising: a prosthesis (50) comprising: a stem (30) having a proximal portion (33,35); a distal portion (30) and at least one rib (31) extending along the stem (30); said proximal portion (33,35) comprising a proximal geometry (35) shaped to conform to a proximal cavity (21) formed in a bone (20) to receive the prosthesis (50); and an alignment guide (10) being removable when the prosthesis (50) is inserted in the bone cavity (21) and comprising: a body having an outer shape corresponding to the proximal cavity (21) of the bone (20), an opening in said body for receiving the fluted stem (30) of said prosthesis, said opening forming an inner wall (15) having at least one groove (16) therein for receiving at least one rib (31) of said stem (30). The implant system of claim 11 wherein said alignment guide (10) further comprises means (14) for removing said guide from said stem (30). The implant system of claim 11 or 12 wherein said alignment guide (10) further comprises means (14) for removing said guide from the proximal cavity (21) of the bone (20).

Inventors: MANASAS MARK, MANASAS, MARK
Applicants: DEPUY PRODUCTS INC, DEPUY PRODUCTS, INC.
Application year: 1997
Main classification: A61F2
IPC codes: A61F2