CA2101941C

CA2101941C - Method for implanting a patellar prosthesis

Info

Publication number: CA2101941C
Application number: CA002101941A
Authority: CA
Inventors: W. E. Michael Mikhail
Original assignee: Individual
Current assignee: Individual
Priority date: 1991-02-08
Filing date: 1992-02-06
Publication date: 1995-11-14
Anticipated expiration: 2012-02-06
Also published as: EP0570500A1; ZA92876B; US5284482A; CA2101941A1; AU651044B2; DE69227761D1; JP2567191B2; ATE173908T1; AU1376092A; US5180384A; EP0570500A4; DE69227761T2; WO1992013503A1; JPH06507325A; EP0570500B1

Abstract

A method for preparing a patella for receiving a patellar implant and for implanting a prosthesis (24) therein. An elongat-ed passageway (76) is formed in the patella which is then reamed to form a cavity (22) of a size and configuration to receive the patellar prosthesis (24) using a cannulated reamer (10) telescoped over a guide rod (50) positioned in the elongated passageway (76).

Description

~ 1 21 0 1 94 1 22236-587 DESCRIPTION
APPARATUS FOR PREPARING A PATELLA TO RECEIVE A PATELLAR PROSTHESIS
BACKGROUND OF THE INVENTION
The present invention is directed to apparatus for preparing a patella to receive for implanting a patellar prosthesis.
In total knee replacement surgery, a prosthesis is provided in which one component is fastened to the distal end of the femur which has been resectioned and another component is fastened to the proximal end of the tibia which has been resectioned so that the two components will act together in permitting the leg to bend and straighten out. In performing such surgery, the patella is not normally replaced but rather is resected such that the interior crown portion facing the condyles is cut and reamed to form a cavity in which a patellar prosthesis is implanted. The patellar prosthesis has a crown facing inwardly to engage the patellar or trochlear groove of the femoral component.
Heretofore, in preparing a patella for an implant, it was necessary to engage the patella with a clamp having a circular cross-sectional configuration and, using the interior surface of the clamp as a guide, ream a cavity in the patella of sufficient size to receive the patellar implant intended to be used.
Depending upon a number of factors including the size of the patient, the patellar implant could be one of a number of different sizes. As a result of this, it was necessary to have available a number of clamps each having a different diameter for guiding various size reamers. Typical prior art methods of `-- 21 01 941 forming a cavity for implanting a patellar prosthesis are shown and described in the following publications. Brochures entitled "The AMK Total Knee System Design Nationale and Surgical Procedure" (page 25), DePuy, Division of Boehringer Mannheim Corporation, Warsaw, Indiana, and "WHITESIDE ORTHOLOC~ Modular KNEE SYSTEM", copyright 1989 by Dow Corning Wright, Arlington, Tennessee.
There has recently been introduced a new design of patellar prosthesis having a tapered surface on the side away from the crown. One such prosthesis is the subject matter of Canadian Patent application Serial No. 2,076,663, filed March 4, 1991, by the applicant herein. The present apparatus for preparing a patella to receive a patellar prosthesis is well-suited for patellar prostheses of the type disclosed in such patent application; however, it should be understood that the apparatus of the present invention is not so limited and may be used for a wide variety of patellar prostheses. It has a significant advantage over the prior art for implanting a patellar prosthesis or a type in which one of a number of different sizes is to be used depending upon the patient in that the apparatus of the present invention does not rely upon the patella clamp to guide the reamer. Accordingly, in utilizing the apparatus of the present invention, it is not necessary to have available a plurality of clamps of varying sizes.
SUHHARY OF THE INVENTION
The present invention provides a new apparatus for preparing a human patella for implanting a patellar prosthesis : ~, `-- 21 01 941 therein. As is well-known in performing knee replacement surgery, the patella is everted and retained in a position permitting the surgeon to have access to the articular surface which is normally engaged in the intercondylar notch between the condyles. Under the present invention, with the patella so supported, the surgeon, using a saw or similar tool for performing osteotomy, removes the top portion of the articular surface, thus leaving a flat surface near the central portion of the patella. Desirably, only a small portion of the articular surface is removed in order to leave as much of the original patella intact as possible. Thus, as pointed out in the above-identified patent application, it is desirable that as little of the human patella be removed as possible.
Following removal of the top of the articular surface a thread guide wire or pin is used to drill a passageway in the central portion of the patella at substantially right angles to the flat surface. Then, using the threaded guide wire which may be left in the passageway or a rod of similar size to that of the threaded guide wire positioned in said passageway, a cannulated reamer is placed over the threaded guide wire or other guide rod and, using such threaded guide wire or guide rod as a guide, the reamer is utilized to ream the patella thereby forming a cavity having a size and configuration suitable for receiving the patellar prosthesis. Following such reaming, the cavity is cleaned, bone cement placed therein and the patellar prosthesis implanted therein. If desired, the reaming could be performed in stages, initially using a reamer sized to form a relatively small cavity and thereafter using a reamer sized to form the cavity for receiving the patella prosthesis.

A

It is also within the contemplation of the present invention to drill the passageway without cutting the apex of the articular surface or otherwise forming a flat surface.
According, it is an object of the present invention to provide apparatus for preparing a human patella for implanting a patellar prosthesis therein.
It is a further object of the present invention to provide apparatus for cutting, and reaming a patella in preparation for implanting a patellar prosthesis to provide accurate positioning while minimizing the amount of bone required to be removed.
According to a broad aspect of the invention there is provided apparatus for preparing a patella having an articular surface with an apex to receive a patellar prosthesis having a body portion including an upper dome and a lower stem on the opposite side of said body portion from said dome, comprising:
(a) means for drilling a passageway in said patella inwardly from the side having said articular surface;
(b) an elongated guide means having a first portion adapted to be received in said passageway and a second portion adapted to protrude from said passageway;
(c) a reamer having a head with upper and lower sides, cutting means depending from said lower side and a central cannulation extending through said cutting means and said head, said cannulation having a size to fit over said second portion of said guide means, said head having a plurality of apertures extending therethrough from said lower to said upper side, whereby said reamer is adapted to be positioned over said 4a 22236-587 elongated guide means to ream a cavity in said patella having a size and configuration to receive said patellar prosthesis while using said guide means as a guide to determine the position of said cavity and debris formed during reaming of the cavity is expelled through the apertures in said head.
. Other objects and advantages of the present invention will become apparent from the following detailed description in conjunction with the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is an elevational view showing a cannulated reamer having cutting knives of a configuration suitable for preparing a patella for implanting of one type of patellar prosthesis.
Figure 2 is a top plan view of the cannulated reamer of Figure 1.
Figure 3 is a bottom plan view of the cannulated reamer of Figure 1.
Figure 4 is a sectional view taken along line 4-4 of Figure 1.

A

WO g2/13503 PCI`/US92/OOg?42 Fig. 5 is a fragmentary sectional view of the reamer head taken along line 5-5 of Fig. 3.
Fig. 6 is an elevational view showing the threaded guide wire for forming a guide passageway in the patella.
Fig. 7 is an end view of the threaded guide wire of Fig. 6 looking in the direction of the arrows 7-7.
Fig. 8 is a view similar to Fig. 3 showing a modified reamer.
Fig. 9 is a fragmentary elevational view of the modified reamer of Fig. 8.
Fig. 10 is a sectional view of a patella during the initial step of removing the apex of the articular surface to form a flat surface.
Fig. 11 is a view similar to Fig. 10 showing the next step of drilling a passageway at substantially right angles to the flat surface formed as shown in Fig. 10.
Fig. 12 is a view similar to Fig. 11 showing the reaming step using the drill bit or other guide rod to guide the reamer during reaming.
Fig. 13 is a sectional view showing a patellar prosthesis implanted in a patella prepared in accordance with the present invention.
Fig. 14 is a sectional view of a patella during the initial step of a modified method of preparing, a patella wherein a passageway is formed without first forming a flat surface.
Fig. 15 is a view similar to Fig. 14 showing one of a plurality of reaming steps using the threaded ? guide wire or other guide rod to guide the reamer during reaming.
Fig. 16 is a view similar to Fig. 15 showing the second reamer beginning to ream the final cavity.
Fig. 17 is a view similar to Fig. 16 showing completion of reaming the final;~avity.

:

21019ql Flg. 18 ls a sectlonal vlew showlng a patellar pros-thesls lmplanted ln a patella prepared ln accordance wlth the present lnventlon.
DESCRIPTION OF THE ~ ~K~ EMBODIMENT
Referrlng now to Flgs. 1-5, there ls shown a reamer generally deslgnated by numeral 10 havlng a head 12 mounted on the end of a cannulated stem 14 extendlng along an axls A.
The head 12 has a upper surface 13 and a lower surface 15. A
cuttlng assembly 16 extends downwardly from the head 12 and lncludes a houslng 18 and a plurallty of cuttlng blades 20 lntegrally formed wlth and extendlng radlally outwardly from the houslng 18. In the embodlment of Flgs. 1-5, four cuttlng blades 20 are provlded at substantlally 90 from each other.
As can be seen partlcularly ln Flg. l, the shape of the cuttlng blades are substantlally ldentlcal and have a con-flguratlon tallored to form a cavlty of a slze and shape sultable for recelvlng the speclflc patellar prosthesls lntended for lmplantatlon.
For example, referrlng brlefly to Flg. 13, there ls shown a patella P ln whlch a cavlty 22 has been reamed and ln whlch a patellar prosthesls 24 has been lmplanted utlllzlng the apparatus of the present lnventlon. The patellar pros-thesls 24 of Flg. 13 has a body portlon 26 wlth a dome 28 faclng away from the patella P ln a posltlon to engage the patellar or trochlear groove of the femoral component of a total knee lmplant (not shown). The dome 28 termlnates at lts outer perlphery at an edge 30 whlch deflnes a clrcle from whlch a ~hort cyllndrlcal wall sect lon ~2 depends . A~ can be seen ln Flg. 13 the edge 30 ls preferably above the upper sur-face of the patella P about 1-2 mm; however, lt could meet the upper surface of the patella and thus provlde a smooth tran-sltlon . y ~ 2 1 0 1 94 1 between the dome 28 and the upper surface of the patella P.
Tapering inwardly toward the central axis and downwardly in a direction away from the dome 28 is an inner wall surface 34 from which a stem 36 depends. The stem 36 may have one of a wide variety of shapes including the shapes shown in the brochures identified on page 1 hereof or the shape shown in my aforementioned Canadian application Serial No. 2,076,663. A layer of bone cement 37 such as polymethylmethacrylate is used to bond the patellar prosthesis 24 in the cavity.
As will be appreciated from viewing Figure 1 and Figure 13, the cross-sectional shape of that portion of the patellar prosthesis 24 facing away from the dome 28 determines the shape defined by the cutting blades 20 and the shape of the cavity to be formed thereby. Thus, each of the blades 20 has a first cutting edge 20a substantially parallel to the Axis A of the stem 14, a second cutting edge 20b tapering inwardly toward such axis A and away from the head 12, a third cutting edge 20c substantially parallel to such axis and a fourth cutting edge 20d extending radially inwardly from the third cutting edge 20c and joined to the housing 18. It should be understood, however, that the shape of the cutting blades 20 may vary depending upon the configuration of the patellar prosthesis intended to be implemented. In forming a cavity of the configuration shown in Figures 12 and 13 for receiving the prosthesis 24, the third cutting edge 20c and fourth cutting edge 20d will form a lower cylindrical portion of the cavity 22 intended to receive the stem 36, the second cutting 2t 01 941 `_, 7a 22236-587 edge 20b will form the portion of the cavity 22 flaring upwardly and outwardly from the lower cylindrical portion for receiving the portion of the prosthesis defined by the tapering k~

W092/13503 PCT/US92/~942 21019~1 - 8 - _-inner wall surface 34 and the first cutting edge 20a will form the upper cylindrical portion of the cavity 22 for receiving the short cylindrical wall section 32 of the patellar prosthesis 24.
As can be seen in Figs. 1 and 12, the cutting blades 20 do not extend outwardly to the outer periphery of the head 12. Thus, the first cutting edge 2Oa is closer to the axis A than is the outer periphery of the head 12. This construction permits the lower surface 15 to contact the patella P and function as a stop for determining the proper depth for the cavity 22 and insure against inadvertent reaming to an excessive depth.
The reamer 10 has a cylindrical passageway 40 ext~n~ing throughout the stem 14, head 12 and housing 18. Additionally, the head 12 has a plurality of inclined passageways 42 extending therethrough from a position on the lower surface 15 between the cutting blades 20 and ext~n~ing out of the upper surface 13.
These inclined passageways 42 are intended to provide a means for expelling the debris from the cavity 22 being reamed. Thus, as the blades 20 ream the patella P, the bone material cut therefrom will be propelled into the end of the inclined passageway 42 at the lower face 15, through inclined passageway 42 and out of it at the upper face 13.
The stem 14 of the reamer 10 has an enlarged area 44 which may be provided with opposing flat surfaces 45 for engagement by rotatable power means for rotating the head 12 and the cutting blades 20 carried thereby.
Referring now to Figs. 6 and 7, there is shown a threaded guide wire 50 having a cutting head 52, a helical thread 54 and an elongated shank 56 having a diameter slightly smaller than that of the cylindrical passageway 40 and a length sufficiently long to extend , _ .
completely through the stem 14 of reamer 10. The cuttlng head 52 has three trlangular shaped flats 58 extending to a tlp 60 wlth the edges between the ad~olnlng flats 58 functlonlng as the prlmary cutters.
Flgs. 8 and 9 show a modlfled reamer 10' havlng a head 12' wlth elght cuttlng blades 20' as contrasted wlth the prevlous embodlment havlng four cuttlng blades 20. In thls embodlment, there are provlded elght lncllned passageways 42' extendlng through the head for expelllng debrls durlng the cuttlng operatlon.
Referrlng now to Figs. 10-12, there ls shown a human patella P havlng an artlcular surface lncludlng an apex 70 whlch, ln a normal knee prlor to surgery, engages the lnter-condylar notch between the condyles at the dlstal end of the femur. Accordlng to the present lnventlon, the top of the apex 70 ls cut wlth a standard cuttlng blade 72 to form a substan-tlally planar surface 74 as shown ln Flgs. 10 and 11. There-after, the threaded gulde wlre 50 powered by a drlll (not shown) ls utlllzed to drlll a passageway 76 ln the patella P.
Followlng drllllng of the passageway 76 the drlll ls dlsconnected from the threaded gulde wlre 50, leavlng the threaded gulde wlre 50 ln the passageway 76. Then, uslng the threaded gulde wlre 50 as a gulde, the reamer 10 ls placed thereover and ls connected to power means whlch rotates lt thereby causlng the cuttlng blades 20 to form the cavlty 22 havlng a conflguratlon determlned by the conflguratlon of the cuttlng edges 20a, 20b, 20c and 20d of cuttlng blades 20. In the drawings it is shown as havlng the deslred conf lgurat lon to recelve the patellar prosthesls 24. Durlng such cuttlng the threaded gulde wlre 50, snugly recelved ln the passageway 40, serves to accurately gulde the reamer 10 on the correct axlal path ln reamlng the patella P to form the cavlty 22.

~r 22236-587 , Thus, the threaded gulde wlre 50 prevents the reamer 10 from drlftlng off such path and formlng a larger cavlty than deslred. As prevlously noted, durlng such reamlng process, debrls wlll be expelled through the lncluded passagewayæ 42 extendlng through the head 12. Completlon of the reamlng step occurs when the lower surface 15 of the head 10 engages the patella P. As prevlously noted, the deslgn of the reamer head 12 to cause engagement of such lower surface 15, prevents the reamer from reamlng to a greater depth than deslred.
Followlng completlon of the reamlng step, the reamer 10 and the threaded gulde wlre 50 are removed, the cavlty 22 18 cleaned of debrls and prepared ln accordance wlth standard surglcal lmplantatlon technlques lncludlng appllcatlon of bone cement such as polymethylmethacrylate and afflxlng of the patellar prosthesls 24 thereln. Preferably, prlor to placlng bone cement ln the cavlty 22, pulverlzed bone chlps and/or bone slurry wlll be placed ln the end portlon 76a of the passageway 76 extendlng below the bottom of that portlon of the cavlty 22 formed by the lower cuttlng edge 20d. Such bone chlps and/or bone slurry serve as a graft lnduclng bone growth lnto such end portlon 76a. However, lt ls posslble that such end portlon be fllled only wlth bone cement.
Irrespectlve of whether the cuttlng head has four cuttlng blades 20 shown ln the embodlment of Flgs. 1-5, or elght cuttlng blades 20' shown ln the embodlment of Flgs. 8 and 9 or fewer or more of such cuttlng blades, the apparatus of the present lnventlon permlts the lmplantatlon of a patellar prosthesls ln a hlghly accurate manner wlth a mlnlmal removal of bone.
Referrlng now to Flgs. 14-18, there ls shown a modlfled apparatus for preparlng a patella P' and for lmplantlng a patellar prosthesls 24' thereln.

X

.
As shown in Fig. 14, there ls provlded a threaded gulde wire 50' havlng a head 52' wlth cuttlng flats 58' ex-tendlng to a tlp 60'. A hellcal thread 54' extends upwardly from the head 52'.
Under thls embodlment, the apex 70' of the patella P' ls not cut to form a flat surface as ln the prevlous embodl-ment, but rather the threaded gulde wlre 50' dlrectly engages the artlcular surface at a deslred locatlon ln the vlclnlty of the apex 70. As wlll be appreclated by those skllled ln the art, durlng thls step, the patella P' wlll be held by a sultable clamplng mechanlsm whlle the drlll powerlng the threaded gulde wlre 50' ls used to form a passageway 76' ln the patella P'.
The drlll ls then dlsconnected from the threaded gulde wlre 50' and a flrst or pllot reamer 90 havlng a head 92 mounted on the end of a cannulated stem 94 ls posltloned over the threaded gulde wlre 50'. The head 92 has a plurallty of cuttlng blades 96 extendlng downwardly therefrom. As can be seen from Flg. 15, the head 92 and cuttlng blades 96 of the pllot reamer 90 are much smaller than requlred to form a cavlty of the slze lntended for the patellar lmplant 24' as shown ln Flg. 18. Thus, the flrst or pllot reamer 90 forms a relatlvely small cavlty 98. As shown ln Flgs. 16 and 17, a second reamer 10" slmllar or ldentlcal to the reamer 10 of the embodlment of Flgs. 1-5 ls provlded to form a flnal cavlty 99 havlng a slze and conflguratlon sultable for recelvlng the patellar lmplant 24'. It may be preferable to the surgeon to perform the reamlng ln two steps, partlcularly lf the surgeon does not wlsh to form the flat surface by cuttlng the apex of the artlcular surface. In performlng the reamlng ln two steps, the surgeon forms flrst a relatlvely small cavlty 98 uslng the threaded gulde wlre 54' or other gulde means positloned ln the passageway 76' to gulde the dlrectlon of the flrst or pllot reamer 90 and thereafter formlng the flnal cavlty 99 wlth reamer 10' agaln uslng the threaded gulde wlre 50' or other gulde means. As ln the prevlous embodlments the end portlon 76a ls preferably fllled wlth bone chlps or bone slurry to serve as a graft lnduclng bone growth thereln.
Although the lnventlon has been descrlbed uslng a cannulated reamer 10 wlth flat cuttlng blades 20, lt should be understood that a wlde varlety of reamers could be used. For example, a convex grater type reamer wlth a cannulated center to accommodate the gulde wlre ls one whlch could be used.
Many modlflcatlons and embodlments wlll become read-lly apparent to those skllled ln the art. Accordlngly, the scope of the present lnventlon should be determlned only by the scope of the appended clalms.

X

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. Apparatus for preparing a patella having an articular surface with an apex to receive a patellar prosthesis having a body portion including an upper dome and a lower stem on the opposite side of said body portion from said dome, comprising:
(a) means for drilling a passageway in said patella inwardly from the side having said articular surface;
(b) an elongated guide means having a first portion adapted to be received in said passageway and a second portion adapted to protrude from said passageway;
(c) a reamer having a head with upper and lower sides, cutting means depending from said lower side and a central cannulation extending through said cutting means and said head, said cannulation having a size to fit over said second portion of said guide means, said head having a plurality of apertures extending therethrough from said lower to said upper side, whereby said reamer is adapted to be positioned over said elongated guide means to ream a cavity in said patella having a size and configuration to receive said patellar prosthesis while using said guide means as a guide to determine the position of said cavity and debris formed during reaming of the cavity is expelled through the apertures in said head.

2. Apparatus as claimed in claim 1 further including a stop member engageable with said articular surface when said cavity has been reamed to a desired depth.

3. Apparatus as claimed in claim 1, wherein said head includes a lower face extending radially outwardly beyond said cutting means, said lower face having a stop means engageable with said articular surface to limit the depth of such cavity.

4. Apparatus as claimed in claim 1, wherein said cutting means includes a first portion adjacent said head, a second portion extending from said first portion having a cutting edge tapering inwardly toward said cannulation and away from said head, and a third portion having a cutting edge substantially parallel to said cannulation, wherein said cutting means produces a cavity in such patella having a cylindrical lower portion centered on said guide means and sized to receive the stem of the patellar prosthesis and an upper portion having a body wall tapering upward toward the articular surface and outwardly from said guide means to receive the body portion of the patellar prosthesis.

5. Apparatus as claimed in claim 4 wherein said cutting means first portion has a cutting edge substantially parallel to said cannulation and sized to cut said articular surface.

6. The apparatus of claim 1 further including a clamp having an enlarged opening through which access to a central portion of the articular surface is obtained and wherein said head of said reamer is sized smaller than said enlarged opening.