US20070288029A1 - Milling system for resecting a joint articulation surface - Google Patents

Abstract

A milling system for use in resecting at least a portion of a joint articulation surface of a bone includes an alignment guide having a top surface and an opposing bottom surface with an opening extending therebetween. Fasteners are used to secure the alignment guide to the bone so that the alignment guide is suspended above the bone. A template is removably mounted to the alignment guide so that a plurality of guide paths extending through template are aligned with the opening in the alignment guide. A mill extends down through the guide path and has a burr on the end thereof for resecting the bone.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS
• This application is a divisional of U.S. patent application Ser. No. 11/149,912, filed Jun. 10, 2005, which is incorporated herewith by reference.
BACKGROUND OF THE INVENTION
• 1. The Field of the Invention
• The present invention relates to milling systems and related guides and mills for resecting at least a portion of a joint articulation surface of a bone and mounting an implant thereat.
• 2. The Relevant Technology
• The human body has a variety of movable orthopedic joints such as the knee joint, hip joint, shoulder joint, and the like. These joints are formed by the intersection of two bones. The intersecting end of each bone has a smooth articular surface that is comprised of articular cartilage. As a result of injury, wear, arthritis, disease or other causes, it is occasionally necessary to replace all or part of an orthopedic joint with an artificial implant. This procedure is referred to as a joint replacement or arthroplasty. For example, a total knee arthroplasty comprises cutting off or resecting the articular surfaces at both the distal end of the femur and the proximal end of the tibia. Complementary artificial implants are then mounted on the distal end of the femur and the proximal end of the tibia. Where only a portion of a joint is damaged, a partial joint arthroplasty can be performed. In this procedure, one or more artificial implants replace only a portion of a joint.
• Although joint replacement is now a common procedure that has met with popular success, conventional implants and related mounting techniques have significant shortcomings. One significant drawback of many joint replacements is the extended and painful patient recovery. For example, a traditional knee replacement requires an open procedure wherein a relatively large incision is made which severs a portion of the muscle bounding the femur. The large incision is made so as to fully expose the respective ends of the femur and tibia.
• This exposure is necessary when using conventional techniques to resect the femur and tibia and to mount the implants. For example, resecting the femur and tibia is typically accomplished by a reciprocating saw which requires substantially full exposure of the respective ends of the femur and tibia. Furthermore, some conventional tibial implants are screwed directly into the resected end face of the tibia. Mounting such screws again requires substantially full exposure of the resected end face. In yet other embodiments, the implants are formed with posts projecting therefrom. The posts are received within sockets formed on the resected end face of the tibia and femur. Forming of the sockets and inserting the posts into the sockets requires substantially full exposure of the resected end face of the tibia and femur.
• Substantially the same procedures are often used when resurfacing only a portion of a joint articulation surface. That is, the joint is exposed and a reciprocating saw is used to resect half or a portion of the articular cartilage. The implant is then mounted by using screws or posts. Thus, even in procedures where only a portion of the joint articulation surface is being resurfaced, conventional procedures make an invasive retraction of the soft tissue and remove a large portion of the bone.
• In general, the more invasive the surgery, the more painful, difficult, and time consuming the patient recovery. Furthermore, extensive resection of bone not only increases bone trauma but can also make subsequent replacement operations more difficult.
• Accordingly, what is needed are systems and methods for preparing a joint articulation surface to receive an implant which are easy to use while minimizing the impact on soft tissue and the amount of bone resection. What is also needed are implants which can be used with such systems that can be mounted with minimum trauma.
BRIEF DESCRIPTION OF THE DRAWINGS
• Various embodiments of the present invention will now be discussed with reference to the appended drawings. It is appreciated that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of its scope.
• FIG. 1 is a perspective view of the distal end of a femur;
• FIG. 2 is a perspective view of the femur shown inFIG. 1 having a guide assembly mounted on a condyle thereof;
• FIG. 3 is an exploded view of the guide assembly shown inFIG. 2;
• FIG. 4 is a bottom perspective view of the assembled guide assembly shown inFIG. 2;
• FIG. 5 is a perspective view of an alternative embodiment of the positioning guide shown inFIG. 3;
• FIG. 6 is a perspective view of the alignment guide shown inFIG. 3 mounted on the femur;
• FIG. 7 is a perspective view of the alignment guide shown inFIG. 6 having a template mounted thereon and a mill assembly interacting therewith;
• FIG. 8A is a top plan view of the template shown inFIG. 7;
• FIG. 8B is an elevated side view of the template shown inFIG. 8A;
• FIG. 8C is an elevated end view of the template shown inFIG. 8A;
• FIG. 9 is a perspective view of the mill assembly shown inFIG. 7;
• FIG. 10 is an exploded view of the mill assembly shown inFIG. 9;
• FIG. 11 is an elevated side view of the template shown inFIG. 7 having the mill assembly extending therethrough;
• FIG. 12 is a perspective view of the femur shown inFIG. 7 having a recessed pocket formed thereon;
• FIG. 13A is a top plan view of an alternative embodiment of the template shown inFIG. 7A;
• FIG. 13B is an elevated end view of the template shown inFIG. 13A;
• FIG. 14 is a top perspective view of a condylar implant;
• FIG. 15 is a bottom perspective view of the condylar implant shown inFIG. 14;
• FIG. 16 is a perspective view of the femur shown inFIG. 12 having the implant shown inFIGS. 14 and 15 mounted within the recessed pocket thereof; and of an alternative embodiment of the
• FIG. 17 is a perspective view of an alternative embodiment of the alignment guide shown inFIG. 3.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
• The present invention relates to milling systems and related guides, templates, and mills for use in resecting an articulation surface of an orthopedic joint so that an implant can be mounted on the resected surface. As used in the specification and appended claims, the term “articulation surface” is broadly intended to include all surfaces of natural articular cartilage forming a portion of an orthopedic joint and all articulation wear surfaces of a bone forming a portion of orthopedic joint that, as a result of wear, trauma, disease or other causes, have all or a portion of the natural articular cartilage removed.
• In the below illustrated embodiment of the present invention, milling systems and related guides, templates, and mills are shown which are specifically designed for mounting a condylar implant at the distal end of a femur. It is appreciated, however, that the illustrated embodiments are simply examples of the present invention and that the same technology can also be used for resecting a portion of the articulation surface at a different location on the same articulation surface or on a variety of other joint surfaces to receive a variety of other different types of implants. By way of example and not by limitation, the present invention can be used for resecting all or a portion of a condyle and then mounting a unicondylar or partial condylar implant.
• The present invention can also be used for resecting all or a portion of the trochlear groove of a femur and then mounting an implant thereat. In still other embodiments, the present invention can be used for resurfacing any articulation surface of a knee joint, ankle joint, hip joint, shoulder joint, elbow joint, wrist joint, interfrangial joint, or other joints. As such, the milling systems of the present invention can be used for preparing the articulation surface at the proximal or distal end of the femur, tibia, humors, radius, and ulna and on other articulation surfaces of the scapula, pelvis, bones within the foot and hand, and other bone articulation surfaces.
• Depicted inFIG. 1 is adistal end10 of afemur12.Distal end10 has amedial side14 and alateral side16 that each extend between ananterior side18 and aposterior side20.Distal end10 offemur12 terminates at amedial condyle22 and alateral condyle24 with atrochlear groove26 disposed therebetween.Articular cartilage28 defines an articulation surface fordistal end10 offemur12.Articular cartilage28 terminates at amargin30.
• On occasion, due to arthritis, disease, trauma, or the like, it is necessary to replace all or a portion ofmedial condyle22 orlateral condyle24. In the depicted embodiment of the present invention, the illustrated milling system and related guides, templates, and mills are designed to form a recessed pocket onmedial condyle22 so that an implant can be mounted within the recessed pocket.
• Depicted inFIG. 2 is aguide assembly34 incorporating features of the present invention and forming a portion of a milling system.Guide assembly34 comprises analignment guide36, apositioning guide38, and ahandle40 that removablycouples positioning guide38 onalignment guide36. As depicted inFIG. 3,alignment guide36 has atop surface44 and an opposingbottom surface46 that each extend between afirst end48 and an opposingsecond end50.Surfaces44 and46 also extend between afirst side52 and an opposingsecond side54.
• In the presentembodiment alignment guide36 has a substantially continuous arch extending fromfirst end48 to opposingsecond end50. That is,bottom surface46 has a substantially constant concave curvature whiletop surface44 has a substantially constant convex curvature. This configuration helps to minimize the size ofalignment guide36 to facilitate the greatest ease of insertion during use. In alternative embodiments, however, one or both oftop surface44 andbottom surface46 can be flat or have any other desired configuration.
• To further facilitate complementary positioning ofalignment guide36 overmedial condyle22 while minimizing size,alignment guide36 can also have an arched curvature extending between opposingsides52 and54. That is,bottom surface46 can have a substantially constant concave curvature extending between opposingsides52 and54 while thetop surface44 can have a substantially constant convex curvature. As previously discussed, these surfaces can also be flat or have other configurations. It is appreciated that the configuration ofalignment guide36 can vary depending on the articulation surface being resected. For example, where trochlear groove26 (FIG. 1) is being resected,alignment guide36 can have a substantially V-shaped configuration such thatalignment guide36 can sit withintrochlear groove26. Although not required,alignment guide36 is typically designed so as to have a contour complementary to the contour of the portion of the bone over which alignment guide36 sits during use.
• Alignment guide36 also has aninterior surface56 that bounds anopening58 extending throughalignment guide36 betweentop surface44 andbottom surface46. As will be discussed below in greater detail, opening58 generally corresponds to the size of the pocket that will be formed on the bone. It is appreciated that opening58 can have a variety of different sizes and shapes depending on the size and location of the area to be resurfaced. In the embodiment depicted,alignment guide36 completely encircles opening58 having substantially linear sides and semi-circular ends. In other embodiments,alignment guide36 can bound only a portion ofopening58. For example, alignment guide can have a substantially C-shaped configuration. In other embodiments, opening58 can have a substantially circular, elliptical, polygonal, irregular, or other configuration.
• Alignment guide36 can also be defined as having abody portion60 that bounds opening58 and has the surfaces as discussed above, afirst bracket62 that projects fromside52 ofbody portion60, and asecond bracket64 that projects fromside54 ofbody portion60. Both ofbrackets62 and64 project away frombody portion60.
• Extending throughfirst bracket62 are a pair of spaced apart mountingholes68A and68B. A mountinghole68C also extends throughsecond bracket64. Although not required, in the embodiments depicted each mountinghole68A-C has anannular shoulder70 that radially, inwardly projects into the corresponding mounting hole at a location between the opposing ends thereof. As will be discussed below in greater detail, fasteners are designed to pass through mountingholes68A-C and engagefemur12 so as to securealignment guide36 tofemur12. A pair of spaced apart, threaded coupling holes72 can also be formed onfirst bracket62. Coupling holes72 are used in the attachment ofpositioning guide38 toalignment guide36.
• Positioningguide38 comprises asupport78 having anarm80 projecting therefrom.Support78 has atop surface82 and an opposingbottom surface84 with anexterior side surface86 extending therebetween.Exterior side surface86 has a configuration complementary tointerior surface56 ofalignment guide36 such thatsupport78 can be received within opening58 ofalignment guide36. Although not required,support78 also has aninterior surface88 bounding anopening90 extending betweentop surface82 and opposingbottom surface84.
• Arm80 projects fromtop surface82 and has a pair of spaced apart couplingholes92 extending therethrough. Coupling holes92 are configured so that whensupport78 ofpositioning guide38 is received within opening58 ofalignment guide36, coupling holes92 are aligned with coupling holes72. A threadedtip94 ofhandle40 can then be passed down through one of coupling holes92 and engaged with a correspondingcoupling hole72. As tip is threaded intocoupling hole72, ashoulder96 onhandle40 biases againstarm80 so that handle40 facilitates a releasable, secure engagement betweenalignment guide36 and positioning guide38 as depicted inFIG. 2. Due to the elongated nature ofhandle40, handle40 can be easily held and operated by the surgeon to facilitate proper positioning and removal ofguides36 and38. It is appreciated that any number of different types of fasteners can be used to removablysecure guides36 and38 together. For examples, clamps, expansion bolts, or other forms of threaded connection can be used. Furthermore, handle40 is not required and can be replaced with bolts, screws, or other fasteners that extend through one or both sets of coupling holes72 and92.
• As depicted inFIG. 4,positioning guide38 is configured such that when positioningguide38 is mated withalignment guide36,support78 of positioning guide38 projects a distance belowbottom surface46 ofalignment guide36. As a result,positioning guide38 can be used to mountalignment guide36 onfemur12 so thatalignment guide36 is suspended abovefemur12. Specifically, during use,alignment guide36 is coupled withpositioning guide38 usinghandle40 as discussed above. As depicted inFIG. 2, through the use ofhandle40, the coupled guides36 and38 are then positioned onmedial condyle22 so that opening58 ofalignment guide36 is positioned over the portion ofarticular cartilage28 that is desired to be resurfaced by an implant.
• Here it is again noted that during the positioning,support78 ofpositioning guide38 rests directly againstarticular cartilage28 while alignment guide36 is suspended above or spaced apart fromarticular cartilage28 so that it does not directly contactarticular cartilage28. As a result of formingopening90 onsupport78 only a narrow ring portion ofsupport78 rests onarticular cartilage28. This configuration enables greater stability ofpositioning guide38 onarticular cartilage28. In yet other embodiments,support78 can be formed with a plurality of legs projecting therefrom that rest against thearticular cartilage28. For example,support78 can be formed with three or more spaced apart legs. The use of three spaced apart legs enablessupport78 to be easily stabilized on an uneven surface ofarticular cartilage28.
• It is appreciated thatsupport78 need not have a circular configuration but can have any desired configuration that can be received within opening58 ofalignment guide36 so as to project belowbottom surface46 and that can be seated in a stable fashion onarticular cartilage28. For example, depicted inFIG. 5 is an alternative embodiment of apositioning guide38A having asupport118 extending fromarm80.Support118 comprises three, spaced apart, downwardly projectinglegs120A-C withlegs120B and C being mounted onelongated braces122 and123, respectively. During use,legs120A-C rest directly againstarticular cartilage28. The configuration ofpositioning guide38 can vary depending on the configuration of thearticulation cartilage28 to be removed.
• Once positioningguide38 is seated onarticulation cartilage28, fasteners are then used to removablysecure alignment guide36 tofemur12. Specifically, as depicted inFIG. 3, in one embodiment of the present invention means are provided for securingalignment guide36 tofemur12. By way of example and not by limitation, fasteners are designed to pass through mountingholes68A-C and engagefemur12 so as to removablysecure alignment guide36 tofemur12. In the depicted embodiment, the fasteners comprise threadedscrews93A-C. Each screw93 comprises anelongated shaft95 having afirst end97 and an opposingsecond end98.Threads100 are formed alongshaft95 while anenlarged head102 is formed atfirst end97. In the embodiment depicted,enlarged head102 comprises aflange104 that encircles and radially outwardly projects fromfirst end97. Anengagement head106 extends aboveflange104 and has a polygonal or non-circular cross section so that a driver can be connected toengagement head106 for selective rotation of screws93.
• It is appreciated thatenlarged head102 can be formed with a socket, slot(s), or other engaging surfaces to engage with other types of drivers. Eachscrew93A-C is configured so thatsecond end98 can be received within and slid through a corresponding mountinghole68A-C ofalignment guide36.Enlarged head102 is larger than mountingholes68A-C and thus functions as a stop. In alternative embodiments, screws93A-C can be replaced with other conventional forms of fasteners such as bone anchors, expansion bolts, barbed shafts, and the like.
• Once guides36 and38 are appropriately positioned, screws93A-C are passed throughcorrespondence mounting holes68A-C onalignment guide36 so as to rigidly fixalignment guide36 at the desired orientation and position. As depicted inFIG. 6, it is appreciated thatbrackets62 and64 and mountingholes68A-C are positioned so thatscrews93A-C screw intofemur12 atmargin30 ofarticular cartilage28 or spaced apart fromarticular cartilage28. This prevents any unwanted damage toarticular cartilage28.
• In one embodiment, screws93A-C can be used in association with guide sleeves. By way of example, guidesleeves136A-C are depicted inFIG. 3. Each guide sleeve136 comprises atubular stem138 having afirst end139 and an opposingsecond end141. A passageway140 centrally extends throughstem138 between opposing ends139 and141. Aflange142 encircles and radially outwardly projects fromfirst end139 ofstem138. Eachguide sleeve136A-C is configured so thatsecond end141 can be received within and slid through a corresponding mountinghole68A-C. In the depicted embodiment, each mountinghole68A-C is counter bored so as to form internal constrictingshoulder70 as previously discussed.Flange142 is sized to rest onshoulder70 so as to preventguide sleeves136A-C from passing completely through corresponding mountingholes68A-C.
• In part, guidesleeves136A-C function as guides forscrews93A-C. That is, as a result ofpositioning guide38 projecting belowalignment guide36,bottom surface46 ofalignment guide36, and thus the bottom of mountingholes68A-C, are spaced abovefemur12. However, as a result of this gap or space between the bottom of mountingholes68A-C andfemur12, there is a potential forscrews93A-C to become misaligned from the central longitudinal axis of each corresponding mountinghole68A-C as screws93A-C are passed from mountingholes68A-C tofemur12. This misalignment can cause binding ofscrews93A-C againstalignment guide36 which in turn can cause unwanted displacement or improper securing ofalignment guide36. By usingguide sleeves136A-C which extend from mountingholes68A-C to or adjacent tofemur12, guidesleeves136A-C help maintain proper orientation and alignment of eachscrew93A-C.
• Specifically, once guides36 and38 are appropriately positioned, eachguide sleeve136A-C is advanced through a corresponding mountinghole68A-C so thatsecond end141 of each guide sleeve136 is disposed adjacent to or butts againstarticulation surface28.FIG. 4 shows guidesleeves136C projecting belowbottom surface46 ofalignment guide36. Screws93A-C are then passed throughguide sleeves136A-C and screwed intofemur12. Screws93A-C are advanced untilflange104 biases against the first end of acorresponding guide sleeve136A-C, thereby securely fixing eachguide sleeve136A-C tofemur12. It is noted thatflange142 ofguide sleeves136A-C need not bias directly againstalignment guide36.Flange142 primarily functions to preventguide sleeves136A-C from falling through mountingholes68A-C during placement ofalignment guide36. In alternative embodiments,flange142 can be eliminated.
• Here it is noted that each mountinghole68A-C has a centrallongitudinal axis110A-C (FIG. 4), respectively, along which eachscrew93A-C is intended to extend. Mountingholes68A-C are oriented at different angles relative to each other so that merely screwingscrews93A-C intofemur12 throughguide sleeves136A-C positioned within mountingholes68A-Ccause alignment guide36 to be locked in place. That is, it is not necessary forscrews93A-C to downwardly bias directly againstalignment guide36 to securealignment guide36 relative tofemur12. Due to the offset angles ofscrews93A-C and thus the offset angles of theguide sleeves136A-C, it is sufficient if thescrews93A-C merely secure guide sleeves136 in place to lockalignment guide36 in place.
• Once eachscrew93A-C is secured in place so thatalignment guide36 is secured in place, positioningguide38 is removed fromalignment guide36. This is accomplished by simply unscrewinghandle40 and then lifting offpositioning guide38. As depicted inFIG. 6,alignment guide36 is then securely fixed to and suspended abovefemur12 at the appropriate location. Suspendingalignment guide36 abovefemur12 ensures thatalignment guide36 does unintentionally damagearticular cartilage28 during mounting ofalignment guide36 and/or resecting. Although positioningguide38 directly sits uponarticular cartilage28, that portion ofarticular cartilage28 is ultimately resected and thus any damage caused by positioningguide38 is irrelevant. In general, the area ofarticular cartilage28 bounded byalignment guide36, i.e., the area within opening58, is the portion ofarticular cartilage28 that will be resected and is referred to herein as cuttingsurface66.
• Turning toFIG. 7, once positioningguide38 is removed fromalignment guide36, a template is mounted onalignment guide36. Depicted inFIGS. 7 and 8A-8C is one embodiment of atemplate150 incorporating features of the present invention which can be used with the inventive milling systems. With reference toFIG. 8A,template150 comprises a base152 having anarm154 projecting therefrom.Base152 has atop surface156 and an opposingbottom surface158 each extending between afirst end160 and an opposingsecond end162. Base also has afirst side164 and an opposingsecond side168.
• Base152 can be further defined as having anouter body163 having aninterior surface170 that bounds anopening172 extending throughbody163 fromtop surface156 tobottom surface158. In the embodiment depicted,body163 has substantially the same configuration asbody portion60 ofalignment guide36 and is designed to rest ontop surface44 thereof. For example,body163 can have parallel sides that terminate at semi-circular ends. Other shapes such as elliptical, circular, polygonal, irregular, or the like, can also be used. Opening172 ofbody163 can have substantially the same size and configuration as opening58 ofalignment guide36.
• Projecting frominterior surface170 ofbody163 intoopening172 are a plurality ofinterconnected partition walls174. In general, eachpartition wall174 has opposing side faces176 and178.Partition walls174 divide opening172 into a plurality ofguide paths180, some of which are interconnected. Specifically, guidepaths180 are bounded between opposing side faces ofadjacent partition walls174 and are formed betweeninterior surface170 ofbody163 and a side face on anadjacent partition wall174. As will be discussed below in greater detail, guidepaths180 function as guides for a mill used in resecting cuttingsurface66.
• In the depicted embodiment,interior surface170 and the side surfaces of partition walls175 are disposed in parallel alignment. That is, in contrast to having surfaces that slope relative to each other so that projections of such surfaces diverge and intersect, projections of the interior and side surfaces ofbase152 can all intersect a common plane at right angles. As will be discussed below in greater detail, other designs can also be used.
• Turning toFIG. 8B,base152 has a substantially constant curvature extending betweenfirst end160 and opposingsecond end162. Specifically,top surface156 has a convex curvature whilebottom surface158 has a concave curvature extending between opposing ends. Similarly, as depicted inFIG. 8C,top surface156 has a substantially convex curvature extending between opposingsides164 and168 whilebottom surface158 can have a complementary concave curvature. In this regard,top surface156 andbottom surface158 have a substantially dome-shaped configuration. As will be discussed below in greater detail, the configuration oftop surface156 in part dictates the configuration of the floor of the recessed pocket.Bottom surface158 ofbase152 is typically configured complimentary totop surface44 ofalignment guide36 but can be other desired shapes.
• Returning toFIG. 8A, a pair of spaced apart couplingholes182 extend througharm154.Arm154 andcoupling holes182 are configured such that whenbase152 is mounted onalignment guide36, coupling holes182 oftemplate150 are aligned withcoupling holes72 ofalignment guide36. As a result, handle40 can be used to securetemplate150 toalignment guide36 through alignment holes72 and182 in substantially the same manner that positionguide38 was removable attachedalignment guide36, as previously discussed. Again, other removable mounting techniques can be used. It is appreciated that alignment holes72 and182 can each comprise one hole or three or more holes. The formation of more than one alignment hole can be used for additional fasteners or for selective placement ofhandle40.
• As shown inFIG. 7, oncetemplate150 is secured toalignment guide36, amill assembly200 is used in conjunction withtemplate150 to resect cuttingsurface66. Depicted inFIGS. 9 and 10 is one embodiment ofmill assembly200 incorporating features of the present invention.Mill assembly200 comprises amill202 having anelongated shaft204 extending between afirst end206 and an opposingsecond end208.Shaft204 has anannular shoulder210 encircling and radially outwardly projecting atsecond end208. Anannular locking groove212 is centrally formed onshaft204.Mill202 further comprises aburr214 mounted onsecond end208 ofshaft204 so thatburr214 radially outwardly projects fromshaft202.Burr214 is comprised of a plurality of cuttingteeth216 that enablesburr214 to cut from the side and the bottom. As used in the specification and appended claims, the term “burr” is broadly intended to include any arrangement of cutting teeth or cutting surfaces that when mounted onshaft204 can be used to cut bone whenshaft204 is rotated. For example, in contrast to having one or more defined cutting teeth,burr214 can also comprise a rough surface that can grind or cut away bone.
• Mill assembly200 further comprises a bearinghousing220. Bearinghousing220 has aninterior surface226 that bounds apassageway228 extending between afirst end222 and asecond end224. Bearinghousing220 can be further defined as comprising a tubularfirst sleeve230 formed atfirst end222 that bounds acompartment234 and a tubularsecond sleeve232 formed atsecond end224.First sleeve230 has an outer diameter larger thansecond sleeve232 with a roundedtapered shoulder236 extending betweensleeves230 and232.
• During assembly, second end223 of bearinghousing220 is advanced overfirst end206 ofshaft204 untilsecond end232 of bearinghousing220 comes to rest onsupport shoulder210 ofmill202. A pair ofbearing238 and240 are also advanced overshaft204 so as to be received withincompartment234 offirst sleeve230. Aclip242 is then received within lockinggroove212 so as to secure bearinghousing220 andbearings238 and240 onmill202.Bearings238 and240 can be ball bearings, roller bearings, or other forms of bearings. In one alternative, one or three or more bearings can be used.
• Depicted inFIG. 7, during use,burr214 is passed throughtemplate150 so thatshaft204 is disposed within aguide path180. In one embodiment, guidepaths180 have a minimum diameter D extending betweenadjacent partition walls174 or between thepartition walls174 andinterior surface170 ofbase152 that is smaller than the maximum diameter ofburr214. As such,burr214 is prevented from traveling through or out ofguide paths180. However, guidepaths180 are formed so that an area of intersectingguide paths180 forms anaccess area250 having an area sized so that burr can pass therethrough. Either before or after passingmill202 throughtemplate150, a drill or other form of driver is coupled withfirst end206 ofshaft206 so as to enablerapid rotation shaft204 about the longitudinal axis thereof.
• Asshaft204 is rotated,burr214 cuts away atarticular cartridge28 of cuttingsurface66.Burr214 cuts down througharticular cartridge28 untilshoulder236 of bearinghousing220 comes to rest ontop surface156 oftemplate150 as shown inFIG. 11.Shoulder236 thus defines the depth at whichburr214 cuts. During the procedure, the surgeon slowly advancesmill assembly200 along each ofguide paths180 so as to resect cuttingsurface66 and thereby form the recessed pocket. Because the cutting depth ofburr214 is regulated by the interaction betweenshoulder236 andtop surface156 oftemplate150, movement of millingassembly200 about the curvedtop surface156 oftemplate150 produces a recessed pocket having a floor with a contour similar to the contour oftop surface156.
• Furthermore,burr214 has an effective radius that extends fromshaft204 to the maximum outer radius ofburr214. The effective radius is equal to or greater than at least half the thickness of eachpartition wall174. As a result, asmill202 is advanced down aguide path180 on adjacent sides of apartition wall174,burr216 undercuts thepartition wall174 so as to remove all of the articular cartridge directly below thepartition wall174.Burr176 also undercutsinterior surface170 oftemplate150.
• During the milling process, asshoulder236 of bearinghousing220 rides alongtemplate150,first sleeve232 of bearinghousing220 is disposed within thecorresponding guide path180. In one embodiment, each guide path has a diameter substantially equal to but slightly larger then the outer diameter offirst sleeve232 of bearinghousing220. This configuration enables free movement of bearinghousing220 alongguide paths180 but prevents unwanted lateral tipping ofmill202. As a result, the recessed pocket can be formed with greater precision and tolerance. In one embodiment, the minimum diameter of a guide path is typically less than 15% greater than the maximum diameterfirst sleeve232 and is typically less than 10% or 5% greater than the maximum diameterfirst sleeve232. In alternative embodiments, the minimum diameter of aguide path180 can be greater than the maximum diameter ofburr214.
• Oncemill202 has been advanced down each ofguide paths180 so as to complete the resection of cuttingsurface66,mill assembly200 is removed.Template150 and alignment guide36 can then also be removed, thereby exposing resectedpocket310 as depicted onFIG. 12.Pocket310 is bounded by afloor312 having anencircling side wall314 upstanding around the perimeter thereof.Pocket310 has opposingsides316 and318 that extend between aproximal end317 and an opposingdistal end318. Due to the controlled movement ofmill202,floor312 has a convex curvature that extends between opposing ends317 and318 and a convex curvature that extends between opposingsides315 and316. As will be discussed below in greater detail, the configuration of recessedpocket310 enables the use of a low profile implant having substantially uniform thickness. Furthermore, the formation ofpocket310 produces a stable platform for the implant having a complementary configuration.
• It is appreciated thattemplate150 used in formingpocket310 can come in a variety of different sizes, shapes, and configurations depending on the location, size, and contour of articular cartilage to be removed. Depicted inFIG. 13A is one alternative embodiment of atemplate254 that can replacetemplate150.Template254 comprises a base256 havingarm154 projecting therefrom.Base256 has atop surface257 having an arched contour substantially the same astop surface156 oftemplate150.Base256 includes anouter body258 having aninterior surface259 that bounds anopening260. Projecting frominterior surface259 are a plurality ofpartition walls262 that bound a plurality ofguide paths264. By comparingtemplates150 and254, it is appreciated that the partition walls and guide paths, can have any desired configuration, contour and/or layout as long as they enablemill202 to properly removearticular cartilage28. In this regard, the partition walls and guide paths can be interconnected, separated, or combinations thereof. The partition walls and guide paths can also be linear, curved, or have other desired orientations.
• Furthermore, in contrast totemplate150 wherein the side faces are in parallel alignment as discussed above, intemplate254 select side faces of thepartition walls262 are sloped at different angles relative to each other. Specifically, as depicted inFIG. 13B, the various side faces ofpartition walls262 andinterior surface259 ofbody258 intersect at substantially right angles withtop surface257 ofbase256. Expressed in other terms, guidepaths264 projecting fromtop surface257 ofbase256, as depicted by dashedlines266, project normal totop surface257. This is in contrast totemplate150, as depicted inFIG. 8C, where many of theguide paths180 project fromtop surface156 at orientations that are not normal totop surface156. One of the benefits oftemplate254 is that during use,mill202 is oriented normal to thefinal floor312 of recessedpocket310. As a result, the use oftemplate254 results infloor312 of recessedpocket310 having a more uniformly smooth, arched surface in comparison tofloor312 resulting from the use oftemplate150.
• Returning toFIG. 12, once recessedpocket310 is finished, atunnel330 can be formed extending frompocket310 to a location spaced apart from thearticular cartilage28, such asmedial side14 orlateral side16 offemur12.Tunnel330 can be formed by simply using a drill to manually form the tunnel. That is,tunnel330 can be drilled by starting at recessedpocket310 and extending to the lateral or medial side of thefemur12. Other techniques, guides and instruments for formingtunnel330 are disclosed in U.S. patent application Ser. No. 10/901,941, filed Jul. 28, 2004 which is incorporated herein by specific reference.
• Oncetunnel330 is formed, an implant is then secured within the recessedpocket310. Depicted inFIGS. 14 and 15 is one embodiment of acondylar implant320 incorporating features of the present invention.Condylar implant320 comprises anelongated body322 having afirst side324 and an opposingsecond side326 that each extend between opposing ends328 and330.Body322 also has a curvedarticular surface322 and an opposingbottom surface334. In one embodiment, articular surface332 can have a continuous convex curvature that extends between opposingsides324 and326 and a continuous convex curvature that extends between opposing ends328 and330.
• A pair ofpockets344A and B are formed onbottom surface334 and are separated by abridge346. Disposed within eachpocket344A and B is aninlay348A and B of porous bone ingrowth material.Bridge346 andinlays348A and B substantially comprise abone apposition surface350.Bone apposition surface350 can have a configuration complementary to the formation of recessedpocket310.Bone apposition surface350 can also have a configuration complementary to articular surface332. In one embodiment,bone apposition surface350 can have a continuous concave curvature which extends between opposingsides324 and326 and a continuous concave curvature which extends between opposing ends328 and330. As a result, condylar implant can have a substantially uniform thickness along its length. In other embodiments, implant340 may be slightly tapered along aperimeter edge352 thereof Thus, at all locations at least 2 mm in from theperimeter edge352,body322 can have a thickness extending between thebone apposition surface350 and thearticular surface322 that does not vary by more than 30%, 20%, or more commonly 15%. Other percentages can also be used. The actual thickness depends on the desired implant and is typically in a range between about 3 mm to about 10 mm.
• Connected to bridge346 is aflexible line360. As used in the specification and append claims, the term “line” is broadly intended to include wire, cable, cord, suture, braded line, combinations thereof or any other type of flexible filament. The line can be made of metal, alloys, synthetics, composites, or any other desired material. In one embodiment of the present invention the line comprises braded filaments of a cobalt chrome alloy having a diameter in a range between about 0.25 mm to about 5 mm with about 0.5 mm to about 3 mm being more common and about 0.5 mm to about 2 mm being most common. Other dimensions can also be used. The line can be of any desired length.
• In one embodiment, the line can also be defined in that for an unsupported length of line of 4 cm, the line has substantially no compressive strength. In yet other embodiments, for an unsupported length of line of 4 cm, the line fails under buckling when an axial compressive load of 0.25 Newtons (N), 1 N, 2 N, 5 N, 20 N, or 50 N is applied. That is, different lines can be used that fail under different loads. Stiffer lines can also be used.
• It is also appreciated that the line can be static or resiliently stretchable. In one embodiment where the line is resiliently stretchable, the line can be comprised of a material having shape memory of pseudo elastic properties. One example of such a material is a nickel titanium alloy sold under the name Nitinol. In yet other embodiment, it is appreciated that sections of the line could be replaced with a spring member such as a coiled spring or rubber or bungee type member. It is appreciated thatline360 can be permanently or removably attached toimplant320. Examples of methods for attachingline360 to implant320 are disclosed in U.S. patent application Ser. No. 10/901,941 which was previously incorporated by reference.
• It is appreciated thatimplant320 as discussed above and depicted herein is only one example of an implant that can be used in association with the present invention. In alternative embodiments,implant320 can have a variety of different sizes, shapes, configurations, components, and other modifications. For example, spikes or other forms of projections can be formed projecting frombone apposition surface350. Furthermore, conventional implants using conventional mounting techniques can be secured within recessedpocket310. Examples of alternative implants that can be used with the present invention are disclosed in U.S. patent application Ser. No. 10/901,941 which was previously incorporated by reference.
• Finally, turning toFIG. 16,condylar implant320 is secured within recessedpocket310 offemur12. In the depicted embodiment, this is accomplished by passing line360 (FIG. 15) within tunnel300 (FIG. 12) and then using a tensioner and anchor assembly to secureline360 withintunnel300. Examples of bone anchors and tensioners that can be used in association with the present invention are disclosed in U.S. patent application Ser. No. 10/901,941. Again, other conventional techniques can be used to secure implant withinpocket310. In such other techniques,line360 can be eliminated.
• The above disclosure discusses a number of different guides, mills, templates, and other related instruments, implants and methods. It is appreciated that the individual components and sub-combination of components are novel and can be used independently or mixed and matched with other conventional systems. For example, in one alternative embodiment the function ofpositioning guide38 can be integrally incorporated intoalignment guide36. Depicted inFIG. 17 is analignment guide126 wherein like elements between alignment guides36 and126 are identified by like reference characters.
• Alignment guide126 includesbody portion60 boundingopening58.Bracket62 projects frombody portion60 and has coupling holes72 formed thereon. However,bracket64 and mountingholes68A-C have been eliminated.Alignment guide126 further includeshubs128A-C projecting frominterior surface56 ofbody portion60 intoopening58.Support legs130A-C downwardly project fromhubs128A-C, respectively, so thatsupport legs130A-C project below the bottom surface ofbody portion60. Extending down through eachhub128A-C andsupport leg130A-C is a corresponding mountinghole132A-C.
• During use,alignment guide126 is positioned onarticular cartilage28 so thatsupport legs130A-C directly rest againstarticular cartilage28 andbody portion60 is suspended abovearticular cartilage28. Fasteners, such as screws93 (FIG. 3), are then passed down through mountingholes132A-C so as to securealignment guide126 tofemur12.Template150 is then mounted onalignment guide126 and cuttingsurface66 is resected in substantially the same matter as discussed above. After removal ofalignment guide126, the portion ofarticular cartilage28 disposed belowsupport legs130A-C is manually removed, such as with a hand held mill, so as to complete the formation of recessedpocket310. Because the portion ofarticular cartilage28 on which supportlegs130A-C rests is ultimately resected, any damage toarticular cartilage28 bysupport legs130A-C resting thereagainst or screws penetrating therein, is irrelevant. Further disclosure with regard to this method for mounting a guide is disclosed in U.S. patent application Ser. No. 11/138,016, filed May 26, 2005, entitled Milling System and Method for Resecting a Joint Articulation Surface in the name of Carlyle J. Creger et al., which is incorporated herein by specific reference.
• Different features of the present invention provide a number of benefits over conventional systems and methods. For example, in contrast to many conventional processes which require the removal of an entire articulation surface for the mounting of an implant, the present invention enables the resurfacing of an isolated location on the articulation surface. As a result, the procedure is less invasive and recovery time is increased. The milling systems of the present invention enable the formation of the pocket while minimizing retraction of soft tissue, minimizing the amount of bone removal, and minimizing the time required to remove the bone and mount the implant. Using a high speed burr, as opposed to a saw blade or rasp, also has advantages in that the burr requires less effort to cut and can more precisely remove sections of bone. Furthermore, unlike saw blades and rasps which during use often cover a portion of the bone that is desired to be removed, burrs allow for greater visibility of the bone during removal, thereby improving accuracy of bone removal.
• The milling system is also unique in that the milling system is either suspended above the articulation surface or is mounted only over the area of the articulation surface that is to be resurfaced. As a result, the potential for unintentional damage to the portion of the surrounding articular surface that is not to be resurfaced is minimized. Another advantage of the present invention is that it provides a system that is easy to mount and use on uneven or irregular surfaces, is easy to operate, and is easy to remove. The present invention also provides other advantages which will be apparent to those skilled in the art.
• The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.

Claims (12)

1. A milling system for use in resecting at least a portion of a joint articulation surface of a bone, the system comprising:

an alignment guide having a top surface and an opposing bottom surface with an opening extending therebetween;

means for removably mounting the alignment guide to a bone;

a template having a top surface and an opposing bottom surface with a plurality of guide paths extending therebetween, the plurality of guide paths being elongated and extending along both the top surface and the opposing bottom surface; and

means for removably securing the template to the alignment guide so that the plurality of guide paths are aligned with the opening of the alignment guide.

2. The milling system as recited inclaim 1, wherein at least a portion of the plurality of guide paths are interconnected.

3. The milling system as recited inclaim 1, wherein the top surface of the template has a convex curvature.

4. The milling system as recited inclaim 3, wherein the plurality of guide paths intersect with the top surface of the template at an orientation substantially normal to the top surface of the template.

5. The milling system as recited inclaim 3, wherein at least a portion of the plurality of guide paths intersect with the top surface of the template at an orientation substantially normal to the top surface of the template.

6. The milling system as recited inclaim 1, wherein at least a portion of the plurality of guide paths are curved along the length thereof.

7. The milling system as recited inclaim 1, wherein the template comprises:

a body that at least partially bounds an opening extending through the body; and

a plurality of partition walls disposed within the opening of the body and connected to the body, the plurality of partition walls bounding the plurality of guide paths.

8. The milling system as recited inclaim 1, further comprising:

a mill comprising an elongated shaft having a burr mounted on an end thereof, the burr radially outwardly projecting beyond at least a portion of the shaft; and

the plurality of guide paths of the template having a first portion sized so that the burr can pass therethrough and a second portion sized so that the shaft can pass therethrough but the burr cannot pass therethrough.

9. The milling system as recited inclaim 8, further comprising a bearing housing mounted on the shaft of the mill and at least one bearing disposed within the bearing housing.

10. The milling system as recited inclaim 8, wherein each of the plurality of guide paths has a portion sized so that the shaft of the mill can pass therethrough but the burr cannot pass therethrough.

11. The milling system as recited inclaim 8, further comprising:

the burr having an effective radius radially outwardly extending from the exterior surface of the shaft to a maximum outer radius of the burr; and

a template comprising:

a body at least partially bounding an opening; and

a partition wall disposed within the opening of the body and connected to the body, the partition wall having opposing side surfaces with a thickness extending therebetween, the thickness being not more than twice the effective radius of the burr.

12. The milling system as recited inclaim 8, further comprising a tubular bearing housing encircling the shaft of the mill such that the mill can freely rotate within the bearing housing, the bearing housing having a lower stem portion received within a select one of the plurality of guide paths of the template and an annular shoulder resting on a top surface of the template.

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