US20040162561A1 - Modular patella instrument - Google Patents

Abstract

A patella clamp has a first part including a reference surface engageable with the anterior surface of a patella. The first part includes a stop surface spaced from the reference surface. A second clamping part is provided which is moveable with respect to the first clamping part. A cutting element coupled to the first clamping part is moveable with respect to the first part. The cutting element includes a shaft with an adjustable collar mounted on the shaft for movement with respect to the longitudinal axis of the shaft and cutting element. The adjustable collar on the shaft is engageable with a stop surface on the first part for spacing the cutting element a desired distance from the reference surface. A pair of gages are provided for selectively setting the position of the adjustable collar with respect to either the amount of patella bone being removed or the amount of patella bone remaining.

Description

BACKGROUND OF THE INVENTION
• A patellar clamp and reamer are used during a total knee arthroplasty procedure to prepare the posterior surface of a patellar bone to accept a prosthetic implant.[0001]
• Typically, a surgeon will select to install a patellar prosthesis either by utilizing a resurfacing technique wherein the prosthetic patella will be positioned on the prepared surface of the patella or by an insetting technique wherein the prosthetic patella will be recessed or inset into the prepared surface of the patella. Accordingly, two varieties of guides could be available for connection to the patellar clamp and could be interchangeably connectable to the clamp. The interchangeable guides permit a surgeon to use the patellar clamp during either a total patellar bone resurfacing procedure or a patella insetting procedure.[0002]
• In either a total resurfacing procedure or a patella insetting procedure, it is important that a sufficient amount of bone stock remain after resection to accept the fixation pegs of the patellar prosthesis and maintain the integrity of the remaining patellar bone.[0003]
• Prior art devices for aiding the surgeon in performing patella resections are well known to those skilled in the art. For example, Peterson, in U.S. Pat. No. 4,633,862, teaches a method and instruments for the installation of a patella button prosthesis which involves performing a patella resection.[0004]
• In particular, Peterson describes a saw guide which comprises a pliers-like instrument having a pair of mutually pivotable jaw members. The jaw members are designed so as to enable them to surround the outer periphery of the patella with each jaw member having a respective handle, integrally formed therewith, which handles may be pivoted so as to pivot the jaw members to and from engagement with the patella periphery. At the ends of the handles, a locking device is provided which enables the locking of the jaw members about the patella periphery. The Peterson device requires that a flat saw blade be guided over the face of the jaw members after the patella has been set to the correct depth between the members.[0005]
• U.S. Pat. No. 5,147,365 relates to a patella osteotomy guide in which the jaw members include a slot for guiding the flat saw blade and an arm for setting the saw blade depth in the patella.[0006]
• Milling instruments are known in the preparation of the femur for a prosthetic implant. One such milling system is disclosed in U.S. Pat. No. 4,721,104 in which the area between the condyles of a femur is shaped. U.S. Pat. No. 5,417,695 shows the use of a milling instrument to prepare the condylar area of a femur prior to receiving an implant.[0007]
• U.S. Pat. No. 5,486,177 relates to a patella milling instrument having a clamp which contacts the underside of the patella. A similar clamping tool is shown in U.S. Pat. No. 5,284,482.[0008]
• U.S. Pat. No. 5,222,955 relates to a reaming system designed to cut a conical bore in a patella surface while the patella is being held in a patella clamp similar to that disclosed in U.S. Pat. No. 5,284,482.[0009]
• U.S. Pat. No. 5,941,884, the teachings of which are incorporated herein by reference, relates to a patella clamp which includes indicia of both the amount of bone resected and the amount of bone remaining. The resection depth is set via a stop collar on a toothed extension. Corvelli et al. does not provide any method of setting the depth of the patella milling based on the amount of bone remaining. U.S. Pat. No. 5,575,793 is similar in that a gage is provided to set the amount of bone to be removed.[0010]
SUMMARY OF THE INVENTION
• It is an object of the invention to provide an improved apparatus and method for facilitating the preparation of the natural patella to receive a patellar prosthesis.[0011]
• It is an additional object of the invention to provide a clamping system which can hold the patella in position during resection and which can be set to either resect a predetermined amount of bone from the patella or, alternately, to set the depth of the remaining bone on the patella.[0012]
• It is an additional object of the invention to provide a clamping system wherein various modular instruments may be easily attached and removed from the gripping portion of the clamping system.[0013]
• These and other objects and advantages of the invention are provided by a patella clamp which has a first part, including a jaw reference surface engageable with an anterior surface of the patella and includes a stop surface spaced from the patella engaging surface. A second part is moveable with respect to the first part and a cutting element also moveable with respect to first part is provided. The preferred cutting element includes a shaft having an adjustable collar mounted on the shaft for movement with respect to the longitudinal axis of the shaft. The adjustable collar is engageable with the stop surface on the first part for spacing the cutting element a desired distance from the first jaw reference surface. The collar position may be set with at least one gage to limit the movement of the reamer based on either the desired amount of bone remaining or the amount of bone removed. A separate marker is provided for indicating the position of the reamer with respect to either the patella bone remaining or the amount of bone removed.[0014]
• In a preferred embodiment, two gage elements are provided, one for setting the position of the collar along the shaft with respect to the first jaw patella contacting reference surface based on the amount of bone remaining and one based on the amount of bone removed. The two gage elements may either be independent of the structure of the patella clamp or can be made part of the clamp.[0015]
• The shaft includes at one end a cutting element such as a reamer or end mill which is used to shape the posterior surface of the patella. At the other end the shaft includes a coupling portion for engaging a rotary tool such as a drill chuck mounted on an electric battery or air powered tool. The shaft has a collar engaging portion with external ratchet like teeth which selectively engage complementary internal teeth on the collar. The teeth on the collar may be moveable into and out of engagement with the teeth on the shaft so that the collar may be easily adjusted axially along the shaft.[0016]
• The second jaw part also includes a clamping element or jaw which is tubular and has circumferential teeth for engaging the bone of the patella. The cutting element may be cylindrical in shape and extend within the tubular clamping jaw. Thus, the tubular jaw holds the patella in position as the bone removal operation with the cutting element progresses. Cutting of the patella proceeds after the first and second part are locked in position with the patella firmly clamped between the tubular clamping jaw and the patella engaging surface which engages the anterior side of the patella. The cutting element then moves independently of the first and second clamping parts.[0017]
• The tubular clamping jaw and the opposite engaging surface mounted on the first part are removably attached to the body or frame of the clamp. This permits not only different size clamping parts to be utilized but allows for the use of other cutting tools to be mounted on the clamp.[0018]
• The shaft has a flange or stop surface for engaging a second or outwardly facing surface of the collar and upon engagement of the collar surface and shaft surface the surface of the collar which contacts the stop surface on the first part is spaced from the reference surface a distance allowing the cutting element base to be positioned adjacent the reference surface engageable with the anterior surface of the patella when the collar and said stop surface contact. Thus, the distance between the flange and corresponding collar surface is identical to the amount of the bone remaining on the patella after the cutter removes bone until the corresponding collar and first part stop surface is engaged. Similarly, the distance between the collar stop surface and the stop surface on the first part equals the amount of bone to be removed.[0019]
• A pair of gage elements are provided with each gage having a plurality of steps of different height for varying for the bone remaining or bone removing thicknesses for setting the position of the collar along the shaft. The steps can be in 1 millimeter increments with six (6) steps being on each gage element. Obviously, fewer or a greater number of steps may be included. The bone remaining thickness gage is inserted between the stop surface on the collar and the stop surface on the first jaw part and the bone remaining gage would be inserted between the flange on the shaft and the top surface of the collar.[0020]
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 is an isometric view of the patella clamp of the present invention including the reaming system for milling the posterior face of the patella;[0021]
• FIG. 2 is an isometric view of the patella clamp of FIG. 1 minus the reaming system;[0022]
• FIG. 3 is an isometric elevation view of the patella clamp of FIG. 1 including the reaming system with a patella mounted therein;[0023]
• FIG. 4 is an enlarged isometric view of the patella clamp of FIG. 3;[0024]
• FIG. 5 is an isometric view of the patella clamp of FIG. 1 including a modular drill guide template mounted thereon;[0025]
• FIG. 6 is an isometric view of the drill guide template disengaged from the patella clamp of FIG. 5;[0026]
• FIG. 7 is an isometric view of the outermost portion of the reaming system of the present invention including a bone remaining depth gage;[0027]
• FIG. 8 is an isometric view of the depth gage shown in FIG. 7;[0028]
• FIG. 9 is an isometric view of the outermost portion of the patella cutting system including a bone removing depth gage capable of setting the amount of bone removed from the patella;[0029]
• FIG. 10 is an alternate embodiment of the patella clamp in which a pair of jaw members intended to grip the periphery of the patella are provided; and[0030]
• FIG. 11 is an isometric view of the patellar clamp of the present invention including a modular clamp for engaging the posterior surface of a polyethylene patella implant.[0031]
DETAILED DESCRIPTION
• Referring now to the drawings, and especially to FIG. 1 thereof, an apparatus constructed in accordance with the present invention is shown in the form of a[0032]patella clamp20 having aframe22. An upper arm handle24 is affixed to theframe22 and a lower arm handle26 is mounted upon theframe22 atpin28 for sliding movement in aslot33 offrame22 toward and away from theupper handle24. Asupport platform30 is attached to frame22 at alower end32 of aside bar34 of theframe22. Preferably,platform30 is removably attached to acarrier43 which in turn is fixed toside bar34. Apin35 mountsarm24 to frame22.Platform30 includes a bone contactingreference surface36 extending laterally across the upper surface ofplatform30.Side bar34 also includeslot33 in whichpin28 slides. In the preferred embodiment, a patella clamping member shown in the form of a barrel or tubular shapedclamp member40.Clamp40 is attached tolower arm26 by amodular carrier42 mounted for movement withinslot33 ofside bar34 viapin28.Clamp40 is coupled with thelower handle26 so that pivotal movement of thelower handle26 with respect toarm24 aboutpin39 will move thecarrier42 longitudinally along theside bar34 offrame22 toward and away fromplatform30.
• As best seen in FIG. 3, the posterior side of a[0033]patella50 which is to be prepared for the reception of a patellar prosthesis (not shown), is held in a preparation position within thepatella clamp20 byclamp40 andplatform30. This is done by evertingpatella50 and applyingpatella clamp20 to the everted patella, with thehandles24 and26 essentially perpendicular to the mechanical axis of the leg. Alternatively, the patella may be retracted by rotating it less 180° and theclamp20 applied.Patella50 includes ananterior surface56, which contacts surface36 ofplatform30 and aposterior surface58 facingclamp40. Thepatella50 has a bone thickness extending betweenanterior surface56 andposterior surface58. Theposterior surface58 provides the articular surface ofpatella50 and is to be prepared for the reception of a patellar prosthesis. In the preferred construction,bone contacting surface36 of thereference platform30 includesspikes57 to contact and positively locate theanterior surface56 of thepatella50.Clamp40 includesteeth63 around thebone contacting rim60 and is dramatically sized to extend around the bony periphery of the patellar.
• In the preferred embodiment, as shown in FIG. 2, the[0034]clamp member40 is modular and is removably coupled tocarrier42 ofarm26 by asnap connection59. Likewise,platform30 is preferably removably coupled tocarrier43 ofarm24 by asnap connection61. Thus, two ormore clamp members40 of different size can be used. When theclamp40 is selected from a plurality of clamp members of different size, the appropriate size is chosen so thatarcuate rim60 ofclamp barrel40 fits closely around the perimeter ofpatella50 while resting upon the peripheral bone ofpatella50. Preferably, rim60 includes a plurality ofserrated teeth63 to hold the patella in position during milling. While only twocarriers42,43 are shown, additional carriers could be mounted onarms24,26 if it was desired to include additional modular instruments onclamp20.
• [0035]Clamp20 is applied topatella50 by movingclamp member40 towardreference platform30 until the bone ofpatella50 is engaged withpatella50 centrally positioned withinrim60 ofclamp member40. At this point, thepatella clamp20 is secured in place by locking thelower handle26 against movement away from theupper handle24, as by a locking ratchet system withratchet teeth65 engaged by atrigger lock67. Alternatively, as shown in U.S. Pat. No. 5,941,884, a lock on one arm can engage a toothed locking rod mounted to the other arm. In this design, a reliable lock button is selectively actuated to release the lock to permit relative movement of the arms and to lock the arms in the selected location by engaging the lock rod.
• Turning now to FIGS. 3 and 4, a bone-cutting tool is employed in the resection of[0036]patella50, and is shown in the form of a reamer orend mill80 having arotary cutting face82 which engagesposterior patella face58, and ashaft88 for rotatingend mill80. In the preferred embodiment,end mill80 is releasably attached toshaft88 byconnector89. Thus end mills of different size can be attached toshaft88 as desired.Shaft88 is driven by amodular adapter84 which includes adrive socket86 adapted to engage a standard power tool such as a drill (not shown). Preferably,shaft88 is journaled for rotation in abushing member90, about a central longitudinal axis L of thebushing member90.Shaft88 is free to move linearly within thebushing member90 in a direction along the longitudinal axis L. Afirst stop surface98 extends laterally along the upper end of thebushing member90. As best seen in FIG. 7, a stop member in the form of astop collar100 includes asecond stop surface102 juxtaposed with and confronting thefirst stop surface98.Collar100 can be adjusted alongtoothed portion104shaft88. Preferably,collar100 is releasably engaged withtoothed portion104 at the upper end of thereamer shaft88. Thestop collar100 is coupled to thetoothed portion104 ofshaft88 by a coupler which includes anactuator button106 selectively operated to release thestop collar100.Stop collar100 moves longitudinally along thetoothed portion104 andbutton106 is used to selectively lock thestop collar100 at a selected location along thetoothed extension104, for purposes to be described hereinafter. In the preferred embodiment,button106 has internal teeth (not shown) which selectively engagetooth portion104 to selectively permit movement ofcollar100.Toothed portion104 terminates at aflange105.Flange105 may include asocket107 for receivingmodular drive adapter84. In thepreferred embodiment flange105,toothed portion104 and the lower portion ofshaft88 are made of one piece. The markings shown may be etched on the lower portion.
• In the preferred embodiment,[0037]reamer80,reamer shaft88,collar100 andbushing member90 together comprise anoutrigger cutting assembly110 which is affixed to frame22 via anattachment92 as shown in FIG. 2.Attachment92 is integral withframe22. A releasable connection including apin93 is coupled toassembly110 so thatassembly110 may be releasably coupled to frame22 of thepatella clamp20 viaattachment92. This connection locates thebushing member90 accurately in position relative to theplatform30reference surface36 with the axis L intersecting thereference platform surface36 generally perpendicular to and at the approximate center of the patella preparation position. Thus, the longitudinal axis L is the axis of rotation ofshaft88 andreamer80 as well as the center ofclamp40.
• Once the[0038]outrigger cutting assembly110 is secured to frame22 ofpatella clamp20, as illustrated in FIGS.1 to4, thereamer80 is allowed to drop downwardly, with thereamer shaft88, until the cuttingsurface82 of thereamer80 rests upon theposterior surface58 of thepatella50, as shown in FIG. 4. At this point in the procedure, the surgeon is able to determine the thickness of thepatella50 merely by observing an indicator in the form of avisible scale120 onshaft88 at the top ofrecess122 on thebushing member90. Thus, as best seen in FIG. 4, as well as in FIG. 3,recess122 is located accurately relative toplatform30,reference surface36 andscale120 is calibrated in terms of distance between cuttingsurface82 ofreamer80 andreference surface36 on whichanterior surface56 ofpatella50 rests. In this manner, the surgeon is provided with a quick and accurate direct intra-operative measurement which the surgeon will use to determine the amount of bone to be removed during subsequent resection ofpatella50, without the necessity for introducing supplementary instruments or interruption of the procedure.
• Once the surgeon determines the amount of bone to be removed during resection, the depth of resection is selected readily, again intra-operatively, directly and without the necessity for supplemental instruments or other apparatus. As discussed below, the surgeon may set the amount of bone to be removed based either on the desired amount of bone the surgeon wants remaining or the amount the surgeon wants to remove. Referring now to FIGS. 3 and 7-[0039]9, the longitudinal distance between thefirst reference surface98 and thesecond reference surface102 determines the extent of longitudinal travel of thereamer80 as thereamer80 resects the bone ofpatella50. Thus, by setting position of thestop collar100 on thetoothed portion104, the depth of resection is determined. The toothed configuration ofportion104 assures that thestop collar100 is moved in precisely determined fixed longitudinal increments related to prescribed increments in the depth of resection. Typically, the increments are provided with a magnitude of one millimeter.
• As seen in FIGS.[0040]7-9, the depth of resection may be set in two ways. First, as shown in FIGS. 7 and 8, adepth gage300 may be used to set the amount of bone remaining.Depth gage300 includes, in the preferred embodiment, six separate depth gage elements302-312 which set the amount of bone remaining onpatella50 after engagement ofsurface102 andsurface98. In the preferred embodiment, depth gage elements302-312 start at a minimum of 11 millimeters and increase to 16 millimeters in 1 millimeter increments. Thus, the thickness of the bone remaining may be varied between 11 and 16 millimeters. The bone remaining is set by adjusting the difference betweenupper surface107 ofstop collar100 and the bottom ofsurface109 offlange105. This requires that whensurface109 offlange105 abutssurface107 ofcollar100 andsurface102 then contacts topsurface98 ofbushing90, cuttingface82 is flush withsurface36 ofplatform30.
• In the preferred embodiment, each gage element[0041]302-312 is in the form of aU-shaped recess314 surrounded by asurface316 recessed fromtop surface318. The distance betweensurface316 andtop surface318 ofgage300 varies to produce a thickness between the bottom surface and thesurface316 equal to the 11 to 16 millimeter desired bone remaining onpatella50. Alternately, the amount of bone removed can be set with agage400 which is in all respects similar to gage300 (i.e., preferably includes six (6) gage elements402-412) with the exception that to set the bone removing amount, the gage is inserted betweensurface98 andsurface102 ofstop collar100. In the preferred embodiment,gage400 has the identical U-shaped recesses, however, the distance between recessedsurfaces416 andtop surfaces418 are varied to indicate the distance of travel betweensurface98 andsurface102 during reaming and indicating how much bone is removed. This is indicated on the top surface of the gage with the six (6) U-shaped openings varying from −7 millimeters to −12 millimeters.
• The surgical method of the present invention will now be described. After exposing the patella in a standard manner, the surgeon measures the patella thickness using any one of a number of suitable instruments. Typical ranges of patella thickness as measured between the anterior and posterior surfaces of the natural patella vary from 8 to 40 millimeters and from 30 to 55 millimeters in diameter. Referring to FIG. 2, the surgeon selects a properly sized barrel shaped[0042]clamp member40 and attaches it tocarrier42 which carrier is moveable inslot33 ofside bar34 by the actuation ofhandles24 and26.Platform30 is then attached viamodular connection61 tocarrier43 which carrier is stationary with respect toside bar34 andcarrier42. As indicated above, a plurality of differentsize clamping barrels40 may be used so that the periphery of various size patellas may be engaged. In the preferred embodiment, five (5) clamping barrel sizes from 34 millimeters to 50 millimeters in 4 millimeter increments are included in a kit. Theteeth63 ofbarrel40 are designed to engage the patella and not the surrounding ligaments. As seen in FIG. 2, aratcheting mechanism65,67 is provided so the surgeon can lock the relative position ofcarriers42 and43 once the patella is firmly clamped as discussed below.
• The surgeon now assembles the reaming or milling[0043]assembly110 by choosing a resurfacing patella cutter which matches the clampingbarrel40 size. The assembled cuttingassembly110 is then assembled to frame22 by means of aconnection92,93. In the preferred embodiment, the lock is obtained when an audible click is heard, i.e.pin93 engagesextension92 onframe22. Of course, any connection
• The assembled patella clamp is then applied to the everted or retracted[0044]patella50 with thehandles24,26 with axis L preferably perpendicular to the long axis of the leg. As stated above, theteeth63 ofbarrel40 are moved by the movement ofarms24,26 towards one another into engagement with the peripheral bone of thepatella50. Theratchet mechanism65,67 may be then utilized to lock the clamp in position. Reamer orend mill82 is then moved into position contacting theposterior surface58 ofpatella50. The current patella thickness is shown onscale120 as best seen in FIG. 4. The surgeon then has two choices for determining the amount of bone to resect from the patella articulating surface. He may either decide to use the bone remaining method as shown in FIGS. 7 and 8 or the bone removing shown in FIG. 9. As indicated above with regard togages300 and400, there are preferably 6 different bone remaining or bone removing options. With regard togage300 the 6 options are 11 millimeters to 16 millimeters in 1 millimeter increments. The utilization ofgage300 as shown in FIG. 7 will determine how much bone the surgeon wishes to remain on the patella.Bone gage300 is placed onshaft104 in contact withupper surface111 ofstop collar100.U-shaped opening314 must sit flush withreamer shaft111 and must be placedtop flange105 andtop surface107 ofcollar100. Of course,depth gage300 must be removed prior to milling.
• The surgeon also may wish to set the resection level based on the amount of bone removed. In this situation, a[0045]gage400, as shown in FIG. 9, is utilized in a similar manner togage300 with the exception that it is located betweensurface98 ofbushing90 andbottom surface102 ofstop collar100. In the preferred embodiment, the six (6) depth removing gage portions include six (6) different bone removing options, −2 millimeters and −8 millimeters to −12 millimeters in 1 millimeter increments. The bone removingdepth gage400 is designed so there can never be less than 10 millimeters left of bone. Again, theU-shaped portion414 must sit flush aroundreamer shaft104 to ensure that the proper depth is set.
• Once the depth has been set by locating[0046]collar100 based on either the desired bone remaining or the desired bone to be removed, thedrive84,86 is coupled to recess107 inflange105 and the reaming operation is commenced.Reamer80 is simultaneously rotated and advanced. The reamer shaft is advanced untilsurface102 ofcollar100 contacts surface98 ofbushing90. The remaining thickness of the resectedpatella50 may then be read fromscale120 onshaft88. Should the surgeon determine that further resection is required, thestop collar100 is merely reset to the desired further amount of resection and thereamer80 then is advanced through the corresponding further amount of linear travel. Once reaming is complete, the surgeon unlocks the ratchet lock usingtrigger mechanism65,67 and releases pin93 so that theoutrigger assembly110 may be removed thereby exposing the newly created resectedsurface130 of the resectedpatella50 as shown in FIG. 6.Resected surface130 is essentially planar and normal to axis L.
• Referring to FIGS. 5 and 6, fixation hole placement can be done in a well known manner utilizing the[0047]drill template140 and the drill assembly141. To accomplish this,barrel clamp40 is removed fromcarrier42 and thetemplate140 which includes aconnector59, is inserted into place incarrier42. Again, in the preferred embodiment, there is a series of drill templates for various size prosthetic patellas with the template chosen providing the most complete coverage of the resurface patella without any overhang. Withpatella clamp20 secured in place so that thedrill template140 is located in position against resectedsurface130, as illustrated in FIGS. 5 and 6, an assembly141 includingdrill142 is advanced through theapertures144 in thedrill template140 for appropriate location of holes inpatella surface130. These holes correspond to the lugs of a typical patellar prosthesis (not shown). As is well known, a trial prosthesis may be placed onsurface130 of the resectedpatella50 and the overall anterior/posterior thickness may be measured to determine whether the proper patella thickness has been restored. The patella tracking can then be assessed prior to the permanent implantation of the prosthetic patella implant. Normally, the prosthetic patella is made of polyethylene and a clamping element shown in FIG. 11 may be provided for attachment to arm26 and used in a manner similar tobarrel clamp40 anddrill template140. Referring to FIG. 11 there is shown aclamp part500 for pressing on the posterior side of thepatellar implant502 whileclamp platform30 presses on the anterior bony portion of the patella. This clamping can be performed during the curing of bone cement holding the polyethylene implant to the prepared patella surface. Also shown in FIG. 11 arerelease buttons504 which are used to disengage the various clamping elements fromcarriers42,43.
• Thus, after forming the holes,[0048]template140 would be removed and a modular clamp shaped to receive the posterior surface of the polyethylene implant would be mounted onconnector42. The activation ofhandles24,26 then applies pressure on the implant forcing, in the preferred embodiment, the three lugs on the implant into the three drilled holes. The implant may be either press fit or cemented into place on the remaining bone of the patella. If cementing is used, theclamp20 may be utilized to maintain pressure while the cement cures (see FIG. 11).
• Referring to FIG. 10 there is shown an alternate embodiment of the patella clamp of the present invention. The body of the[0049]clamp including handles24,26,frame22,carriers42,43 remains the same. However, instead ofplatform30 and barrel shaped clampingmember40, a pair ofarms200,202 are provided with connection portions similar to59 and61. Thus, prior to insertion ofplate30 andmember40 or after the removal ofplate30 andbarrel member40,arms200,202 are snapped into position incarriers42,43.Arms200,202 havebone engaging teeth204 designed to engage the periphery of the patella. The clamp can now grip the periphery of a patella. Asaw guide206 can be attached to either or botharms200,202 for guiding a saw blade (not shown). Thus, afterarms200,202 securely grippatella50, the posterior surface thereof may be resected in a known manner.Arms200,202 of different size can be provided and may be provided as part of a kit which may include all or some of theclamp20, two ormore platforms30 and clampelements40 of different size, gages300,400, and two ormore clamps500 and two ormore cutters80.
• In the preferred embodiment,[0050]buttons304 have recesses designed to receive and lockingly engageelements59,61.Buttons504 are spring loaded so that when the buttons are released they lock ontopins59,61. Depressingbuttons504 then releases thepins59,61 so that the modular instruments/clamping elements may be removed. A similar system is used toreleasably mount assembly110 to pin92 viabutton93.
• Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.[0051]

Claims (34)

1. A patellar resurfacing clamp comprising:

a first part having a first surface engageable with a surface of the patella and including a second surface spaced from said first surface;

a second part moveable with respect to the first part;

a patella cutting element coupled to said first part and moveable with respect to said first part, said cutting element having a shaft and an adjustable collar mounted on the shaft for movement with respect to a longitudinal axis of the shaft, said adjustable collar on said shaft having a first stop surface engageable with said second surface on said first part for spacing said cutting element a distance from said first surface; and

at least one gage element for selectively setting the position of said adjustable collar on said shaft with respect to the first surface contacting the patella based on either the amount of patella bone being removed or the amount of patella remaining.

2. The patella clamp as set forth inclaim 1 wherein there are two gage elements, one for setting the position of said collar along the shaft with respect to said amount of bone removed and one for setting the position of said collar along the shaft with respect to the amount of bone remaining.

3. The patellar clamp as set forth inclaim 1 wherein the shaft is a drive shaft.

4. The patellar clamp as set forth inclaim 3 wherein said shaft has a portion having external teeth for engaging the collar.

5. The patellar clamp as set forth inclaim 4 wherein said collar has an internal locking element for selectively engaging said external teeth on said shaft to set the adjustment of said collar along said longitudinal axis.

6. The patellar clamp as set forth inclaim 5 wherein said collar is moveable from a first position where said collar may slide with respect to said shaft to a second position where said teeth on said shaft and said collar engage and prevent further axial movement.

7. The patellar clamp as set forth inclaim 1 wherein said second part includes a tubular clamping jaw for engaging a surface of the patella opposite a patella surface engaging said first surface of said first part.

8. The patellar clamp as set forth inclaim 7 wherein said tubular clamping jaw acts as a guide for said cutting element.

9. The patellar clamp as set forth inclaim 8 wherein said tubular clamping jaw is removably attached to said second part so that a size of said jaw may be varied by providing a plurality of clamping jaws of different diameters.

10. The patellar clamp as set forth inclaim 7 wherein said clamping jaw includes teeth for engaging the patella bone.

11. The patellar clamp as set forth inclaim 1 wherein said second part includes a scale indicating a posterior-anterior thickness of said patella.

12. The patellar clamp as set forth inclaim 1 wherein said cutting element is an end mill.

13. The patella clamp as set forth inclaim 1 wherein said cutting element is a reamer.

14. The patellar clamp as set forth inclaim 1 wherein said shaft includes a stop surface for engaging a second stop surface on said collar and upon engagement of said surfaces said collar first stop surface is spaced from said first part second stop surface a distance allowing a cutting face of said cutting element to be positioned adjacent said first surface of said first part when said collar first stop surface and said first part second surface contact.

15. The patellar clamp as set forth inclaim 14 wherein the distance between said collar second stop surface and said shaft stop surface element along said longitudinal axis is equal to the bone remaining on the patella after cutting the patellar by moving said cutting element until said collar first stop surface engages said second surface of said first part.

16. The patellar clamp as set forth inclaim 15 wherein said at least one gage element has a plurality of steps of different height for varying the bone remaining thickness on the patella by spacing the second stop surface of the collar a desired distance from said stop surface on said shaft.

17. The patellar clamp as set forth inclaim 16 wherein the distance between said collar first stop surface and said first part second surface is equal to the bone to be removed from the patella.

18. The patella clamp as set forth inclaim 17 wherein said at least one gage has a plurality of steps of different height for varying the amount of patella bone removed by spacing the collar first stop surface a desired distance from said first part second surface.

19. A patella clamping system comprising:

a first clamp part having a reference surface engageable with an anterior surface of a patella, said first part including a stop surface spaced from said reference surface along an axis;

a second clamp part moveable with respect to said first clamp part along said axis;

a cutting element for resecting bone from a patella rotatably mounted on said first clamp part and moveable with respect to said axis, said cutting element having a first adjustable stop surface engageable with said stop surface on said first clamp part;

a first gage element for setting the position of said adjustable stop surface with respect to the reference surface on said first clamp based on the amount of bone to be removed from the patella; and

a second gage element for setting the position of said adjustable stop surface with respect to the reference surface on said first clamp based on the amount of bone to remain on the patella.

20. The patellar clamp as set forth inclaim 19 wherein said cutting element includes a shaft having a stop surface for engaging a second adjustable stop on said cutting element surface and upon engagement of said surfaces, said first adjustable stop surface on said cutting element is spaced from said first part stop surface a distance allowing a cutting face of said cutting element to be positioned adjacent said reference surface of said first part when said adjustable first stop surface and said first clamp part stop surface contact.

21. The patellar clamp as set forth inclaim 20 wherein the distance between said second adjustable stop surface and said shaft stop surface along said axis is equal to the bone remaining on the patella after cutting the patella by moving said cutting element until said first adjustable stop surface engages said stop surface of said first clamp part.

22. The patellar clamp as set forth inclaim 21 further comprising at least one gage element having a plurality of steps of different height for varying the bone remaining thickness on the patella by spacing the second adjustable stop surface of a desired distance from said stop surface on said shaft.

23. The patellar clamp as set forth inclaim 22 wherein the distance between said first adjustable stop surface and said first clamp part stop surface is equal to the bone to be removed from the patella.

24. The patella clamp as set forth inclaim 23 wherein said at least one gage has a plurality of steps of different height for varying the amount of patella bone removed by spacing the first adjustable stop surface a desired distance from said first clamp part stop surface.

25. A kit of instruments for preparing a patella for receiving an implant comprising:

a clamp having at least two carriers for releasably mounting clamping elements;

at least two cutting elements of different size for engaging a posterior surface of the patella and adapted for releasably mounting on said clamp; and

at least two clamping elements adapted to engage a peripheral surface of the patella extending between the posterior surface and an anterior surface of the patella said clamping elements adapted for releasably mounting on said carriers.

26. The kit as set forth inclaim 25 further comprising at least two clamping elements of different size for engaging a posterior surface of said patella, said two clamping elements adapted to releasably engage at least one of said carriers.

27. The kit as set forth inclaim 26 further comprising at least two clamping elements of different size shaped to engage the anterior surface of a patellar implant, said implant engaging clamps adapted for releasably mounting on at least one of said carriers.

28. The kit as set forth inclaim 26 further comprising at least two clamping elements in the form of drill guides for engaging the posterior side of a patella, said drill guide adapted to releasably engage at least one of said carriers.

29. The kit as set forth inclaim 25 further comprising at least two clamping elements shaped to engage the posterior surface of a patellar implant, said implant engaging clamps adapted for releasably mounting on at least one of said carriers.

30. The kit as set forth inclaim 25 further comprising at least one gage element for setting the amount of bone to be removed from the patella during preparation and at least one gage element for setting the amount of bone to remain on the patella after preparation.

31. The kit as set forth inclaim 26 wherein said clamping elements for engaging the posterior surface of the patella have a tubular shape.

32. The kit as set forth inclaim 31 wherein a circumferential surface of said tubular clamping element contacting said patella has teeth for engaging patellar bone.

33. The kit as set forth inclaim 25 wherein a bone contacting surface of said two clamping elements engaging the periphery of the patella include teeth.

34. The kit as set forth inclaim 25 wherein the at least two cutting elements are milling cutters.

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