SIZING AND CUTTING GUIDE FOR RESECTING THE DISTAL END OF THE FEMUR

Abstract: A guide, and a method of use of the guide, for making resections to the distal end of a femur during the replacement of a knee joint. The guide comprises a miter block, a posterior guide shoe and an interior guide stylus. The miter block has a plurality of guide slots for alignment and orientation of a blade for making the cuts to be made to fit a particular sized implant. The posterior guide shoe is adapted to contact the posterior curved surface of the femur to position the miter block in the posterior/anterior sense against the distally resected femur. The anterior guide stylus is adapted for gauging the size of the femur relative to the size of an artificial knee implant corresponding to the guide. The tip of the anterior guide stylus is at a predetermined location relative the upper surface of the miter block such that the position of the tip will coincide with the anterior end of the articulation zone of the femur when the posterior guide shoe is properly positioned if the correct size miter block and accordingly implant have been chosen. The predetermined location is such that when the miter block is later used as a guide to the anterior resection, the cut will exit the anterior condyle at that end of the articulation area.

Description: SIZING AND CUTTING GUIDE FOR RESECTING THE DISTAL END OF THE FEMUR This invention relates to implantation of artificial knee joints, and more particularly to a sizing and cutting guide and a method of preparing the femur to receive the implant. Background of the Invention The geometry of a condylar knee implant is optimized to transmit the normal forces experienced during the walking process, from the femur, through the implant and down through the joint to the tibia. The complex geometry of the normal knee provides an articulating surface with a constantly varying radius of curvature to allow for this transmission of force to be optimized for all angles of bend. An implant aims to recreate this. To assist in this, the inner surface of the condylar implant should ideally follow a similar varying radius of curvature to maintain the same thickness of material throughout the implant. Because it is impractical to achieve this degree of shaping of the distal end of the femur, the design compromise adopted uses a number of flat surfaces approximating the curved surface. The usual design adopted is made up of five flat surfaces, with the posterior three divided by the cruciate cleft. Five surfaces must therefore be prepared on the distal condyles to exactly match the implant. This is especially important for a press-fit implant where good bone apposition is critical. It is also important to choose a correctly sized knee implant from the range of sizes available to fit the particular individual since individuals knee joints do vary substantially. The choice of the correct implant is important because if too small an implant is used, then the articulation of the knee will be seriously affected and may be grossly unstable with tensioning problems at the extremes of motion. The correctly sized implant will imitate the exact dimensions and radii of curvature of the normal knee, by replacing onlyiethat bone which has been removed. Join -tensioning will—be constant throughout the full range of movements and the joint will be stable. With a larger implant the joint will be "tight" with either restricted flexion or laxity and instability during leg extension. The approximate size of a knee implant can be determined prior to the operation by analysis of X-rays of the knee. However, the surgeon will need to make his final size assessment during the process of preparing the femoral condyles. The initial preparation of the condylar bone involves removal of the most distal bone surface perpendicular to the mechanical axis of the knee articulation and is accomplished by means of a device which relates the cut surface to a varus angle to the axis of the femur. This preparation affects the final orientation of the implant, but does not determine the size or position (mediolateral or anterior-posterior) of the final implant. The positioning of the implant should be relative to available anatomic landmarks, and the correctly sized cutting guide should be placed with respect to these landmarks in order to align the implant correctly. Implant location is in the sagittal plane of the leg and therefore the anatomic landmarks should, ideally, be picked up from this plane for the most satisfactory positioning data. Summary of the Invention The invention has therefore been made with these points in mind and according to the invention in one aspect there is provided a method of aligning the cuts to be made to the femoral condyles during the replacement of a knee joint with an artificial implant, in which, after a first distal resection at the end of the femur has been made in a plane perpendicular relative to the mechanical axis of the leg, the surgeon fixes to the resected end of the femur a miter block having an upper surface with abuts the resected end of the femur, the miter block being chosen from a range of such blocks each corresponding to one of a range of implant sizes, the surgeon choosing the miter block which corresponds to the expected size of the implant, e.g., as previously determined from X-ray analysis of the joint, the miter block having posterior guide means projecting upwardly from the miter block to position the miter block such that the posterior guide means contacts the posterior curved surface of the femur with the upper surface of the block abutting the resected surface of the femur, the miter block additionally having anterior guide means including a tip which is positioned at a predetermined location relative the upper surface of the miter block, that predetermined location being such ±hat when the miter block is later used as a guide to the anterior resection, the cut will exit the anterior condyle at that end of the articulation area, determining whether the tip coincides with the visually discernible point on the anterior condyle which is the end of the articulation area of the joint, and in the event that the tip does not coincide with that point, then choosing a different miter block and therefore ultimately a different implant such that for the ultimately chosen miter block the tip is a best fit relative that visually discernible point on the anterior condyle which is the end of the articulation zone of the joint. The selected miter block can thereafter be used as a guide to make additional femoral cuts before the selected implant is fitted over the resected femur. Also according to the invention there is provided a guide for making additional resections to the distal end of a femur during the replacement of a knee joint, comprising a miter block having a flat upper surface to be placed face to face with a distally resected femur and having a number of guide slots for the alignment and orientation of a saw blade to make the cuts to fit a particular sized implant, posterior guide means projecting upwardly from the posterior of the miter block so as to enable the block to be positioned with the posterior guide means contacting the posterior curved surface of the femur and therefore position the miter block in the posterior/anterior sense against the distally resected femur, and anterior guide means projecting upwardly from the anterior of the miter block and including a tip which is at a predetermined location relative the upper surface of the miter block such that the position of the tip will coincide with the anterior end of the articulation zone of the femur if the correct implant and accordingly miter block have been chosen, the said predetermined location being such that when the miter block is later used as a guide to the anterior resection, the cut will exit the anterior condyle at that end of the articulation area. Posteriorly, the articulating surfaces of the knee are separated by the cruciate cleft into the lateral and medial curved surfaces. The posterior part of the articulating surface is therefore used as a reference against which the posterior guide means abut. The posterior guide means therefore indicates the most posterior section of the subsequent implant relative the posterior face of the miter block which has previously been determined by X-ray overlay to be the preferred size. Once this position has been determined, the locations for the subsequent cuts are fully referenced to this point and should ensure a satisfactory matching of the implant to the amount of bone which has been removed, provided, as is explained below, the correct implant size has been chosen. The most posterior cut will remove an amount of articular bone equivalent to the thickness of the posterior section of the implant. All other cuts are angled and referenced to this. Different anterior guide means may be provided for each miter block. Preferably however a single anterior guide means will be provided which can be removably attached to each of the range of miter blocks corresponding to the range of i " ant sizes, the position of the tip of the anterior guide raeans being adjustable to alter the spacing of the tip froi t le upper surface of the chosen miter block. In the latter case, the anterior guide means desirably includes a main t r / having means for ready attachment to the anterior face of a miter block, supporting means for slidably supporting a stylus with the said tip located at one end thereof so that the spacing of its tip can be adjusted relative the upper surface of the miter block, and scale means providing a reading of the correct adjustment of the tip relative the particular guide block chosen. Anteriorly, the articulating surfaces of the knee, under the patella, form a single curved surface with a prominent curved depression, the facia patellaris. This articulating surface is asymmetric, the lateral portion extending more proximal than the medial portion. The margins of the articulating surfaces form a pronounced cusp at the point where the facia patellaris meets the cortical bone of the knee. This cusp is also manufactured into the condylar knee implant and may therefore act as a secondary point of reference between the anatomic, and the replacement device. The location of the cusp differs for each knee size, being a proportionate perpendicular distance frr-> the cut surface of the bone. A noted above it is preferred that the anterior guide means fit directly on to the anterior face of all the sizes of miter blocks. Its tip is adjustable in a superior or inferior direction to align with the cusp on the knee. A graduated scale on t ? movable stylus represent the estimated size of tne replacement knee. The tip of the guide means is mar ined to lie a fixed dis :.nce above the upper face of the ~ er-guide cu : ng block for a set knee size. The most anterior cut indicated by t.ie miter guide cutting block is aligned to coincide with the tip, which, for a set cut miter block size, will be a fixed distance anterior, and superior, to the posterior guide means. When the anterior guide has been set the same as the chosen miter block size, then the tip should, if the implant size has been correctly estimated, just touch the margin of the cusp between the two articulating spurs. This will indicate that the anterior cut is in the correct position to allow for optimum bone replacement by the implant. If the tip does not touch the bone, or it contacts the bone before locking into position on the block, this is indicative of an incorrectly estimated implant size. In both cases, the anterior cut will result in less than optimal bone removal. The margin of the cusp between the two articulated spurs is a visible reference point since it marks the end of the articulation zone. In addition, this is the point at which one wishes the cut made for the anterior resection to exit from the bone. A tight fitting tip for the anterior guide indicates overestimation of implant size, and if this situation is not rectified, the anterior cut will remove more bone than will be replaced by the anterior portion of the implant. A loosely fitting tip indicates an under-estimation of implant size and will lead to insufficient bone removal and the likelihood that the anterior back face of the implant will not be fully supported by the bone. In either case, remedial action is required. The miter guide cutting block should be removed and the next larger size (if the tip is too tight) , or smaller size (if the tip does not contact bone) , be attached, again with the posterior guide means in contact with the posterior margin of the articulating surface. The anterior guide should be adjusted according to the new block, and the implant size reassessed. If no satisfactory combination can be obtained, i.e., an intermediate implant size between the available sizes is required, then the surgeon must decide whether to use a slightly smaller or larger implant than is optimum. The arguments for either choice are a matter of surgical practice. Obviously the larger the number of intermediate sizes of implants available, the less this will be a problem. The posterior guide means is preferably in the form of one or more shoes which are attached to the posterior side of the miter block and are upstanding therefrom to be brought into contact with the posterior surfaces of the two posterior condyles. Preferably however, the posterior shoes are removable so that once the miter block has been fixed in place, then the shoes are removed so as not to interfere with the subsequent cutting of the bone. The anterior guide means are also preferably removably attached to the miter block so that once it has been decided that the correct miter block and therefore final implant have been chosen, this anterior guide can be removed to enable the anterior resection cuts to be made without damage to the guide. The miter cutting block is known and should be affixed firmly to the femoral condyle after the final distal resection. This can be achieved by, for example, using a pair of angled nails whose axes are angled to one another. This ensures a good firm attachment of the block to the condyle during the cutting process. The nails are thereafter removed once the miter block itself is removed when all of the cuts have been completed. The miter block itself is well known and includes a number of grooves at the appropriate angles relative the surface which contacts the first distal resection on the femoral condyle and guides the surgeon in making cuts at the required angle. In a preferred embodiment of the invention there are five femoral cuts which remove an approximately constant amount of bone around the articulation surface of the femoral condyle. The larger the number of cuts the more closely this approximation can be achieved and five cuts is a satisfactory number. Other features will be pointed out hereinafter. Brief Description of the Drawing The invention will now be described, by way of example, with reference to the accompanying drawings wherein corresponding reference characters indicate corresponding parts throughout the several views of the drawing, and wherein: Figure 1 is a perspective view of a miter block used to guide the making of the cuts in the distal end of a femur; Figure 2 is a diagram showing the initial fitting of a miter block to the distal end of a femur using the posterior guide to position the block; Figure 3 is a diagram similar to Figure 2 showing the miter block attached in place; Figure 4 is a diagram taken at right angles to the diagram of Figure 3; Figure 5 is a diagram similar to Figure 3 but showing the attachment and use of the anterior guide; Figure 6 is a perspective detail showing the fitting of the anterior guide to the miter block; Figure 7 is a perspective detail showing the fitting of the posterior guide to the miter block; Figure 8 is top plan view of another embodiment of the miter block of the invention; Figure 8A is a perspective view of the miter block of figure 8, with handles mounted on the miter block; Figure 9 is a cross-sectional view substantially along line 9-9 in figure 8; Figures 10A, 10B and 10C are perspective views of another embodiment of the invention comprising an indicator block, illustrating respectively a correctly sized indicator block relative to the femur, a large indicator block relative to the femur and a small indicator block relative to the femur, which thereby indicate how the corresponding implant and miter block would fit; and Figure 11 is a cross-sectional view illustrating the indicator block of figures 10A, 10B and IOC mounted on the distal end of the femur that has been resected along a plane generally perpendicular to the mechanical axis of the femur. Detailed Description of Preferred Embodiments A miter block 10 as used to guide the making of cuts through the femoral condyles during the preparation of the femur to receive an implant is shown in Figure 1. This is largely a known item and comprises a rectangular shaped miter block 10 having an upper planar surface 12 which is designed to abut the resected end of the femur, and posterior and anterior sides 14 and 16 at right angles to the upper surface 12. As used herein, "upper" or "lower" as in upper surface 12 means the surface of the miter block 10 that faces generally upwardly or downwardly relative to the body of the patient so that the "upper" surface 12 faces generally toward the head of the patient when the miter block 10 is mounted on the femur, and the "lower" surface faces generally toward the feet of the patient. In the body of the block 10 are provided a number of guide slots 16 to 24, which are used to guide a saw when resecting the end of the femur. Removably fixed to the posterior side 14 of the miter block 10, is a posterior guide means 25 comprising a pair of shoes 26 which have guide surfaces 27 at right angles to the surface 12. The posterior guide means 25 includes a rectangular shaped projection or tab 28, which is engagable in a corresponding shoe-mounting opening 14a (Figure 5) in the posterior side 14 of the miter block 10. The shoe-mounting opening 14a of the miter block 10 has a generally rectangular cross section complementary to the rectangular cross section of the tab 28 of the posterior guide means 25 to closely receive the tab 28 in the show- mounting opening 14a. At least one, but preferably a pair of spring-loaded detent balls 29 are mounted in the miter block 10 and ~ biased into the shoe-mounting opening 14a for _ 1Q _ releasably securing the posterior guide means 25 on the miter block 10. detent balls 29 engage small detent depressions in the tab 28. Initially a cut 30 is made across the distal end of the femur, that cut having been made in a plane at right angles to the mechanical axis of the knee articulation, and a guide which forms no part of the present invention is used to determine the position of the cut and so the amount of bone removed. The resulting femur is shown if Figure 2. Having previously examined X-rays of the knee and by laying transparencies of a size corresponding to the various sizes of implants available over this, the surgeon has chosen a knee implant size. Then he takes a miter block 10 corresponding to the size of that implant and, as best shown in Figure 2, places this against the cut end 30, whilst using the posterior shoes 26 as a guide. Thus the surfaces 28 contact the posterior articulation regions of the condyle and together with the abutment of the cut end 30 against the surface 12 locate the block 10. Next an anterior guide means 36 is attached to the anterior side 16 of the miter block 10. The anterior guide means 36 includes a bracket 38 removably attached to the anterior side 16 of the miter block 10, and an elongate stylus 40 slidably supported in the bracket 38 so that the spacing of the tip 42 of the stylus 40 can be adjusted relative to the upper surface 12 of the miter block 10. A scale 43 is provided between the stylus 40 and the bracket 38 to show the position of the stylus 40 to provide an indication of the correct adjustment of the tip 42 relative to the bracket 38 and thus the miter block 10. The stylus 40 can be adjusted to and temporarily held at a number of preselected positions, each corresponding to a particular sized miter block 10, by means of a spring-loaded ball (not shown) housed in the body 38 and engaging in one of a number of detents (not shown) in the rear surface of the stylus 40. The bracket 38 also has a projection 44 which can be fixed in a hole 46 in the block 10. As best shown in Figure 6, the projection 44 has a reduced diameter portion 44a and a small ball 48 is held in a bore 50 and loaded by a spring 52 held by a grid screw 34 against the projection 44. The ball 48 therefore acts as snap-fit to allow the guide 36 to be fixed to or removed from the block 10 and engages in the portion 44a to hold the guide 36 temporarily in place. If the anterior guide 36 has been set the same as the chosen miter block size, then the tip 42 of the stylus 40 should, if the implant size has been correctly estimated, just touch the margin of the cusp between the tvo articulating spurs. This will indicate that the anterior cut is in the correct position to allow for optimum bone replacement by the implant. If the tip 42 of the stylus 40 does not touch the bone, or it contacts the bone before locking into position on the miter block 10, this is indicative of an incorrectly estimated implant size. In both cases, the anterior cut will result in less than optimal bone removal. If the implant size has not been correctly estimated the surgeon will need to replace the miter block 10 with the next largest or smallest miter block 10 corresponding to the next largest or smallest implant and the above steps repeated until he is satisfied he has the best fit. When satisfied of this, the miter block 10 is fixed in place by a pair of nails 32 passing through holes 34 in the miter block 10. This orientation of the nails 32 is best shown in Figure 4 and is such that their axes are crossed, so rigidly fixing the miter block 10 in place. Thereafter the surgeon removes the shoes 26 and the anterior guide 36 so that these do not interfere with cutting, an then makes the required cuts in the femur guided by the slots 18 to 24. Figures 8, 8A and 9 illustrate another embodiment of the miter block, herein designated 100, similar in many respects to the miter block 10 of figures 1-7. Miter block 100 includes a plurality, e.g., four, guide slots 102, 104, 106 and 108 for guiding a saw blade to make the desired cuts to the femur. Each of these guide slots 102, 104, 106 and 108 are generally continuous and stop short of the opposite ends 110 and 112 of the miter block 100. The miter block 100 also includes at least (and preferably) two generally elongate locating pegs 114 that are adapted to be closely received in locating holes drilled into the distal end of the femur. Also provided are two nail-guiding bores 116 provided in lugs 118 extending from the opposite ends 110 and 112 of the miter block 100. The nail-guiding bores 116 are provided at an angle, e.g., approximately 30-45 degrees, from the longitudinal axis of the locating pegs 114 to guide the nails 117 into the distal end of the femur. Most preferably, the lower faces of the lugs 118 are provided at an angle such that the lower faces are generally perpendicular to the longitudinal axis of the nails 117. The locating pegs 114 and nail-guiding bores 116 constitute one preferred embodiment of the means for mounting the miter block 100 on the resected surface of the distally resected femur, with the upper surface 120 of the miter block 100 mating face-to-face with the resected surface. The miter block 100 also has an opening 124 therethrough between the upper and lower surfaces 120 and 122 of the miter block 100 defining a window 124 for visualization of the posterior cruciate ligament when mounting the miter block 100 and when making the cuts to the femur. The window 124 is preferably generally rectangular in cross section and somewhat elongate in the direction extending between the posterior and anterior sides 126 and 128 of the miter block 100. The guiding slot 108 is intersected by the window 124, but is still considered generally continuous because the two segments of the slot 108 are not separated by a solid section of the miter block 100. The miter block 100 may include two threaded bores 130 in the opposite ends 110 and 112 of the miter block 100 for receiving two handles 132. The threaded bores 130 are preferably provided at an angle to the upper surface 120 of the miter block 100. The miter block 100 may also include a tab- receiving slot or recess 134 having a generally T-shaped cross section for receiving a generally T-shaped-cross- section tab on a shoe. If used with the sizing guide 200 illustrated in figures 10A, 10B, 10C and 11, the miter block 100 may be formed without such a tab-receiving recess 134. The locating pegs 114 are sufficient to locate the miter block 100 relative to the distal end of the femur. Figures 10A, 10B, 10C and 11 illustrate yet another embodiment of the invention, in which a novel sizing guide, herein indicated 200 is provided. Many aspects of the sizing guide 200 are similar to the miter blocks 10 and 100 described above with reference to figures 1-9. The sizing guide 200, however, does not include guide slots for guiding a saw blade. As illustrated in figures 10A-10C, the sizing guide 200 comprises an indicator block 202, anterior guide means 204 and posterior guide means 206. The anterior guide means 204 is similar to the anterior guide means 36 of figures 1-7, and as such comprises a generally elongate stylus 208 and a bracket 210 for adjustably mounting the stylus 208 relative to the upper planar surface 212 of the indicator block 202. Most preferably, a single anterior guide means 204 is provided in a system comprising a plurality, e.g., 5, indicator blocks 202 of various sizes each corresponding to a size miter block 100 and implant. As described above with reference to anterior guide means 36, the tip 214 of the stylus 208 is adjustable relative to the upper surface 212 of the indicator block 202, and a suitable means is provided to releasably lock the stylus 208 in a number (e.g., 5) predetermined locations relative to the upper surface 212 of the indicator block 202. A suitable scale means (similar to that shown at reference numeral 43 in figure 6) is provided to provide an indication of the correct adjustment of the tip 214 relative to the bracket 210 and thus relative to the upper surface 212 of the indicator block 202. Most preferably, the stylus 208 is generally elongate, with the end portion 216 being bent at an angle relative to the main portion 218 of the stylus 208 in the direction toward the femur 220. The end portion 216 is tapered toward the tip 214 of the stylus 208. The posterior guide means 206 is similar to the posterior guide means illustrated at reference numeral 25 in figure 7. As such, the posterior guide means 206 comprises one or more guide shoes, preferably two guide shoes similar to shoes 26 which are spaced apart but have co-planar guide surfaces. The posterior guide means 206 is preferably removably attached to the posterior side of the indicator block 202, and is upstanding from the indicator block 202 to adapt the shoes for contact with the two posterior condyles. Most preferably, posterior guide means 206 is provided with a tab 222 having a generally T-shaped cross section as illustrated in figures 10A-10C to adapt the tab 222 to be slid into a complementary shoe-mounting recess 224 having a generally T-shaped configuration. The shoe- mounting recess 224 is elongate in the direction extending between the medial and lateral sides of the indicator block 202. A depression to provided in the tab 222, and a spring-loaded detent ball is provided in the shoe-mounting recess 224, with the detent ball received in the depression to lock the posterior guide means 206 in place. Preferably, three different size posterior guide means 206 are provided as part of the system. The small size posterior guide means 206 would correspond to the #3 and #5 positions indicated on the scale in figure 6. The medium size or large size posterior guide means 206 would correspond to the #7, #9 or #11 positions. These positions correspond to a known sizing convention for femoral knee implants. As illustrated in figure 11, the indicator block 202 is provided with two drill guide holes 226 for guiding a bone drill to drill locating holes in the distal end of the femur 220. The locating holes in the femur 220 are then used to receive the locating pegs 114 of the miter block 100. An opening 227 may be provided in the indicator block 202 to receive a femoral intramedullary rod (not shown) to ensure that the indicator block 202 is positioned centrally with respect to the medullary canal. The opening 227 is elongate in the direction between the posterior and anterior sides 229 and 231 of the indicator block 202 so that the position of the indicator block 202 in the posterior/anterior direction is determined by the posterior guide means 206 and not by an intramedullary rod. Two threaded bores 228 may be provided in the indicator block 202 to allow mounting handles similar to handles 132 of figure 8A on the indicator block 202. OPERATION The sizing or gauging aspect of the invention will be described with reference to the sizing guide 200 of figures 10A-10C. Use of the miter block 10 as a gauge is similar. In figures 10A-10C, the stylus 208 has been adjusted and locked in place in its appropriate position relative to the upper surface 212 of the indicator block 202. The distal end of the femur 220 has been resected along a plane generally perpendicular to the mechanical axis of the femur. To facilitate placement of the apparatus 200, the knee should be fully flexed and all debris removed from the condylar region. X-ray analysis will have provided an indication of the likely size of the femoral condylar implant required. A sizing guide 200 corresponding to this size should be selected, and the handles mounted on the selected indicator block 202. The corresponding posterior guide means is slid into position on the indicator block 202. Figure 10A illustrates the situation when the correct sized indicator block 202 and posterior guide means 206 has been selected. The shoes of the posterior guide means 206 abut the most posterior aspect of the femoral condyles, the upper surface 212 of the indicator block 202 is in face-to-face engagement with the resected end of the femur 220, and the tip 214 of the anterior guide means 204 engages the femur 220 at the visually discernable point 230 on the anterior condyle that is the end of the articulation area of the joint. The phantom line 232 indicates that the anterior cut would intersect the visually discernable point 230. Figure 10B illustrates the situation where the indicator block 202 is too large for the femur 220, which means that the corresponding miter block and implant would also be too large. In figure 10B, the shoes of the posterior guide means 206 abut the most posterior aspect of the femoral condyles, and the upper surface 212 of the indicator block 202 is in face-to-face engagement with the resected end of the femur 220. The tip 214 of the anterior guide means 204, however, is spaced more than 2mm from the visually discernable point 230 on the anterior condyle that is the end of the articulation area of the joint, and does not engage the femur 220. Another, smaller indicator block 202 and posterior guide means 206 should be selected and the stylus 208 adjusted until a better fit is obtained. Figure 10C illustrates the situation where the indicator block 202 is too small for the femur 220, which means that the corresponding miter block and implant would also be too small. In figure 10C, the shoes of the posterior guide means 206 abut the most posterior aspect of the femoral condyles, and the upper surface 212 of the indicator block 202 is in face-to-face engagement with the resected end of the femur 220. The anterior guide means 204, however, cannot be mounted on the indicator block 202 without bending the stylus 208. The reference numeral 234 indicates the amount of interference between the stylus 208 and the femur 220. Another, larger indicator block 202 should be selected, the stylus 208 adjusted and a corresponding posterior guide means 206 selected until a better fit is obtained. After the proper sizing guide 200 has been selected, the indicator block 202 is held flush to the cut end of the femur 220 using the attached handles, and two locating holes are drilled into the femur 220 with the guidance of the drill guide holes 226. The approp r iate miter block 100 is then placed on the resected en. of the amur 200, with its locating pegs 114 inserted into the locating holes in the femur. The miter block 100 is then used as described above to guide a saw blade in making the additional cuts to the distal end of the femur. As various changes could be made in the above constructions and methods without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

Claims: CLAIMS: 1. A guide for making resections to the distal end of a femur during the replacement of a knee joint, the guide being adapted to be mounted on a distally resected end of the femur that has been resected along a plane generally perpendicular to the mechanical axis of the femur, the guide comprising: a miten block having posterior and anterior sides, a generally planar upper surface adapted to be placed face-to-face with a distally resected femur, and a plurality of guide slots for alignment and orientation of a blade for making the cuts to be made to fit a particular sized " implant; posterior guide means, projecting upwardly from the posterior side of the miter block, for positioning the miter block with the posterior guide means contacting the posterior curved surface of the femur and therefore position the miter block in the posterior/anterior sense against the distally resected femur; an anterior guide means, projecting upwardly from the side anterior of the miter block, for gauging the size of the femur relative to the size of an artificial knee implant corresponding to the guide, the anterior guide means having a tip which is at a predetermined location relative the upper surface of the miter block such that the position of the tip will coincide with the anterior end of the articulation zone of the femur when the posterior guide means is properly positioned if the correct size miter block and accordingly implant have been chosen, the said predetermined location being such that when the miter block is later used as a guide to the anterior resection, the cut will exit the anterior condyle at that end of the articulation area; and means for mounting the miter block on the resected surface of the distally resected femur, with the upper surface of the miter block mating face-to-face with the resected surface. 2. A system comprising a plurality of knee implants of various sizes, anc 5 a plurality of guides of various sizes, corresponding .* the sizes of the knee implants, for making resections to the distal end of a femur during the replacement of a knee joint, each guide being adapted to be mounted on a distally resected end of the femur that has been resected along a plane generally perpendicular to the mechanical axis of the femur, each of the guides comprising: a miter block having posterior and anterior sides, a generally planar upper surface adapted to be placed face-to-face with a distally resected femur, and having a plurality of guide slots for alignment and orientation of a blade for making the cuts to be made to fit a particular sized implant; posterior guide means, projecting upwardly from the posterior of the miter block, for positioning the miter block with the posterior guide means contacting the posterior curved surface of the femur and therefore position the miter block in the posterior/anterior sense against the distally resected femur; an anterior guide means, projecting upwardly from the anterior of the miter block, for gauging the size of the femur relative to the size of an artificial knee implant corresponding to the guide, the anterior guide means having a tip which is at a predetermined location relative the upper surface of the miter block such that the position of the tip will coincide with the anterior end of the articulation zone of the femur when the posterior guide means is properly positioned if the correct size miter block and accordingly implant have been chosen, the said predetermined location being such that when the miter block is later used as a guide to the anterior resection, the cut will exit the anterior condyle at that end of the articulation area; and means for mounting the miter block on the resected surface of the distally resected femur, with the upper surface of the miter block mating face-to-face with the resected surface. 3. A guide or system as claimed in claims 1 or 2 in which the anterior guide means comprises a single anterior guide means that can be removably attached to each of a range of sizes of miter blocks corresponding to a range of implant sizes, the anterior guide means comprising: an elongate stylus having the aforesaid tip; a bracket removably attached to the anterior side of the miter block, the bracket slidably supporting the stylus so that the spacing of the tip of the stylus can be adjusted relative to the upper surface of the miter block; scale means for providing an indication of the correct adjustment of the tip relative to the bracket and thus the guide block; and means for releasably locking the stylus in position on the bracket with the tip of the stylus at one or more predetermined location relative to the upper surface of the miter block. 4. A guide or system according to claim 3 in which the means for releasably locking the stylus in position on the bracket comprises: a spring-loaded detent ball in the bracket biased toward the stylet; and a plurality of detent-ball-receiving depressions in the stylet for receiving the detent ball to hold the stylus in various positions on the bracket with the tip of the stylus at one or more predetermined location relative to the upper surface of the miter block. 5. A guide or system according to claim 4 further comprising snap-fit means in the bracket and miter block for releasably locking the bracket on anterior side of the miter block so that, once it has been decided that the correct miter block and therefore implant have been chosen, the anterior guide means can be removed from the miter block to enable the anterior resection cuts to be made without damage to the anterior guide means. 6. A guide or system according to claims 1, 2 or 5 in which the posterior guide means comprises a shoe removably attached to the posterior side of the miter block and upstanding therefrom so as to adapt the shoe for contact with the two posterior condyles, and so that, once the miter bloc has been fixed in place on the distally resected end of the femur, the shoe can be removed so as not to interfere with the subsequent cutting of the bone. 7. A guide or system according to claims 1 or 2 in which the miter block has an opening therethrough defining a window through the upper surface of the miter block allowing visualization of the posterior cruciate ligament. 8. A guide or system according to claims 6 or 7 in which the anterior guide means is removably attached to the miter block so that, once it has been decided that the correct miter block and therefore final implant have been chosen, the anterior guide means can be removed from the miter block to enable the anterior resection cuts to be made without damage to the guide means. 9. A guide or system according to claim 6 in which the miter block includes: a shoe-mounting recess in the posterior side of the miter block; and at least one spring-loaded detent ball mounted in the miter block and biased into the shoe-mounting recess for releasably securing the shoe on the posterior side of the miter block; the shoe including a tab having a depression for securely receiving the detent ball of the miter block to releasably secure the shoe on the miter block. 10. Apparatus for determining the desired size of knee implant to implant in a particular knee, and for determining the corresponding size of a femoral miter block, the apparatustbeing adapted to be placed on a distally resected eaάtef the femur that has been resected along a plane general_ perpendicular to the mechanical axis of the femur, the'apparatus comprising: an indicator block having posterior and anterior sides, a generally planar upper surface adapted to be placed face-to-face with a distally resected femur, and at least two drill guide holes in the indicator block for guiding a bone drill to drill locating holes in the distal end of the femur to receive locating pegs of the corresponding miter block;; posterior guide means, projecting upwardly from the posterior side of the indicator block, for positioning the indicator block with the posterior guide means contacting the posterior curved surface of the femur and therefore position the indicator block in the posterior/anterior sense against the distally resected femur; and an anterior guide means, projecting upwardly from the anterior side of the indicator block, for gauging the size of the femur relative to the size of an artificial knee implant corresponding to the guide, the anterior guide means having a tip which is at a predetermined location relative the upper surface of the indicator block such that the position of the tip will coincide with the anterior end of the articulation zone of the femur when the posterior guide means is properly positioned if the correct size indicator block and accordingly implant and miter block have been chosen, the said predetermined location being such that when a corresponding miter block is later used as a guide to the anterior resection, the cut will exit the anterior condyle at that end of the articulation area. 11. A system for determining the desired size of knee implant to implant in a particular knee, and for determining the corresponding size of a femoral miter block, the system comprising: a plurality of indicator blocks, each of a different size than the others to correspond to a variety of sizes of knee implants and miter blocks, each indicator block having posterior and anterior sides, a generally planar upper surface adapted to be placed face-to-face with a distally resected femur that has been resected along a plane generally perpendicular to the mechanical axis of the femur, and at least two drill guide holes in the indicator block for guiding a bone drill to drill locating holes in the distal end of the femur to receive locating pegs of the corresponding miter block;; posterior guide means, projecting upwardly from the posterior side of the indicator block, for positioning the indicator block with the posterior guide means contacting the posterior curved surface of the femur and therefore position the indicator block in the posterior/anterior sense against the distally resected femur; and an anterior guide means, projecting upwardly from the anterior side of the indicator block, for gauging the size of the femur relative to the size of an artificial knee implant corresponding to the guide, the anterior guide means having a tip which is at a predetermined location relative the upper surface of the indicator block such that the position of the tip will coincide with the anterior end of the articulation zone of the femur when the posterior guide means is properly positioned if the correct size indicator block and accordingly implant and miter block have been chosen, the said predetermined location being such that when a corresponding miter block is later used as a guide to the anterior resection, the cut will exit the anterior condyle at that end of the articulation area. 12. Apparatus or system according to claims 10 or 11 in which the anterior guide means comprises a single anterior guide means that can be removably attached to each of a range of sizes of indicator blocks corresponding to a range of implant sizes. 13. Apparatus or system according to claim 12 in which the anterior guide means comprises: an elongate stylus having the aforesaid tip; a bracket removably attached to the anterior side of the indicator block, the bracket slidably supporting the stylus so that the spacing of the tip of the stylus can be adjusted relative to the upper surface of the indicator block; scale means for providing an indication of the correct adjustment of the tip relative to the bracket and thus the indicator block; and means for releasably locking the stylus in position on the bracket with the tip of the stylus at one or more predetermined location relative to the upper surface of the indicator block. 14. Apparatus or system according to claim 13 in which the means for releasably locking the stylus in position on the bracket comprises: a spring-loaded detent ball in the bracket biased toward the stylet; and a plurality of detent-ball-receiving depressions in the stylet for receiving the detent ball to hold the stylus in various positions on the bracket with the tip of the stylus at one or more predetermined location relative to the upper surface of the indicator block. 15. Apparatus or system according to claim 14 further comprising snap-fit means in the bracket and indicator block for releasably locking the bracket on anterior side of *he indicator block so that, once it has been decided that the correct indicator block and therefore implant and miter block have been chosen, the anterior guide means can be removed from the indicator block. 16. Apparatus or system according to claims 12 or 15 in which the posterior guide means comprises a shoe removably attached to the posterior side of the indicator block and upstanding therefrom so as to adapt the shoe for contact with the two posterior condyles. 17. Apparatus or system according to claim 16 in which the anterior guide means is removably attached to the indicator block so that, once it has been decided that the correct indicator block and therefo. miter block and .inal implant have been chosen, the anterior g ^ ide means - n be removed from the indicator block. 18. Apparatus or system according to claim 16 in which the indicator block includes: a shoe-mounting recess in the posterior side of the indicator block; and at least one spring-loaded detent ball mounted in the indicator block and biased into the shoe-mounting recess for releasably securing the shoe on the posterior side of the indicator block; the shoe including a tab having a depression for securely receiving the detent ball of the indicator block to releasably secure the shoe on the indicator block. 19. Apparatus or system according to claim 18 in which the indicator block has lateral and medial sides extending between the anterior and posterior sides of the indicator block, the shoe-mounting recess and tab each being generally elongate having generally T-shaped, complementary cross sect is, one end of the shoe-mounting recess opening through one of the lateral and medial sides of the indicator block to allow the tab to be inserted into the shoe-mounting recess and slid along the posterior side of the indicator block until the detent ball of the indicator block is received in the depression in the tab to releasably lock the shoe on the indicator block. 20. A guide for making resections to the distal end of a femur during the replacement of a knee joint, the guide being adapted to be mounted on a distally resected end of the femur that has been resected along a plane generally perpendicular to the mechanical axis of the femur, the guide comprising: a miter block having posterior and anterior sides, a generally planar upper surface adapted to be placed face-to-face with a distally resected femur, a plurality of guide slots for alignment and orientation of a blade for making the cuts to be made to fit a particular sized implant, and an opening therethrough defining a window through the upper surface of the miter block allowing visualization of the posterior cruciate ligament; and means for mounting the miter block on the resected surface of the distally resected femur, with the upper surface of the miter block mating face-to-face with the resected surface. 21. A guide according to claim 20 in which the means for mounting the miter block on the resected surface of the distally resected femur comprises: at least two locating pegs adapted inserted into locating holes drilled into the distally resected femur to accurately position the miter block relative to the distal end of the femur; and at least two nail guiding bores in the miter block for receiving nails that can be driven into the distal end of the femur to fix the miter block on the distally resected femur, the nail guiding bores being offset at an angle with respect to the locating pegs.

Inventors: EGAN JOHN, SOWDEN BJORN K, EGAN, JOHN, SOWDEN, BJORN, K.
Applicants: MINNESOTA MINING & MFG, MINNESOTA MINING AND MANUFACTURING COMPANY
Application year: 1993
Main classification: A61B17
IPC codes: A61B17, A61F2