Patent Publication Number: US-8529573-B2

Title: Distal femoral cutting guide

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 11/800,137 filed May 4, 2007. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to knee replacement surgery, and in particular relates to preparation of the distal end of a patient&#39;s femur to receive a part of a prosthetic knee joint. 
     Surgery to replace an entire knee joint has become relatively common in recent years, and various types of prosthetic knee joints have been designed. Each replacement knee joint requires preparation of the femur and the tibia of the patient to receive portions of the prosthetic joint that operate together to provide mobility approaching that of the patient&#39;s natural knee joint. For a replacement knee to operate optimally and for the patient to be able to move with a natural gait, the prosthetic knee joint parts must be installed in precisely the right positions and alignment. 
     A portion of the distal end of the femur must be removed to provide a seat for the femoral prosthetic part. According to earlier procedures for location of the portions of a prosthetic knee joint, an intramedullary rod is installed in the femur being prepared, and the proper location and orientation of a saw guide is referred to such an intramedullary rod, as taught, for example, by Cripe et al., U.S. Pat. No. 6,193,723. 
     Dunn et al, U.S. Pat. No. 4,759,350 discloses another cutting guide located on a patient&#39;s femur through the use of an intramedullary rod to guide in cutting away portions of the distal end of a femur in order to receive a prosthetic knee joint. 
     Many patents, including McNulty et al., U.S. Pat. No. 5,688,279, D&#39;Antonio, U.S. Pat. No. 5,810,831, Dunn et al., U.S. Pat. No. 4,759,350, Lackey, U.S. Pat. No. 5,053,037, Hodge, U.S. Pat. No. 5,486,178, Samuelson et al., U.S. Pat. No. 5,611,802, Marik et al., U.S. Pat. No. 5,417,694, and Booth, Jr. et al., U.S. Pat. No. 5,688,280, disclose various devices intended to aid surgeons in properly locating and orienting cuts which must be made to prepare the distal end of the femur to receive the relevant portion of an artificial knee joint. 
     Recent practice, however, has involved the use of infrared measuring devices communicating with a computer in a navigation system to determine the proper orientation of the femur and tibia with respect to each other and thus to determine the required locations for the portions of a prosthetic knee joint. It has become possible to utilize information determined through use of such an infrared navigating system to locate saw guides used to make an initial cut as part of preparing the distal end of the femur. 
     For example, the femoral portion of a prosthetic knee joint must be properly aligned with the central longitudinal axis of the femur and must also be oriented at the proper varus/valgus angle with respect to the longitudinal axis of the femur. It must also be mounted in the correct position of rotation about the hinge axis of the prosthetic knee joint to provide for the correct range of articulation. 
     It is desired, then, to provide a distal femoral cutting guide that can be used either with an intramedullary rod or with the assistance of infrared or other computer-aided navigation methods to locate a guide block properly for making a transverse cut across the condyles of the femur. 
     SUMMARY OF THE INVENTION 
     The present invention provides an answer to some of the aforementioned needs for an improved apparatus and method for its use in preparing the distal end of a femur to receive a portion of a prosthetic knee joint, as set forth in the claims appended hereto. 
     Apparatus according to one preferred embodiment includes an alignment body that is fastened adjustably to the distal end of a femur and which adjustably carries a cutting guide block. 
     A feature of one preferred embodiment of the apparatus is a varus/valgus adjustment arrangement used to adjust the position of the alignment body with respect to the femur. 
     A feature of one embodiment of the apparatus is that the alignment body can be attached to a femur either with or without the presence of an intramedullary rod, permitting adjustment of the orientation of a cutting guide block about all axes in either case. 
     In one embodiment of the apparatus a pair of prism shaped mounting bars fit in corresponding receptacles in the cutting guide block and also fit over mounting pins in an anterior face of a femur so that the position of the cutting guide block can be revised by reorienting the mounting bars on the pins. 
     In accordance with one embodiment of the method the alignment body is placed adjacent the distal end of a femur, then adjusted in position by rotation about a first axis that is generally parallel with the longitudinal axis of the shaft of the femur, adjusted about an anterior-posterior axis normal to the first axis, to provide a desired varus/valgus-related orientation, and then fixed in place with respect to the femur, after which a cutting guide block attached to the alignment body is rotated as necessary about an axis extending laterally with respect to the femur to establish an orientation of a cut in the femur to provide a desired position of maximum extension of the prosthetic joint. 
     As another aspect of the method the cutting guide block is thereafter attached to the femur, and the alignment body and a guide block support arm are then separated from the guide block and the femur, leaving the guide block securely located on the femur as a guide for making a properly oriented and unobstructed initial cut to remove portions of the medial and lateral condyles, along a plane extending generally transversely with respect to the longitudinal axis of the femur. 
     In one embodiment of the method, location of the alignment body with respect to the femur is informed by use of an infrared navigation system including sensors and a computer to refer to the position and orientation of the shaft of the femur. 
     The foregoing and other objectives, features, and advantages of the invention will be more readily understood upon consideration of the following detailed description of the invention taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an isometric view, taken from the upper right front of a distal femoral cutting guide which is an exemplary embodiment of the present invention. 
         FIG. 2  is an isometric view from the upper left rear of the distal femoral cutting guide shown in  FIG. 1 . 
         FIG. 3  is a front elevational view of the apparatus shown in  FIGS. 1 and 2 , showing the guide installed on the distal end of a femur. 
         FIG. 4  is a right side elevational view of the distal femoral cutting guide shown in  FIGS. 1-3 , showing the guide in use to establish the position for a preliminary cut on the distal end of a femur, in preparation for installation of the femoral portion of a prosthetic knee joint. 
         FIG. 5  is a view taken in the direction indicated by line  5 - 5  in  FIG. 4 , showing the rear end of the guide block locating arm. 
         FIG. 6  is a partially cutaway bottom plan view of the distal femoral cutting guide, showing the alignment body fastened to the distal end of a femur to establish a desired position for the cutting guide block. 
         FIG. 7  is a top plan view of the distal femoral cutting guide shown in  FIGS. 1-4 , together with the distal end of a femur. 
         FIG. 8  is a right side elevational view of the distal end of a femur with the guide block installed thereon, showing the alignment body and the guide block locating arm separated from the cutting guide block and showing a saw in use as guided by the guide block. 
         FIG. 9  is a left side elevational view of a distal femoral cutting guide assembly which is an alternative embodiment of the assembly shown in  FIGS. 1-8 . 
         FIG. 10  is a front elevational view of the apparatus shown in  FIG. 9 . 
         FIG. 11  is a right side elevational view of the apparatus shown in  FIGS. 9 and 10 , together with a portion of a femur, shown in broken line, with the distal femoral cutting guide in use to establish the position for a preliminary cut on the distal end of the femur, in preparation for installation of the femoral portion of a prosthetic knee joint. 
         FIG. 12  is a top plan view of the cutting guide block portion of the assembly shown in  FIGS. 9-11 , taken in the direction indicated by the line  12 - 12  in  FIG. 1 , together with a portion of a guide block locating arm in place in the cutting guide block. 
         FIG. 13  is a fragmentary sectional view taken along the line  13 - 13  in  FIG. 11 . 
         FIG. 14  is a left side elevational view of a distal femoral cutting guide which includes another embodiment of the apparatus disclosed herein. 
         FIG. 15  is a front elevational view of the distal femoral cutting guide apparatus shown in  FIG. 14 . 
         FIG. 16  is a right side elevational view of the distal femoral cutting guide apparatus shown in  FIGS. 14 and 15 . 
         FIG. 17  is an isometric view from the upper right front, at an enlarged scale, of a detail of the distal femoral cutting guide assembly shown in  FIGS. 14-16 . 
         FIG. 18  is an exploded isometric view of the structures shown in  FIG. 17 . 
         FIG. 19  is a front elevational view of a cutting guide block for use in making an adjustment cut at an angle in an anterior or posterior direction. 
         FIG. 20  is a right side elevational view of the cutting guide block shown in  FIG. 19 . 
         FIG. 21  is a front elevational view of a cutting guide block for making an adjustment cut at an angle to the left or right. 
         FIG. 22  is a top plan view of the cutting guide block shown in  FIG. 21 . 
         FIG. 23  is a sectional view of the alignment body shown in  FIG. 15 , taken along line  23 - 23 , and showing an attachment screw for use with the adjustment body. 
         FIG. 24  is an isometric view from the upper right front of a distal femoral cutting guide which is another alternative embodiment of the apparatus shown in  FIGS. 1 and 10 . 
         FIG. 25  is a right side elevational view of the apparatus shown in  FIG. 24 , with the cutting guide block shown spaced a small distance apart from the support arm. 
         FIG. 26  is a left side elevational view of the apparatus shown in  FIG. 24 . 
         FIG. 27  is a top plan view of the apparatus shown in  FIG. 24 . 
         FIG. 28  is a sectional view of a detail of the cutting guide assembly, taken along line  28 - 28  in  FIG. 26 . 
         FIG. 29  is a front elevational view of the cutting guide block shown in  FIGS. 24-26 . 
         FIG. 30  is a sectional view of the cutting guide block shown in  FIG. 29 , taken along line  30 - 30 , and showing a portion of a guide block support arm, also in sectional view, mated with the cutting guide block. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Referring now to the drawings which form a part of the disclosure herein, in  FIGS. 1 and 2  a distal femoral cutting guide assembly  10  includes a cutting guide block  12  and an alignment body  14 . Extending upward from a main or lower portion  16  of the alignment body  14  is a support member  18 , which may be an integral part of the alignment body  14 . A guide block locating arm  20  is fastened to the support member  18  by a screw or other adjustable fastener  22 , and the guide block  12  is mounted removably on the distal, or rear, end  24  of the guide block locating arm  20 . 
     In describing the distal femoral cutting guide disclosed herein, directions such as horizontal, upward or downward, and front and rear will be used in a manner consistent with reference to the distal femoral cutting guide assembly  10  in its ordinary position during performance of total knee replacement surgery, assuming that the patient is supine and the femur is supported in a generally horizontal orientation during the procedure. 
     The alignment body  14  has a front face  26  and a rear face  28 , which in the embodiment shown herein are flat and parallel with each other, although they need not be flat nor parallel with each other. A pair of horizontal slots  30  and  32  extend through the alignment body  14  from the front face  26  to the rear face  28 , each slot defining a respective horizontal plane. The slots  30  and  32  are shown as being coplanar, although it is not essential that they be coplanar, provided that they define planes that are parallel with each other. Each of the slots  30  and  32  has a height  34  which may be, for example, about 3.2 millimeters, and each slot  30  or  32  may, for example, be about 11.1 millimeters long, extending laterally on the front face  26 . The slots  30  and  32  may be separated from each other laterally of the alignment body  14  by a distance  36  of about 34.9 millimeters, in a distal femoral cutting block assembly  10  intended for use with an average size adult male person, in order to be most effective in fixing the alignment body  14  in a required position with respect to the distal end of a femur. 
     Spaced a short distance above the horizontal slots  30  and  32  are a pair of varus/valgus adjustment pins  38 ,  40 , each adjustably mated with the alignment body  14 , as by threads defined in a respective threaded bore  42 , and each extending straight through the alignment body  14 . The varus/valgus adjustment pins  38  and  40  may extend proud of the rear face  28  of the alignment body  14 , and each preferably has a sharp tip  44 , which may be conical, in order to engage a surface of a femur during use of the distal femoral cutting guide assembly so as to prevent the alignment body  14  from moving laterally with respect to the distal end of such a femur, as will be explained in greater detail presently. The bores  42  may be separated from each other laterally in the alignment body  14  by a center-to-center separation  46  of about 51 millimeters, for example, although a different distance  46  may be provided in an alignment body  14  intended for use on smaller or larger femurs. 
     Located generally centrally in the alignment body  14 , and between the bores  42 , is a central through-hole  48  extending through the alignment body  14  from its front face  26  to its rear face  28 . Within the central through-hole  48  a swivel block  50  is held in place by a pair of pivot pins  52  engaging the alignment body  14  and defining a vertically extending adjustment axis  54  which may be oriented normal to the horizontal planes defined by the slots  30  and  32 . The axis  54  provides for rotation of the swivel block  50  with respect to the alignment body  14 . The swivel block  50  defines a bore  56  large enough to receive an intramedullary rod (not shown) with an easily sliding yet not loose fit, so that the distal femoral cutting guide assembly  10  can be used in connection with an intramedullary rod (not shown) when desired, although, as will be explained presently, the alignment body  14  can be used independently. Thus the diameter  58  of the bore  56  may, for example, be 7.95 millimeters, while the swivel block  50  is large enough to provide ample strength to hold the pivot pins  52 , and to fit snugly between the top and bottom of the through-hole  48 . The hole  48  is wider than the swivel block  50  by an amount permitting the swivel block  50  to pivot about the adjustment axis  54  through a small angle, for example, at least about four degrees of arc in either direction, to allow varus/valgus adjustment. Thus, in one embodiment of the alignment body  14 , the swivel block  50  may have the general form of a cube about 12.7 millimeters on each side, while the through-hole  48  may have a width  59  of about 15.25 millimeters. 
     Located above the threaded bores  42  and extending through the alignment body  14  are two pairs of bores, a pair of divergent oblique locating pin holes  60  and, slightly above them, a pair of parallel straight-through locating pin holes  62  which may be normal to the rear face  28  of the alignment body  14 . All of the pin holes  60  and  62  extend from the front face  26  through the alignment body  14  to its rear face  28 , and all may have the same diameter  64 , for example, about 3.2 millimeters, to correspond with commonly used surgical drills and locating pins. 
     As may be seen in  FIG. 3 , the oblique locating pin holes  60  are closer together on the front face  26  of the alignment body  14  than are the straight-through locating pin holes  62 , although both pairs of holes  60  and  62  are located with equal spacing on the rear face  28 . Thus the holes  60  and  62  and the laterally outward end of the horizontal slot  30  or  32  are aligned with each other vertically at the rear face  28  of the alignment body  14 , which is shown herein as planar, although planarity is not critical. 
     For simplicity in manufacture and ease of reference and alignment during use, the alignment body  14  may be of flat plate material such as surgical stainless steel with a thickness  66  of about 12.7 millimeters, for example. The alignment body  14  may, for example, have a width  68  of about 79 millimeters. The shape of the alignment body  14 , as seen best in  FIG. 3 , may resemble an inverted “T” with the ends of its cross member rounded, in order for the alignment body  14  to have ample strength yet not be so large that it would be difficult to use within the available space surrounding an exposed distal femoral end. 
     The support member  18  portion of the alignment body  14  may extend upward above the main, lower portion  16  of the alignment body  14  to a distance  70  of about 69 millimeters above the through hole  48 , with the upper 25 millimeters thereof being reduced to a width  72  of, for example, about 6.35 millimeters. A planar side face  74  of the support member  18  is oriented normal to the rear face  28 , defining an alignment plane, and thus, in the embodiment depicted herein, the planar face  74  is also normal to the front face  26  of the alignment body  14  and to the horizontal planes defined by the slots  30  and  32 . 
     As may be seen in  FIG. 2 , the guide block locating arm  20  has a planar side face  76  resting against the planar face  74  of the support member  18 . The fastener  22  holds the guide block locating arm  20  tightly against the support member  18  with the planar faces  74  and  76  in contact with each other, and thus the guide block locating arm  20  is held in a selected position with respect to the support member  18  by friction between the planar faces  74  and  76 . 
     Referring now also to  FIG. 4 , it can be seen that a height adjustment slot  78  extends transversely through the narrow upper part of the support member  18 . A length  80  of the slot  78  extends vertically, permitting the fastener  22  to move through a distance of about 12.7 millimeters, for example, from top to bottom of the slot  78 . As shown in  FIG. 2 , the head of the fastener  22  may be countersunk within the narrow upper part of the support member  18 , being supported by a shoulder  82  defining the slot  78 . A corresponding slot  84  is defined in the guide block locating arm  20 , extending transversely through the guide block locating arm  20  and extending longitudinally along the guide block locating arm  20 . Thus, when the fastener  22  is loosened the guide block locating arm  20  is free to move longitudinally rearward and forward with respect to the support member  18 , as well as being able to move upward and downward along the narrow upper part of the support member  18  through the available range of movement of the screw  22  in the slot  78 , and being able to rotate in the plane of the faces  74  and  76 . 
     Indicia such as uniformly apart-spaced lines  86  are provided on the guide block locating arm  20 , to be used to gauge the distance to which the guide block locating arm  20  is extended beyond the rear face  28  of the alignment body  14 . The slot  84  has a length  88  permitting adjustment of the position of the guide block locating arm  20  in a longitudinal direction throughout a range of 25.4 centimeters, for example, in order to be able to support the guide block  12  where necessary to guide a saw to cut through the femur at the required location. 
     As may be seen best in  FIGS. 3 and 4 , the fastener  22  fits snugly within the slots  78  and  84 , and may include a transversely protruding, small pin  90  to secure a collar  92  and to limit rotation of the fastener  22  between a position of maximum looseness and a position of sufficient tightness. When tightened the fastener  22  holds the guide block  12  and the guide block locating arm  20  with the planar faces  74  and  76  in tight, frictional, contact against each other to support to guide block  12  in a desired location. Thus the fastener  22  may be, for example, a screw mated with threads in the collar  92 , or may include a cam acting against the shoulder  82 . 
     Referring to  FIG. 5 , the rear end  24  of the guide block locating arm  20  extends to a width  94  equal to the width  96  of the support member  18  below its narrow upper part, with a left leg  98  extending laterally so that a left side  100  is aligned with the left side  102  of the support member  18 . A rear end of the arm  20  mates with the guide block  12  and has a rear end face  104  which is rectangular, while a trapezoidal lower rear end face  106  is inclined downwardly away from the rear end face  104  and toward the alignment body  14 . A correspondingly shaped receptacle such as a socket  108  is provided in the guide block  12  in the form of a cavity which snugly receives a part of the rear or distal end portion  24  of the guide block locating arm  20 , so that the guide block  12  is precisely and stably located on the guide block locating arm  20  when the rear end  24  is fitted matingly in the socket  108  as shown in  FIGS. 1-4 . The rear end face  104  may be oriented normal to the length of the guide block locating arm  20 , and thus parallel with the rear face  28  of the alignment body  14  when the guide block locating arm  20  is located as shown in  FIGS. 1-4 , oriented normal to the rear face  28  of the alignment body  14 . It will be understood that other shapes of the rear end  24  and corresponding shapes of the socket  108  may be used if they can mate so as to hold the guide block  12  stably on the locating arm  20 . 
     The guide block  12  has a planar saw guiding face  112  through which the socket  108  extends. An upper margin  114  of the guide block  12  extends generally horizontally, joining a pair of parallel upright sides  116  and  118  through smoothly arcuate corners, provided in order to avoid having any of a patient&#39;s tissue be caught on the guide block  12 . A rear portion  120  of the guide block  12  is tapered to a narrow width, with a rounded tip  122  defined at the rear ends of the sides  116  and  118 , which extend rearwardly in mirror-opposite ogival shapes, as may be seen in plan view in  FIG. 6 . An upper rear face portion  124  is flat and generally parallel with the saw guiding face  112 , from which it is spaced apart by a thickness  126  sufficient to provide ample strength and rigidity, for example, about 3.2 millimeters. A top surface  128  extends downwardly and rearwardly from the portion  124  toward the tip  122  and may have a concave shape as shown in  FIGS. 2 and 4 , and may extend laterally to intersect with the sides  116  and  118 . A bottom surface  130  is downwardly concave, and may have a transversely oriented non-circular cylindrical shape, as may be seen in  FIG. 4 , intersecting with the sides  116  and  118 . 
     Three pairs of mounting pin holes  132 ,  134 , and  136  extend vertically through the guide block  12 , parallel with the saw guiding face  112  and with each other, as may be seen in  FIGS. 3 ,  4 , and  6 . The locations of the pairs  132 ,  134 , and  136  of mounting pin holes are staggered, with the holes of each pair being spaced apart from each other by equal distances, and both holes of each pair being spaced apart from the saw guiding face  112  by equal distances, for reasons which will be understood better in connection with explanation of the use of the cutting guide assembly  10 . For example, the holes  132 ,  134 , or  136  of each pair may be separated from each other by a lateral distance  138  of at least about 30 millimeters, to provide stability of the guide block  12  in use. The mounting pin holes  132 ,  134 , and  136  may be similar to the previously mentioned locating pin holes in the alignment body, and thus may have a diameter of, for example, about 3.2 millimeters. 
     In preparation of the distal end of a femur  140 , shown in  FIGS. 3 ,  4 ,  6 ,  7 , and  8 , the distal femoral cutting guide assembly  10  is utilized by placing the alignment body  14  in a selected initial location with its rear face  28  confronting the distal end of the femur  140 , with the rear face  28  of the alignment body  14  located closely adjacent to the lateral and medial condyles and oriented approximately normal to the longitudinal axis  141  of the femur  140 . 
     For convenience in illustrating the apparatus, the guide block  12  and guide block locating arm  20  are shown in  FIGS. 3 and 4  as being attached to the support member  18 , although the locating arm  20  might be removed temporarily from the support member  18  by appropriate manipulation of the screw or other fastener  22  until the position of the alignment body  14  has been adjusted. 
     The initial position for the alignment body  14  is selected by observation of known anatomical features on the surface of the distal end of the femur  140 , as by aligning the through-hole  48  with the location of the intramedullary canal within the femur  140 . Alternatively, if an intramedullary rod  142  has already been inserted into the distal end of the femur  140  as shown in  FIG. 4 , the alignment body  14  is placed adjacent to the distal end of the femur  140  by sliding the swivel block  50  onto and along the intramedullary rod  142 , with the rod  142  extending through the bore  56 . The alignment body  14  is rotated about the intramedullary rod  142  if it is present, or about an axis generally parallel with the longitudinal axis  141  of the shaft of the femur  140 , to a position in which the support member  18  extends toward the anterior face of the distal end of the femur  140 , generally along the groove between the lateral and medial condyles. Infrared navigation equipment, in conjunction with computerized locating systems, can also be used to aid in establishment of the best position of rotation of the alignment body  14  about the longitudinal axis  141  of the femur. 
     Once the alignment body  14  is in the appropriate position of rotation about an intramedullary rod  142  or the longitudinal axis  141 , a locating pin  144 , which may be in the form of a drill, is inserted through the horizontal slot  30  or the horizontal slot  32 , into the distal end of the femur  140 , and a second locating pin or drill  146  is inserted through the other one of the horizontal slots  30  and  32 , as shown in  FIGS. 3 ,  4 ,  6 , and  7 . The locating pins  144  and  146  thus establish a plane in which alignment body  14  can be translated laterally across the distal end of the femur, within the limits established by the locations of the locating pins  144  and  146  in the slots  30  and  32 , if there is no intramedullary rod  142  in the bore  56 . The alignment body  14  at this point of the procedure also remains free to move in a forward or rearward direction, toward or away from the femur  140 , and to rotate to at least a limited degree about an axis parallel with the axis  54  about which the swivel block  50  is free to rotate. 
     In order to align the pivot axis of the prosthetic knee joint to the femur to give the correct varus/valgus angle, it is necessary to orient the alignment body  14  correctly about the axis  54  or an axis parallel with the axis  54 . While the correct alignment can be estimated by the surgeon, the use of computerized infrared navigation or the like can also assist in determining the proper orientation of the alignment body  14 , and that orientation can be established and maintained by placing the tips  44  of the varus/valgus adjustment pins  38  and  40  into contact with the surfaces of the distal end of the femur  140 , as may best be seen in  FIGS. 4 ,  6 , and  7 . The adjustment pins  38  and  40  may be extended or retracted appropriately to bring both of the tips  44  into contact with the distal end of the femur  140  to adjust and maintain the orientation of the alignment body  14  with respect to the femur  140 . Once the surgeon determines that the alignment body  14  is in, or at least very near, the correct position, a hole is bored into the distal end of the femur  140  through one of the locating pin holes  62  and another locating pin  148  is placed through that locating pin hole  62  into the hole in the femur. This may be repeated using the other locating pin hole  62  and another alignment pin  148 . While urging the alignment body  14  toward the femur  140  and maintaining contact of the varus/valgus adjustment pins  38  and  40  against the femur  140 , at least one further hole may be bored into the femur, guided by one or each of the obliquely oriented locating pin holes  60 , and an alignment pin  150  may then be inserted through that or each locating pin hole  60  into the hole in the femur, effectively preventing the alignment body  14  from thereafter moving with respect to the femur  140 . 
     Thereafter, with the guide block  12  fitted onto the guide block locating arm  20 , and with the rear, or distal, end  24  of the locating arm  20  fitted in the socket  108  of the guide block  12 , and with the screw or other fastener  22  loosened, the guide block locating arm  20  may be adjusted with respect to the support member  18  to place the saw guiding face  112  at the desired distance from the alignment body  14 , using the spaced lines  86  for guidance in movement of the locating arm  20  with respect to the support member  18 . Using computer-aided infrared navigation, if available, to determine the correct inclination of the guiding face  112 , the fastener  22  may be raised or lowered within the slot  78  as required to permit the bottom face  130  of the guide block  12  to rest upon the anterior face  152  of the distal end of the femur  140 , with the guiding face  112  inclined properly about a transverse axis parallel with the fastener  22 . This will assure that a cut guided by the guiding face  112  is oriented correctly to receive the femoral portion of a prosthetic knee so as to establish the desired position of full extension. Once the guide block  12  is thus positioned correctly with respect to the anterior face  152  of the femur, holes are drilled into the anterior face  152 , guided by selected ones of the mounting pin holes  132 ,  134 , and  136  in the guide block  12 , and a pair of mounting pins  154  and  156  are placed into those holes in the femur through respective ones of the holes  132 ,  134 , or  136 . Since all of the holes  132 ,  134 , and  136  are parallel with each other, the guide block  12  is free to slide along the mounting pins  154  and  156  into contact with the anterior face  152  of the femur  140 , if the guide block when supported by the locating arm  20  is not firmly in contact with the anterior face  152  of the femur  140 . If it is determined that the guide block  12  is too near or too far from the distal end of the femur the guide block  12  can be removed from the anterior face  152  by sliding it up along the mounting pins  154  and  156 , after which the guide block  12  can be placed adjacent the anterior face by sliding it down along the mounting pins  154  and  156  with the mounting pins extending through a different pair of the holes  132 ,  134 , or  136 . 
     Once the position of the guide block  12  is thus established, the fastener  22  can be loosened, and the rear end  24  of the guide block locating arm  20  can then be removed from engagement in the socket  108 . The alignment body  14  can then be removed from the distal end of the femur  140 , by first retracting the locating pin or pins  150  from the oblique hole or holes  60 . The locating pins  144 ,  146 , and  148  can then also be retracted and the alignment body  14  can be removed from its position adjacent the femur  140 . The intramedullary rod  142 , if one had been used, is also removed from the femur  140 , and, with the guide block  12  retained on the anterior face  152 , a saw  158  may be used as shown in  FIG. 8 , to cut away the distal end portion  160  of the femur  140  along the optimal plane, guided by the face  112  as shown in  FIG. 8 . 
     Referring next to  FIGS. 9-12 , a distal femoral cutting guide  170  is generally similar to the distal femoral cutting guide assembly  10 . The assembly  170  includes a cutting guide block  172  and an alignment body  174  including a lower portion  176  and a support member portion  178 . A guide block locating arm  180  is connected with the support member  178  by an adjustment screw  182  or other adjustable fastener, and the cutting guide block  172  is mounted removably on the distal, or rear, end  184  of the locating arm  180 , where an attachment screw  186 , shown in  FIG. 12 , is engaged in the guide body  172  and can be tightened to fasten the guide body  172  securely to the locating arm  180 . 
     The alignment body  174  is generally similar to the alignment body  14 , but may have a concave rear face  188 , as shown herein. The alignment body  174  defines locating pin holes  190  and  192 , and slots  194 , corresponding to the holes  60  and  62  and slots  30  and  32  in the distal femoral cutting guide assembly  10 . Varus/valgus adjustment pins  196  and  198  may be similar to the pins  38  and  40  in the distal femoral cutting guide assembly  10  and are engaged adjustably in threaded holes extending through the alignment body  174 . 
     A swivel block  200  is located within a through-hole  202  defined in the alignment body  174 , where it is held in place as shown best in  FIG. 13 , by a pivot pin  204  in threaded engagement with the alignment body  174  and extending upward into the through-hole  202 . A spring-loaded pivot pin  206  is located in a bore  208  and kept in place by a simple fastener such as a roll pin  210  retained in the alignment body  174  as by being press fitted into a transversely extending bore  212 . The spring loaded pin  206  utilized in mounting the swivel block  200  conveniently provides some friction against the swivel block  200  yet permits it to move during adjustment of the varus/valgus orientation of the alignment body  174 . 
     As may be seen most clearly by reference to  FIGS. 9 ,  11 , and  13 , the guide block locating arm  180  is attached adjustably to the support member  178  by threaded engagement of the adjustment screw  182  with a nut  214 , which is located in a recessed slideway  216  defined in the lateral side of the support member  178 . The nut  214  is shaped so that it can slide along the slideway  216 , but it is prevented from rotating by engagement of its sides with the lateral surfaces  218  that define the slideway. 
     A washer  220  may be located between the locating arm  180  and the medial side of the support member  178 , and may include a reduced diameter portion  222  fitted within a guide channel  224  defined in the medial side  226  of the support member  178 , the side that faces toward the cutting guide block locating arm  180 . The washer  220  may be made of a suitably hard plastics material, for example, so as to be compressible enough to provide firm frictional contact with both the support member  178  and the opposed planar face  227  of the cutting guide block locating arm  180  to hold the arm  180  securely with respect to the support member  178  when the screw  182  is tightened into the nut  214 . 
     Indicia may be provided on the medial side  226  of the support member  128 , as at  228 , to indicate when the locating arm  180  is perpendicular to the front face  230  of the alignment body  174 . Indicia such as lines shown at  232  may also be provided on the top of the guide block locating arm  180 , as may be seen in  FIG. 12 , to indicate the distance between the support member  178  and the saw guiding face  234  of the cutting guide block  174 . 
     While the overall configuration of the cutting guide block  172  is similar to that of the guide block  12 , there are also bores  236  defined in the cutting guide block  172 , extending to the saw guiding face  234 , as locations for installation of computer-aided infrared or electromagnetic navigation system components that can be used to provide information useful in proper placement of the saw cutting guide block  172 . While the bores  236  are shown herein as all being of the same size, it will be understood that bores  236  may be provided in different configurations to accommodate different navigation system components. 
     The cutting guide block  172  defines a pair of mounting bar holes, receptacles in the form of through-holes  238  and  240 , shown herein as being in the shape of regular hexagons. The through-holes  238  and  240  are parallel with each other and with the saw guiding face  234 , and are separated from the saw guiding face  234  by equal distances  242  and  244 , respectively. 
     Fitting slidably within the through-holes  238  and  240  are respective hexagonal mounting bars  246  and  248 , and each of the mounting bars  246  and  248  defines a respective mounting pin hole  250 ,  252 . Each mounting pin hole  250  or  252  is located eccentrically within the respective mounting bar  246  or  248  and extends entirely through the respective mounting bar from end to end, oriented parallel with the respective mounting bar, so that with the mounting bars  246 ,  248  in place in the through-holes  238  and  240  the mounting pin holes  250  and  252  are parallel with each other and with the saw guiding face  234 . Since the mounting bars  246 ,  248  and through-holes  238 ,  240  are shaped as regular prisms, the mounting bars  246  and  248  can be located in the through-holes  238  and  240  in any of six positions of rotation, as indicated by the arrows  254 . 
     By placing both of the mounting bars with similar orientations of the eccentric mounting pin holes  250  and  252 , the orientation of the cutting guide block  172  can be maintained while its position is adjusted by reorienting the mounting bars  246 ,  248  equally. When each mounting bar  246 ,  248  is rotated clockwise  120  degrees, for example, the mounting pin holes  250  and  252  will be located in the positions shown in broken line in  FIG. 12 , so that the mounting pin holes remain parallel with each other and separated from each other by the same distance  256 , and a plane defined by the mounting pin holes  250  and  252  remains in the same orientation with respect to the saw guiding face  234 . It will be understood that any regular prismatic shape might be used for the mounting bars and the corresponding through-holes in the guide block  172 , depending upon the number of incrementally different positions desired to be provided. Thus triangular, or square, mounting bars would be useful instead of the hexagonal bars shown. 
     Use of the distal femoral cutting guide assembly  170  is generally similar to that described above with respect to the distal femoral cutting guide assembly  10 . The use of the mounting bars  246  and  248  in conjunction with the through-holes  238  and  240 , however, permits adjustment of the position of the cutting guide block  172  with respect to the femur without having to raise the guide block  172  away from the femur in the same fashion as necessary with the guide block  12 , since the mounting bars  246  and  248  can be raised along respective mounting pins such as the mounting pins  154  and  156  shown in  FIG. 8  in connection with the guide block  12 , remaining on the mounting pins. 
     Once the locating arm  180  has been removed from the guide block  172  the guide block  172  is free to slide downward along the mounting bars  246  and  248  until it comes into contact with the anterior face  152  of the femur. The position of the guide block  172  can thus be adjusted by raising the mounting bars  246  and  248  to clear the top of the guide body  172  as shown in  FIG. 11  in broken line. With each mounting bar  246 ,  248  rotated in the same direction an equal distance to an available mating position within the respective through-hole  238  or  240 , the cutting guide block  172  can be moved an incremental distance to permit reinsertion of the mounting bars  246 ,  248  into the through-holes  238 ,  240  more simply than by removing the guide block from the mounting pins. Rotation of the mounting bar  246 ,  248  to the orientation indicated by the positions of the mounting pin holes  250  and  252  as shown in broken line in  FIG. 12  would thus result in movement of the cutting guide block  172  to the position shown partially in broken line in  FIG. 12 , resulting in displacement of the saw guiding face  234  proximally along the femur through the short distance  258  as shown in  FIG. 12 , while incidentally also moving the cutting guide block  172  laterally, and without reorientation of the saw guiding face  234 . 
     Referring next to  FIGS. 14-18 , a distal femoral cutting guide  260  has an alignment body  262  that is generally rectangular and more compact than the alignment body  14  or the alignment body  174  described above. An upwardly extending arm  264  includes a threaded hole  266  to receive a screw  268  used to attach an upwardly extending support member  270  to the arm  264 . When the screw  268  is loosened the support member  270  may be adjusted angularly about a horizontal axis  271  defined by the screw  268  through an angle  272  with respect to the alignment body  262 , as will be explained more fully presently. A generally horizontally extending guide block locating arm  274  is mounted on a sliding support assembly  276  including a slide body  278  that includes a protruding rectangular central portion  280  that fits in the slot  282  defined by the upwardly extending support member  270 . A pair of shoulders  284  of the slide body  278  rest against the medial face  286  of the upwardly extending support member  270 . A pair of ribs  288  extend horizontally protrude and away from the medial face  286 , and, together with a generally planar vertical surface parallel with the medial face  286 , form a channel  290  in which the guide block locating arm  274  is held slidably. The slide body  278  thus keeps the guide block locating arm  274  oriented at right angles with respect to the support member  270 , while allowing it to be moved up or down along the support member  270 . 
     A slot  292  extends through and along the guide block locating arm  274 , and a recessed shoulder  294  surrounds the slot  292  on the left, or medial, side of the guide block locating arm  274 . The head of a screw  296  engages the shoulder  294 , while the threaded body of the screw extends through the slots  292  and  282  and through a hole  297  that extends through the slide body  278 , and the screw  296  is mated with the threads of a nut  298  riding on shoulders  300  recessed in the right, or lateral, side of the support member  270 . The support member  270  thus defines rails  302  extending alongside the shoulders  300 , and the nut  298  fits closely enough alongside the rails  302  so that the nut  298  is prevented from rotating, although it remains free to move along the rails  302  with the slide body  278  and the screw  296 . 
     With the screw  296  loosened slightly, the guide block locating arm can be moved up and down along the support member  270  along with the slide body  278  and can be moved longitudinally within the channel  290  in a forward or rearward direction with respect to the alignment body  262 . Thus, once the support member  270  has been placed at the selected angle  272  with respect to the alignment body  262 , the guide block locating arm  274  can be moved with respect to the support member  270  to place the guide block  304  in a desired location. The angle  272  of the support member  270  about the axis  271 , with respect to the alignment body  262 , is determined by the surgeon to establish a desired posterior/anterior angle of extension for the prosthetic knee joint, and the position of the guide block  304  relative to the anterior face  152  of the femur can be adjusted easily without varying the orientation of the saw guiding face  306  unintentionally. 
     A screw  308  may be threaded into the cutting guide block  304  and tightened into contact with the top of the guide block locating arm  274  to keep the cutting guide block  304  located properly on the guide block locating arm  274  until the guide block is attached to the femur, as will be explained presently. Hexagonal mounting bars  310  similar to the hexagonal mounting bars  246  and  248 , and also including eccentrically located mounting pin holes  312 , fit slidably within corresponding receptacles in the form of hexagonal holes  314  extending parallel with each other and the saw guiding face  306  of the cutting guide block  304 , so that any pair of correspondingly located longitudinal axes of the hexagonal mounting bars  310  define a plane parallel with the saw guiding face  306 , as shown herein. It will be understood that the locations of the hexagonal holes  314  might be arranged otherwise, and that the hexagonal holes  314  might be oriented otherwise than shown herein, or that the bars  310  and the corresponding holes  314  might be of a different regular polygonal cross-section shape, as by being pentagonal or square in cross section. 
     Similar to the alignment body  14  and the alignment body  174 , the alignment body  262  includes horizontal slots  316 , and may include straight pin holes  318  and oblique pin holes  320 , and a pair of varus/valgus adjustment pins  322  and  324  are mated in corresponding bores  326  and  328 . Similarly, a swivel block  334  is mounted to pivot on an adjustment axis  335  in a through-hole  336  in the alignment body  262  and defines a bore  338  similar to the bore  56  through the swivel block  50 , capable of snugly but slidably receiving an intramedullary rod. 
     Sockets  307  may be located on the saw guiding face  306  of the cutting guide block  304  and extend into the cutting guide block  304 , as shown best in  FIG. 15 , to receive and hold suitable infrared computer-aided navigation beacons or other desired devices. 
     The distal femoral cutting guide assembly  260  may be used in a manner basically similar to the use of the distal femoral cutting guide assembly  170  described above. Once the alignment body  262  is located on the distal end of the femur it is adjusted for varus/valgus angle using the adjusting pins  322  and  324 , and mounting pins may be inserted through selected ones of the slots  316  and holes  318  and  320  to keep the alignment body  262  in the adjusted varus/valgus position. The swivel block  334  may also be utilized with an intramedullary rod in the same manner as that described with respect to the swivel block  50  or the swivel block  200 . Thereafter, the support member  270  may be rotated to an appropriate angle  272  about the horizontal axis  271 . The screw  268  can then be tightened to hold the support member  270  at the selected angle  272  with respect to the alignment body  262  to provide the anterior-posterior angular orientation of the saw guiding face  306  thought to be correct. The guide block locating arm  274  and the sliding support  276  are then raised or lowered along the support member  270  and the guide block locating arm  274  is adjusted rearwardly or forwardly in the channel  290  of the slide body  278  as appropriate to place the cutting guide block  304  correctly adjacent to the anterior face  152  of the distal end of the femur  140 , as shown in  FIGS. 3 ,  4 , and  11  with respect to the cutting guide blocks  12  and  172 . 
     Once the cutting guide block  304  is in the desired location with respect to the distal end of the femur and is properly aligned as described above, holes are drilled into the anterior face of the femur, guided by the mounting pin holes  312  in the hexagonal mounting bars  310 . The drills used may be left in the femur, extending through the mounting pin holes  312  in the hexagonal mounting bars  310  to serve as mounting pins  315 . 
     Once the mounting pin holes are drilled into the anterior face  152  of the femur, with the drills extending as mounting pins  315  through the mounting pin holes  312  in the hexagonal mounting bars  310  and with the cutting guide block  304  attached to the anterior face of the distal end of the femur, the guide block locating arm  274  may be released from the cutting guide block  304 , and the alignment body  262  may be removed from the femur. 
     When the guide block locating arm  274  has been removed the guide block  304  can be slid down along the hexagonal guide bars  310  into contact with the anterior face  152 , as described previously with respect to the cutting guide block  172  and the hexagonal mounting bars  246  and  248 , placing the cutting guide block  304  close to the femur to guide the surgeon in cutting away a portion of the distal end of the femur. 
     Once the saw cut guided by the saw guiding face  306  has been made through the distal end of the femur as described above with respect to the guide block  12  and the guide block  172 , if trial placement of the femur portion of the prosthetic joint shows that the saw cut is incorrectly located or that the resulting surface of the distal end of the femur is improperly oriented, the hexagonal mounting bars  310  can be removed from the guide block  304  and both mounting bars  310  can be rotated through an equal angle, as described above with respect to the guide block  172 , to relocate the guide block  304  to a revised position to guide another cut parallel to the first cut. 
     Alternatively, the original guide block  304  can be replaced either by an adjustment guide block  340 , shown in  FIGS. 19 and 20 , to adjust the angle of extension of the prosthetic joint in an anterior or a posterior direction, or by an adjustment guide block  342 , shown in  FIGS. 21 and 22 , to correct the orientation of the sawed surface of the distal end of the femur with respect to the varus/valgus angle. Such an adjustment block  340  or  342  may be put into position over the same hexagonal mounting bars  310 , in place of the original cutting guide block  304 . 
     The adjustment guide block  340  as shown in  FIGS. 19 and 20  is symmetrical about a horizontal plane, except for the orientation of its saw guiding face  344 . In the adjustment block  340  the saw guiding face  344  is oriented at an anterior/posterior adjustment angle  346  of 3 degrees in the anterior direction relative to the orientation of the saw guiding face  306  of the mounted cutting guide block  304 , as indicated by the legend, “A3.degree.” visible in an upright orientation in  FIG. 19  at  348 . At the same time, a legend “P3.degree.” is visible inverted at  350  in  FIG. 19 . With the adjustment cutting guide block  340  inverted, as by rotation about an imaginary longitudinal horizontal axis  352  before being slid down onto the hexagonal mounting bars  310 , the adjustment angle  346  would be effective to adjust the cut by 3 degrees in the posterior direction. 
     A set of adjustment cutting guide blocks in a desired number of different angular variations may be provided so as to establish, for example, one degree, two degrees, three, four, or five degrees of angular variation from the original orientation of the saw guiding face  306  of the cutting guide block  304 , and the saw guiding face  344  of each may be marked as at  348  and  350 , with a corresponding legend to indicate the direction and the size of the angle  346  provided by each such adjustment cutting guide block of a set. 
     Similarly, in the adjustment cutting guide block  342 , an adjustment angle  352  of 3 degrees toward the left from the orientation of the saw guiding face of the original cutting guide block  304  as mounted on the hexagonal mounting bars  310  is provided by the orientation of the saw guiding face  354 , as shown by the upright and legible legend reading, “L 3.degree.,” at  356  on the saw guiding face  354  as shown in  FIG. 21 . Inversion of the adjustment cutting guide block  342  about the longitudinal horizontal axis  358  before mounting it on the hexagonal mounting bars  310  would result in the direction of the angle  352  being reversed, as would be indicated by the legend, “R 3.degree.” at  360  in  FIG. 21  then being upright and legible to the surgeon. Each adjustment guide block  342  is labeled, as by being engraved with the appropriate letter R or L and the appropriate number of degrees, so that when each block is in place on the hexagonal mounting bars the angle and direction of orientation of the adjustment saw guiding face  354  are legible in view of the surgeon. The upper and lower surfaces  362  and  364  of each of the cutting guide blocks  340  and  342  are similar, so that inversion of either of the cutting guide blocks  340  and  342  makes no difference in the way the cutting guide block  340  or  342  rests upon the distal end of the femur. 
     As shown in  FIG. 23 , a preliminary fixation screw  366  with a main body  368  of such a size that it fits slidably within the intramedullary pin bore  338  in a swivel block  334  has a threaded outer end  370  which can be engaged in a hole drilled in the distal end of the femur in the appropriate location, which is readily identifiable by the surgeon. Once the threaded outer end  370  is firmly engaged in the femur, the compression spring  372 , located between the shoulder  374  and the swivel block  334  then urges the alignment body  262  toward the distal end of the femur while the varus/valgus adjustment pins  322  and  324  are adjusted to orient the alignment body correctly with respect to varus or valgus. While the slots  316  and holes  318  and  320  are available in the alignment body  262 , the surgeon may choose to use fixation pins in none or only a few of those holes or slots to hold the alignment body  262  more or less fixedly in position on the distal end of the femur while the positions are determined for drilling holes into the anterior face  152  of the distal end of the femur through the mounting pin holes  312  defined in the hexagonal mounting bars  310 . 
     In a distal femoral cutting guide assembly  368  which is an alternative embodiment of the device, as shown in  FIGS. 24-30 , a guide block locating arm  370  may be attached to the support member  270 ′, which is generally similar to the previously described support member  270 , to support a cutting guide block  372  that is removably attached to the guide block locating arm  370 . The guide block locating arm  370  may be attached to and clamped to the support member  270 ′ at a selected height relative to the alignment body  262  from which the support member  270 ′ extends upward, by a sliding support assembly whose function is similar to that of the slide assembly  276  described above with respect to the distal femoral cutting guide assembly  260 . The sliding support assembly includes a slide body  373  having a central portion  374  fitting slidably, but not rotatably, in the slot  282  defined by the upwardly extending support member  270 ′. The central portion  374  thus maintains a selected angular relationship of the slide body  373  with the support member  270 ′. A support block portion  375  of the slide body  373  extends medially outward beyond the medial face  286  of the support member  270 ′ and may be pressed against shoulders  376  between rails  377  on the medial side of the support member  270 ′ by tightening a clamping screw  378  in a threaded bore  379 , as shown best in  FIG. 28 . The clamping screw  378  may have its head countersunk in a clamping plate  380 , and the clamping screw  378  extends through a bore  381  to mate with the threaded bore  379  in the central portion  374  of the slide body  373  to clamp the slide body  373  to the support member  270 ′ at a selected height. The clamping plate  380  may be disposed slidably on the shoulders  300  and between the rails  302  on the lateral side of the support member  270 ′ in the same manner as the nut  298  described previously. The support block portion  375  holds the guide block locating arm  370  may thus be kept at a constant angle  382 , such as 90 degrees, to the support member  270 ′, as will be explained in greater detail presently. 
     The cutting guide block  372  is attached to a rear end portion  383  of the locating arm  370 , so that the cutting block  372  is located closely adjacent to the main portion of the guide block locating arm  370 , which may have the form of a long narrow oval including a top member  384  and a bottom member  386  which are parallel with each other. As shown best in  FIG. 26 , a long depth adjustment screw  388  extends parallel with and between the top and bottom members  384  and  386 , with a rear end of the screw  388  supported rotatably in a bearing  390  at the rear end of the locating arm  370 . A near or front end of the depth adjustment screw  388  extends through a bore  392  defined in the front end of the guide block locating arm  370 , and a suitable arrangement is provided to support the depth adjustment screw  388  with respect to thrust forces. For example, a circumferential groove  394  may be defined in a front end portion of the screw  388 , and a grub screw  396  may be mounted in a corresponding threaded bore in the locating arm  370  so as to have a rounded tip of the screw  396  engaged in the groove  394  to keep the depth adjustment screw  388  from moving longitudinally in the locating arm  370 . 
     An adjustment knob  398  is attached to the front end of the depth adjustment screw  388  to rotate the adjustment screw  388 . The adjustment screw  388  is mated in a threaded bore  400  in the support block portion  375  of the slide body  373 , as shown best in  FIG. 28 , and thus keeps the guide block locating arm  370  closely alongside the medial face  286  of the support member  270 ′. The threaded bore  400  is parallel with the medial face  286  of the support member  270 ′ and with top and bottom surfaces  402  and  404  of the support block portion  375 . The top and bottom surfaces  402  and  404  may be in sliding relationship to inner surfaces of the top and bottom members  384  and  386  of the guide block locating arm  370  to help keep it oriented at the angle  382  to the support member  270 ′. Rotation of the adjustment screw  386  thus moves the guide block locating arm  370  rearward or forward alongside the support member  270 ′, to carry the cutting guide block  372  to a desired depth relative to the support member  270 ′. 
     As a useful indication of the position or the amount of adjustment of the depth of the cutting guide block  372  while the location of the cutting guide block  372  is being established with respect to a patient&#39;s femur, indicia  405  may be provided at useful intervals on the top member  384  of the guide block locating arm  370 . For example a line may be provided at each millimeter, with a label for each five millimeters, to indicate a position of the guide block locating arm  370  relative to the support member  270 . 
     The cutting guide block  372 , shown also in  FIGS. 29 and 30 , may be similar in most ways to the cutting guide block  172 , shown in  FIGS. 9-12 . Instead of being attached to the guide block locating arm  370  by a fastening screw  186 , which may not be easily accessible when it is desired to release the cutting guide block  372  from the locating arm  370 , the cutting guide block  372  may be connected to the rear end portion  383  securely, yet removably by a detent, such as a spring loaded ball detent  406  that may be mounted in a threaded bore  408  in the bottom of the cutting guide block  372  so that the ball protrudes up into the receptacle  409  in the guide block  372 . A corresponding dimple  410  may be provided in the rear end portion  383  of the guide block locating arm  370  to receive the spring-loaded ball when the cutting guide block  372  is mounted on the locating arm  370 . 
     A procedure for using the distal femoral cutting guide assembly  368  is similar to that for using the cutting guide assembly  260 , shown in  FIGS. 14-23 , with the alignment body  262  being mounted on the femur, and adjusted about its longitudinal axis, and then adjusted for varus/valgus. Next the support member  270 ′ may be placed at the desired angle  272  about a transverse extension/flexion axis, and the slide body  373  may then be set and clamped at the required height along the support member  270 ′. The knob  398  may then be turned to rotate the depth adjustment screw  388  as needed to move the support arm  370  rearward to the required depth position for the guide block  372 . Then, once the cutting guide block  372  is pinned to the femur  140  by pins  156  through the bores  250 ,  252  in the mounting bars  246 ,  248  the alignment body  262  may be released from the femur, and rear end portion  383  may be disconnected from the guide block  372  by overcoming the ball detent and retracting the rear end portion  382  from the receptacle  409 . 
     The terms and expressions which have been employed in the foregoing specification are used therein as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding equivalents of the features shown and described or portions thereof, it being recognized that the scope of the invention is defined and limited only by the claims which follow.