Patent Publication Number: US-2005137600-A1

Title: Articular cartilage repair implant delivery device and method of use

Description:
FIELD OF THE INVENTION  
      The present invention relates to repair of articular cartilage in joints and, more particularly, to a technique and instruments for preparing subchondral tissue and bone, and implanting an articular cartilage repair unit therein.  
     BACKGROUND OF THE INVENTION  
      Articular cartilage is a type of hyaline cartilage that lines the surfaces of the opposing bones in a diarthrodial joint (e.g., knee, hip, shoulder, etc.). Its primary function is to permit smooth, near frictionless movement during articulation between bones of the joint by providing a low-friction interface between the contacting cartilage surfaces of the joint. Articular cartilage is also load bearing, and serves to transmit and distribute compressive joint loads to the underlying subchondral bone (i.e. bone beneath the cartilage or subchondral tissue).  
      Articular cartilage is typically damaged in one of two ways, acute trauma inflicted through physical activity (such as twisting motion of the leg, sharp lateral motion of the knee, or repetitive impact), or degenerative conditions (such as arthritis or other systemic conditions). In addition, as a person ages, articular cartilage loses mechanical strength, rendering the cartilage even more susceptible to trauma, such that even common motions (e.g. squatting, stair climbing, etc.) can cause articular cartilage tears. Because articular cartilage tissue is aneural (little or no nerves) and avascular (little or no blood vessels), the spontaneous healing of damaged articular cartilage is limited. As a result, focal (localized) defects can tend to lead toward progressive degeneration of the joint surface(s) until total joint replacement is eventually necessary.  
      Surgical methods are available for treatment of damaged articular cartilage tissue with their aim being to partially or completely repair the chondral defect and decrease the risk of the development of osteoarthritic changes within the joint. These surgical methods can be loosely classified into three categories: 1) debridement and stabilization of loose or worn articular cartilage, 2) stimulation of a repair process from the subchondral bone, and 3) repair or replacement of the damaged articular surface.  
      With respect to debridement and stabilization of loose or worn cartilage, the basic strategy is to stabilize the defect by removal of any partially attached flap(s) of cartilage or badly worn areas that may be present. This method typically involves procedures such as arthroscopic debridement of the loose cartilage and removal of any detached cartilage tissue bodies that may be floating with the joint space, which could also be a potential source of inflammation. Arthroscopic debridement is considered when medical management has failed to satisfactorily alleviate symptoms. In addition, it is generally agreed that while this method is able to produce short-term alleviation of pain, the long-term effect is frequently eventual deterioration of the joint surface(s).  
      With respect to stimulation of a repair process from the subchondral bone, the basic strategy is to enhance the intrinsic capacity of the cartilage (and the subchondral bone) to heal itself. This is done by stimulating healing by recruiting cells from the underlying bone marrow in the subchondral bone. This method typically involves penetrating the subchondral bone by drilling, microfracture, or abrasion. It is generally agreed that with the techniques that are available today for executing this method, the results are similar to debridement and stabilization in that short-term pain may be alleviated through the growth of fibrous tissue. However, over the long-term, the effect typically is the eventual deterioration of the joint surface(s).  
      With respect to repair or replacement of the damaged articular surface, the basic strategy is to regenerate a new joint surface by transplanting chondrocytes, chondrogenic cells or tissue that has the potential to grow new cartilage. This method typically involves techniques such as osteochondral autographing (mosaicplasty), in which “plugs” of cartilage tissue and subchondral bone are harvested from a patient and implanted into the damaged cartilage area, or autologous chondrocytes transplantation, in which cartilage cells are harvested from a patient, cultured, and then implanted into the damaged cartilage area.  
      While the most preferred treatment method is restoration and repair of the damaged cartilage, the most common method today is debridement and stabilization, followed by stimulation of a repair process from the subchondral bone. Additionally, and as indicated above, while the first two categories of methods may be effective in the short-term relief of pain and discomfort to the patient, the long-term effect is typically an eventual deterioration of the cartilage surface, leading to the need for a total joint replacement.  
      With respect to repair of damaged articular cartilage, various devices have been developed in order to facilitate such repair. DePuy Orthopedics of Warsaw, Indiana (and assignee of the present invention) has developed such a device termed an Articular Cartilage Repair Unit (ACRU) whose function is based on the second category explained above, i.e. stimulation of a repair process from the subchondral bone. The ACRU utilizes a resorbable mesh material that acts as a scaffold or matrix for cell infiltration and proliferation.  
      The ACRU and other implants requires that the material be removed from the existing defect to expose the subchondral bone, allowing the scaffold or matrix and autologous cells access to stimulate the healing of the tissue. Such implants are preferably implanted arthroscopically. Particularly, the general surgical technique for implantation of the implant requires that the articular cartilage surrounding the damaged cartilage be prepared. Thereafter, the subchondral bone beneath the damage cartilage is prepared, and a pilot hole prepared into the subchondral bone.  
      Although various techniques and instruments have been developed that have attempted to address the need for articular cartilage repair, such techniques and instruments have not been optimal. For instance, either they are not arthroscopic in nature (see e.g. U.S. Pat. No. 6,171,340) or have a relatively difficult surgical procedure associated with such implantation (see e.g. WO96/24304).  
      In view of the above, it is an object of the present invention to provide a device for implanting an articular cartilage repair device into subchondral bone.  
      In view of the above, it is an object of the present invention to provide a device for arthroscopically implanting an articular cartilage repair device into subchondral bone.  
      In view of the above, it is an object of the present invention to provide a device for preparing an articular cartilage site for implantation of an articular cartilage repair device into subchondral bone.  
      In view of the above, it is an object of the present invention to provide a device for arthroscopically preparing an articular cartilage site for arthroscopic implantation of an articular cartilage repair device into subchondral bone.  
      In view of the above, it is an object of the present invention to provide a combination articular cartilage cutter and instrument guide for preparation of an articular cartilage site and/or the implantation of an articular cartilage repair device in subchondral bone.  
      In view of the above, it is an object of the present invention to provide a combination articular cartilage reamer and implantation borer for implantation of an articular cartilage repair device into subchondral bone.  
      In view of the above, it is an object of the present invention to provide a set of surgical instruments for the preparation of an articular cartilage site for implantation of an articular cartilage repair device into subchondral bone.  
      In view of the above, it is an object of the present invention to provide a set of surgical instruments for the arthroscopic preparation of an articular cartilage site for arthroscopic implantation of an articular cartilage repair device into subchondral bone. These and other objects of the present invention will become readily apparent to one skilled in the art.  
     SUMMARY OF THE INVENTION  
      The present invention is, in one form, an instrument set and surgical procedure (technique or method) for implanting an articular cartilage repair unit (ACRU) or device at an articular cartilage joint site.  
      A technique for the arthroscopic delivery and fixation of an articular cartilage repair unit (ACRU) fixation device or implant is provided. The technique includes the use of a cannula tube that functions as both a cartilage cutter and a guide to pass instruments into the body arthroscopically. One such instrument is an end-cutting reamer that both prepares the subchondral bone by re-surfacing it down to a specified depth and also simultaneously drills a pilot hole in the subchondral bone to accept the ACRU fixation device. A delivery device is utilized to hold and deliver the ACRU fixation device to the delivery site.  
      According to one aspect of the principles of the present invention, there is provided a cannula. The cannula includes a tubular body that defines a proximal and a distal end, a bore disposed in the tubular body and extending from the proximal end to the distal end, and a blade disposed at a tip of the distal end of the tubular body and configured to incise about an articular cartilage area. According to another aspect of the present invention, there is provided a surgical instrument guide and articular cartilage cutter. The surgical instrument guide and articular cartilage cutter includes a tubular body having a longitudinal instrument bore extending from a proximal end of the tubular body to a distal end of the tubular body, a surgical instrument stop defined at the proximal end of the tubular body and configured to provide an abutment for limiting a length of travel of a surgical instrument, and an articular cartilage cutting blade defined at the distal end of the tubular body and configured to incise about an articular cartilage area.  
      According to another aspect of the principles of the present invention, there is provided a surgical cutting tool. The surgical tool includes a shaft defining a proximal end and a distal end, an attachment head disposed at the proximal end of the shaft and configured to be received in a rotation device, and a reamer disposed at the distal end of the shaft and configured to ream about an incised articular cartilage area and to simultaneously prepare a bore in subchondral bone underneath the incised articular cartilage area.  
      According to another aspect of the principles of the present invention, there is provided a surgical drill for preparing an area of damaged articular cartilage on subchondral bone of a joint. The surgical drill includes a drill shaft having a proximal end and a distal end, an attachment tip on the proximal end of the drill shaft and configured to be received in a rotation device, and a site preparation tip on the distal end of the drill shaft and configured to ream an incised area of the damage damaged articular cartilage and to simultaneously prepare a bore in the subchondral bone underneath the reamed area of the damaged articular cartilage.  
      According to another aspect of the principles of the present invention, there is provided an implant delivery device. The implant delivery device includes a handle defining a proximal end and a distal end, a shaft extending from the distal end of the handle and having an application end with a retention slot configured to releasably receive an articular cartilage repair assembly comprising an articular cartilage repair unit releasably retained on an articular cartilage implant retainer, and a retaining sleeve disposed on the insert and operative in a first mode to allow the articular cartilage implant retainer to be received in the retention slot, and in a second mode that prevents egress of the articular cartilage implant retainer from the retention slot.  
      According to another aspect of the principles of the present invention, there is provided an implant delivery device. The implant delivery device includes a tubular sleeve having a longitudinal bore and defining a proximal end and a distal end, and an insert extendable from and retractable into the longitudinal bore of the tubular sleeve, the insert having an application end with a retention slot configured to releasably receive an articular cartilage repair assembly comprising an articular cartilage repair unit releasably retained on an articular cartilage implant retainer.  
      According to another aspect of the principles of the present invention, there is provided a set of surgical tools for preparing a damaged articular cartilage site on subchondral bone of a joint and implanting an articular cartilage repair device. The device includes a cannula, surgical drill and implant delivery device. The cannula has a tubular body defining a proximal and a distal end a bore disposed in the tubular body and extending from the proximal end to the distal end, a blade disposed at a tip of the distal end of the tubular body and configured to incise about an articular cartilage area. The surgical drill has a drill shaft having a proximal end and a distal end, an attachment tip on the proximal end of the drill shaft and configured to be received in a rotation device, and a site preparation tip on the distal end of the drill shaft and configured to ream an incised area of the damaged articular cartilage and to simultaneously prepare a bore in the subchondral bone underneath the reamed area of the damaged articular cartilage. The implant delivery device has a handle defining a proximal end and a distal end, a shaft extending from the distal end of the handle and having an application end with a retention slot configured to releasably receive an articular cartilage repair assembly comprising an articular cartilage repair unit releasably retained on an articular cartilage implant retainer. The retaining sleeve is disposed on the insert and is operative in a first mode to allow the articular cartilage implant retainer to be received in the retention slot, and in a second mode that prevents egress of the articular cartilage implant retainer from the retention slot.  
      According to yet another aspect of the principles of the present invention, there is provided a method of implanting an articular cartilage repair device into an area of damaged articular cartilage. The technique includes the steps of (a) providing access to a joint space having damaged articular cartilage through an arthroscopic portal in the body of a patient, (b) using an obturator to insert a combination instrument guide and articular cartilage cutter cannula through the arthroscopic portal, (c) removing remnants of damaged articular cartilage at a damaged articular site through the inserted cannula, (d) simultaneously preparing the damaged articular cartilage site and underlying bone with a surgical drill having a combination reaming and boring tip through the cannula, and (e) implanting an articular cartilage repair assembly onto the prepared articular cartilage site through the cannula. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a side view of one embodiment of an exemplary cannula in accordance with an aspect of the principles of the subject invention;  
       FIG. 2  is an enlarged side view of the distal tip of the exemplary cannula of  FIG. 1  taken along circle  2 - 2  thereof;  
       FIG. 3  is a perspective view of an exemplary obturator in accordance with an aspect of the principles of the subject invention that may be used with the exemplary cannula of  FIGS. 1 and 2 ;  
       FIG. 4  is a side view of an exemplary reamer in accordance with an aspect of the principles of the subject invention that may be used with the exemplary cannula of  FIGS. 1 and 2 ;  
       FIG. 5  is a side view of another exemplary cannula in accordance with the principles of the subject invention;  
       FIG. 6  is a sectional view of the exemplary cannula of  FIG. 5  taken along line  6 - 6  thereof;  
       FIG. 7  is a sectional view of another exemplary reamer in accordance with an aspect of the principles of the subject invention that may be used with the exemplary cannula of  FIGS. 5 and 6 ;  
       FIG. 8  is an enlarged sectional view of the cutting tip assembly of the exemplary reamer of  FIG. 7 ;  
       FIG. 9  is an enlarged top perspective view of the cutting blade portion of the cutting tip assembly of the exemplary reamer of  FIG. 7 ;  
       FIG. 10  is a fragmentary sectional view of a portion of an exemplary articular cartilage depth gauge in accordance with an aspect of the principles of the subject invention;  
       FIG. 11  is a fragmentary side view of a portion of the depth gauge pin illustrating the degree of curvature in accordance with an aspect of the principles of the subject invention;  
       FIG. 12  is fragmentary perspective view of an exemplary implant delivery device in accordance with an aspect of the principles of the subject invention, the implant delivery device shown in a pre-loaded non-extended state;  
       FIG. 13  is a fragmentary perspective view of the exemplary implant delivery device of  FIG. 12  shown in a pre-loaded extended state ready for receipt of an ACRU assembly;  
       FIG. 14  is a perspective view of an exemplary ACRU implant assembly for use in the exemplary implant delivery device of  FIG. 12 ;  
       FIG. 15  is a perspective view of an exemplary implant retainer for use with the exemplary implant delivery device of  FIG. 12 ;  
       FIG. 16A  is a bottom perspective view of an ACRU implant assembly with an implant retainer in accordance with an aspect of the principles of the subject invention;  
       FIG. 16B  is a side view of the ACRU implant assembly with an implant retainer of  FIG. 16A ;  
       FIG. 17  is a fragmentary side view of the exemplary implant delivery device in a loaded and extended state;  
       FIG. 18A  is an enlarged perspective view of another exemplary embodiment of an implant retainer in accordance with an aspect of the principles of the subject invention;  
       FIG. 18B  is an enlarged perspective view of another exemplary embodiment of an implant retainer in accordance with an aspect of the principles of the subject invention;  
       FIG. 18C  is an enlarged perspective view of another exemplary embodiment of an implant retainer in accordance with an aspect of the principles of the subject invention;  
       FIG. 19  is a perspective view of another exemplary implant delivery device in accordance with an aspect of the principles of the subject invention, the implant delivery device in an unloaded state;  
       FIG. 20  is a perspective view of the exemplary implant delivery device of  FIG. 19 , the implant delivery device in a pre-load state;  
       FIG. 21  is a perspective view of the exemplary implant device of  FIG. 19 , the implant delivery device in an initially loaded state;  
       FIG. 22  is a perspective view of the exemplary implant device of  FIG. 19 , the implant device in a loaded and ready to implant state;  
       FIG. 23  is a perspective view of yet another exemplary implant device in accordance with an aspect of the principles of the subject invention, the implant delivery device in an unloaded state;  
       FIG. 24  is a perspective view of the exemplary implant delivery device of  FIG. 23 , the implant delivery device in a pre-loaded state;  
       FIG. 25  is a perspective view of the exemplary implant device of  FIG. 23 , the implant delivery device in an initially loaded state;  
       FIG. 26  is a perspective view of the exemplary implant device of  FIG. 23 , the implant device in a loaded and ready to implant state;  
       FIG. 27  is a perspective view of another alternative embodiment of an implant delivery device;  
       FIG. 28  is a side view of the tip portion of the implant delivery device of  FIG. 27  with an ACRU assembly attached thereto;  
       FIG. 29  is an enlarged side view of an exemplary ACRU implant assembly with implant retainer wire for purposes of illustrating the manner in which the ACRU assembly is implanted, the ACRU assembly shown in an initially implanted state;  
       FIG. 30  is an enlarged side sectional view of the exemplary ACRU implant assembly with implant retainer wire of  FIG. 29  illustrating the beginning of ACRU assembly release;  
       FIG. 31  is an enlarged side sectional view of the exemplary ACRU implant assembly with implant retainer wire of  FIG. 29  illustrating continuous ACRU assembly release;  
       FIG. 32  is an enlarged side sectional view of the exemplary ACRU implant assembly with implant retainer wire of  FIG. 29  illustrating a final phase of ACRU assembly release;  
       FIG. 33  is a side sectional view of a portion of subchondral bone in which the ACRU implant assembly of  FIG. 29  has been implanted;  
       FIG. 34  is a side view of an alternative embodiment of an implant delivery device;  
       FIG. 35  is a side view of a curved cannula in which the implant delivery device of  FIG. 34  may be utilized; and  
       FIG. 36  is a flowchart of an exemplary method or technique utilizing the instruments of the present invention in accordance with the principles of the subject invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that there is no intent to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the invention as defined by the appended claims.  
      Referring now to  FIG. 1 , there is depicted an exemplary embodiment of one form of a cannula or cannula construct, generally designated  40 , fashioned in accordance with an aspect of the principles of the subject invention. While the cannula  40  is an instrument unto itself, the cannula  40  is one of a set of instruments or devices for performing a surgical procedure on articular cartilage, the other instruments of the set being shown in the other figures and described herein. While described more fully below, the surgical procedure and one or more of the various instruments of the present instrument set, guides the various instruments through an incision of the body, gauges the depth of articular cartilage at a cartilage defect or focal lesion (site) of a joint that is proximate the incision, prepares the site, and allows implanting of an ACRU at the site.  
      The cannula  40  is made from a suitable surgical material such as metal and, preferably, but not necessarily, from stainless steel. Other suitable materials, however, can be used and are contemplated. The cannula  40  is defined by a cylindrical, tubular or similarly shaped body  42  having a first portion  44  and a second portion  46 . A bore  50  extends the axial length of the body  42  through the first portion  44  and the second portion  46 . The bore  50  defines a first opening  52  in an axial (proximal) end of the first portion  44  and a second opening  54  in an axial end (distal tip  56 ) of the second portion  46 .  
      While the bore  50  may have the same diameter throughout the first portion  44  and the second portion  46 , the outer diameter of the first portion  44  is greater than the outer diameter of the second portion  46 . This creates an annular ledge  48  defining a boundary between the outer diameter of the first portion  44  and the outer diameter of the second portion  46 . The bore  50 , and thus the cannula  40  itself, serves as a guide to pass and/or utilize the various instruments of the present instrument set (and other instruments not shown and/or described herein) through an incision in the body. While the incision and the procedure is preferably arthroscopic in nature, the various instruments of the present instrument set may be utilized in surgical procedures that are not arthroscopic in nature.  
      It should be appreciated that the bore  50  may be made in various diameters. As such, the outer diameter of the first and second portions  44 ,  46  may be fashioned in various diameters. A surgical set of cannula tubes  40  of various outer diameters and/or various diameter bores may be provided. In this manner, a surgeon may have a choice of sizes of cannula  40  in order to accommodate ACRU implant assemblies of varying diameters.  
      Referring additionally to  FIG. 2 , the cannula  40  terminates at a distal end in a distal tip  56 . The distal tip  56  is configured to be a cartilage cutter that is utilized to prepare and/or aid in the preparation of the articular cartilage site. The distal tip  56  includes one or more windows or openings  58 . The distal tip  56  of the cannula  40  has four windows  58   a ,  58   b  (that is diametrically opposite window  58   a  and thus is not readily discernable in the figures),  58   c  and  58   d  (that is diametrically opposite window  58   c ). Placement and number of windows may vary as desired and/or appropriate. Additionally, the windows  58   a - d  are fashioned as ovals or ovoid shaped openings. The shape and/or size of the windows may vary.  
      The distal tip  56  also has an annular cutting section  60 . The cutting section  60  is here formed as a reduced diameter portion and as such, defines an annular rim  62 . At the end of the cutting section  60  is a blade  64 . The blade  64  is annular and defined by a tapered, angled or beveled edge  66 . The blade  64  is shown as annular, but may be fashioned in other shapes if desired. Typically, the blade has the same shape as a cross section of the body of the cannula. The blade  64  is adapted, configured, and/or operative to cut an area of cartilage (e.g. a focal lesion or damaged cartilage) from the articular cartilage site. The length of the blade  64  determines the maximum depth of articular cartilage cut. The incised area of cartilage corresponds to the shape of the blade  64  and thus corresponds, as well, to the size of the bore  50  at the distal bore end  54 . The cannula  40  is both a guide for instruments via passing of an instrument through the bore  50  thereof, and an articular cartilage cutter through utilization of the distal tip  56 . The cannula  40  is thus a dual purpose instrument.  
      Referring now to  FIG. 3 , there is shown an exemplary obturator generally designated  70  fashioned in accordance with an aspect of the principles of the subject invention. As such, the obturator  70  may be part of the instrument set for preparing the articular cartilage site and implanting an ACRU. The obturator  70  is characterized by a body  72  formed as an elongated tube, cylinder or the like. The body  72  is fabricated from a material suitable for surgical use. The body  72  terminates at a distal conical shaped end  74  in a rounded tip  76 .  
      The body  72  is of a diameter that permits the body  72  to pass through the bore  50  of the cannula  40 . As well, the body  72  is of sufficient length to allow the tip  76  to either extend beyond or be at/near the end  55  (see  FIG. 2 ) of the cannula  40  when the body  72  is passed into and through the bore  50  of the cannula  40 . This places the tip  76  proximate the articular cartilage site when the cannula  40  has been inserted into the body of a patient through an appropriate (e.g. regular or arthroscopic) incision. It should be appreciated that the articular cartilage site refers to a damaged area of articular cartilage.  
      A handle  78  is provided at a proximal end of the body  72 . The body  72  is also of sufficient length to allow the bulb  78  to be sufficiently beyond the end  53  (see  FIG. 1 ) of the cannula  40  when the tip  76  is in a proper position with respect to the cannula  40 . The obturator  70  may be fabricated in various sizes (e.g. tube length, tube outer diameter, tube or hollow inner diameter) to be accommodated in various sizes of cannula.  
      Referring now to  FIG. 4 , there is depicted a reamer generally designated  90  in accordance with an aspect of the principles of the subject invention. As such, the reamer  90  may be part of the instrument set for preparing the articular cartilage site and implanting an ACRU as described herein. The reamer  90  is characterized by a body  92  that is fabricated from a suitable surgical material such as metal (e.g. stainless steel) or other material as appropriate. The body  92  includes a shaft  94  that is configured and/or adapted to be attached to a drill (not shown) or like rotation device for rotating the reamer  90 . As such, the shaft  94  may be configured in various manners in order to be accommodated in the rotation device. The attachment shaft  94  terminates in a stop or stop portion  96  that is sized larger than the attachment shaft  94 . The stop portion  96  may be annular or cylindrical in shape. Since the stop portion  96  is larger (i.e. has a greater diameter than the attachment shaft  94 ), the stop portion  96  defines a stop surface  95  at the junction of the attachment shaft  94  and the stop portion  96 . The stop surface  95  provides a stop for insertion of the reamer  90  into the rotation device.  
      The body  92  further includes an elongated shaft  98  that is connected to the opposite side of the stop portion  96 . The shaft  98  is preferably cylindrical and has a diameter that is able to be accommodated in the bore  50  of the cannula  40 . The diameter of the elongated shaft  98 , however, is less than the diameter of the stop portion  96 . As such, a stop surface  97  is defined at the junction of the stop portion  96  and the elongated shaft  98 . The stop surface  97  provides a stop for insertion of the reamer  90  in the cannula  40 . Particularly, when the reamer  90  is fully inserted into the bore  50  of the cannula  40 , the stop surface  97  abuts the end  53  of the first portion  44  of the body  42  of the cannula  40 .  
      The reamer  90  includes a cutting or reaming head or portion  100  at the distal end of the elongated shaft  92  that is adapted, configured and/or operative to cut through cartilage (e.g. meniscus and articular) and to simultaneously bore a hole in subchondral bone. As such, the reaming head  100  has helical blades  102  and  103 . Of course, it should be appreciated that while two helical blades are shown, the reaming head  100  may have more helical blades and/or other styles of blades.  
      A cutting tip  104  axially extends from an end  106  of the blades  102 ,  103 . The cutting tip  104  is adapted, configured and/or operative to bore a hole in the subchondral bone underneath the reamed articular cartilage. The size and length of the cutting tip  104  is selected so as to bore a hole appropriate for receiving the stem of an articular repair device such as is known in the art. Thus, as the reamer  90  is rotated, the appropriate sized hole is bored into the subchondral bone while the blades  102 ,  103  ream out the previously incised area of articular cartilage.  
      The reamer  90  (i.e. the various parts thereof) may be fashioned in various dimensions in order to be accommodated in a particular cannula and/or to effect appropriate cutting depths of both the bore in the subchondral bone for the shaft of the articular cartilage repair device and the cartilage at the cartilage repair site (having been previously cut via the cutting blade  66  of the cutting head  56  of the cannula  40 ). In all cases, however, the length L of the elongated shaft portion  98  including the cutting portion  100  (i.e. from the stop surface  97  to the end  106 ) is sized such that when the stop surface  97  abuts the end  53  of the cannula  40 , a portion of the blades  102 ,  103  (from the end  106  rearward toward the stop surface  97 ) extends beyond the end  55  of the cutting portion  56  of the cannula  40 . The amount of blade extension is sufficient to ream out the incised depth of the articular cartilage.  
      While the cannula  40  of  FIG. 1  is axially straight (i.e. non-curved), a cannula made in accordance with aspects of the principles of the subject invention may be curved in various degrees. As such, referring now to  FIGS. 5 and 6 , there is depicted a curved embodiment of a cannula generally designated  110 . At the outset, it should be appreciated that the degree of curve (i.e. the amount of offset from axially straight) is only exemplary. As such, a cannula may be made in accordance with the principles of the subject invention that are curved less than the degree of curvature of the cannula  110 , or may be greater. Additionally, the cannula may be of different lengths.  
      The cannula  110  is one of a set of instruments or devices for performing a surgical procedure on articular cartilage, the other instruments of the set being shown in the other figures and described herein. Again, while described more fully below, the surgical procedure and one or more of the various instruments of the present instrument set, guides the various instruments through an incision of the body, gauges the depth of articular cartilage at a cartilage defect or focal lesion (site) of a joint that is proximate the incision, prepares the site, and allows implanting of an ACRU at the site.  
      The cannula  110  is made from a suitable surgical material such as metal and, preferably, but not necessarily, from stainless steel. Other suitable surgical materials, however, can be used and are contemplated. The cannula  110  is defined by a cylindrical, tubular or similarly shaped body  112  having a first portion  114  and a second portion  116 . A bore  120  extends the length of the body  112  through the first portion  114  and the second portion  116 . The bore  120  defines a first opening  122  in a proximal end of the cannula  110  and a second opening  124  in a distal end of the cannula  110 .  
      While the bore  120  has the same diameter throughout the first portion  114  and the second portion  116 , the outer diameter of the first portion  114  is greater than the outer diameter of the second portion  116 . This creates an annular ledge  118  defining a boundary between the outer diameter of the first portion  114  and the outer diameter of the second portion  116 . The bore  120 , and thus the cannula  110  itself, serves as a guide to pass and/or utilize the various instruments of the present instrument set (and other instruments not shown and/or described herein) through an incision in the body. While the incision and the procedure is preferably arthroscopic in nature, the various instruments of the present instrument set may be utilized in surgical procedures that are not arthroscopic in nature.  
      It should be appreciated that the bore  120  may be made in various diameters. As such, the outer diameter of the first and second portions  114 ,  116  may be fashioned in various diameters. A surgical set of cannula tubes of various outer diameters and/or various diameter bores may be provided. In this manner, a surgeon may have a choice of sizes of cannula.  
      In like manner to the cannula  40  of  FIGS. 1 and 2 , the cannula  110  terminates at a distal end in a distal tip  126 . The distal tip  126  is configured to be a cartilage cutter that is utilized to prepare and/or aid in the preparation of the articular cartilage site. The distal tip  126  includes one or more windows or openings  128 . The distal tip  126  of the cannula  110  has four windows  128   a ,  128   b  (that is diametrically opposite window  128   a ),  128   c  and  128   d  (that is diametrically opposite window  128   c ). Placement and number of windows may vary as desired and/or appropriate. Additionally, the windows  128   a - d  are fashioned as ovals or ovoid shaped openings. The shape and/or size of the windows may vary.  
      The distal tip  126  also has an annular cutting section  130 . The cutting section  130  is here formed as a reduced diameter portion and as such, defines an annular rim  132 . At the end of the cutting section  130  is a blade  134 . The blade  134  is annular and defined by a tapered, angled or beveled edge  136 . The blade  134  may be fashioned in another shape if desired. The blade  134  is adapted, configured, and/or operative to cut an area of cartilage (e.g. a focal lesion or damaged cartilage) from the articular cartilage site. The length of the blade  134  determines the maximum depth of articular cartilage cut. The incised area of cartilage corresponds to the shape of the blade  134  and thus corresponds, as well, to the size of the bore  120  at the distal bore end  124 . The cannula  110  is both a guide for instruments via passing of an instrument through the bore  120  thereof, and an articular cartilage cutter through utilization of the distal tip  126 . The cannula  110  is thus a dual purpose instrument.  
      In order for the obturator  70  (see  FIG. 3 ) to be able to bend through the curvature of the bore  120  of the cannula  110  (and, of course, all curved cannula) the body  72  may be made of a bendable or resilient material. This would allow the obturator to appropriately extend through the bore  120 , but return to its original shape. Alternatively, while not shown, an obturator may be made whose body has the same degree of curvature as the cannula in which it is to be used. Therefore, a set of obturators may be provided in the instrument set to correspond to a set of like-curved cannula in the instrument set.  
      Because the cannula  110  is bent or curved, it is not possible for the rigid reamer  90  of  FIG. 4  to extend through the bore  120 . In view of this, the reamer must take another form. Referring now to  FIG. 7 , there is depicted a reamer, generally designated  140 , that may be used with any curved cannula. This is because the reamer  140  is flexible. The nature of the flexibility of the reamer  140  will become evident with the below description.  
      The reamer  140  includes a flexible shaft  142  fabricated from a braided, segmented, coiled or similar construction material suitable for surgical use. The flexible shaft  142  is constructed such that the shaft  142  may bend to fit the curvature of the bore of the selected cannula, while still allowing rotation of the shaft to effect reaming/cutting by rotation of a reaming/cutting head  146  attached to a distal end of the shaft  142 . The proximal end of the shaft  142  is non-rotatably connected to an attachment device  144  that is adapted, configured and/or operative to be attached to a rotation device (not shown). The attachment device  144  includes an attachment shaft  148  for receipt by the rotation device. A socket portion  150  extends from an end of the attachment shaft  148  and includes a bore  152  that receives an end of the shaft  142 . The shaft  142  is non-rotatably received in the bore  152  such that as the attachment device  144  is rotated, the shaft  142  is also rotated.  
      The reamer  140  also includes a reaming, cutting and/or site preparation head or tip  146  that is provided on a distal end of the shaft  142 . The reaming/cutting head  146  is non-rotatably attached to the end of the shaft  142  and is configured and/or operative to cut through cartilage (e.g. meniscus and articular) and to simultaneously bore a hole in subchondral bone. As seen in  FIG. 8 , the reaming/cutting head  146  is characterized by a body  156  having a shaft bore  160  that receives the shaft  142 . Moreover, the reaming/cutting head  146  has a plurality of reaming/cutting blades  164 , here embodied as four such blades, of which two of these blades  164   a  and  164   b  are seen in  FIG. 7 .  FIG. 9  may be referenced for depicting all four blades  164   a ,  164   b ,  164   c  and  164   d.  Of course, it should be appreciated that while the reaming/cutting head  146  has four blades, the reaming/cutting head  146  may have more or less blades as well as other styles of blades.  
      Referring additionally to  FIGS. 8 and 9 , the reaming/cutting head  146  has a boring tip  158  that axially extends from a bore  162  in the body  156 . The boring tip  158  is adapted, configured and/or operative to bore a hole in the subchondral bone underneath the reamed articular cartilage. The size and length (dimensions) of the boring tip  158  is selected so as to bore a hole appropriate for receiving the stem of an articular repair device such as is known in the art. Thus, as the reamer  140  is rotated, the appropriate sized hole is bored into the subchondral bone while the blades  164  ream out the previously incised area of articular cartilage.  
      The reamer  140  (i.e. the various parts thereof) may be fashioned in various dimensions in order to be accommodated in a particular length of cannula and/or to effect appropriate cutting depths of both the bore in the subchondral bone for the shaft of the articular cartilage repair device and the cartilage at the cartilage repair site (having been previously cut via the cutting blade of the cutting head of the cannula). In all cases, however, the length of the elongated shaft  142  including the reaming/cutting head  146  (i.e. from a stop surface  153  defined on the socket head  150 , see  FIG. 7 , to an end of the cutting blades  164 ) is sized such that when the stop surface  153  abuts the end  123  of the cannula  110  (see  FIG. 5 ), at least a portion of the blades  164  extends beyond the end of the cutting portion  126  of the cannula  110 . The amount of blade extension is sufficient to ream out the incised depth of the articular cartilage.  
      Referring now to  FIG. 10 , there is depicted an operative portion of an exemplary articular cartilage thickness gauge, generally designated  170  in accordance with an aspect of the principles of the subject invention. The articular cartilage thickness gauge  170  may be part of the instrument set for preparing and/or implanting an ACRU as described herein. Only an operative portion of the articular cartilage thickness gauge is depicted, since the other aspects of the thickness gauge may be fashioned in a number of known manners.  
      The articular cartilage thickness gauge  170  includes a tube  172  that is preferably, but not necessarily, made of a resilient material. The tube  172  has an inner bore  173  in which is disposed a needle, probe or the like  174 . The probe  174  terminates in a tip  176  and includes a number of gauge marks  177 . The gauge marks correspond to various depths measured from the end of the tip  176 . Such gauge marks may be demarcated in millimeters or other small increments. An end of the probe  174  that is not seen in  FIG. 10  is attached to a handle mechanism that allows the probe  174  to extend and retract from the tube  172 . Thus, the probe  174  is slidably disposed in the bore  173  such that the tip  176  may retract into the tube  172  (i.e. its tip being within the bore  173 ) when not in use or during insertion through a particular cannula, and may extend beyond the end of the tube  172  during use.  
      Referring additionally to  FIG. 11 , the probe  174  is formed with a bend  180  proximate the tip  176 . The bend  180  provides an angle a of preferably less than 45° as shown in  FIG. 11 . Then, when deployed, the probe  174  will have an angle α of approximately 45°. When the probe  174  is disposed in the tube  172  as depicted in  FIG. 10 , the bend  180  causes the probe to have two contact points  181  and  182  with the inner wall of the bore  173 . The contact point  181  is at or proximate the bend  180 , while the contact point  182  is further down the probe. The contact points provide stability to the probe  174  when deployed and/or taking a depth measurement of the articular cartilage.  
      Referring now to  FIG. 12 , there is depicted an exemplary embodiment of an implant delivery device generally designated  190 . The implant delivery device  190  fashioned in accordance with an aspect of the principles of the subject invention. While the implant delivery device  190  is an instrument unto itself, the implant delivery device  190  is one of a set of instruments or devices for performing a surgical procedure on articular cartilage, the other instruments of the set being shown in the other figures and described herein.  
      The implant delivery device  190  is adapted, configured and/or operative to receive, hold, implant, and release an articular cartilage repair unit (ACRU) or device and articular cartilage matrix (collectively, ACRU device) such as that shown in  FIG. 14  and described hereinbelow. The implant delivery device  190  includes an outer sleeve, tube, cylinder or the like  192  that defines an inner bore  194 , the inner bore  194  having a given inner diameter. The sleeve  192  has an outer diameter that is sized to be receivable in the bore of a selected cannula as described herein. The implant delivery device  190  is therefore adapted, configured and/or operative to be received in and extend through the selected cannula.  
      The implant delivery device  190  further includes a pusher rod or cylinder  196  disposed within the bore  194  of the sleeve  192 . The pusher rod  196  is axially slidable within the sleeve  192 , the purpose of which will become evident with the below description. The pusher rod  196  includes a configured cutout  198  for receiving and holding an implant retainer (see  FIG. 15 , for example, and its accompanying description below) that itself retains an ACRU assembly for eventual implantation of the ACRU thereof. The configured cutout  198  includes a retainer slot  200  and wire slot  202  that extends from the retainer slot  200  to an end  203  of the pusher rod  196 . The retainer slot  200  is configured in the same shape as a head of the implant retainer, while the wire slot  202  is shaped to receive a wire of the implant retainer.  
      The implant delivery device  190  is depicted in  FIG. 13  in a pre-loaded (i.e. before an ACRU assembly and implant retainer has been inserted or received therein), but extended state ready to receive the ACRU assembly and implant retainer. The pusher rod  196  is thus extended from the sleeve  192  and ready to accept the ACRU assembly on the implant retainer.  
      Referring to  FIG. 15 , there is depicted an exemplary implant retainer, generally designated  218 . The implant retainer  218  has a retainer or retainer portion  224  that holds a wire  220 . The retainer  224  is cylindrical or tubular in shape. The wire  220  is preferably fabricated from nitinol or other suitable metal material that is bendable without breaking. The wire  220  includes a bend  222  distal from the retainer portion  224 . The wire  220  thus forms a “J” and may therefore be known as a J-wire.  
      The retainer  218  may be formed of a suitable, surgical appropriate plastic in which case the J-wire  220  may be integrally molded therein, such as via insert molding. Alternatively, the retainer  218  may be formed of a suitable, surgical appropriate metal in which case the retainer  218  may be crimp-fit around the J-wire  220 . Other materials and/or methods of attachment, however, may be used. The retainer  218  is shaped at least substantially the same as the retainer slot  200 , while the wire slot  202  is configured to receive the J-wire  220 .  
      It should be appreciated that the retainer of the implant retainer may take different forms.  FIG. 18A  depicts an alternative implant retainer generally designated  230  that has a rectangular shaped retainer  232 . A wire  234  having a bend  236 , forming a J-wire, extends from the retainer  232 .  FIG. 18B  depicts another alternative implant retainer generally designated  240  that has a conical shaped retainer  242 . A wire  244  having a bend  246 , forming a J-wire, extends from the retainer  242 .  FIG. 18C  depicts yet another alternative implant retainer generally designated  250  that has a flat circular disk shaped retainer  252 . A wire  254  having a bend  256 , forming a J-wire, extends from the retainer  252 . In all cases, of course, the retainer slot  200  would be configured accordingly to accommodate the configuration of the retainer.  
      Referring now to  FIG. 14 , there is depicted an exemplary ACRU assembly  205  that may be implanted into subchondral bone as provided herein by one of the present implant delivery devices. The ACRU assembly  205  includes an ACRU fixation device  206  with an articular cartilage matrix or the like  208  such as is known in the art. The ACRU fixation device  206  is preferably fabricated from a suitable surgical-appropriate polymer such as is known in the art. The ACRU fixation device  206  includes a stem  210  that axially extends from a plurality of spokes  214 . Particularly and preferably, the stem  210  axially extends from a center of the spokes  214 . The stem  210  includes a plurality of fins, barbs or the like  212  that radially extend from the stem  210 . A bore  211  is provided through the stem  210  and center of the spokes  214 . The bore  211  is sized to receive the J-wire of an implant retainer.  
       FIGS. 16A and 16B  depict an ACRU implant assembly  226  that includes an ACRU assembly  205  situated on the implant retainer  218 . Particularly, the J-wire  220  extends through the bore  211  such that the bend  222  extends beyond the end of the stem  210 . Therefore, the length of the wire  220  from the retainer  224  to the bend  222  is such that it allows the receipt of the ACRU fixation device  206  thereon, with the bend  222  proximate but beyond the end of the stem  210 , and the length of the exposed wire between the retainer  224  and the top of the matrix  208  sufficient to span the length of the area between the end  203  of the pusher rod  196  and the retainer slot  200 .  
      In  FIG. 17 , the ACRU implant assembly  226  is shown captured or retained in the pusher rod  196 . The ACRU assembly is now ready to be implanted by the implant delivery device through the particular cannula. The retainer  224  is situated in the retainer slot  200 , while the J-wire  220  is situated in the wire slot  202 . The articular cartilage matrix  208  is adjacent (preferably abutting) the end  203  of the pusher rod  196 . The sleeve  192  is shown in a retracted position as it would be when inserting the ACRU implant assembly thereon. Thereafter, the sleeve  192  would cover the ACRU assembly for implanting the ACRU assembly through the selected cannula.  
      Referring now to  FIGS. 19 and 20 , there is depicted another exemplary embodiment of an implant delivery device, generally designated  260 , in accordance with an aspect of the principles of the subject invention. The implant delivery device  260  provides a sliding sleeve lock mechanism for receiving and retaining an ACRU implant assembly. The implant delivery device  260  includes a handle  262  that is sized to be received in the bore of the selected cannula. A reduced diameter shaft  264  axially extends from the handle  262  and terminates in a seating ring  266 . The seating ring  266  is of a larger diameter than the shaft  264 . The seating ring  266  defines a seating surface  270  on an end face thereof.  
      The shaft  264  includes a retainer slot  272  configured to receive one of the retainers of the implant retainers described herein. A wire slot  268  extends from the retainer slot  272  to the end  270 . A sliding sleeve  274  is disposed around the shaft  264  between the seating ring  266  and the handle  262 . The sliding sleeve  274  is biased such as by spring loading to be in a closed position as depicted in  FIG. 19 . Movement of the sleeve as depicted by the arrow in  FIG. 19  exposes the retainer slot  272  and a portion of the wire slot  268  as depicted in  FIG. 20 . The shaft  264  from the retainer slot  272  to the handle  262  is sized to accommodate the length of the sleeve  274  in order to fully exposed the retainer slot  272 . The implant delivery device is now ready to receive an ACRU implant assembly such as the ACRU implant assembly  226  depicted in  FIGS. 16A and 16B .  
       FIG. 21  depicts the ACRU implant assembly  226  inserted in and retained by the implant delivery device  260 . It should be appreciated that the sleeve  274 , being biased to be in a closed position as depicted in  FIG. 19  (and indicated by the arrow in  FIG. 21 ), must be held against such bias by an operator (not shown). After inserting the ACRU implant assembly  226  into the implant delivery device  260  and the release of the sleeve  274 , the sleeve  274  is biased against the seating ring  266  as depicted in  FIG. 22 . The sleeve  274  thus covers the retainer slot  272  and a portion of the wire slot  268 . The ACRU assembly is now ready to be implanted through the cannula.  
      Referring now to  FIGS. 23 and 24 , there is depicted yet another exemplary embodiment of an implant delivery device generally designated  280 . The implant delivery device  280  may be one instrument of the set of instruments. The implant delivery device  280  has a handle  282  that is sized to fit into the bore of the selected cannula. The handle  282  includes a reduced diameter shaft portion  284  (shown in phantom) on an axial end thereof. The shaft portion  284  includes a seating ring  286  on an axial end thereof that defines an end or face  288  thereof. The shaft portion  284  includes a retainer slot  290  (shown in phantom) and a wire slot  292  (shown in partial phantom) that extends from the retainer slot  290  though the end  288  of the seating ring  286 . The retainer slot  290  is configured the same as the retainer of the particular implant retainer, while the wire slot  292  is sized to receive the J-wire of the implant retainer.  
      A cylindrical sleeve  294  is disposed around the shaft portion  284  and includes a retainer port  296  and a wire channel  298  that extends from the retainer port  296 . The cylindrical sleeve  294  is limitedly rotatable about the shaft portion  284 . In  FIG. 23 , the sleeve  294  is in a closed position, but is rotatable as indicated by the arrow. In  FIG. 24 , the sleeve  294  is in an open position, but is rotatable as indicated by the arrow. The sleeve  294  is thus rotatable between the open and closed positions. In the closed position as depicted in  FIG. 23 , the retainer port  296  of the sleeve  294  does not register (align) with the retainer slot  290  of the shaft portion  284 . Additionally, the wire channel  298  of the sleeve  294  does not register (align) with the wire slot  292  of the shaft portion  284 . In the open position as depicted in  FIG. 24 , the retainer port  296  of the sleeve  294  registers (aligns) with the retainer slot  290  of the shaft portion  284 . Additionally, the wire channel  298  of the sleeve  294  registers (aligns) with the wire slot  292  of the shaft portion  284 .  
      Preferably, but not necessarily, the sleeve  294  is biased into the closed position by a spring mechanism or the like. Therefore, in order to position the sleeve  294  into the open position as depicted in  FIG. 24 , the bias may be overcome manually. The open position as depicted in  FIG. 24  allows the insertion of the ACRU implant assembly  226 .  
      Referring to  FIG. 25 , the sleeve  294  is shown in the open position. The ACRU implant assembly  226  has been inserted into and thus has been received by the implant delivery device  280 . In  FIG. 26 , the sleeve  294 -has rotated into the closed position (as illustrated by the arrow in  FIG. 25 ). The ACRU implant assembly  226  is not able to be removed without rotating the sleeve  294  back into the open position. The ACRU assembly is ready to be implanted. Again, this is preferably, but not necessarily, accomplished through the cannula of the present invention.  
      Referring now to  FIG. 27 , there is depicted another alternative embodiment of an implant delivery device generally designated  400 . The implant delivery device  400  includes a handle, tube, body or the like  402  that is dimensioned to extend through a cannula as herein provided. An end  403  of the body  402  has an ACRU implant retainer  404  that is operative, configured and/or adapted to releasably retain an ACRU assembly. In the embodiment of the implant retainer  404  of  FIG. 27 , the implant retainer  404  is formed by a wire. The ACRU implant retainer  404  may be a nitinol type wire such as discussed above.  
      The implant retainer  404  is sized to receive and releasably retain an ACRU.  FIG. 28  provides a side view of the implant delivery device  400  with an ACRU  205  retained thereon. Particularly, the implant retainer  404  extends through the bore  211  of the ACRU to releasably retain the ACRU. The matrix  208  is adjacent the end  403  of the body  402  when the ACRU is appropriately situated on the implant retainer  404 .  
       FIGS. 29-32  illustrate how the ACRU assembly  205  (the fixation device  206  and the matrix  208 ) is implanted or released from any one of the implant retainers described herein. Only the ACRU assembly  205  is shown, not the bone or surrounding articular cartilage. In  FIG. 29 , the ACRU assembly  205  is shown in an initially implanted state. In  FIG. 30 , as the implant delivery device begins to pull (as represented by the upward pointing arrow) the wire  220  from the ACRU  206  (by virtue of the retainer portion of the implant retainer that is attached to the wire  220 ) the bend  222  of the wire  220  begins to straighten. In  FIG. 31 , upon further extraction of the wire  220  as represented by the arrow above the wire, the bend or hook  222  continues to straighten. Finally, as illustrated in  FIG. 32 , continued extraction of the wire  220  from the ACRU fixation device  206  by the implant delivery device completely straightens out the bend (and therefore not seen in  FIG. 32 ) so that the wire  220  freely exits from the ACRU fixation device  206 . Thereafter, the implant delivery device may be removed from the cannula.  
      Referring now to  FIG. 33 , there is depicted a representation of the ACRU assembly  205  implanted into subchondral bone  300 , the matrix  208  being aligned with the natural articular cartilage  305 . Particularly, the stem  210  is implanted into a bore  301  formed in the subchondral bone  300  by the tip of the reamer, while the matrix  208  and support structure  214  rests in a reamed out portion  306  of the articular cartilage  305  by the reamer blades.  
      It should be appreciated that the various implant delivery devices as described above are usable only with the axially straight (non-curved) cannula. This is due to the rigid nature of the components. In order to alleviate this problem and thus be able to utilize any one of the various implant delivery devices, any of the above-described implant delivery devices may be formed as shown in  FIG. 34 . In  FIG. 34 , there is depicted an elementary exemplary embodiment of a flexible implant delivery device generally designated  310 .  
      The flexible implant delivery device  310  has a distal tip  312  that is made of a hard, surgical-appropriate material. The tip  312  includes a retainer cutout or slot  318  that is configured to receive a retainer portion of an implant retainer. A wire slot  320  extends from the retainer cutout  318  to the end  319  of the tip  312 . The flexible implant delivery device  310  also includes a proximal end  314  that is fabricated of a hard, surgical-appropriate material. A shaft  316  is disposed between the tip  312  and the end  314 . The shaft  316  is fabricated from a flexible, surgical-appropriate material. The flexible shaft  316  is thus operative to bend or curve in any direction and/or amount in order to be accommodated in a cannula of any curvature. The flexible shaft  316  is also resilient such that the shaft will, without external bias, tend to remain in (or go back into) a straight configuration.  
      The ability to flex or bend is illustrated in  FIG. 35 .  FIG. 35  depicts a curved cannula  328  having a curved bore  325 . The flexible implant delivery device  310  is shown disposed in the bore  325  with the flexible shaft  316  bent to fit the curvature of the bore  325 . The distal tip  312  is shown retaining an ACRU assembly  330  as provided herein. The handle (proximate end  314 ) extends out from the cannula  318  for use in inserting the ACRU assembly  330  into the prepared articular cartilage site and for implanting the ACRU assembly  330  in the subchondral bone underneath the prepared articular cartilage.  
      An exemplary method or technique of preparation of an articular cartilage site and implantation of an articular cartilage repair unit/device or ACRU in accordance with an aspect of the principles of the subject invention will now be described utilizing a set of instruments as described herein that includes at least some, if not all of the present instruments. As well, reference will be made to  FIG. 36 .  FIG. 36  depicts a flowchart, generally designated  350 , of the exemplary method or technique. It should initially be appreciated that the blocks or steps of the method  350 , relate to a technique for repairing a damaged articular cartilage site (damaged articular cartilage, e.g. focal lesion). This technique includes the use of the tools (implements or components) described herein.  
      In block or step  352 , an incision or incisions is first made in the body of a patient proximate to the affected joint in a manner known in the art. The incision(s) may be for an arthroscopic procedure or not. Once the incision(s) has been made, in block  354 , an obturator is used to insert a selected cannula in accordance with the principles of the subject invention through the incision (or one of the incisions). The selected cannula may be a straight cannula or may be a curved cannula. If the selected cannula is a curved cannula, the surgeon must select the degree of curvature. Additionally, the size (diameter) of the cannula must be selected. Therefore, the instrument set should include a plurality of cannula from straight to variously curved cannula each coming in various sizes.  
      In block  354 , the selected cannula is inserted through the incision using the obturator and situated adjacent (i.e. over) the affected or damaged articular cartilage site. This positions the cutting tip/blade of the cannula around the damaged articular cartilage site. The obturator is then removed from the cannula (block  355 ).  
      In block  356 , once the cannula is in a proper position over the damaged articular cartilage site, the damaged articular cartilage is cut or incised by the cannula blade. The cartilage is incised to the proper depth. The depth of cutting may first be ascertained by use of the articular cartilage depth gauge instrument that may be part of the instrument set.  
      Thereafter, in block  358 , an appropriate reamer is selected and inserted into the cannula. The reamer is attached to a rotation device for rotation of the reamer. In block  360 , the articular cartilage incised by the cannula is then reamed by the blades of the reamer. The reamer also reams the subchondral bone under the articular cartilage flat or smooth. Simultaneously, in block  362 , a bore is drilled in the subchondral bone for receipt by the stem of the ACRU fixation device. In block  364 , the reamer is then removed from the cannula. The site is now ready to receive the ACRU implant.  
      In block  366 , an ACRU assembly is attached to an implant retainer. Thereafter, in block  368 , the ACRU implant assembly is attached to the implant delivery device. In block  370 , the implant delivery device is then inserted through the cannula to the prepared site. The ACRU assembly, in block  372 , is then implanted into the prepared site. In block  374 , the implant delivery device is then removed from the cannula. Thereafter, the cannula  376  is removed from the incision.  
      While not specifically mentioned in the above procedure, typical and necessary measures and procedures (e.g. closing the incision(s)) would be performed. Such are known in the art.