Abstract:
A method and apparatus for repairing isolated chondral defects using allograft implants. Lesions in articular tissue are corrected by forming a recipient socket in the tissue. A donor graft of a size corresponding to the recipient socket is harvested from a partial tissue specimen obtained from allograft material. The donor graft is implanted into the recipient socket.

Description:
[0001]     The present provisional application is related to U.S. application Ser. No. 10/638,489, filed Aug. 12, 2003, the disclosure of which is incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to the surgical treatment of isolated articular chondral defects and, more specifically, to methods and instruments for replacement of articular cartilage in the knee using grafts harvested from a partial distal allograft femur or condyle.  
         [0004]     2. Description of the Related Art  
         [0005]     Methods and apparatus for surgical treatment of isolated articular chondral defects by autograft and allograft transplantation are known. See, for example, U.S. Pat. Nos. 5,919,196, 6,591,581, and 6,592,588, having common assignment with the present application.  
         [0006]      FIG. 1  illustrates a prior art procedure for obtaining an allograft hemi-condyle for use in an osteochondral repair procedure. A cadaveric distal femur  10  is cut into two hemi-condylar portions  12  and  14 . Disadvantageously, harvesting of bone material from the allograft hemi-condyle leaves significant portions of the hemi-condyle as waste. In addition, hemi-condyles do not provide an intact trochlear region. Repair of defects in the trochlear region requires whole distal femurs, which results in further, significant tissue loss since residual condyles are discarded.  
         [0007]     Cutting the distal femur into partial condyles would provide a more efficient use of the distal femur. Reducing the size of the partial condyles also facilitates processing of the allogeneic graft material. Processing of the allogeneic material is facilitated, for example, by increasing available surface area for graft cleaning, and reducing blood and lipid residuals that may impact negatively the viability of chondrocytes, an important factor in procedure outcome.  
         [0008]     Accordingly, it would be advantageous to provide a method and system for creating and utilizing partial allograft femurs or condyles in the repair of isolated chondral defects.  
       SUMMARY OF THE INVENTION  
       [0009]     The present invention provides methods and apparatus for repair of isolated chondral defects using partial allograft distal femurs or condyles. The procedure can be utilized, for example, to anatomically reestablish a structural load-bearing surface to a damaged load bearing surface of a patient&#39;s femoral condyle. Osteochondral implants used in the procedure are harvested from partial allograft specimens. Partial and full-thickness osteochondral lesions, 1.5-3.5 centimeters in diameter, are particularly amenable to treatment according to the methods of the present invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  illustrates a prior art method of obtaining hemi-condyles from an allograft distal femur.  
         [0011]      FIG. 2  illustrates a method of obtaining three-cut partial condyles from an allograft distal femur in accordance with the present invention.  
         [0012]      FIG. 3  illustrates a method of obtaining four-cut partial condyles from an allograft distal femur in accordance with the present invention.  
         [0013]      FIG. 4  illustrates a surgical step of sizing a lesion according to the present invention;  
         [0014]      FIG. 5  illustrates a surgical step of marking an articular surface according to the present invention;  
         [0015]      FIG. 6  illustrates a surgical step of drilling a guide pin into bone according to the present invention;  
         [0016]      FIG. 7  illustrates a surgical step of marking a partial allograft condyle according to the present invention;  
         [0017]      FIG. 8  illustrates a surgical step of scoring peripheral cartilage according to the present invention;  
         [0018]      FIG. 9  illustrates a surgical step of boring into bone to form a recipient socket site according to the present invention;  
         [0019]      FIG. 10  illustrates a surgical step of securing the partial allograft condyle in a workstation according to the present invention;  
         [0020]      FIG. 11  illustrates a surgical step of harvesting a core from the partial allograft condyle secured in the workstation according to the present invention;  
         [0021]      FIG. 12  illustrates a surgical step of transferring depth measurements to the core according to the present invention;  
         [0022]      FIG. 13  illustrates a surgical step of cutting the harvested core to length according to the present invention;  
         [0023]      FIG. 14  illustrates a surgical step of dilating the recipient socket site according to the present invention;  
         [0024]      FIG. 15  illustrates a surgical step of placement of the harvested core into the recipient socket using a delivery tube according to the present invention; and  
         [0025]      FIG. 16  illustrates a complete core implant according to the present invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0026]     In the present invention, a partial tissue specimen, such as a three-cut partial condyle, or a four-cut partial condyle, is obtained from allograft material, as described in greater detail below. The partial condyle is delivered to a surgeon, along with a set of surgical socket-forming and donor graft harvesting instrumentation. Based on a pre-operative assessment, the tissue specimen is obtained so as to provide material sufficient for the surgeon to harvest an appropriately sized plug for performing the indicated repair.  
         [0027]     In addition, the specimen is selected to provide an articular surface that closely approximates that of the anatomical tissue being repaired. The surgeon uses the instrumentation provided to fashion a donor graft, or plug, from the partial tissue specimen. The plug is used for osteochondral repair of the damaged articular surface. The procedure is described below, with reference to the accompanying drawings.  
         [0028]     Referring to  FIGS. 2 and 3 , partial allograft tissue specimens are obtained by cutting distal femur  20  into sections. As shown in  FIG. 2 , three-cut partial condyles  22  and  24  are obtained by cutting the distal femur  10  into three sections to achieve a lateral condylar portion  22 , a medial condylar portion  24 , and a trochlear portion  26 .  FIG. 3  illustrates a four-cut procedure in which four portions are achieved from distal femur  10 , including lateral and medial condylar portions  32  and  34 , and two trochlear portions  36  and  38 . The condylar portions obtained by the four-cut procedure generally are smaller than those obtained by the three-cut procedure.  
         [0029]     After the cutting procedure, the portions are measured for adequacy of core yield. Referring to  FIG. 2 , the two partial condyles  22 ,  24  each are sized by measuring a width lateral to medial and a length anterior to posterior of the remaining articular surface. A 20 mm sizing dowel is used to confirm that at least one single 20 mm diameter core may be obtained from each partial. Additional sizing dowels may be used if the graft is able to yield additional or larger cores. All measurements and core yield determinations are recorded.  
         [0030]     The portion  26  including the trochlear groove also is sized to confirm adequate yield. The processed donor trochlear grooves are sized by measuring a width across the patellar surface from the cut of one lateral groove to the cut made at the medial groove. A length measurement is taken from the bottom of the groove to the top of the cartilage. Finally, a depth measurement is taken by placing a straightedge across the patellar surface at midlevel and measuring the depth at the deepest point. All measurements and core yield determinations are recorded.  
         [0031]     Referring to  FIG. 3 , 4-cut partials condyles  32 ,  34 ,  36 ,  38  are sized by measuring the width lateral to medial and the length anterior to posterior of the remaining articular surface of each partial. A 15 mm sizing dowel is used to assure that at least one single 15 mm core may be obtained from the graft. Additional sizing dowels may be used if the graft is capable of yielding additional or larger cores. All measurements and core yield determinations are recorded.  
         [0032]     Condylar portions thus obtained are sized to indicate the largest single plug that can be obtained from each. Preferably, at least a 15 or 20 mm plug can be harvested from each of the partial condyles. Selected partial condyles are sent upon request to surgeons to be used as partial allograft condyle in the surgical repair procedure described below.  
         [0033]     Referring to  FIG. 4 , the surgical procedure for osteochondral repair begins with standard pre-operative examination and diagnostic studies to confirm the size and extent of the lesion  42  on an articular surface of femoral condyle  43 , a standard para-patellar arthrotomy is carried out to expose the defect. Cannulated sizers  44  in various diameters are selected to estimate and approximate coverage of the lesion  42 . Sizers  44  preferably are provided in sizes of 12, 14, 15, 16, 18, 20, 25, 30, and 35 millimeter diameters, typically in various combinations.  
         [0034]     Referring to  FIG. 5 , once the appropriate size for the recipient socket is determined, a marker  55  is used to form a circumferential mark  56  on the damaged condyle  43  around the cylinder of sizer  44 . As shown in  FIG. 6 , a guide pin  68  is drilled through the sizer  44  past the lesion  42  and into bone. The sizer  44  is removed and a reference mark  60  is placed in a superior 12:00 o&#39;clock position.  
         [0035]     Referring to  FIG. 7 , markings are placed on a partial allograft condyle  71  using the sizer  44  which was previously utilized to establish the recipient defect size and mark the damaged condyle  43 . A method of obtaining the partial condyle  71  is described above. The sizer  44  is placed over the partial allograft condyle  71  and is used to circumferentially mark  72  the surface of the partial allograft  71  in an area corresponding to that of the lesion  42  on the damaged articular surface of condyle  43 . The sizer is removed and a reference mark  73  is placed in a superior 12:00 o&#39;clock position on the inside of the circle mark  72  on the partial allograft condyle  71 .  
         [0036]     Referring to  FIG. 8 , the sizer is replaced by an appropriately-sized recipient harvester  84 . Peripheral cartilage surrounding the damaged condylar surface is scored to the underlying subchondral bone. Scoring the peripheral cartilage obviates ancillary damage to the undamaged, peripheral articular surface. The harvester  84  is removed, leaving the guide pin  68  in place.  
         [0037]     Referring to  FIG. 9 , a cannulated calibrated recipient counterbore  96  is secured to the drill and placed over the drill pin  68 . Recipient socket  97  ( FIG. 12 ) is drilled into the lesion  42  and subchondral bone to a depth of 8 to 10 mm. Bleeding subchondral surfaces should be confirmed.  
         [0038]     Preparation of the donor graft is described with reference to  FIGS. 10-13 . Referring to  FIG. 10 , donor partial condyle  71  is secured in a workstation  108 . As shown in  FIG. 11 , a workstation bushing  110  of corresponding size is placed into a top housing  111  over the donor partial condyle  71  and set to the exact angle necessary to match the recipient&#39;s contour. The housing  111  is fastened securely.  
         [0039]     A calibrated donor harvester  112  is connected to a drill and passed through the bushing  110  into the proximal graft housing  111  and rested upon the surface of the donor partial condyle  71 . The harvester  112  is drilled through the entirety of the donor partial condyle  71 . The harvester  112  is removed from the graft housing, securely holding the corresponding cylindrical donor graft core  114 , which can be visualized through slot  115 . Donor graft  114  is extracted gently from the harvester  112  so as not to disturb the articular surface or underlying subchondral bone.  
         [0040]     Referring to  FIG. 12 , a depth measurement guide  126  is used to measure the recipient depth in four quadrants: north, south, east, and west. The depth measurements are transferred to the allograft graft core  114 , which is appropriately measured and marked  127  by referencing the four quadrant depths recorded from the recipient socket  97  that was created.  
         [0041]     Referring to  FIG. 13 , the donor graft  114  is secured in holding forceps  130  and trimmed by a reciprocating saw  132  to achieve the appropriate press fit accommodation of the recipient socket depth. The donor graft  114  is positioned with the articular surface inferior to cut.  
         [0042]     Referring to  FIG. 14 , a calibrated dilator  140  is inserted into the recipient socket site  97  to achieve a one half mm socket dilation. The end of the dilator is tapped lightly with a mallet. Dilation also smooths the recipient socket surfaces.  
         [0043]     Referring to  FIG. 15 , once the precise depth of the donor plug (matching the recipient socket) is obtained, the donor plug  114  is line to line fitted with reference to the marks  60  and  73  into the recipient socket. Cancellous graft is inserted into the bed prior to insertion of the donor plug, if necessary. The donor graft  114  is inserted into a slotted, transparent, calibrated delivery tube  150  for insertion into the recipient socket  97 . A tamp corresponding to the graft&#39;s size is positioned against the plug. Gentle taps are recommended for seating the graft  114  into the socket  97 . Referring to  FIG. 16 , the plug  114  is implanted until all edges are flush with the surrounding cartilage rim.  
         [0044]     In situations necessary for plug removal, a graft retriever may be secured into the plug to facilitate extraction. At the conclusion of the procedure, the wound is closed in a routine fashion. Sterile dressing and a protective brace are applied during the initial wound-healing phase. Ambulation with the use of crutches and weight-bearing allowances are determined based on the size and the extent of the weight-bearing lesion reconstructed.  
         [0045]     Although the present invention has been described in connection with preferred embodiments, many modifications and variations will become apparent to those skilled in the art.