Abstract:
A surgical procedure for implanting a graft according to which a dilator is inserted in a recipient opening and the graft is inserted in the dilator to cause outward expansion of the dilator into engagement with the portion of a bone surrounding the opening. After the dilator is removed from the opening, the bone surrounding the opening collapses around the graft to secure the graft in the opening.

Description:
BACKGROUND 
     This invention relates to an improved osteochondral implant fixation method and, more particularly, to such a method in which a recipient hole is prepared for receiving a graft. 
     In the human body, the knee consists of three bones—a femur, a tibia, and a patella—that are held in place by various ligaments. The corresponding chondral areas of the femur and the tibia form a hinge joint, and the patella protects the joint. Portions of the latter areas, as well as the underside of the patella, are covered with an articular cartilage which allow the femur and the tibia to smoothly glide against each other without causing damage. 
     The articular cartilage often tears, usually due to traumatic injury (often seen in athletics) and degenerative processes (seen in older patients). This tearing does not heal well due to the lack of nerves, blood vessels and lymphatic systems; and the resultant knee pain, swelling and limited motion of the bone(s) must be addressed. 
     Damaged adult cartilages have historically been treated by a variety of surgical interventions including lavage, arthroscopic debridement, and repair stimulation, all of which provide less than optimum results. 
     Another known treatment involves removal and replacement of the damaged cartilage with a prosthetic device. However, the known artificial prostheses have largely been unsuccessful since they are deficient in the elastic, and therefore in the shock-absorbing, properties characteristic of the cartilage. Moreover, the known artificial devices have not proven able to withstand the forces inherent to routine knee joint function. 
     In an attempt to overcome the problems associated with the above techniques, osteochondral transplantation, also known as “mosaicplasty” and “OATS”, has been used to repair articular cartilages. This procedure involves removing injured tissue from the articular opening and drilling cylindrical holes in the base of the opening and underlying bone. Cylindrical plugs, consisting of healthy cartilage overlying bone, are obtained from another area of the patient, typically from a lower weight-bearing region of the joint under repair, or from a donor patient, and are implanted in the holes. However, in these cases, if the hole is too large, the graft can rotate in the hole and become loose, which will prevent integration with the surrounding tissues. If the hole is too small, significant cellular damage can occur to the graft during the implantation. 
     An embodiment of the present invention involves a graft implantation technique that overcomes the above problems. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         FIG. 1  is a elevational view of a human knee with certain parts removed in the interest of clarity. 
         FIG. 2  is an exploded view, illustrating the grafting technique according to an embodiment of the invention. 
         FIGS. 3 and 4  are enlarged sectional views depicting steps in the grafting technique. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1  of the drawing, the reference numeral  10  refers, in general, to a knee area of a human including a femur  12  and a tibia  14  whose respective chondral areas are in close proximity to form a joint. A cartilage  16  extends over a portion of the chondral area of the femur  12 , and a meniscus  18  overlies a portion of the chondral area of the tibia  14  and extends between the tibia and the cartilage. The patella, as well as the related tendons and quadriceps that also form part of the knee, are not shown in the interest of clarity. 
     It will be assumed that a portion of the cartilage  16  in the chondral area of the femur  12  has been damaged and removed by the surgeon, or has worn away, exposing a damaged area, or defect  12   a , and that it is desired to implant a graft in the defect. 
     Referring to  FIG. 2 , a graft  20  is obtained from one of several sources. For example, it could be harvested from another area of the patient/recipient, such as a undamaged non-load bearing area of the femur or tibia that has cartilage extending over a portion of its chondral area. Alternately it could be obtained from a cadaveric donor, a living donor, or it could be of xenogenic origin, or of an artificial substitute material. 
     The graft  20  has a circular cross-section and includes a bony portion  22  and a cartilage portion  24  overlying the bony portion  22 . 
     A recipient opening  12   b  is formed in the defect  12   a  that is shaped the same as the graft  20 , but has a diameter that is slightly smaller than that of the graft. An exemplary technique for forming the opening  12   b  would be to drill a hole in the femur  12  to a depth substantially corresponding to the height of the graft  20 . 
     A dilator  30  is provided that consists of a hollow body member  32  having a wall that tapers radially inwardly from one end  32   a  of the body member to its other end  32   b  to form a hollow frusto-cone. An annular lip  32   c  extends outwardly from the end  32   a , and a series of spaced, longitudinal slits, or slots,  32   d  are formed through the wall forming the body member  32  to add flexibility to the wall, for reasons to be described. 
     The diameter of the end  32   b  of the body member  32  is less than the diameter of the opening  12   b  so that the end can be inserted in the opening. The diameter of the end  32   a  is greater than that of the opening  12   b  to cause expansion of the opening in a manner to be described. The diameter of the end  32   a  of the body member  32  is greater than the diameter of the graft  20  so as to receive the graft, and the diameter of the end  32   b  is less than that of the graft so that, when the graft is inserted in the body member, the body member will expand, also in a manner to be described. 
     Referring to  FIGS. 2 and 3 , after the opening  12   b  is formed during the surgical procedure, the end  32   b  of the dilator  30  is initially inserted into the opening  12   b  either by hand or using any suitable instrument. Then, as the dilator  30  is pushed, or forced, in an axial direction into the opening  12   b , its tapered outer surface engages the inner wall of the opening and exerts outwardly-directed radial forces against the latter wall. Sufficient force is exerted to drive the dilator  30  axially into the opening until the end  32   b  engages the bottom of the opening  12   b  and the lip  32   c  engages the chondral surface of the femur  12  surrounding the opening  12   b . Due to the fact that the diameter of the end  32   a , as well as a portion of the tapered body member  32  adjacent the latter end (the lower portion of the dilator  32  as viewed in  FIG. 2 ), is greater than that of the opening  12   b , the opening, and, more particularly, the tissue and bony portion of the femur  12  defining the opening, is expanded radially outwardly as the dilator moves to its completely embedded position in the opening shown in  FIG. 3 . 
     The graft  20  is then inserted into the opening  12   b  either by hand or using any suitable instrument. The graft  20  is then pushed, or forced, in an axial direction into the body member  32  with the outer surface of the graft engaging the inner surface of the tapered inner wall of the body member  32 , to exert outwardly-directed radial forces against the latter wall. Due to the fact that the diameter of the graft  20  is greater than the upper portion of the tapered body member  32  as viewed in  FIGS. 2 and 3 , the body member is expanded radially outwardly, aided by the slots  32   d , as the graft moves axially in the body member. This expansion of the body member  32  causes corresponding additional expansion of the opening  12   b . This movement continues until the leading end of the graft  20  engages the bottom of the opening  12   b , as shown in  FIG. 3 . In the position of  FIG. 3 , the dilator  30  extends in the opening  12   b  in a snug fit and the graft  20  extends in the dilator in a snug fit. 
     With reference to  FIG. 4 , the dilator  30  is manually extracted from the opening in the direction shown by the arrow, thus forming an interface between the graft  20  and the wall of the femur  12  defining the opening  12   b . The expanded bony portion and tissue of the femur  12  surrounding the graft  20  will then collapse around the graft, thus producing compression that retains the graft in the opening  12   b . This prevents any relative movement between the graft  20  and the opening  12   b  and promotes integration of the graft with the surrounding bone and tissue of the femur  12 . 
     Variations 
     1. The dimensions of the graft, the dilator and/or the opening, can vary within the scope of the invention. 
     2. The relative dimensions between the graft, the dilator and/or the opening, can vary within the scope of the invention. 
     3. The shape of the graft, the dilator, and or the opening can vary within the scope of the invention. For example, the cross-section of the graft, the dilator, and the opening can be of a polyagonal shape as disclosed in copending U.S. patent application Ser. No. 11/120,136, filed Apr. 30, 2005, the disclosure of which is hereby incorporated by reference. 
     4. The procedure and dilator discussed above are equally applicable to any animal species in addition to humans. 
     5. The graft can be harvested from the patient or another human, or can be a xenogenic source, or can be a substitute material. 
     6. The spatial references mentioned above, such as “upper”, “lower”, “under”, “over”, “between”, “outer”, “inner” and “surrounding” are for the purpose of illustration only and do not limit the specific orientation or location of the components described above. 
     Those skilled in the art will readily appreciate that many other variations and modifications of the embodiments described above can be made without materially departing from the novel teachings and advantages of this invention. Accordingly, all such variations and modifications are intended to be included within the scope of this invention as defined in the following claims. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents, but also equivalent structures.