in a preferred embodiment , described below by way of example only , there is provided a bone block harvester for use in anterior cruciate ligament graft surgery using a patellar tendon graft . anterior cruciate ligament ( acl ) reconstruction surgery involves replacing a torn acl with a graft ligament that can be taken from the patient &# 39 ; s own body ( autologous ) or made from synthetic material or from a cadaver ( allograft ). of the total number of surgeries performed around 85 % are performed using autologous grafts . of this number approximately 65 % are performed using a graft ligament taken from the central third of the patellar tendon , including bone from the superior tibia and the patella . these are referred to as bone - patellar tendon - bone ( bptb ) grafts . there are several alternative grafts available for acl reconstruction , including hamstring grafts and allografts , but the bptb graft offers the advantage that the bone blocks heal into the surrounding bone of the patient after the attachment of the graft , providing fixation as strong as that of the original acl . with reference to fig1 , the harvester 100 comprises a cylindrical handle 12 rigidly joined to an elongate body 2 extending substantially along the axis of the handle 12 . the body 2 , as shown in this embodiment , is a strip of rectangular cross section which is straight over a proximal portion 16 , and curves vertically , i . e . in a plane parallel to the axis of the handle 12 and perpendicular to the largest side of the strip 2 , over a distal portion 14 . there are two projections 10 of the strip 2 laterally in the distal portion 14 , near the lowest point of the curved section , which limit the length of the bone block harvested . the tip of the body 2 comprises a chiseled cutting edge 4 for cutting into the bone to be harvested . a coupling bar 6 is mounted to the body 2 , the bar 6 running approximately parallel to the body 2 at the distal end of the body 2 between the lateral projections 10 and the cutting edge 4 . the bar 6 is disposed above the body 2 and to one side , and curves down to join the body at one of the lateral projections 10 . at the tip of the coupling bar 6 , above the cutting edge 4 , a perpendicular guiding bar 8 is mounted extending across the width of the cutting edge 4 . the guiding bar arrangement controls the depth of the bone block harvested . a possible method for using the harvester will now be described with reference to fig2 . prior to the harvester being used , the central third of the patellar tendon 24 is separated from the surrounding tendon . in the operation of the harvester 100 , the guiding bar 8 is positioned to abut the upper surface 18 of the central third of the patellar tendon and the cutting edge 4 is disposed beneath the tendon 24 . the surgeon operates the harvester using the handle 12 , held at an angle to the patellar tendon 24 . the surgeon applies sufficient force to the handle to slide the cutting edge 4 into the patella 26 . as the cutting edge 4 of the harvester 100 is pushed into the patella 26 , the guiding bar 8 rides over the upper surface of the tendon 18 and then the upper surface of the patella 20 , ensuring that the cutting edge 4 follows a substantially horizontal path through the bone at a predetermined maximum depth defined by the vertical distance between the guiding bar 8 and the cutting edge 4 . the length of the bone block 22 is limited by the lateral projections 10 disposed partway along the curved distal portion of the body 2 , which abut the front surface of the patella 26 and prevent further intrusion of the cutting edge 4 into the bone when a predetermined maximum length of bone block 22 is reached . when harvesting a bone block , by cutting as deep as the guiding bar will allow , and optionally cutting to the length allowed by the lateral projections , using an embodiment of the present invention the surgeon can easily ensure that an even , appropriately sized and shaped bone block is produced , while minimising the risk of damage to the donor site . the device can be made in as many different widths as a surgeon may require and can also be manufactured to allow the depth of the bone block to be controlled to the surgeon &# 39 ; s requirements . in an alternative embodiment , not shown , the size of the controlled dimension ( depth ) of the bone block may be adjustable , for example by having the arm position adjusted by a set screw . however , for ease of use and sterilization , preferably the depth is fixed for a given instrument . a set of instruments may be provided wherein the respective sizes of the controlled dimensions of the bone block are mutually different . for example , a set of standard increments may be provided , for example 3 , 4 , 5 , 6 , 7 , 8 mm depths . the harvester may be used for various applications and various sizes of bone blocks . preferred bone block controlled dimensions , preferably depths , are at least 1 mm and preferably no more than 10 mm , more preferably 3 - 8 mm . the width of the harvested portion is preferably at least 3 mm wide and preferably no wider than 20 mm , more preferably 5 to 15 mm , most preferably 6 - 12 mm . the length of the harvested portion , which may be selected by the surgeon by adjusting the depth of penetration of the cutter is preferably no longer than 50 mm , preferably less than about 25 mm ( 1 inch ). the length is preferably at least 3 mm , typically at least 5 or 10 mm . the dimensions may be independently chosen . however , the device is most suitable for harvesting a bone block having a depth in the range about 3 to 8 mm , a width in the range of about 6 to 12 mm and a length of about 5 to 25 mm . the embodiment described above is not intended to be limiting and it will be appreciated that other embodiments are possible within the scope of the invention as defined by the following claims . specifically , the bone block harvester may be used in several different surgical procedures and the application of the invention is not limited to any one type of surgery unless so limited by the attached claims .