with reference to the above fig1 - 3 , the retainer is generally designated by the reference numeral 1 and comprises a cylindrical body 2 having , at one end , a cambered flange 3 . a plurality of notches 4 are formed in the flange 3 , are diametrically mutually opposite to the axis of the body 1 and are angularly mutually equidistant . a quadrangular eyelet 5 protrudes from the opposite side of the body 2 with respect to the flange 3 . the eyelet 5 lies on a diametrical plane that passes through the axis of the body 1 and has a substantially ellipsoidal cross - section . the described retainer is completed by a hexagonal recess 6 which is formed axially in the body 1 and is open at the center of the flange 7 . the recess 6 is meant for the engagement of a tool , for example an allen wrench , whereby the retainer can be turned once it has been installed in the seat meant to receive it . the semitendinous tendon b and the gracilis tendon c are first released through an incision a formed with an arthroscope ; however , said tendons remain inserted on the tibia with one end . two sutures d , for example of the type known as brunnel suture , are then applied to the free ends of the two tendons b and c to allow the coupling of the thread e for pulling the tendons through the articulation of the knee . the arthroscope is then reinserted through a second supracondylar incision f and is used to form , according to conventional methods , the outer percondylar hole g and the tibial hole h ( fig5 ). by using a suitable ligature carrier i , the tendons b and c are then passed through the tibial hole h and through the femoral hole g until they fully exit from the incision f ( fig6 ). at this point , the tendons b and c are guided through the eyelet 5 of the retainer 1 ( fig8 ). by using a second traction wire l , the tendons are reinserted in the femoral hole g and in the tibial hole h , until they again exit from the tibial hole h ( fig8 and 9 ). the traction applied by the tendons to the retainer 1 causes the partial engagement of the retainer 1 in the inlet of the femoral hole g . by using a suitable boneset , the retainer is fully inserted in the femoral hole g until the flange 3 abuts against the outer cortex of the femur ( fig1 ). an adequate traction of the free ends of the tendons allows them to slide on the eyelet 5 . when the pretensioning of all four bundles of tendons has reached a preset value , one and two staples m ( fig1 ) are arranged so as to straddle the tendons at the exit of the tibial hole h . at this point , valid stabilization of the knee has already been achieved . however , the retainer allows an additional and final tensioning by twining the tendon bundles inside the femoral hole g and the tibial hole h . for this purpose , an allen wrench n is inserted in the recess 6 and turned through the necessary angle , for example approximately 360 ° ( fig1 ). the direction of rotation of the tendon bundles is clockwise for the right knee and counterclockwise for the left knee . the tensioning force of the tendons can be controlled with a torque wrench . when the tendons have reached the intended tension , the retainer 1 is fixed against possible rotary and axial displacements by positioning a staple o so as form a bridge on the flange 3 , so that the teeth of the staple o engage the notches 4 ( fig1 ). it is evident that the described retainer perfectly achieves the intended aim and object . in particular , the retainer allows to simultaneously perform pretensioning and final tensioning of the tendons during the operation , at the chosen degrees of flexing and for the time deemed most suitable by the operator , allowing to take advantage of the visco - elastic properties of tendons . according to a different embodiment of the invention , illustrated in fig4 instead of the hexagonal recess 3 a threaded hole 7 is provided which is suitable to receive a screw - on plug that , by preventing the growth of bone inside its internal hole , facilitates the optional engagement of a tool for the removal of the retainer , if and when required . in a further embodiment , the eyelet 5 is open so as to form a sort of hook .