An anchor for fixing a ligament or tendon replacement in a bore formed in a bone has two parts. A first partially cylindrical part has a semi-circular bore therethrough extending along an axis. The bore tapers conically inwardly with respect to the axis from a larger radius at a first end to a smaller radius at second end. The outer surface of the partially cylindrical part is spaced at a constant radius from the axis between the first and second ends. The first and second parts have side walls formed between the bore and the outer surface which walls extend along a plane which forms an angle with respect to the central axis. When the two parts are engaged along their side wails and slide with respect to the axis the outer diameter of the two parts enlarges.