A method and bone anchor assembly apparatus for attaching suture material to bone tissue includes a hollow anchor body having a rectilinearly-bounded transverse cross-section with a maximum dimension corresponding to the diameter of the bone tunnel drilled to receive the anchor. A longitudinally displaceable plug received within the anchor body is contoured to interact with inwardly biased bone tissue engaging barbs formed on the sides of the anchor body, defining a first position wherein the barbs are allowed to uninterferingly retract within the anchor body and a second position wherein the plug forces the barbs outward into engaging contact with the bone tunnel sidewalls. Suture material is passed around the anchor assembly, through a transverse slot defined in the assembly distal end and the plug is positioned in the first position with barbs retracted. The assembly is inserted into the bone tunnel and the plug is urged into the second position with barbs engaged in bone tissue. Removal of the assembly is made possible by urging the plug back into the first position.