The utility model relates to a bone anchor comprising a spiral nail, a flange having a return line extending hole allowing an injured bone return line to penetrate and be connected therein, and a joint structure for coaxially jointing the flange with the spiral nail and keeping each of the flange and the spiral nail rotate freely. Based on that the spiral nail and the flange are joined in such a manner of keeping the flange and the spiral nail rotate freely, the flange is kept to be positioned without rotating in the rotation process of planting the spiral nail into a bone; therefore, the problem of twisting and winding of the injured bone return line is avoided.