A bioabsorbable, cannulated expandable tissue anchor for sutureless soft tissue fixation to bone, particularly in arthroscopic shoulder surgery. The anchor is provided with a ribbed shaft and a head for securing the soft tissue to bone. The shaft of the anchor is divided into at least two legs by longitudinal slots which extend from the distal end of the anchor. After the anchor is installed through tissue and into bone, a dowel is inserted into the proximal end of the cannulated shaft to axially spread apart the legs of the shaft by opening the longitudinal slots, thereby securing the anchor in the bone.