Patent ID: 8591559

Claim:
A fixation assembly comprising at least one insertion member that includes one or more expandable and retractable anchoring inserts positioned along at least a portion of the insertion member; the insertion member comprising a screw having a shaft with a helical thread formed on at least a portion of an outer surface of the shaft; and, one or more of the expandable and retractable anchoring inserts being positioned along at least a portion of the shaft between one or more adjacent helical threads, the anchoring insert being comprised of at least two antagonistic materials: a retractor segment and a protractor segment, at least a portion of the protractor segment being comprised of a material that expands or contracts in response to an appropriate change in temperature, and at least a portion of the retractor segment being comprised of a material which has an austenite transformation temperature different from the temperature at which the protractor segment expands or contracts; wherein the protractor segment defines a channel that receives at least a portion of the retractor segment.