A bone anchor including a bone engaging portion, a tool engaging portion configured for engagement with an anchor removal tool, a head portion having a transverse base portion and two arm portions that together define a U-shaped channel, and a reduced strength portion extending between the tool engaging portion and the head portion and defining a region of reduced strength to provide a pre-defined fracture initiator or break zone. In another embodiment, the bone anchor includes a proximal head and a threaded shank having a plurality of thread turns adapted for anchoring to bone and extending along a threaded length that is at least twice the overall height of the proximal head, and a plurality of grooves circumferentially interrupting at least one of the thread turns along a proximal region of the threaded shank and sized and shaped for engagement with an anchor removal instrument.