Abstract We report a rare case of a taper-locked femoral inner head that have been completely separated from the stem neck. A 76-year-old man who had hip fracture of the right hip had disassembly of inner head and stem neck after revision of bipolar hip prosthesis. This force could have been amplified by the pumping phenomenon generated after the revised inner head. We suspect the sealed air pushes back the stem neck, and unlocks the taper lock of the inner head, causing separation of the stem neck from the inner head. To prevent pumping phenomenon, we recommend manual testing of the taper lock to confirm that it has been assembled correctly and its integrity before implantation when the bloody and fatty membrane is adequately removed from stem neck.