To allow for greater ease of rod installation in a bone fixing screw having a threaded portion, and to prevent an installed rod from slipping out of place, there is formed at an outer end of a thread 11, a rod-receiving portion 12 having an opening obliquely placed with respect to the axial direction...http://www.google.es/patents/US6074393?utm_source=gb-gplus-sharePatente US6074393 - Bone fixing screws
