Polyaxial locking fastener with negative threads

Abstract

A polyaxial ball-and-socket fastener is disclosed that provides enhanced locking performance through intersecting negative thread profiles formed on complementary hemispherical surfaces. The fastener includes a saddle assembly having a hemispherical socket with a right-hand negative thread profile and an anchor member having a spherical head with a left-hand negative thread profile. When the saddle assembly is advanced toward the anchor member, the oppositely oriented negative thread profiles intersect and counter-rotate relative to one another to generate multidirectional frictional interference along the curved ball-and-socket interface. This interaction produces a strong locking effect without requiring proportionally increased torque or compressive force, while still permitting wide-range polyaxial articulation prior to tightening. The configuration increases resistance to micro-motion and cyclic loading, maintains a substantially spherical geometry for smooth pre-lock articulation, and enables controlled deformation of the thread profiles during final tightening to further enhance fixation stability.

Dependencies are inferred from the claim text.