Polyaxial Bone Fixation Element

A fastener device configured to secure a spinal rod relative to a bone, the fastener device comprising:

• an anchor body including an anchor body housing, the anchor body defining a through hole that extends through the anchor body housing, the anchor body further defining a rod-receiving channel that is configured to receive the spinal rod and that is offset with respect to the through hole, the anchor body further including an upper end, a lower end, and an inner surface that defines a least a portion of the through hole, at least a portion of the inner surface defining a portion of a first sphere;
• and
• a fastener including a head, a threaded shaft that extends out with respect to the head in a distal direction, and a neck that extends between the head and the threaded shaft, the head including an outer surface, at least a portion of the outer surface defining a portion of a second sphere, and the head further including a concave surface of the fastener that extends along both the head and the neck
• wherein the fastener device defines a configuration in which both:
• 1) the portion of the outer surface rides along the portion of the inner surface, and 2) the anchor body abuts the neck at a location that is spaced in the distal direction from an entirety of the concave surface such that movement of the fastener relative to the anchor body in at least one direction is blocked.

A fastener device configured to secure a spinal rod relative to a bone, the fastener device comprising:

• an anchor body including an anchor body housing, the anchor body defining a through hole that extends through the anchor body housing, the anchor body further defining a rod-receiving channel that is configured to receive the spinal rod and that is offset with respect to the through hole, the anchor body further including an upper end, a lower end, and an inner surface, the inner surface defining at least a portion of the through hole;
• and
• a fastener including a head, a threaded shaft that extends out with respect to the head in a distal direction, and a neck that extends between the head and the threaded shaft, the head including a convex outer surface, a portion of the convex outer surface both defining a portion of a sphere and being configured to articulate along the inner surface when the fastener head is positioned in the through hole, the fastener including a concave surface that extends along both the head and the neck,
• wherein the fastener is configured such that all lines that:
• 1) lie entirely within a plane parallel to the distal direction, and 2) are tangent to the portion of the convex outer surface are noncollinear with all lines that:
• 1) lie entirely within the plane, and 2) are tangent to the concave surface.

A fastener device configured to secure a spinal rod relative to a bone, the fastener device comprising:

• an anchor body including an anchor body housing and a central axis, the anchor body defining a through hole that extends through the anchor body housing along the central axis, the anchor body further defining a rod-receiving channel that is configured to receive the spinal rod and that is offset with respect to the through hole, the anchor body further including an upper end, a lower end spaced from the upper end in a first direction, and an inner surface, defining at least a portion of the through hole, the inner surface including:
• 1) a first portion that is curved and defines a portion of a sphere having a first diameter, 2) a second portion that is cylindrical and that defines a second diameter that is equal to or greater than the first diameter, and 3) a third portion that defines a third diameter that is greater than both the first diameter and the second diameter, wherein the first portion is closer to the lower end with respect to the first direction than the third portion is from the lower end with respect to the first direction, and the third portion is closer to the lower end with respect to the first direction than the second portion is from the lower end with respect to the first direction;
• and
• a fastener including a head and a threaded shaft that extends out with respect to the head, the head including an outer surface configured to articulate along the first portion of the inner surface when the fastener head is inserted in the through hole.