Bone anchor
An anchor assembly can be couplable to a bone and can include an anchor and a housing. The anchor can include a shank securable to bone and a head coupled to a proximal portion of the shank. The housing can include a proximal portion including an anchor bore and a distal portion including a secondary bore configured to engage the anchor to limit angulation of the anchor relative to the housing.
1 . An anchor assembly couplable to bone, the assembly comprising:
an anchor comprising:
a shank securable to bone; and
a head coupled to a proximal portion of the shank; and
a housing comprising:
a proximal portion including an anchor bore extending distally into the housing along a longitudinal axis of the housing, the anchor bore configured to retain the head of the anchor therein; and
a distal portion including a secondary bore configured to engage the anchor to limit angulation of the anchor relative to the housing, the secondary bore comprising:
a first portion configured to limit the angulation of the anchor to a first angle relative to the longitudinal axis; and
a plurality of second portions each configured to limit the angulation of the anchor to a second angle relative to the longitudinal axis that is greater than the first angle;
wherein one of:
the secondary bore has a geometric shape substantially of a square with rounded corners from a distal perspective; and
the first portion is defined by a first chamfer extending radially outward from the secondary bore, wherein each of the plurality of second portions are defined by a plurality of bevels extending radially outward, and wherein each of the plurality of bevels curves along a face of each of the plurality of bevels.
2 . The anchor assembly of claim 1 , wherein the secondary bore is positioned at a distal end of the distal portion, and wherein the secondary bore is substantially coaxial with the anchor bore and the longitudinal axis.
3 . The anchor assembly of claim 2 , wherein the anchor further comprises a neck including a neck diameter that is smaller than a diameter of the shank and a diameter of the head, and wherein contact between the neck and the housing Is configured to limit the angulation of the anchor to the second angle relative to the longitudinal axis.
4 . The anchor assembly of claim 2 , wherein the housing includes two open sides, each open side substantially forming a U shape configured to receive a connecting member therethrough.
5 . The anchor assembly of claim 1 , wherein each of the plurality of second portions each is configured to receive the shank therein and to create a desired angular trajectory for the shank in reference to the housing.
6 . The anchor assembly of claim 1 , wherein the secondary bore comprises a plurality of first portions including the first portion, each of the plurality of second portions connected by the plurality of first portions.
7 . The anchor assembly of claim 6 , wherein the plurality of first portions and plurality of second portions are arranged symmetrically about a sagittal plane and a coronal plane of the housing.
8 . The anchor assembly of claim 6 , wherein each of the plurality of first portions is substantially planar.
9 . The anchor assembly of claim 8 , wherein the shank is threaded and wherein housing includes a helical groove configured to receive the threaded shank therethrough.
10 . The anchor assembly of claim 9 , wherein the helical groove terminates substantially at connection between one of the plurality of first portions and one of the plurality of second portions.
11 . The anchor assembly of claim 1 , the assembly further comprising:
a lower piston disposable in the anchor bore and configured to engage the head;
an upper piston disposable in the bore and configured to support a connecting member; and
a biasing element disposable between the lower piston and the upper piston to bias the upper piston away from the lower piston.