SPINAL FIXATION DEVICE
A spinal fixation device includes a housing assembly and a bone screw. The housing assembly includes an inner housing and an outer housing selectively slidable relative to each other between a locked position and an unlocked position. The bone screw includes a head portion selectively securable within the inner housing of the housing assembly, a neck portion, and an elongated body portion including a proximal region and a distal region. The distal region includes a threaded section having threads and an unthreaded section extending distally from the threaded section and terminating at a distal tip. The threaded section includes a cutting flute defined therein proximal to the unthreaded section.
1 . A spinal fixation device comprising:
a housing assembly including an inner housing and an outer housing selectively slidable relative to each other between a locked position and an unlocked position; and
a bone screw including:
a head portion selectively securable within the inner housing of the housing assembly;
a neck portion extending distally from the head portion; and
an elongated body portion extending distally from the neck portion, the elongated body portion including a proximal region and a distal region, the distal region including a threaded section having threads and an unthreaded section extending distally from the threaded section and terminating at a distal tip, the threaded section including a cutting flute defined therein proximal to the unthreaded section.
2 . The spinal fixation device of claim 1 , wherein the cutting flute has a radius of curvature of about 13.7 mm to about 14.2 mm.
3 . The spinal fixation device of claim 2 , wherein the radius of curvature is 13.97 mm.
4 . The spinal fixation device of claim 2 , wherein a center of curvature of the cutting flute is about 3.3 mm to about 3.8 mm from the distal tip.
5 . The spinal fixation device of claim 4 , wherein the center of curvature is about 3.56 mm from the distal tip.
6 . The spinal fixation device of claim 1 , wherein a ratio of a length of the threaded section to a length of the unthreaded section is about 3:1.
7 . The spinal fixation device of claim 1 , wherein a length of the unthreaded section of the distal region of the elongated body portion is about 2.67 mm to about 2.92 mm.
8 . The spinal fixation device of claim 7 , wherein the length of the unthreaded section is about 2.79 mm.
9 . The spinal fixation device of claim 7 , wherein a length of the threaded section of the distal region of the elongated body portion is about 8.94 mm to about 9.45 mm.
10 . The spinal fixation device of claim 9 , wherein the length of the threaded section is about 9.2 mm.
11 . The spinal fixation device of claim 1 , wherein the threads of the threaded distal region are dual lead threads.
12 . The spinal fixation device of claim 11 , wherein a pitch of the threads is about 2.2 mm to about 2.4 mm.
13 . The spinal fixation device of claim 12 , wherein the pitch is about 2.25 mm.
14 . The spinal fixation device of claim 11 , wherein each of the threads has a leading angle of about 26° to about 28° and a trailing angle of about 2° to about 4°.
15 . The spinal fixation device of claim 14 , wherein the leading angle is about 27°.
16 . The spinal fixation device of claim 14 , wherein the trailing angle is about 3°.
17 . The spinal fixation device of claim 11 , wherein the proximal region of the elongated body includes single lead threads.
18 . The spinal fixation device of claim 7 , wherein the unthreaded section of the distal region of the elongated body has a conical shape defining a cone angle of about 35° to about 37°.
19 . The spinal fixation device of claim 18 , wherein the cone angle is about 36°.
20 . The spinal fixation device of claim 1 , wherein the neck portion has a diameter that is at least equal to a major diameter of the elongated body portion.