Bone anchor assemblies and related instrumentation
Bone anchor assemblies and related instrumentation are disclosed herein. In some embodiments, a modular bone anchor assembly allows for a bone anchor to be driven into bone and a head or receiver member to be attached thereto at some later point in time. The bone anchor can have a smaller footprint than the complete assembly, which can improve visualization and anatomical spatial awareness during insertion of the bone anchor and during other surgical steps performed prior to attaching the head or receiver member to the bone anchor. A variety of modular head types are disclosed, as are various instruments for driving a bone anchor, attaching a head to a bone anchor, removing a head from a bone anchor, and making a unilateral attachment to a head of a bone anchor assembly. Drive interfaces for driving a bone anchor are disclosed, as are features that allow a bone anchor to act as a fixation point for soft tissue retraction, disc space distraction, derotation, and the like.
1. A head insertion instrument, comprising:
a sleeve having opposed arms movable towards and away from one another to selectively couple the sleeve to a head of a bone anchor assembly;
a push rod disposed within the sleeve and configured to translate axially with respect to the sleeve, the push rod having a first bearing surface; and
a release element disposed within the sleeve and configured to translate axially with respect to the sleeve and the push rod, the release element including a second bearing surface and opposed arms aligned with the opposed arms of the sleeve;
wherein the instrument prevents separation of a head of a bone anchor assembly from the sleeve when the head is not fully seated on a bone anchor.
2. The instrument of claim 1 , wherein, when a head coupled to the sleeve is not fully seated on a bone anchor, advancement of the push rod advances the release element without spreading the arms of the release element or the arms of the sleeve, thereby preventing separation of the head from the instrument.
3. The instrument of claim 1 , wherein, when a head coupled to the sleeve is fully seated on bone anchor, advancement of the push rod causes the first bearing surface to cam over the second bearing surface to spread the arms of the release element and the arms of the sleeve, thereby separating the head from the instrument.
4. The instrument of claim 1 , wherein the arms of the sleeve include arcuate shelves that extend radially-inward from the arms, the shelves being configured to be received within corresponding grooves formed in a head of a bone anchor assembly.
5. The instrument of claim 1 , wherein the arms of the sleeve include a shoulder to limit distal travel of the release element relative to the sleeve.
6. The instrument of claim 1 , wherein a proximal end of the push rod is coupled to a button or lever that can be depressed to translate the push rod longitudinally with respect to the sleeve.
7. The instrument of claim 1 , wherein the push rod is biased proximally with respect to the sleeve.
8. The instrument of claim 1 , wherein the first and second bearing surfaces are ramped.
9. The instrument of claim 1 , wherein the first bearing surface is formed on an exterior of the push rod and the second bearing surface is formed on an interior of the arms of the release element.
10. The instrument of claim 1 , wherein the release element includes a distal projection configured to protrude from a distal end of the sleeve to contact a bone anchor.
11. The instrument of claim 1 , wherein the release element includes opposed tabs that slide within corresponding channels formed in the sleeve to restrict rotation of the release element relative to the sleeve.
12. The instrument of claim 1 , wherein a proximal end of the push rod extends proximal to the sleeve.
13. The instrument of claim 12 , wherein the proximal end of the push rod includes a button configured to be depressed to release the head of the bone anchor assembly from the sleeve.
14. The instrument of claim 1 , wherein the push rod is biased in a proximal direction relative to the sleeve.
15. A head insertion instrument, comprising:
a sleeve having opposed arms movable towards and away from one another to selectively couple the sleeve to a head of a bone anchor assembly, the sleeve having a longitudinal axis extending therethrough;
a push rod disposed within the sleeve and configured to translate axially with respect to the sleeve, the push rod having a first bearing surface; and
a release element disposed within the sleeve and configured to translate axially with respect to the sleeve, the release element including a second bearing surface and opposed arms aligned with the opposed arms of the sleeve, the opposed arms of the release element being configured to move between a radially-inward position and a radially-outward position relative to the longitudinal axis of the sleeve;
wherein the instrument prevents separation of a head of a bone anchor assembly from the sleeve when the head is not fully seated on a bone anchor, and
wherein the opposed arms of the sleeve are configured to engage with the head of the bone anchor assembly when the opposed arms of the release element are in the radially-inward position and the opposed arms of the sleeve are configured to disengage from the head of the bone anchor assembly when the opposed arms of the release element are in the radially-outward position.