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 bone anchor assembly, comprising:
a receiver member having proximal and distal ends that define a central proximal-distal axis;
an insert attached to the receiver member, the insert and the receiver member defining a cavity;
a collet disposed in the cavity and retained within the cavity by the insert, the collet including a plurality of fingers; and
a shank that extends through the insert, the shank having a head portion retained within the fingers of the collet,
wherein the insert is prevented from moving proximally or distally relative to the receiver member by the receiver member.
2. The assembly of claim 1 , wherein the insert includes a ridge received within a groove formed in the receiver member to attach the insert to the receiver member.
3. The assembly of claim 1 , wherein the insert is radially collapsible and expandable to facilitate insertion of the insert into the receiver member.
4. The assembly of claim 1 , wherein the insert is threaded into an open distal end of the receiver member.
5. The assembly of claim 1 , wherein the collet is insertable into the distal end of the receiver member without deforming the collet.
6. The assembly of claim 1 , wherein the receiver member comprises first and second opposed arms that define a rod-receiving recess therebetween.
7. The assembly of claim 1 , wherein the fingers of the collet are configured to deform from a resting position as the head portion of the shank is loaded into a distal end of the collet and, once the head portion is advanced into the collet, the fingers are configured to return towards their resting position to capture the head portion within the collet.
8. The assembly of claim 1 , wherein the shank is free to pivot relative to the collet when the head portion is received within the fingers of the collet before the collet is locked to the receiver member.
9. The assembly of claim 1 , wherein proximal advancement of the receiver member with respect to the collet wedges the collet fingers between the head portion of the shank and the interior of the insert, thereby locking movement of the shank with respect to the receiver member.
10. The assembly of claim 1 , wherein the collet comprises a compression cap and a collet ring.
11. The assembly of claim 10 , wherein the compression cap and the collet ring are independently longitudinally-translatable relative to the receiver member when disposed within the cavity.
12. The assembly of claim 10 , wherein the compression cap is slidably received within an opening formed in the collet ring.
13. The assembly of claim 10 , wherein the collet ring includes a proximal opening in which the compression cap is slidably received and wherein the fingers of the collet extend distally from the collet ring.
14. The assembly of claim 10 , wherein the compression cap includes one or more flats that interact with respective one or more flats of the receiver member to limit rotation of the compression cap relative to the receiver member about the central proximal-distal axis.
15. The assembly of claim 10 , wherein the cavity includes an upper portion having a cylindrical inner sidewall that constrains a cylindrical outer sidewall of the collet ring when the collet ring is received therein.
16. The assembly of claim 10 , wherein tightening a closure element to the receiver member (i) urges a bearing surface of the compression cap against a proximal portion of the head of the shank and (ii) urges the collet fingers against a distal portion of the head of the shank.
17. A bone anchor assembly, comprising:
a receiver member having proximal and distal ends that define a central proximal-distal axis;
an insert attached to the receiver member, the insert and the receiver member defining a cavity;
a collet disposed in the cavity and retained within the cavity by the insert, the collet including a plurality of fingers; and
a shank that extends through the insert, the shank having a head portion retained within the fingers of the collet,
wherein a central opening of the insert is sized and positioned to retain the shank in the distal end of the receiver member by preventing expansion of the plurality of fingers when the insert is disposed in the receiver member.
18. The assembly of claim 17 , wherein the central opening is larger than an outer diameter of the head portion when retaining the shank in the distal end of the receiver member.