Length adjustable modular screw system
A length adjustable modular screw includes a neck assembly and a shank. The neck assembly has proximal and distal ends and includes an expander component and a collet component that are slidably engagable by insertion of the expander component in a through channel of the collet component along a common axis. The length adjustable modular screw also includes a shank suitable for insertion and retention within a bone, the shank including a threaded portion between proximal and distal ends and a socket adapted to coaxially receive at least a portion of the distal end of the neck assembly. The length adjustable modular screw has a length that is selected by splaying at least a portion of the distal end of the engaged expander and collet components of the neck assembly within the socket of the shank.
1. A surgical method for installing a bone anchor system for spinal fixation, comprising:
(i) selecting each of:
(a) a length adjustable modular screw comprising: a neck assembly that includes an expander component and a collet component, the neck assembly having proximal and distal ends and including expander and collet components that are slidably engagable by insertion of the expander component in a through channel of the collet component along a common axis, and a shank suitable for insertion and retention within a bone, the shank including a threaded portion between its proximal and distal ends and a socket adapted to coaxially receive at least a portion of the distal end of the neck assembly, wherein the length adjustable modular screw has a length that is selected by splaying at least a portion of the distal end of the engaged expander and collet components of the neck assembly within the socket of the shank, wherein the length adjustable modular screw is one of monoaxial, uniaxial, and poly-axial; and
(b) at least one spinal rod defining a longitudinal axis;
(c) two or more retaining housings, each retaining housing adapted for engaging and securing a bone anchor and the at least one spinal rod;
(d) two or more locking elements, each locking element adapted for securing the at least one spinal rod to a bone anchor
(ii) either before or after seating the neck assembly in a retaining housing, assembling a length adjustable modular screw, comprising the steps of:
(a) engaging the components of the neck assembly into engagement, and inserting the neck assembly into the socket of the shank,
(b) contacting the distal end of the shank with a bone,
(c) with a suitable driver, engaging a drive recess of the neck assembly to splay at least a portion of the distal end of the engaged expander and collet components of the neck assembly within the socket of the shank,
(d) driving the threaded portion of the shank into the bone,
(e) either before or after provisionally securing the at least one spinal rod into the retaining housing, adjusting the length of the length adjustable modular screw by sliding the neck assembly along the common axis within the socket of the shank;
tightening one of the locking elements within the retaining housing to compress the at least one spinal rod against the neck assembly and to lock the neck assembly within the socket of the shank.
2. The surgical method according to claim 1 , wherein the length adjustable modular anchor system is fully assembled prior to engagement of the threaded portion of the shank with the bone.
3. The surgical method according to claim 1 , wherein the length adjustable modular anchor system is provided pre-assembled.
4. The surgical method according to claim 1 , wherein the first expander component of the neck assembly includes an extension that extends beyond the distal end of the collet component of the neck assembly.
5. The surgical method according to claim 1 , wherein the expander and collet elongate components are matable at their proximal ends when the expander component is inserted in the through channel of the collet component.
6. The surgical method according to claim 1 , wherein the expander component comprises a head at its proximal end and the collet component comprises a seat at its proximal end, wherein the head and seat, when mated form a generally spherical head on the neck assembly.