Polyaxial Bone Anchor Locking Element for Low-Profile Wide-Angle Fixation
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Solution Overview
Problem
Existing bone plate assemblies provide limited angular motion and a higher profile, which restricts their versatility and safety in clinical applications, especially in areas with minimal soft tissue coverage like the cervical spine or small bones.
Innovation Solution
A low-profile bone plate assembly with a locking element that allows up to 35° pivot angle and a motion cone of at least 60°, featuring a simple design with minimal parts, secure locking with low torque, and optional locking elements for full or frictional locking, while preventing pull-out, and accommodating various clinical needs through offset holes and contoured designs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional bone plate assemblies are used, then structural strength is maintained, but the profile height is increased and angular motion range is limited
Solution Approach 1:
The locking element is nested within the bore of the plate, with the bone anchor head positioned inside the locking element's recess. This nested arrangement allows the spherical bearing surface to provide polyaxial motion while the locking element remains compact, achieving a low profile construct with extensive angular motion capability (at least 60° motion cone).
Solution Approach 2:
The invention transitions from a fixed angular position design to a polyaxial design by introducing a spherical bearing surface that enables motion in multiple dimensions. The bone anchor head can pivot within a motion cone of at least 60°, providing angular adjustability in multiple planes while maintaining a low overall profile through the nested locking mechanism.
2Adaptability or versatility
If polyaxial adjustment capability is added, then angular motion range increases, but device complexity increases
Solution Approach 1:
The invention merges the functions of the locking mechanism and the polyaxial adjustment mechanism into a single integrated locking element. The locking element contains both the threaded portion for engagement with the plate bore and the spherical recess for receiving the bone anchor head, eliminating the need for separate locking and bearing components while providing both polyaxial adjustment and secure locking.
Solution Approach 2:
The locking element serves multiple functions simultaneously: it provides polyaxial angular adjustment through its spherical recess, secures the bone anchor through threading engagement with the plate bore, and maintains a low profile through its compact nested design. This multi-functional component reduces the overall number of parts while achieving complex functionality.
3Reliability
If secure locking is implemented, then stability is improved, but torque requirements increase
Solution Approach 1:
The spherical bearing surface in the locking element's recess provides stable polyaxial locking through its curved geometry. The spherical contact surface distributes loads evenly and maintains stable engagement of the bone anchor head at various angles within the motion cone, achieving reliable locking with low torque requirements due to the favorable contact geometry.
Data Source
AI summary
A tool adapted for use with a bone plate assembly includes a driver with an engagement portion configured to engage a locking element, and a tubular holder. The driver may be configured to extend with the engagement portion through the tubular holder, and may be axially movable and rotatable within the holder. The holder may have a radial slot adapted for insertion of the locking element. The holder may include a portion with an internal thread for cooperation with an external thread of the locking element. The locking element may be used with a polyaxial bone anchor.