Variable Axis Locking Mechanism for Orthopedic Implants
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Solution Overview
Problem
Existing orthopedic implants lack the ability to securely fix bones or bone segments at variable angles, limiting their effectiveness in capturing and stabilizing small and long bones, as well as other anatomical areas.
Innovation Solution
A mechanism featuring a convexly rounded locking insert with expansion slots and cam raceways, combined with radially extending camming members on screws or pegs, allows for adjustable angulation and secure locking by creating a friction fit within a concavely rounded opening, enabling at least 25° of angulation relative to the implant's longitudinal axis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a traditional fixed-angle screw or peg is used in an orthopedic implant, then the implant structure is simple and easy to manufacture, but the implant cannot be adjusted to variable angles to best capture bones or bone segments
Solution Approach 1:
The locking insert is designed with an expansion slot that allows it to dynamically change its internal volume. When the camming member is activated, the locking insert expands radially to lock the screw or peg at the desired angle. This dynamic transformation enables the mechanism to transition from a compact state during insertion to a locked state at variable angles, resolving the contradiction between adaptability and complexity.
Solution Approach 2:
The locking insert features a convexly rounded, preferably spherical outer surface that fits into a concavely rounded opening in the implant. This spherical geometry allows the locking insert to rotate and accommodate variable angles (at least 25° relative to the longitudinal axis) while maintaining a secure fit. The curved surfaces enable angular adjustment without requiring complex mechanical linkages.
2Reliability
If a variable angle locking mechanism is implemented, then the implant can securely fix bones at desired angles, but the manufacturing precision and assembly complexity increase
Solution Approach 1:
The locking mechanism is divided into distinct functional segments: the locking insert with expansion slot, the camming member with radial wings, and the cam raceways. Each component has a specific function that can be manufactured and quality-controlled independently. The locking insert provides the angular adjustment function, the camming member provides the locking action, and the cam raceways guide the motion. This segmentation allows for standardized manufacturing processes and reduces the overall manufacturing precision requirements compared to a fully integrated mechanism.
Solution Approach 2:
The camming member is designed to automatically engage the cam raceways and drive the locking insert into its locked position through the expansion slot. The radial wings of the camming member interact with the cam raceways to create a self-locking mechanism that secures the desired angle without requiring additional fasteners or complex assembly steps. This self-service feature simplifies the assembly process and reduces the need for high-precision manual adjustment during surgery.
3Strength
If the locking insert expands radially to create a friction fit, then the screw or peg is securely locked at the desired angle, but the stress concentration on the bone may increase
Solution Approach 1:
The locking mechanism transitions from a one-dimensional linear insertion to a three-dimensional angular adjustment and radial expansion. The locking insert expands radially outward within the concavely rounded opening, distributing the locking force across a broader area of the implant rather than concentrating it at a single point. This dimensional change allows the locking strength to be achieved through surface friction and distributed contact pressure rather than localized stress concentration on the bone.
Solution Approach 2:
The camming member is designed to gradually drive the locking insert into its expanded locked position through the cam raceways. This preliminary action allows the bone and implant to adapt to the increasing locking force in a controlled manner, rather than sudden application of high stress. The camming mechanism progressively increases the radial expansion of the locking insert, distributing the stress over time and reducing peak stress concentrations on the bone.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution enables secure fixation of bones or bone segments at desired angles, enhancing the stability and versatility of orthopedic implants in various anatomical applications, including small bones and long bones, by providing a reliable friction fit that maintains the desired orientation.
Implementation Method 1
cause a friction fit of the locking insert in the opening and to lock the screw or peg at the desired angle
Data Source
AI summary
A locking mechanism assembly to allow locking of a fastener in an orthopedic implant having its axis at a variable angle relative to the axis of a concavely rounded through opening in the implant. The assembly includes a convexly rounded ring shaped locking cam insert which mates with the through opening and further which includes an expansion slot. The cam insert includes two cam raceways on the inside that are engaged by cam members on the head of the fastener. The cam members increase radially and expand the insert in the through opening to hold it in position by friction. The cam insert further includes a stop member that inhibits the cam insert from rotating as the fastener is rotated in the cam insert and locks it into the desired position.