Lumbar Plate Retention Cap Locking for Screw Backout Prevention
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Solution Overview
Problem
During lumbar surgery, bone screws can back out, causing the plate to move and affecting the healing process, and retention caps may not remain securely over the screws, leading to partial backout.
Innovation Solution
A lateral vertebral lumbar plate system with an integrated rotational control mechanism, featuring retention caps and a lumbar plate with assembly guides, locking detents, and a retainer to prevent screw-backout, allowing easy assembly and disassembly while providing tactile feedback.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If retention caps are used to prevent screw backout, then screw retention reliability is improved, but the device complexity increases due to additional components and assembly steps
Solution Approach 1:
The patent combines the retention cap and locking mechanism into an integrated unit that attaches to the plate and secures screws simultaneously. The retention cap incorporates a locking feature with detents that engage with protrusions on the screw head, merging the functions of screw retention and locking into a single component rather than separate elements.
Solution Approach 2:
The retention cap is designed to nest over the screw head, with the locking feature containing detents that receive protrusions from the screw. This nested configuration allows multiple functional elements (retention cap, locking mechanism, detents, protrusions) to be compactly arranged without requiring separate components for each function.
2Reliability
If a locking mechanism with multiple components is used, then screw retention reliability is improved, but the ease of manufacture deteriorates due to increased assembly steps
Solution Approach 1:
The locking mechanism is segmented into distinct functional features: retention cap, locking feature, detents, and protrusions. Each segment can be manufactured independently using standard machining processes, then assembled through simple snap-fit or press-fit connections, reducing overall manufacturing complexity compared to a monolithic design.
Solution Approach 2:
The detents and protrusions are designed to self-align and self-lock during assembly. The protrusions on the screw head automatically engage with the corresponding detents in the retention cap when the screw is inserted, eliminating the need for manual alignment or additional fastening steps during manufacturing.
3Reliability
If retention caps with rotational control are used, then screw retention reliability is improved, but the ease of operation deteriorates due to rotational alignment requirements
Solution Approach 1:
The retention cap and locking mechanism incorporate asymmetric features including non-circular detents and corresponding protrusions, along with keyed slots that permit rotation only in specific directions. This asymmetric design prevents improper rotational alignment while maintaining ease of operation through intuitive tactile feedback during the tightening process.
Solution Approach 2:
The locking mechanism provides tactile feedback through the engagement of detents with protrusions and the operation of keyed slots during rotation. This feedback allows the operator to sense when proper alignment is achieved and when the locking mechanism is fully engaged, eliminating the need for visual inspection or complex alignment procedures.
Data Source
AI summary
A plate system includes a retention cap and a plate. The retention cap includes a head with tangs and a shank. The shank includes protrusions at an end of the shank and relief cut-outs clocked relative to the protrusions. The plate includes screw holes and a locking feature. The locking feature includes an assembly guide adapted to guide the shank and features thereof into the locking feature, locking detents distal to the top surface of the plate and adapted to receive the protrusions and interfere with rotational movement of the retention cap, and a retainer positioned axially between the assembly guide and the locking detents. The retainer is adapted to prevent axial movement of the retention cap. The locking feature is adapted to hold the retention cap with the tangs overlapping the screw holes and with the tangs not overlapping the screw holes.