Spring-Loaded Ratchet Locking Mechanism for Surgical Alignment Stability
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Solution Overview
Problem
Existing alignment jigs for cutting guides in total knee replacement surgery often experience slippage during pinning due to limited torque application and vibration-induced loosening, especially in revision surgeries, which can compromise the accuracy of transverse cuts.
Innovation Solution
A bone cutting instrument with a spring-loaded shuttle mechanism providing tactile and audible feedback for precise adjustments, allowing for easy and secure locking without relying on threaded thumbscrews, ensuring the alignment settings remain stable during cutting operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a threaded thumbscrew is used to lock the alignment settings, then the device structure is simple, but the locking reliability is insufficient due to limited torque application and vibration-induced loosening
Solution Approach 1:
The patent replaces the traditional threaded thumbscrew mechanical system with a ratchet-and-pawl locking mechanism. The pawl engages with ratchet teeth to prevent reverse motion, providing positive locking that is resistant to vibration and does not rely on friction-based torque retention. This mechanical substitution fundamentally changes the locking principle from friction-dependent to geometry-dependent, thereby improving reliability.
Solution Approach 2:
The spring-loaded pawl automatically engages with the ratchet teeth when the alignment setting is adjusted, providing self-locking functionality. The spring ensures the pawl maintains constant contact pressure against the ratchet teeth, automatically compensating for any wear or dimensional variations without requiring manual intervention or additional locking steps.
2Ease of operation
If a thumbscrew locking mechanism is used, then the device is easy to manufacture, but the ease of operation is reduced due to difficulty in applying sufficient torque with slippery gloves
Solution Approach 1:
The ratchet-and-pawl mechanism with a release button replaces the thumbscrew system. The surgeon can adjust the alignment by moving the cutting guide along the rod while the spring-loaded pawl automatically locks at ratchet tooth increments. To release, the surgeon simply presses the button, which retracts the pawl from the ratchet teeth. This eliminates the need to twist a thumbscrew, making operation significantly easier especially when wearing slippery surgical gloves.
3Measurement precision
If the alignment settings are locked by tightening a thumbscrew, then the structure is simple, but the measurement precision is insufficient as slippage occurs during pinning
Solution Approach 1:
The ratchet mechanism provides discrete angular or linear positioning increments defined by the spacing of the ratchet teeth. The alignment setting is precisely determined by which ratchet tooth the pawl engages with, eliminating continuous but unstable thumbscrew positioning. The spring-loaded pawl ensures firm engagement with the selected tooth, preventing slippage during the pinning operation and maintaining measurement precision throughout the procedure.
Solution Approach 2:
The ratchet mechanism provides tactile feedback through distinct engagement stops at each tooth, allowing the surgeon to感知 the precise positioning increments. This mechanical feedback system confirms when the alignment has reached a predetermined setting, enhancing measurement precision without requiring complex electronic sensors or indicators.
4Stability of the object's composition
If a threaded thumbscrew is used for locking, then the device complexity is low, but the stability of the object's composition deteriorates under vibration conditions
Solution Approach 1:
The ratchet-and-pawl system replaces the friction-based thumbscrew with a geometry-based locking mechanism. The pawl's engagement with the ratchet teeth creates a mechanical stop that prevents reverse motion caused by vibration. The spring loading ensures the pawl maintains constant contact pressure, automatically compensating for vibration-induced forces and maintaining alignment stability throughout the cutting operation.
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
The instrument ensures precise and stable adjustments with tactile and audible feedback, preventing slippage and maintaining alignment settings accurately, even in challenging surgical conditions like revision surgeries, enhancing the reliability of transverse cuts in knee replacement procedures.
Implementation Method 1
A spring biased shaft mounted on the rotating body with a first end engagable with the toothed locking member or pawl for moving the toothed locking member relative to the rotating body into locking engagement
Implementation Method 2
A spring loaded wedge-like toothed shuttle is used to lockingly engage a ratchet on angle adjustor when the button is released
Implementation Method 3
The rotating body includes a toothed locking member or pawl moveably mounted thereon for releasable locking engagement with the toothed portion on the slide block
Data Source
AI summary
A locking intramedullary alignment jig for use in bone resection, especially for the proximal tibial has an axially extending intramedullary rod for insertion into the medullary canal of the tibia. A slidable anchoring block is mounted on the rod for movement along the rod in the axial direction, which on the tibia is the proximal-distal direction. The anchoring block has a pivot point at one end thereof and a tooth portion at a second end thereof. A first rotating body is pivotally coupled to the pivot point on the anchoring block for rotation about a first axis. The rotating body includes a toothed locking member for releasable locking engagement with the toothed portion the anchoring block. A second rotating body, including a bone resection guide is connected to the first rotating body. Movement of the first and second rotating bodies allow rotation of the resection guide in both the flexion-extension and varus-valgus directions.