Bone Fixation Instrument Tensioning Mechanism
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Solution Overview
Problem
Conventional sternal fixation systems for approximating and compressing the sternum after open heart procedures face issues with wire breakage due to tensile forces and reliance on surgeon experience, leading to inadequate compression or overtightening, which can cause damage or failure.
Innovation Solution
A bone fixation instrument with a tensioning mechanism that includes a traveler and cutter arm to securely tighten and then cut the bone fixation member, ensuring consistent tension and preventing wire breakage, while allowing for precise control of tension levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If wires are tightened manually using conventional twisting methods, then sternal compression can be achieved, but wire breakage occurs due to excessive tensile forces
Solution Approach 1:
The patent replaces the manual twisting mechanical system with a controlled tensioning device that uses a ratchet mechanism and reel system. This substitution allows for precise control of tensile forces applied to the wire, preventing excessive force that would cause wire breakage while maintaining adequate sternal compression.
Solution Approach 2:
The patent incorporates a ratchet mechanism that provides mechanical feedback control. The ratchet allows the wire to be tensioned in controlled increments and prevents over-tensioning by mechanically locking at predetermined positions, giving the surgeon feedback on the force being applied and preventing wire failure.
2Manufacturing precision
If wires are tightened using conventional methods, then sternal approximation can be achieved, but the outcome relies on surgeon experience leading to inconsistent results
Solution Approach 1:
The patent employs a self-regulating ratchet mechanism that automatically controls the tensioning process. The ratchet system self-limits the force applied to the wire, eliminating the need for surgeon judgment and experience to determine appropriate tension levels, thereby standardizing the outcome.
Solution Approach 2:
The patent incorporates pre-marked indicators and pre-calibrated ratchet positions that guide the surgeon through the tensioning process. These preliminary markings indicate when optimal tension has been reached, removing the need for surgeon experience and ensuring consistent results.
3Force
If wires are overtightened to ensure sternal compression, then compression is achieved, but the wire can cut into or through the sternum
Solution Approach 1:
The ratchet mechanism provides mechanical feedback that prevents force exceeding predetermined limits. The ratchet teeth are designed to engage at specific force thresholds, providing automatic feedback that stops further tensioning before the wire can cut into the sternum, thus preventing bone damage.
Solution Approach 2:
The patent incorporates a mechanical stop or limiting feature in the ratchet system that acts as a cushion against excessive force. This predetermined limit prevents the wire from being tensioned beyond safe levels, protecting the sternum from cutting or damage before it can occur.
4Reliability
If multiple wires are used to ensure adequate compression, then sternal fixation is improved, but the complexity of the procedure increases
Solution Approach 1:
The patent designs a universal tensioning device that can be used with multiple wires simultaneously or sequentially. The instrument incorporates features that allow it to function as both a tensioning device and a cutting device, and can accommodate multiple wires without requiring separate instruments for each, thereby maintaining reliability while managing complexity.
Solution Approach 2:
The patent combines multiple functions into a single integrated instrument: the tensioning mechanism, the cutting mechanism, and the wire guidance system are merged into one device. This consolidation allows multiple wires to be managed with a single instrument, improving reliability without proportionally increasing procedural complexity.
Data Source
AI summary
A bone fixation system includes at least one bone fixation member and a bone fixation instrument. The bone fixation member includes a strap and a locking mechanism. The strap can be pulled through the locking mechanism so as to form a loop about a target bone so as to secure first and second bone segments in an approximated, compressed configuration. The bone fixation instrument is configured to apply tension to the loop about the target bone. The fixation instrument includes a tension assembly that is configured to secure a free end of the bone fixation member to the fixation instrument. The tension assembly is further configured to pull the free end so as to increase tension in the loop while the tension in the loop is less than a select tension. The tension assembly is unable to further increase tension in the bone fixation member once the tension in the bone fixation member has reached the select tension. The fixation instrument further includes a cutter assembly that is configured to cut the free end of the bone fixation member so as to separate the free end from the loop.