Bone Anchor Locking Cap Release Mechanism
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Solution Overview
Problem
Surgeons face difficulty in removing or adjusting locking caps from bone anchor heads due to thread locking caused by bodily fluids, often resulting in excessive torque application and potential cap fracture.
Innovation Solution
A release mechanism comprising a sleeve, an anchor coupling member, and a knob that splay the threads of the bone anchor head from the locking cap, allowing for safe and controlled removal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If cyclic tightening and loosening torque is applied using a torque-limiting handle to address thread locking, then the locking cap may be loosened, but the torque applied frequently exceeds the locking cap's design limits causing fracture of the locking cap
Solution Approach 1:
A release mechanism with a release member and saddle is introduced as an intermediary device between the surgeon's tools and the locking cap. The release member engages with the bone anchor head and applies controlled forces through the saddle to splay the threads apart, preventing direct excessive torque application to the locking cap while still achieving thread separation
Solution Approach 2:
The invention changes the force application parameters from high-magnitude torque (rotational force) to lower-magnitude splaying forces (divergent linear forces). By applying forces that push the bone anchor head and locking cap threads apart in opposite directions, the mechanism achieves thread separation without exceeding the locking cap's torque design limits
2Productivity
If excessive torque is applied to remove a locked locking cap, then the cap may be removed, but the procedure risks patient safety and may bury non-implantable grade stainless steel within the bone screw/implant
Solution Approach 1:
The release mechanism serves as a protective intermediary that mediates between the removal objective and the locking cap's structural limits. It enables efficient thread separation while filtering out harmful excessive forces, preventing metal debris generation and implant contamination
Solution Approach 2:
The release mechanism provides beforehand cushioning by distributing and limiting forces before they reach the locking cap. The mechanism's mechanical design inherently caps the maximum force applied, preventing catastrophic failure modes before they can occur
3Ease of operation
If traditional torque-based methods are used to unlock the locking cap, then removal may be achieved, but the procedure time increases due to difficulty and potential complications
Solution Approach 1:
The invention replaces the traditional torque-based rotational unwinding mechanism with a splaying mechanism that diverges the threads apart. This substitution transforms a difficult torque-limited operation into a simpler force application task, dramatically improving ease of operation and reducing procedure time
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 release mechanism effectively reduces procedure time and risk by allowing for secure and controlled separation of the locking cap from the bone anchor head without exceeding torque limits.
Implementation Method 1
The release mechanism may include a release member configured to engage a bone anchor head and a saddle configured to apply forces to the bone anchor head and the locking cap such that the forces splay the threads of the bone anchor head from the threads of the locking cap
Data Source
AI summary
The present invention is directed to a release mechanism for removing and/or releasing a locking cap from the head of a bone anchor in situ. The release mechanism includes a sleeve, an anchor coupling member and a knob. The anchor coupling member is located within the sleeve and the knob engages both the anchor coupling member and the sleeve. The distal end of the sleeve and anchor coupling member engage the bone anchor causing the bone anchor to splay from the locking cap. A driver may be inserted into the central bore of the release mechanism to release any further threaded engagement of the locking cap and the bone anchor.