Ligament Spacer With Canted Face For Elliptical Bone Tunnel Fixation
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Solution Overview
Problem
Current ACL reconstruction techniques face limitations due to the elliptical shape of bone tunnels created during drilling, leading to incomplete fixation of ligament grafts, which can result in biomechanical instability and 'windshield wiper' effects, where the graft sweeps across the tunnel entrance, causing abrasion and joint laxity.
Innovation Solution
The use of a fixation device comprising a screw with a ligament spacer having a canted face, which creates an interference fit with the graft ligament and the bone tunnel, ensuring complete fixation along the elliptical tunnel periphery and spreading the graft over the natural anatomic footprint of ACL insertions, thereby addressing the geometric challenges of elliptical tunnel entrances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a standard interference screw is used to fixate the ligament graft, then the fixation is simple and quick, but the graft is not secured along the entire periphery of the elliptical bone tunnel, leading to incomplete fixation and potential graft migration
Solution Approach 1:
A ligament spacer is introduced as an intermediary component between the interference screw and the elliptical bone tunnel. The spacer has a canted face that matches the elliptical tunnel geometry and provides a platform for circumferential graft fixation, while the screw provides the driving force for insertion. This intermediary resolves the contradiction by enabling complete periphery fixation without complicating the insertion process.
Solution Approach 2:
The ligament spacer features an asymmetric canted face specifically designed to match the elliptical geometry of the bone tunnel. This asymmetric design allows the spacer to conform to the elliptical tunnel periphery, enabling complete circumferential fixation of the graft along the entire tunnel boundary, which a symmetric cylindrical screw cannot achieve.
2Device complexity
If the femoral tunnel is drilled through the tibial tunnel (transtibial approach), then the surgical procedure is simplified, but the femoral tunnel location ends up higher than the normal anatomic femoral insertion of the ACL
Solution Approach 1:
Instead of drilling the femoral tunnel through the tibial tunnel (inside-out approach), the invention drills the femoral tunnel first through the AM portal, then uses a guide wire passed through the femoral tunnel to guide subsequent tibial tunnel drilling. This inverted sequence allows the femoral tunnel to be created at the correct anatomic location before the tibial tunnel is formed, resolving the anatomic accuracy issue while maintaining procedural simplicity.
3Manufacturing precision
If the knee is put into deep flexion to reach the anatomic ACL footprint on the femur, then the anatomic position can be accessed, but the adjacent condyle and tibial plateau may be damaged by the guide pin and drill
Solution Approach 1:
The femoral tunnel is drilled first through the AM portal at the correct anatomic location while the knee is in a safe position. A guide wire is then passed through this pre-created femoral tunnel. Subsequently, the tibial tunnel is drilled using this guide wire as a safety rail. This preliminary action of creating the femoral tunnel first eliminates the need for deep knee flexion and prevents damage to the condyle and tibial plateau during tunnel creation.
4Adaptability or versatility
If the ligament graft is allowed to sweep across the tunnel entrance (windshield wiper effect), then the graft has some movement freedom, but this causes abrasion, joint laxity, and potential graft failure
Solution Approach 1:
The ligament spacer with its canted face is inserted into the elliptical bone tunnel before the interference screw is fully tightened. The spacer's geometry is designed to prevent the graft from sweeping across the tunnel entrance by providing a physical barrier and proper angular orientation. This preliminary anti-action counteracts the potential windshield wiper effect before it can cause damage, while still allowing appropriate physiological graft movement.
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 provides complete fixation of the ligament graft, eliminates the 'windshield wiper' effect, and achieves a more accurate anatomic reconstruction by securing the graft along the entire periphery of the elliptical tunnel entrance, enhancing stability and reducing the risk of graft failure.
Implementation Method 1
the fixation screw creates an interference fit between the graft ligament and the wall of the bone hole
Implementation Method 2
the ligament spacer creates an interference fit between the graft ligament and the wall of the bone hole
Data Source
AI summary
Apparatus for reconstructing a ligament, the apparatus comprising: a fixation device for maintaining a graft ligament in a bone hole, the fixation device comprising: a fixation screw comprising a body having screw threads formed thereon; and a ligament spacer mounted to the fixation screw, the ligament spacer comprising a canted face disposed opposite the fixation screw; such that when a graft ligament is disposed within a bone hole, the fixation screw and ligament spacer may be advanced into the bone hole alongside the graft ligament so that the fixation screw creates an interference fit between the graft ligament and the wall of the bone hole, and the ligament spacer creates an interference fit between the graft ligament and the wall of the bone hole, with the canted face of the ligament spacer being aligned with the adjacent surface of the bone.