Mid-Flexion Knee Balancing Jig for Arthroplasty Stability
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Solution Overview
Problem
Total knee arthroplasty (TKA) procedures often result in abnormal femoral condyle motion patterns due to the loss of cruciate ligaments, leading to mid-flexion instability and improper balancing, which is typically performed at full extension or 90 degrees, neglecting the critical mid-flexion range where most instability occurs.
Innovation Solution
A knee balancing jig and method that includes a tibial placement guide and balancing assemblies to facilitate ligament balancing at mid-flexion angles between full extension and 90 degrees, using paddles and pin guides to engage condyles and bones, and a gap tensioner to apply forces for precise cuts and alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If ligament balancing is performed at full extension or 90 degrees as traditionally done, then the surgical procedure follows established protocols, but mid-flexion instability occurs due to improper balancing in the critical mid-flexion range
Solution Approach 1:
The balancing jig is set up and positioned on the tibia before the actual balancing cuts are made. The jig pre-establishes the correct mid-flexion angle (30-70 degrees) and guides the surgical instruments to ensure proper ligament balancing occurs at the critical mid-flexion range before final implant placement, preventing mid-flexion instability proactively
Solution Approach 2:
The balancing jig acts as an intermediary device between the surgeon and the bone. It translates the complex requirement for mid-flexion balancing into simple, guided cuts by providing physical guides for saw blades and drills, making the difficult balancing procedure easier to perform accurately
2Reliability
If traditional balancing methods are used without mid-flexion consideration, then the surgical workflow remains simple, but abnormal femoral condyle motion patterns and sliding occur due to loss of cruciate ligaments
Solution Approach 1:
The balancing jig is divided into separate functional modules: a base component that attaches to the tibia, vertical guides that establish the mid-flexion angle, and adjustable paddles that can be positioned to balance both medial and lateral collateral ligaments independently. This segmentation allows each component to perform its specific function while maintaining overall system manageability
Solution Approach 2:
The device changes the critical parameter of knee flexion angle from the traditional 0 degrees (full extension) or 90 degrees to the previously neglected 30-70 degree mid-flexion range. This parameter change addresses the root cause of abnormal motion patterns by ensuring ligaments are balanced at the angle where cruciate ligament deficiency most impacts knee mechanics
3Manufacturing precision
If balancing is performed without specialized mid-flexion equipment, then the surgical process is faster to set up, but precise bone cuts and alignment cannot be achieved at the critical mid-flexion angle
Solution Approach 1:
The jig pre-establishes the exact mid-flexion angle (30-70 degrees) and pre-aligns all cutting guides before the surgeon makes any bone cuts. This preliminary positioning ensures that when cuts are made, they are automatically at the correct angle and position for mid-flexion balancing, achieving high precision without requiring complex intraoperative adjustments
Solution Approach 2:
The device replaces the traditional mechanical method of estimating balancing angles with visual landmarks with a fixed mechanical guide system that physically constrains cutting instruments to the precise mid-flexion angle. This substitution eliminates human error in angle estimation and provides repeatable, precise cuts
Data Source
AI summary
Joint balancing methods and apparatus for arthroplasty procedures are disclosed. An example knee balancing jig may include a tibial placement guide configured for mounting to a tibial reference in a generally medial-lateral orientation in position generally anterior to a knee and/or at least one balancing assembly. The balancing assembly may include a vertical guide configured to releasably mount to the tibial placement guide in a generally inferior-superior orientation, at least one posteriorly extending paddle selectively vertically movable along the vertical guide, the paddle configured to selectively engage a distal femur and/or a proximal tibia, and/or at least one pin guide selectively vertically movable along the vertical guide, the at least one pin guide comprising at least one opening configured to receive at least one of a drill bit and a bone pin therethrough.