Femoral Sizing Jig Medial Posterior Condyle Reference
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Solution Overview
Problem
Conventional total knee replacement (TKR) techniques often result in ligament imbalance and instability due to variable resection depth and external rotation, affecting joint line preservation and co-lateral isometry, leading to unsatisfactory knee functionality and patient outcomes.
Innovation Solution
A femoral sizing jig that uses a medial posterior condyle as a datum for tibio-femoral dependent positioning, allowing rotation about the medial condyle while maintaining constant resection depth, and includes shims for joint line preservation, combining measured resection and ligament balancing techniques to restore normal kinematics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a centrally pivoting sizing guide connected to an intramedullary rod is used to size the knee and set external rotation, then the knee can be sized and external rotation can be established, but ligament imbalance and instability occur due to variable resection depth and altered joint line restoration
Solution Approach 1:
The patent introduces a femoral sizing jig as an intermediary device that mediates between the sizing guide and the actual resection process. The jig incorporates a posterior condylar locator that references the medial posterior condyle, creating a stable intermediate reference point that ensures consistent resection depth and joint line restoration while allowing external rotation setting, thereby maintaining ligament balance and knee stability
Solution Approach 2:
The patent changes the reference parameter from a centrally pivoting guide to a posterior condylar locator referencing the medial posterior condyle. This parameter change ensures that resection depth is measured relative to a fixed anatomical landmark, eliminating the variability in joint line restoration and ligament tension that occurs with central pivoting, thus maintaining reliability while allowing sizing operations
2Reliability
If a tensioner with a central pivot point is used to restore ligament balance by relying on tibio-femoral separation, then ligament balance can be restored, but resection depth relative to the posterior femoral condyle becomes variable resulting in different centre of rotation and affecting ligament isometry
Solution Approach 1:
The femoral sizing jig acts as an intermediary that combines the ligament balancing function with precise resection depth control. The posterior condylar locator references the medial posterior condyle to establish a fixed resection depth, while the sizing guide allows ligament balance assessment, thereby maintaining both reliability and manufacturing precision simultaneously
Solution Approach 2:
The patent merges the ligament balancing function (from the tensioner) with the resection depth control function (from the posterior condylar locator) into a single integrated femoral sizing jig. This combination ensures that ligament balance is restored while maintaining consistent resection depth and accurate centre of rotation positioning
3Ease of operation
If resection depth is varied to accommodate different external rotation values, then external rotation can be set, but joint line preservation is compromised and pre-operative rotation is lost
Solution Approach 1:
The posterior condylar locator serves as an intermediary reference that decouples external rotation setting from resection depth variation. By referencing the medial posterior condyle, it maintains constant resection depth and joint line preservation while allowing the external rotation angle to be independently adjusted and set
Data Source
AI summary
A femoral sizing jig for use in total arthroplasty of left and right knees, comprises a femoral body, an external-rotation-angle arm which is, preferably pivotable, relative to the femoral body for setting an external angular rotation of a left or right femur, at least one of a cutting-jig guide and a cutting jig which is, preferably slidable, relative to the femoral body and in unison with movement of the external rotation-angle arm, and a medial posterior-condylar locator which is movable in unison with the movement of the external-rotation-angle arm, so as to maintain a fixed or substantially fixed relative distance with a medial side of the at least one of a cutting-jig guide and a cutting jig. A posterior-referencing femur resecting system using said femoral sizing jig and a method of resecting a femur at a knee joint relative to the medial posterior condyle are also provided.