Rotating Tibial Insert Axis Positioning for Knee Stability
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Solution Overview
Problem
Conventional knee replacement systems experience instability and abnormal kinematics during deep flexion due to paradoxical anterior translation of the femoral component on the tibial plateau, leading to increased wear and reduced dynamic moment arm, which affects the natural movement and stability of the knee joint.
Innovation Solution
A knee replacement system with a rotating tibial bearing insert whose axis of rotation is strategically positioned to manage internal-external rotation and rollback, mimicking the kinematic behavior of a native knee by adjusting the axis's location relative to the dwell point to enhance stability and conformity during deep knee bending.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional knee replacement system is used, then the prosthesis can replace the damaged knee joint, but paradoxical anterior translation occurs during deep flexion causing instability and abnormal kinematics
Solution Approach 1:
The patent changes the geometric parameters of the femoral component, specifically the radius of curvature and profile shape, to eliminate paradoxical anterior translation. By modifying these parameters, the prosthesis achieves both stability and natural kinematic behavior during deep flexion.
Solution Approach 2:
The patent employs specific curvature profiles on the femoral component surfaces to replicate the rolling and sliding motion of a native knee. The curved geometry is designed to control the contact point trajectory and prevent anterior translation during flexion.
2Ease of operation
If the PCL is retained to maintain natural kinematics, then the native knee movement pattern is preserved, but paradoxical anterior translation and loss of joint stability occur
Solution Approach 1:
The patent modifies the femoral component geometry to work effectively whether the PCL is retained or sacrificed. The changed parameters ensure that the contact point moves naturally along the tibial surface without paradoxical anterior translation, providing stability regardless of PCL status.
3Device complexity
If a fixed radius of curvature is used in the femoral component, then the design is simple, but it cannot replicate the complex rollback and rotation of a native knee during deep flexion
Solution Approach 1:
The patent uses varied curvature radii along the femoral component surface rather than a single fixed radius. This allows the prosthesis to replicate the complex rollback and rotation movements of a native knee during deep flexion while maintaining a relatively simple overall design.
Solution Approach 2:
The patent creates a dynamic interaction between the femoral and tibial components through carefully designed curved surfaces. The geometry allows the contact point to naturally migrate during flexion, replicating the dynamic behavior of a native knee without requiring active control mechanisms.
4Adaptability or versatility
If the contact point translates anteriorly during deep flexion, then the prosthesis can accommodate the range of motion, but the dynamic moment arm is reduced requiring increased quadriceps force
Solution Approach 1:
The patent changes the femoral component geometry to control the contact point trajectory, preventing paradoxical anterior translation. This maintains an optimal dynamic moment arm throughout the range of motion, reducing the quadriceps force required while still achieving deep flexion.
Data Source
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AI summary
A knee replacement system (400) includes a femoral component (406) including a lateral condylar articulating portion (408) and a medial condylar articulating portion (410), a tibial tray (402) including an upper articulating surface (414), and a tibial insert (404). The insert includes (i) a first articulating portion (422) for articulating with the lateral condylar articulating portion with a first condylar dwell point (432), (ii) a second articulating portion (424) for articulating with the medial condylar articulating portion with a second condylar dwell point (434), (iii) a lower articulating surface (418) for articulating with the upper articulating surface, and (iv) a coupling member (428) for coupling with the tibial tray and defining an axis of rotation (438) about which the tibial insert rotates with respect to the tibial tray. The axis of rotation intersects the upper articulating surface at a location posterior to a dwell axis (430) including the condylar dwell points when the dwell axis is projected on to the upper articulating surface.