Medial Pivoting Orthopaedic Insert for Knee Stability
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Solution Overview
Problem
Existing orthopaedic systems for knee replacement do not effectively mimic the natural movement of the knee, leading to instability and potential implant shift due to lack of anterior-posterior stability and unnatural stress on tissues.
Innovation Solution
An asymmetric orthopaedic insert with a medial and lateral half, featuring a medial articular surface with a dwell region and a lateral articular surface that follows an arcuate path, along with an anterior stabilizing surface, to limit anterior-posterior translation and allow medial pivoting, thereby stabilizing the femoral component and mimicking natural knee movement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a symmetric insert design is used, then the device complexity is reduced, but the ability to mimic natural knee movement and provide anterior-posterior stability deteriorates
Solution Approach 1:
The insert employs an asymmetric design where the medial and lateral articular surfaces have different geometries. The medial articular surface features a dwell region with specific curvature that guides the medial condyle, while the lateral articular surface has a different profile. This asymmetry enables the femoral component to pivot medially during knee flexion, closely replicating natural knee kinematics and providing inherent anterior-posterior stability without requiring additional stabilizing structures.
2Ease of operation
If the insert allows free rotation, then the ease of operation is improved, but the control over rotation range and prevention of impingement deteriorates
Solution Approach 1:
The insert utilizes carefully engineered curved surfaces on both the medial and lateral articular surfaces. The medial articular surface has a dwell region with specific radius of curvature that guides the medial condyle through a controlled arc during rotation. The lateral articular surface complements this with its own curvature profile. These spherical/arcuate geometries enable smooth, controlled rotation within a defined range while preventing excessive movement and impingement, all through the inherent geometry rather than mechanical stops or constraints.
3Manufacturing precision
If the medial and lateral articular surfaces have the same clearance, then the manufacturing precision is simplified, but the ability to mimic natural knee kinematics deteriorates
Solution Approach 1:
The insert implements different clearance specifications for the medial and lateral sides. The medial articular surface is designed with a specific clearance profile that allows close conformity and guidance during the majority of the gait cycle when medial pivot occurs. The lateral articular surface has a different clearance profile optimized for its specific functional role. This localized differentiation in clearance requirements enables accurate replication of natural knee kinematics where medial and lateral compartments experience different loading and movement patterns, while still maintaining manufacturability through well-defined geometric specifications.
Data Source
AI summary
An orthopaedic system includes an insert defining an anterior-posterior centerline and including: a medial half on one side of the centerline and defining a medial shape, the medial half having a medial articular surface defining a medial dwell region; and a lateral half on an opposite side of the centerline and defining a lateral shape that differs from the medial shape, the lateral half having a lateral articular surface. A femoral component includes a medial condylar portion bearing on the medial articular surface and a lateral condylar portion bearing on the lateral articular surface. The insert is configured to substantially limit anterior-posterior translation of the femoral component and define a pivot axis that extends through the medial dwell region. The insert is configured such that rotation of the lateral articular surface follows an arcuate path about the pivot axis.