Posterior-stabilised knee prosthesis cam profile
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Solution Overview
Problem
Three-compartment knee prostheses face challenges with posterostability, particularly in flexion, limiting active flexion to 60°-120° and preventing passive hyperflexion beyond 120°, leading to dislocation risks and inability to sit or manually force heel-to-buttocks position due to impingement and subluxation issues.
Innovation Solution
A femoral implant with a profiled element acting as a cam and third condyle, featuring a spherical section and concave tibial plateau, allows linear contact and décaptation of condylar pads, enabling flexion from hyperextension to 120° and passive flexion up to 140° by maintaining contact through a cam profile and third condyle cooperation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a tricompartmental knee prosthesis is used without additional guidance devices, then the prosthesis structure remains simple, but posterior stability is insufficient and dislocation risks appear in active flexion
Solution Approach 1:
The prosthesis is divided into functional segments: the cam-shaped element integrated with the femoral component and the corresponding cam surface on the tibial plateau. This segmentation allows independent optimization of each component's geometry to achieve posterior stability through cam engagement during flexion, while keeping the overall structure relatively simple.
Solution Approach 2:
The cam-shaped element acts as an intermediary mechanism between the femoral and tibial components. During flexion, this cam element engages with the cam surface to provide posterior stability and prevent dislocation, effectively mediating the interaction between the two main components without requiring complex mechanical coupling.
2Reliability
If transverse stop devices are added to guide flexion, then posterior stability is improved, but active flexion range is limited and passive hyperflexion is prevented
Solution Approach 1:
The cam-shaped element provides dynamic stability that adapts to the flexion angle. During active flexion (0°-120°), the cam engagement provides necessary posterior stability. During passive hyperflexion (beyond 120°), the cam geometry allows controlled engagement and disengagement, enabling the tibia to rotate further without rigid constraint, thus accommodating both active and passive flexion ranges.
Solution Approach 2:
The cam surface geometry is specifically designed with varying curvature parameters that change with flexion angle. The cam profile is optimized to provide maximum stability in the active flexion range while allowing gradual transition and controlled engagement in the passive hyperflexion range, thus adapting the mechanical parameters to different functional requirements.
3Reliability
If the cam-shaped profile element is designed with deep hollow impression to maintain contact, then contact is ensured in passive extension, but the complexity of the tibial plateau increases
Solution Approach 1:
The hollow impression in the tibial plateau is designed with moderate depth rather than excessive depth. This partial action approach provides sufficient contact maintenance for the cam element during normal flexion and extension, while avoiding the increased complexity and potential interference with other prosthesis components that would result from a deeper impression.
Data Source
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AI summary
The prosthesis comprises a femoral implant (1) and a tibial implant (2), the femoral implant (1) being constituted by a trochlea (1a) extended on either side of a notch (1b) by two condylar pads (1c) and (1d) cooperating with flexion and rotation capacity with congruent impressions (3d) and (3e) of a tibial plateau (3) which presents a base constituting the tibial implant (2) characterized in that the two condylar pads (1c) and (1d) are joined transversely at their posterior end at the level of the free end of the notch, by a profiled element (1e) in lateral and transverse sections to act as a cam (1e1) and third condyle (1e2) cooperating respectively with the profiled bearing surfaces (3a) and (3c) of a pad (3b) formed as an overhang of the tibial plateau (3) to allow: a posteriorly stabilized flexion up to 120°, and beyond 120°,the lifting of one of the condyles (1c) or (1d) so that it no longer comes into contact with one of the impressions (3d) or (3e) of the tibial plateau (3), so that during the lifting there is total decoaptation between one of the two condyles and the corresponding impression of the tibial plateau.