Posterior Stabilized Knee Cam Spine Mechanism
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Solution Overview
Problem
Current knee prostheses face challenges in accurately mimicking the natural kinematics and stability of the human knee, particularly in maintaining posterior stabilization and preventing subluxation at high flexion angles while allowing for a full range of motion.
Innovation Solution
The design incorporates a femoral component with a cam housing and a tibial component featuring a spine that articulates with complementary curved surfaces, providing posterior stabilization and limiting varus-valgus movement, along with a stiffening pin for added strength, to emulate the natural rollback and prevent subluxation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a mobile bearing knee is designed to accurately mimic natural knee movement, then the range of motion is improved, but the stability of the artificial joint deteriorates
Solution Approach 1:
The knee prosthesis is divided into distinct functional components: a mobile bearing component that allows rotation and translation to mimic natural knee movement, and a fixed base component that provides stable attachment to the tibia. This segmentation enables the mobile bearing to provide full range of motion while the fixed base maintains joint stability.
Solution Approach 2:
The mobile bearing acts as an intermediary element between the femoral component and the tibial base. It mediates the transmission of loads and movements, allowing natural kinematics while distributing forces to maintain stability. The bearing's curved articulating surface guides the motion path to replicate natural rollback while maintaining contact for stability.
2Stability of the object's composition
If features are added to maintain joint stability, then the stability of the artificial joint is improved, but the complexity of the knee system increases
Solution Approach 1:
The mobile bearing is designed to perform multiple functions simultaneously: it provides rotation to mimic natural knee movement, translates to accommodate rollback, supports vertical loads, and guides the articulation path. This multi-functionality reduces the need for separate stability features, thereby limiting complexity while maintaining stability.
Solution Approach 2:
The mobile bearing incorporates a curved articulating surface that works with a corresponding curved cam surface in the tibial base. This curved geometry naturally guides the femoral component through the correct rollback path while maintaining contact for stability. The curvature is optimized to replicate natural knee kinematics without requiring additional complex mechanical constraints.
3Reliability
If the spine contacts cam surfaces to limit anterior-posterior movement, then the posterior stabilization is improved, but the smoothness of movement deteriorates
Solution Approach 1:
The mobile bearing is designed to dynamically adapt its position and orientation during knee flexion and extension. The bearing rotates and translates along a curved path, allowing the spine to contact different portions of the cam surfaces at different flexion angles. This dynamic movement ensures stable posterior restraint while maintaining smooth motion through controlled rolling and gliding contact.
Solution Approach 2:
The design replaces direct rigid mechanical contact between the spine and cam surfaces with a mobile bearing that provides a compliant, rolling contact interface. The bearing's curved articulating surface acts as an intermediary that smooths out the interaction between the spine and cam surfaces, reducing friction and improving movement smoothness while maintaining stabilization.
4Strength
If additional stability features are added to prevent hyperextension, then the strength of the joint is improved, but the natural movement permitted by the knee deteriorates
Solution Approach 1:
The mobile bearing's curved articulating surface is pre-configured to guide the femoral component along a path that naturally prevents hyperextension. As the knee approaches full extension, the geometry of the bearing and cam surfaces creates increasing resistance to further extension, providing preliminary anti-action against hyperextension before it occurs. This maintains natural movement through most of the range while protecting against extreme positions.
Data Source
AI summary
A femoral component of a knee prosthesis has spaced condyle surfaces defining a notch therebetween. The notch defines an elongated cam housing having an anterior cam and a posterior cam at opposite ends of the housing. The tibial component of the knee prosthesis includes a platform and a bearing supported on the platform, the bearing defining bearing surfaces configured to articulate with the condyle surfaces. The tibial component includes a spine projecting superiorly from the bearing that defines an anterior face and a posterior face. The posterior face and the posterior cam define complementary curved surfaces configured for cooperative engagement when the femoral component and the tibial component are at a predetermined flexion angle. The cam housing is configured to form a gap between the posterior cam and the spine when the knee is normally extended. In another feature, the spine includes a stiffening pin extending therethrough.