Tibial Insert Retaining Tab and Deformable Fastener Design

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Solution Overview

Problem

Existing orthopaedic implant systems face issues with coupling mechanisms that can cause pain, damage to surrounding anatomy, inadequate constraints against movement, and loosening of fasteners, particularly in knee implants, leading to spin out, pull out, and undesirable rotations.

Innovation Solution

The proposed solution involves a tibial component with a retaining tab and angled opening that securely couples with a tibial insert, preventing vertical separation and excessive rotation, and the use of deformable fasteners with an interference fit to minimize movement and prevent loosening.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If exposed coupling mechanisms are used to secure the tibial insert, then the insert can be firmly attached to the tibial component, but the coupling mechanism contacts and damages surrounding anatomy including ligamenture and bone

Engineering Contradiction:

Improveattachment securityVSAvoiddamage to surrounding anatomy

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent extracts the harmful exposed coupling mechanism from the anterior aspect of the implant and relocates it to the posterior aspect. The retaining tab and corresponding recess are positioned at the posterior edge, allowing the insert to be securely attached while keeping the coupling mechanism hidden from the anterior view and away from the patella and surrounding anatomy during knee flexion and extension.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent transitions the coupling mechanism from a two-dimensional exposed structure on the anterior surface to a three-dimensional recessed structure at the posterior edge. The retaining tab extends from the posterior edge into the insert, creating a hidden coupling mechanism that operates in a different spatial dimension, thereby eliminating contact with surrounding anatomy while maintaining attachment security.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Reliability

If traditional fasteners are used to secure the tibial insert, then the insert can be attached to the tibial component, but the fasteners may loosen and back out under cyclic loading

Engineering Contradiction:

Improveattachment securityVSAvoidfastener retention over time

Core Design Contradiction:

ReliabilityVSDuration of action of stationary object

Solution Approach 1:

The patent divides the fastening system into two functional segments: a retaining tab structure that provides mechanical interlocking and prevents vertical separation, and a recess structure that accommodates the fastener. This segmentation allows each component to perform its specific function optimally, with the retaining tab preventing pull-out and the recess providing fastener retention, thereby eliminating loosening and back-out issues under cyclic loading.

Inventive Principle:

Principle #1Segmentation

3Adaptability or versatility

If the tibial insert is designed to be rotatable, then it can accommodate varying knee flexion angles, but excessive rotation (spin out) occurs leading to improper orientation

Engineering Contradiction:

Improverotation capabilityVSAvoidorientational accuracy

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The patent employs asymmetric geometry in the retaining tab and recess structures to control and limit rotation. The retaining tab has a specific shape and orientation that fits into the corresponding recess, creating an asymmetric interface that allows controlled rotation within safe limits while preventing excessive rotation (spin out). This asymmetric design ensures the insert remains properly oriented during knee flexion and extension while maintaining adaptability.

Inventive Principle:

Principle #4Asymmetry

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This design enhances the stability and security of the orthopaedic implant system by preventing unwanted movements and irritation, ensuring the tibial insert remains properly aligned and secured, reducing the risk of damage to surrounding anatomy and improving the longevity of the implant.

Implementation Method 1

deformable fasteners with an interference fit to minimize movement and prevent loosening

Methodology Applied

Scientific EffectFriction: Friction

Implementation Method 2

deformable fasteners with an interference fit

Methodology Applied

Scientific EffectInterference fit:

Implementation Method 3

retaining tab with a hooked edge that couples to a tab opening on an inferior surface of the tibial insert

Methodology Applied

Scientific EffectMechanical engagement: Mechanical Fastener

Data Source

PatentUS9668872B2Orthopaedic implant system and fasteners for use therein

Publication Date: 2017.06.06 SMITH & NEPHEW INC

AI summary

Orthopedic assemblies including a tibial component and one of a fixed tibial insert or a rotatable tibial insert. The assemblies may include structure to prevent undesired movement between the tibial component and insert. For example, a retaining tab may be provided on the tibial component that couples to a tab opening on a surface of the tibial insert (either the fixed or rotatable insert). When assembled, the retaining tab may be covered to avoid possible irritation to the patient's surrounding anatomy. The fixed tibial insert may be provided with a tab opening that provides a minimal amount clearance with the retaining tab to help prevent rotation of the fixed tibial insert. The rotatable tibial insert may be provided with a tab opening with more clearance with the retaining tab to allow at least some rotation with the tibial component.