Short-Stem Femoral Implant Geometry for Stable Hip Arthroplasty

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Existing short-stem hip prostheses suffer from subsidence due to lack of stability during initial impaction and early post-operative use, and are difficult to remove during revision surgery.

Innovation Solution

A short-stem femoral implant with a neck portion angled in the sagittal plane and a distal end configured for two-point abutment with the lateral endo-cortex, along with contoured surfaces to redistribute reaction forces and a bone in-growth coating for ease of removal.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of substance

If short-stem femoral implants are used to preserve femoral neck bone, then bone conservation is improved, but stability during impaction and early post-operative use deteriorates leading to subsidence

Engineering Contradiction:

Improvefemoral neck bone lossVSAvoidimplant stability

Core Design Contradiction:

Loss of substanceVSReliability

Solution Approach 1:

The implant geometry parameters are optimized with specific elliptical cross-sectional dimensions and cortical engagement features that provide enhanced stability without requiring traditional long-stem design. The elliptical shape with specific major and minor axis ratios allows for improved fit within the femoral canal while maintaining bone conservation goals.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The implant utilizes a porous coating structure that combines metallic base material with porous surface layer, enabling both primary mechanical stability during impaction and secondary biological fixation through bone in-growth. This composite structure addresses the stability issue while maintaining the short-stem bone-preserving design.

Inventive Principle:

Principle #40Composite materials

2Reliability

If porous coating is applied to encourage bone in-growth, then long-term stability is improved, but ease of removal during revision surgery deteriorates

Engineering Contradiction:

Improvelong-term fixationVSAvoidrevision surgery difficulty

Core Design Contradiction:

ReliabilityVSEase of repair

Solution Approach 1:

The porous coating is applied selectively to specific regions of the implant rather than uniformly across the entire surface. The distal portion has reduced or modified porous characteristics compared to the proximal portion, creating local variations in bone ingrowth potential that facilitate differential removal characteristics during revision while maintaining adequate long-term fixation.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The implant surface is segmented into different zones with varying porous coating characteristics. The proximal segment has full porous coating for strong bone ingrowth, while the distal segment has modified coating properties that allow easier removal, effectively dividing the fixation strategy into functional segments.

Inventive Principle:

Principle #1Segmentation

3Reliability

If conventional rhomboidal cross-section is used for maximum filling, then primary fixation is improved, but adaptability to femoral neck anatomy deteriorates

Engineering Contradiction:

Improveprimary fixationVSAvoidanatomical compatibility

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The implant cross-section is designed as an asymmetric ellipse rather than a symmetric rhomboid, with the major axis oriented to match the natural anatomy of the femoral canal. This asymmetric elliptical shape provides both adequate filling for primary fixation and adaptability to the specific anatomical variations in femoral neck and shaft geometry.

Inventive Principle:

Principle #4Asymmetry

Solution Approach 2:

The implant design incorporates features that allow it to adapt dynamically to the femoral anatomy during impaction and loading. The elliptical cross-section with specific dimensional ratios enables the implant to conform to the femoral canal shape while maintaining stable fixation, providing a dynamic adaptation rather than a fixed geometric match.

Inventive Principle:

Principle #15Dynamics

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

The implant provides improved stability against rotation and sliding, reducing the risk of subsidence and facilitating easy removal during revision surgery.

Implementation Method 1

typically include a porous coating to encourage the surrounding bone of the femur to grow into the implant

Methodology Applied

Scientific EffectOsteoconduction:

Implementation Method 2

contoured surfaces to redistribute reaction forces

Methodology Applied

Scientific EffectStress distribution:

Implementation Method 3

a neck portion angled in a sagittal plane of the subject's femur to enable improved location of a femoral head of the implant

Methodology Applied

Scientific EffectBiomechanical alignment:

Data Source

PatentEP4169487B1Hip prosthesis

Publication Date: 2026.03.25 KIRWAN DAVID PHILLIP

Figure 1
Figure 2
Figure 3~4

AI summary

A short-stem femoral implant (410) suitable for use in hip arthroplasty includes a neck portion (420) angled in a sagittal plane of the subject' femur (220) to enable improved location of a femoral head of the implant with respect to the subject's femoral neck (250) when implanted therein.