Femoral Prosthesis Insertion Cavity Axis Orientation
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Solution Overview
Problem
In minimally invasive hip arthroplasty procedures, the curved tools used for inserting and extracting femoral prostheses often generate a moment that leads to tool rotation and increased manual force requirements, risking tool shearing due to shear stress when attempting to counteract this moment.
Innovation Solution
A femoral prosthesis system with a stem and neck portion featuring an insertion/extraction cavity axis that is not parallel to the proximal stem axis, allowing for coupling with an insertion/extraction instrument whose longitudinal axis is also non-parallel, enabling direct force transfer without generating a moment, and using a threaded member to facilitate secure engagement and force transfer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If curved tools are used for insertion and extraction in minimally invasive procedures, then access to the hip joint is improved, but tool rotation and manual force requirements increase
Solution Approach 1:
Instead of curving the tool to access the joint, the patent inverts the approach by orienting the impact surface perpendicular to the stem axis, allowing the tool to engage the prosthesis at a right angle while maintaining a straight or minimally curved tool path. This reverses the conventional design philosophy and eliminates the moment generation problem.
Solution Approach 2:
The patent extracts the impact surface from the curved tool body and positions it at the distal end, perpendicular to the stem axis. This separation allows the tool shaft to remain curved for access while the impact surface remains oriented correctly for force application without moment generation.
2Ease of operation
If curved tools are used to accommodate access angles, then minimally invasive access is achieved, but shear stress increases risking tool shearing
Solution Approach 1:
The patent inverts the conventional approach by making the impact surface perpendicular to the stem axis rather than following the curved tool path. This ensures that the impact force is always applied parallel to the stem axis, eliminating shear stress regardless of the tool's curvature or access angle.
Solution Approach 2:
The impact surface acts as an intermediary between the curved tool shaft and the linear stem axis. It transfers the curved tool's motion into linear impact force along the stem axis, mediating between the curved access path and the straight insertion direction.
3Force
If impact force is applied to a curved tool, then insertion force is transferred to the prosthesis, but moment generation causes tool rotation
Solution Approach 1:
The patent applies local quality by making the impact surface perpendicular to the stem axis at the distal end of the tool, while the proximal portion of the tool can remain curved for access. This localized orientation change at the impact point ensures force transfer without moment generation, while maintaining overall tool flexibility for access.
Solution Approach 2:
The patent changes the dimensional orientation of the impact surface from being coplanar with the tool curvature to being perpendicular to the stem axis. This dimensional reorientation at the impact surface creates a new reference frame where force application does not generate rotational moments.
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 configuration enhances the efficiency and reduces the risk of error during insertion and extraction by ensuring direct force transfer without tool rotation or shear stress, improving the stability and effectiveness of the procedure.
Implementation Method 1
impacting a proximal end portion of the insertion/extraction instrument... transferring an impact force from the proximal end portion to the femoral prosthesis
Implementation Method 2
coupling the insertion/extraction instrument with the femoral prosthesis includes coupling the instrument with the proximal portion of the femoral prosthesis using a threaded member
Data Source
AI summary
A kit includes a number of femoral prostheses of different sizes and shapes. Each femoral prostheses in the kit includes a femoral stem including a proximal end portion defining a proximal stem axis, a femoral neck portion including a lateral shoulder extending distally and laterally at an angle relative to the proximal stem axis, such that when projected onto a coronal plane including the proximal stem axis, the lateral shoulder is not parallel to the proximal stem axis. Each prostheses further includes an insertion/extraction cavity extending distally from a proximal surface of the neck portion, the cavity defining an insertion/extraction cavity axis which, when projected on to the coronal plane, is not parallel with the proximal stem axis, and the lateral shoulder of each femoral prosthesis is oriented at an angle relative to the proximal stem axis that is different from the angle of each of the other femoral prostheses.