Femoral Fixation Helical Thread Undercut Surface Design
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Solution Overview
Problem
Traditional femoral fastener thread designs fail to provide sufficient fixation and load sharing under multi-axial and off-axis loading conditions, leading to loosening over time during the healing process.
Innovation Solution
The development of femoral fixation devices with helical threads featuring undercut surfaces and chevron or crescent shapes, which are angled to transmit forces effectively between the femoral bone head and neck, enhancing bone fixation and load distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If traditional femoral fastener thread designs are used, then the device structure remains simple, but the fixation strength and load sharing capability are insufficient under multi-axial and off-axis loading conditions
Solution Approach 1:
The patent applies asymmetry by introducing undercut surfaces that are angled relative to the longitudinal axis of the fastener. These undercut surfaces create an asymmetric thread profile that provides superior resistance to multi-axial and off-axis loading conditions compared to traditional symmetric thread designs, thereby improving fixation strength without excessive complexity
Solution Approach 2:
The patent adds a new dimensional element by incorporating undercut surfaces that extend radially outward from the thread flanks. This creates a three-dimensional thread structure with surfaces angled at specific degrees (e.g., 30-60 degrees) relative to the longitudinal axis, adding geometric complexity that enhances load distribution and fixation strength
2Strength
If traditional thread designs are used, then the manufacturing process remains simple, but the load sharing capability between bone and fastener is insufficient
Solution Approach 1:
The patent changes critical geometric parameters of the thread design by specifying undercut surfaces angled at particular degrees (e.g., 30-60 degrees relative to the longitudinal axis). These parameter modifications optimize the distribution of loads between the fastener and bone, enhancing load sharing capability while maintaining manufacturability through defined angular parameters
3Reliability
If traditional femoral fasteners are used, then the device is easy to implant, but the fixation becomes loose over time due to multi-axial forces and off-axis loading
Solution Approach 1:
The asymmetric undercut surface design provides superior resistance to the multi-axial and off-axis loading conditions that cause traditional fasteners to loosen over time. The angled surfaces (e.g., 30-60 degrees) create mechanical interlocking that maintains fixation stability under physiological loads
Solution Approach 2:
The helical thread geometry with undercut surfaces creates curved, three-dimensional load paths that better distribute stresses throughout the bone-fastener interface. This curved geometry helps prevent stress concentration and fixation loosening under cyclic loading conditions
Data Source
AI summary
A femoral fixation device may include a shaft and a helical thread disposed about the shaft between a first location and a second location along the shaft. The helical thread may include a concave undercut surface. The femoral fixation device may be configured such that, when the femoral fixation device is implanted within a neck and a head of a femoral bone: the first location, the second location, and the helical thread therebetween may be disposed within the head of the femoral bone; the concave undercut surface may be oriented toward a proximal end of the femoral fixation device; and the concave undercut surface may be configured to transmit at least one force from the head of the femoral bone to the neck of the femoral bone.