Orthopaedic Fastener Square Cross-Section Expansion

The patent applies asymmetry by transitioning from a conventional circular cross-section to a square cross-section with rounded corners. This asymmetric shape reduces the area moment of inertia compared to a circular section of equivalent area, enabling greater expansion capability while maintaining structural strength. The square geometry with rounded corners optimizes the balance between expansion potential and resistance to plastic deformation.

The patent changes the geometric parameters of the fastener body by adopting a square cross-section with rounded corners instead of a circular one. This parameter change reduces the area moment of inertia, allowing the fastener to achieve larger expansion sizes and improved pull-out strength while preventing plastic deformation through optimized dimensional ratios.

The patent employs a composite structural design where the square cross-section with rounded corners creates a geometry that optimizes both elastic deformation capability and resistance to plastic deformation. The rounded corners specifically prevent stress concentration that would lead to plastic deformation, while the overall square shape enables greater expansion capacity through reduced area moment of inertia.

The patent applies local quality by rounding only the corners of the square cross-section while maintaining straight edges elsewhere. This localized modification specifically addresses stress concentration at corner regions, preventing plastic deformation initiation, while preserving the overall square geometry's advantage of reduced area moment of inertia for enhanced elastic deformation capability.