Figure-8 Femoral Neck Fixation Peg for Rotation and Shortening Control
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Solution Overview
Problem
Current fracture fixation systems for femoral neck fractures, such as cannulated compression screws (CCS) and short head screws (SHS), suffer from angular instability, insufficient rotation control, uncontrolled shortening, and limited resistance against shear forces, particularly in cases of weakened bone adjacent to the fracture site.
Innovation Solution
A fracture fixation system featuring a plate and barrel with a figure-8 shaped peripheral wall and peg, where the peg has a matching figure-8 outer surface, providing angular stability and controlled movement through spring arm hooks and grooves, along with a lag screw for deeper fixation, to maintain proper bone alignment and prevent excessive shortening.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If cannulated compression screws (CCS) are used for femoral neck fracture fixation, then the treatment is simple and widely accepted, but the device lacks angular stability and has insufficient rotation control
Solution Approach 1:
The peg is designed with a non-circular cross-section (oval, triangular, or rectangular) that corresponds to a non-circular recess in the barrel. This asymmetric geometry prevents rotation of the peg within the barrel, providing angular stability and rotation control while maintaining a relatively simple fixation structure.
2Strength
If compression screws are used to fixate the fractured bone, then the bone fragments can be compressed together, but uncontrolled shortening of the femoral neck occurs
Solution Approach 1:
The spring arm mechanism provides dynamic control of compression forces. The spring arm can flex to allow controlled shortening while maintaining compression on the fracture, and the hook can engage with the peg to prevent excessive shortening. This dynamic system balances the need for compression with the need to maintain proper bone length.
3Strength
If the femoral head compresses towards the fracture site to promote healing, then compression forces are applied, but uncontrolled shortening may cause the femoral head to be compressed into the trochanteric region
Solution Approach 1:
The spring arm and hook mechanism is pre-configured to prevent excessive shortening before it occurs. The spring arm is positioned to engage the peg and provide resistance against over-compression, thereby preventing the femoral head from being compressed into the trochanteric region while still allowing therapeutic compression forces.
4Stability of the object's composition
If short head screws (SHS) are used for fixation, then angular stability is improved, but an additional anti-rotation screw is required with limited space in small anatomies
Solution Approach 1:
The anti-rotation function is merged into the barrel-peg assembly. The non-circular cross-section of the peg fitting into the corresponding non-circular recess in the barrel provides both structural support and rotation control in a single integrated component, eliminating the need for separate anti-rotation screws and reducing overall device complexity.
5Strength
If compression forces are applied to promote bone healing, then fracture healing is accelerated, but weakened bone adjacent to the fracture site may be damaged
Solution Approach 1:
The spring arm provides a dynamic, progressive compression system that can adapt to the strength of the surrounding bone. The spring can be designed with appropriate stiffness to provide sufficient compression for healing while limiting peak forces to prevent damage to weakened bone adjacent to the fracture site.
Data Source
AI summary
A fracture fixation system includes a fixation element and a peg. The fixation element has a plate and a barrel, the plate having an outer surface and an inner surface for placement against an exterior surface of a bone, and the barrel extending along a barrel axis and having a peripheral wall protruding from the inner surface of the plate, the fixation element defining a passage through the plate and the barrel that extends along the barrel axis, wherein at least a portion of an inner surface of the peripheral wall of the barrel has a figure-8 shape in a plane perpendicular to the barrel axis. The monolithic peg extends along a peg axis and is configured for insertion into the passage, wherein a body of the peg has an outer surface defining a figure-8 shape in a plane perpendicular to the peg axis.