Telescoping Bone Screw Detent Mechanism
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Solution Overview
Problem
Bone screw migration and 'cut-out' issues occur during the healing process of femur fractures, leading to potential failure of the fixation system due to compression, bone deterioration, or misalignment, as existing bone screws either loosen or break through the femoral head.
Innovation Solution
A bone screw with a plunger assembly and detent assembly that allows independent movement of the plunger within the socket, secured by a lock ring and lock sleeve, preventing rotation and allowing for compression between the femoral head and femur, thus maintaining stability and preventing migration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the bone screw is fixedly secured to the bone nail, then the bone screw maintains its position in the aperture, but the femoral head movement causes the threaded end to cut through the femoral head (cut-out)
Solution Approach 1:
The bone screw is designed with a telescoping mechanism that allows it to move dynamically within the aperture. The screw can slide longitudinally along the bone nail while maintaining rotational fixation, enabling it to adapt to femoral head movement and fracture compression without causing cut-out.
Solution Approach 2:
The bone screw is divided into functionally independent segments: a threaded engagement portion that anchors in the femoral head, a smooth bore section that slides within the aperture, and a detent assembly that provides intermittent locking. This segmentation allows each portion to perform its specific function independently.
2Adaptability or versatility
If the bone screw is allowed to slide freely in the aperture, then the bone screw can accommodate femoral head movement, but the bone screw may migrate or loosen creating failure risk
Solution Approach 1:
The bone screw transitions from a static fixed position to a dynamic system with controlled mobility. The detent assembly provides intermittent locking that allows the screw to slide freely during normal movement accommodation, then lock at specific positions to prevent migration or loosening.
Solution Approach 2:
The detent assembly acts as an intermediary mechanism between the sliding bone screw and the fixed aperture. It mediates between the need for free movement and the need for secure fixation, allowing controlled sliding while preventing uncontrolled migration.
3Adaptability or versatility
If the bone screw head extends significantly past the femur surface due to fracture compression, then the bone screw accommodates compression, but it creates a raised surface causing pain at the hip joint
Solution Approach 1:
The bone screw incorporates a telescoping mechanism that allows the screw to compress telescopically within the aperture rather than extending outward. The plunger assembly slides within the screw body, absorbing compression forces internally while maintaining a constant external profile that prevents pain.
4Reliability
If the bone screw is made telescoping with independent plunger movement, then the bone screw prevents migration and cut-out, but the device complexity increases
Solution Approach 1:
The telescoping mechanism is segmented into simple, discrete components: a plunger assembly with basic sliding motion, a detent member with simple geometric locking surfaces, and a detent assembly with minimal moving parts. Each component is structurally simple despite the complex overall function.
Solution Approach 2:
The detent assembly is designed to engage and disengage automatically based on the position and movement of the plunger assembly, without requiring external actuation or complex control mechanisms. The system self-regulates its locking and unlocking states.
Data Source
AI summary
A bone screw for treating a bone fracture having a detent assembly on a body portion thereof. The detent assembly operative to secure the body from movement relative to a bone nail. The detent assembly includes a detent member, for example, an annular member, movable between a first and second position. Positioning the annular member in the second position operates to secure the body of the bone screw from movement relative to the bone nail.