Screw Drive Integrated Torque Protection Biodegradable Magnesium
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Solution Overview
Problem
Screws, particularly those made of biodegradable magnesium alloys used in osteosynthesis, are prone to mechanical overloading, leading to complications such as jamming, shaft fracture, or over-tightening, which can result in prolonged surgery times and difficulties in removal, especially when the screw head breaks off or the thread is damaged.
Innovation Solution
A screw drive with integrated torque protection, featuring a combination of an internal polygonal drive and a multilobular drive, where the multilobular points break off or shear when maximum torque is exceeded, preventing damage to the screw head, shaft, or thread, and allowing for easy removal by preventing further torque transfer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the screw is made of biodegradable magnesium alloy with strength comparable to bone, then the screw can be resorbed by the body and avoid second operation, but the screw is prone to mechanical overloading and damage during screwing
Solution Approach 1:
The screw drive is segmented into two independent functional parts: an internal polygonal drive (e.g., hexagon) for normal operation and screwing, and an internal multilobular drive (e.g., Torx) with points that can break off. This segmentation allows each part to serve its specific function - the polygonal drive provides stable torque transmission during normal use, while the multilobular drive's breakable points provide overload protection without compromising the screw's biodegradable nature or strength requirements.
Solution Approach 2:
The multilobular drive with breakable points acts as an intermediary protection mechanism between the screwing tool and the screw shaft. When excessive torque is applied, the points break off first, serving as a sacrificial element that prevents damage to the critical screw components (shaft, thread, head). This intermediary structure absorbs the harmful overload before it can reach the load-bearing parts of the screw.
2Strength
If the screw head breaks off or the thread is damaged due to over-tightening, then the screw cannot be removed easily, but the surgeon must perform additional time-consuming procedures
Solution Approach 1:
The screw drive is designed with preliminary protection built in - the breakable points of the multilobular drive are positioned to fail first under excessive torque. This preliminary action prevents the progression to more serious damage like head breakage or thread stripping. By anticipating the overload scenario and providing a predetermined failure path, the design ensures that even after overload, the screw remains removable through the intact polygonal drive.
Solution Approach 2:
The breakable points are designed to be discarded sacrificially under overload conditions. Once the points break off, they are discarded, but the core screw structure and the polygonal drive remain intact and can be recovered for removal. This principle allows the system to withstand and recover from overload events without permanent damage to the critical components, maintaining ease of removal even after mechanical stress events.
3Strength
If the screw is designed with high strength to prevent over-tightening damage, then the screw may cause stress shielding effect and hamper bone healing, but if the strength is reduced to match bone strength, then the screw becomes more susceptible to damage
Solution Approach 1:
The screw drive exhibits local quality differentiation - the multilobular drive points are designed with lower strength and higher brittleness to fail first under overload, while the main screw body maintains bone-appropriate strength for physiological loading. This local quality variation allows the critical path components to have different mechanical properties optimized for their specific functions: the points as sacrificial elements and the screw shaft as load-bearing but biocompatible structure.
Solution Approach 2:
The invention changes the mechanical parameters of different parts of the screw drive system. The breakable points are engineered with specific geometric parameters (sharp points, thin sections) that give them low torque resistance, while the screw shaft maintains parameters (diameter, material composition) that provide bone-appropriate strength. This parameter differentiation across components allows the overall system to achieve both overload protection and bone compatibility simultaneously.
Data Source
AI summary
The present invention relates to a screw drive having integrated torque protection, wherein two screw drives are incorporated in a screw head, one drive being an internal polygonal drive and the second drive being an internal multilobular drive. In addition, the invention relates to a screw having a screw drive.