Overview of Orthopedic Screw Drivers

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The screwdrivers had to retain screws securely until they were anchored in place, offering an easy to use alternative for orthopedic surgeons who currently employ a variety of surgical devices to retain bone screws, which tend to be overly difficult, complex to use and hard to manufacture by the orthopedic instrument manufacturers. 
The initial brief was to develop a range with interchangeable shafts for fixing 1.5, 2.5 and 3.5 mm screws with hexagonal heads. Theoretical and practical studies resulted in a decision to develop a separate design to enhance the capabilities of the 1.5 mm device to achieve the torque used to tighten orthopedic screws.


The pre-production prototype consists of three parts- a shaft, a sleeve and handle- manufactured from different grades of stainless steel to ensure resistance to corrosion and ease of disassembly to allow sterilization.

The shaft is attached to the handle using coupling- a universal coupling used for a range of orthopedic instruments. Because users have been known to accidentally release the coupling when trying to lock it, the coupling on the prototype was adopted by a third party to reverse the unlock function.

The design of screwdriver makes use of frictional principles. The accuracy and size of the slot geometry were determined through practical examination and research and the results were then fed back into the tolerances assigned to other features.  

Testing
Testing was extremely important to determine the strength of the screwdriver due to the presence of the slot significantly increases stress concentration at a given load. A range of samples was tested to determine the best combination of material and geometry. Following these extensive tests, we decided a different design should be used for the size of 1.5 mm. A series of practical and theoretical tests were carried out to help understand the issues and optimize the solution.

FEA simulations on simplified geometry revealed the stress distribution around the most vulnerable areas of the orthopedic implant device. These results were combined with practical examination to create a holistic overview of performance and demonstrate whether the screwdrivers could achieve the standards that are required.
  
Geometry
Creating the driver and sleeve geometry was extremely challenging, especially as some manufacturing processed were being pushed to the limit when it came to meet some definite tolerances. 


The product works better when it costs less to manufacture because it requires fewer parts and is far less complex.

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