Högskolan i Skövde

This report includes the development and design of an angled screw driver for spinal surgery that is based on an existing instrument. The new design shall be CE‑marked. To be CE-marked the design procedure has to follow certain rules and documentation of every part in the procedure is essential.

The existing angled screw driver has some serious flaws. It does not meet the standards involved for surgical instruments; a reason for this is that the instrument is manufactured long before CE-marking initiated. Other problems include the choice of material of the instrument and the impossibility to disassemble it. This is important for the washing and sterilization purposes.

An important and fundamental function of the instrument is to transfer a torque to an angled hex bit. According to the requirement specification the angle should be variable between 20° and 70°, but preferably the angle can vary from 0-90º. Apart from these requirements the height of the angled hex bit should be minimized.

The solution consists of a horizontal shaft with spherical cogs that transfers the torque to the cog holes and on to a hex bit. The cogs and the holes are always in connection regardless of the angle. Spherical cogs have a large connection surface regardless of angle, this is an advantage.

The angled hex bit is modified to minimize the height on the instrument. The hex bit is joined directly on the cog hole with a cog screw.

Before sterilization the instrument can be picked apart and then the water can flow freely through and around all parts.

The materials must be approved for surgical instruments according to standard SS‑EN ISO 16061:2008. The materials used are Nitronic 60, Custom 465 Stainless and BioDur® 316LS Stainless. Radel R5500 is used in the handle. Nitronic 60 is good in respect to galling, this is used in the moving parts of the instrument. Custom 465 Stainless has high yield strength; this is why it is used in parts exposed to high stresses. BioDur® 316LS Stainless is used in the other parts.

The stresses that arise in some parts are higher than the yield strength for the material. Therefore further tests are needed to confirm that the design really withstands the torque. These tests will be performed on a prototype designed specially for this purpose. The tests will be executed by the employees at Elos Medical AB.