Kinematic analysis and design optimisation of a surgical rod cutter for shearing of Ti6Al4V rods

Titanium rods used as spinal implants need to be cut to a suitable length in the operating room. The mechanism used to cut them needs to be entirely manually operated since the interference of electrical and electronic components with the sensitive electronic components cannot be predicted. The mechanism also needs to be as small as possible since it needs to be decontaminated in an autoclave prior to its use. This work explores different options for such a mechanism. The best design from a scarce patent literature was optimised to obtain a 56% reduction in dimension. The manual force was verified with a mechanism simulator (ADAMS). A material model in DEFORM allowed the experimentally determined shearing force to be simulated. This led to the prediction of change in the mechanism’s dimensions with change in the rod’s dimensions.