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Automated Bone Screw Torque Optimisation

 

Overview

Bone screws are used in a variety of orthopedic procedures either to prevent bone movement and assist with the natural healing of fractures, or to hold implants and prosthetics in place. The torque used to tighten these screws has a notable effect on the resilience and longevity of these fixations. Too much torque and the bone may break and weaken the fixation; too little torque and the screw may become loose over time, or inadequately fix implants/fractures. Either case may result in premature failure of the fixation, which may require risky revision surgery to remedy, or may result in direct damage to surrounding tissue.


Surgeons usually tighten screws by feel, and while these professionals are highly skilled, and generally obtain good results, there is still an degree of subjectivity involved, and mistakes can always happen. Furthermore, as we look into the future at the potential for semi- or fully- automated robotic surgery, a more well-defined methodology for optimizing screw tightening torque will be required. Both situations may be resolved by using an automated system to estimate and regulate the optimal insertion torque of a screw.


Current research at ITeM

This project seeks to develop a system that can achieve the goal of determining optimal insertion toque, by using signals (torque, rotation, force) from the bone screw insertion, in conjunction with mathematical models of the bone screw insertion process, and screw tightening/stripping processes. Generally, a parametric model of the screw insertion will be used in conjunction with parameter identification techniques to determine the strength of the bone as a screw is inserted. After the strength is determined, another model will be used to estimate the optimal insertion torque for bone of the identified strength. This process can automatically adapt the insertion and tightening torque to different types of bones across different patients (e.g., with/without osteoporosis).

Current research is focusing on:

  • Model development for the bone screw insertion process
  • Model development for stripping torque/optimal insertion torque calculation
  • Experimental model validation using biomechanical models and ex-vivo animal bone
  • Detailed investigation of the screw insertion and tightening processes using FEM analysis
  • Anticipating practical and social barriers to acceptance of the technology

Cooperations
  • University of Basel, Department of Biomedical Engineering
  • Weber Instrument