Monitoring torsion on a distal end assembly

Apparatus for measuring a torque, comprising:

• a probe, comprising:
• a shaft having a shaft distal end,
• a distal end assembly, configured to be inserted into an organ of a human subject, the distal end assembly having:
• a distal termination,
• a proximal termination connected to the shaft distal end, and
• a longitudinal axis extending from the proximal termination to the distal termination, and
• a position sensor assembly, attached to the distal end assembly in proximity to the distal termination thereof, the position sensor assembly being configured to provide signals indicative of a three-dimensional (3D) position and orientation of the distal termination with respect to the shaft distal end;
• and
• a processor, configured to:
• compute a torsion of the distal termination with respect to the proximal termination, about the longitudinal axis, in response to the signals from the position sensor assembly, and
• compute the torque on the distal end assembly, about the longitudinal axis, in response to the torsion and a predetermined correspondence between the torsion and the torque on the distal end assembly.