Reference markers in computer aided orthopaedic surgery: rotational stability testings and clinical implications

Area of Science:

• Orthopedics
• Surgical Navigation
• Biomechanics

Background:

• Surgical navigation systems rely on stable reference arrays (RA) fixed to bone anatomy.
• Collisions or movements of RAs can lead to measurement failures and reduced navigation precision.
• The torque required to destabilize a reference array is not well-defined.

Purpose of the Study:

• To quantify the torque resistance of standard reference arrays (RA) used in surgical navigation.
• To determine the rotational displacement of RAs under applied torque.

Main Methods:

• A digital torque device applied increasing rotational forces (1, 2, 3 Nm) to RAs fixed to cadaveric bone.
• A navigation system monitored the relative positions of the tested RA and a proximal RA.
• Rotational differences were calculated and statistically analyzed over multiple cycles.

Main Results:

• 1 Nm torque caused minimal rotation (avg. 1.0 degrees) with no significant increase over cycles.
• 2 Nm torque initially caused 1.8 degrees rotation, with significant increases observed after the third cycle.
• 3 Nm torque resulted in 2.9 degrees initial rotation, with significant increases in rotation after each subsequent cycle.

Conclusions:

• Applied torques of 2 Nm or greater may lead to reference array loosening and loss of positional accuracy.
• Surgeons using computer-aided surgery should be aware of potential unrecognized RA movements.
• Gentle collisions appear unlikely to cause significant RA destabilization or affect navigation precision.