gms | German Medical Science

Objective: The accuracy of neuronavigation systems may decrease during surgery for reasons yet unknown. As a possible origin for inaccuracy movements of the patient’s head inside the Mayfield headholder were suspected. To ensure there can be no movement between the patient’s head and the navigation system’s reference array, the headholder was modified.

Method: As modification of the Mayfield headholder a piece was added to allow direct fixation of the navigation system’s reference to the headholder’s pins which are pressed onto the skull. Thus, no flexible parts are between the skull and the reference any more, ruling out movements inside the headholder as origin for growing navigation mismatch. The modified device was tested in a prospective pilot study in 10 patients undergoing navigated cranial surgeries in April and May 2013. During surgery, the navigation system’s accuracy was measured after certain events: Sterile draping, skin retraction, craniotomy, halo-ring attachment, end of surgery. Accuracy, feasibility and security of the device were judged by the surgeon postoperatively.

Results: The modified headholder was judged feasible and secure in all cases. The median navigation accuracy suspected by the surgeons was 4-6 mm. The mean mismatch decreased from 2.87 (SD 1.14) at the beginning of the surgery to 5.52 (SD 2.15) at 6 hours after beginning of the surgery. The modified headholder did not achieve an improvement of neuronavigation accuracy compared to earlier experiments with a standard headholder.

Conclusions: The tested modification of the Mayfield headholder ruled out that movements of the patient’s head inside the headholder negatively influence the accuracy of neuronavigation. Still, the observed accuracy was comparable to experiments using a standard headholder. The origin for the constant decrease in accuracy must be searched in other parts of the system.