Precision implantation with positional confirmation of fine-wire EMG electrodes in the deep posterior neck muscles

Precise electrode placement is essential for obtaining useful electromyographic (EMG) recordings. Our aim was to develop a protocol for computerized-tomography (CT) guided fine-wire (FW) electrode placement that permits confirmation of the final electrode position in the deep posterior cervical multifidus (CM). FW-EMG electrodes were custom-made from three 50-µm diameter Teflon-insulated platinum/iridium wires. The electrodes were inserted bilaterally in the CM in 15 healthy adult subjects through a 45-mm cannula under CT guidance. The final position of the electrode placement was confirmed in reconstructed 2D and 3D images. Electrode placement was within the fascial boundaries of the CM for 21 of the 25 successfully inserted FW-EMG electrodes. The distance from the electrode to the middle of the CM did not increase significantly with target depth until a breakpoint at 63.2 mm (95% CI 59.1-65.3), from where it increased by an additional 2.9 mm per mm increase in target depth (95% CI 1.3-6.6). Viable EMG was obtained from 21 electrodes. CT guided implantation provided excellent visual documentation in three dimensions of the final placement of the tip of the electrode bundle. The technique affords confidence in studies of motoneuron activity in CM.