Customized, rapid-production microstereotactic table for surgical targeting: description of concept and in vitro validation

Abstract

Purpose: To introduce a novel microstereotactic frame, called the Microtable, consisting of a tabletop that mounts on bone-implanted spherical markers. The microtable is customized for individual patient anatomy to guide a surgical instrument to a specified target.

Methods: Fiducial markers are bone-implanted, and CT scanning is performed. A microtable is custom-designed for the location of the markers and the desired surgical trajectory and is constructed using a computer-numerical-control machine. Validation studies were performed on phantoms with geometry similar to that for cochlear implant surgery. Two designs were tested with two different types of fiducial markers.

Results: Mean targeting error of the microtables for the two designs were 0.37 +/- 0.18 and 0.60 +/- 0.21 mm (n = 5). Construction of each microtable required approximately 6 min.

Conclusions: The new frame achieves both high accuracy and rapid fabrication. We are currently using the microtable for clinical testing of the concept of percutaneous cochlear implant surgery.

Fig 1

(a) In the simplest implementation of the microtable concept, three spherical fiducial markers are used. The tabletop is elevated above the spherical fiducial markers using legs to orient it perpendicularly to the trajectory. (b) Two example configurations of bone-implanted anchor and extender for the spherical fiducial marker illustrating that specific location and orientation of the anchors are relatively unimportant.

Fig 2. Flowchart explaining steps involved for clinical application

Fig 3

(a) Spherical fiducial markers atop extenders anchored to the skull; (b) Legs attached to spherical fiducial markers. The planned trajectory is shown as a red cylinder.

Fig 4. Countersinking of the legs such that the tabletop is perpendicular to the trajectory

Fig 5. Microtable with CNC tool paths shown in green

Fig 6. Quality assurance by measuring distances between holes

Fig 7

Coupling mechanism between spherical fiducial marker and table leg. The inset shows a close up of one coupling. Twisting the thumbscrew tightens the grippers, thereby fixing the leg to the marker.

Fig 8

Microtable attached to patient with surgical instrument attached via a holder to the tabletop and ready for procedural intervention.

Fig 9

Phantom as used in coordinate measuring machine (CMM). (a) Microtable mounted on the spherical markers in a phantom. (b) Physical localization of spheres using the CMM.

Fig 10

Microtable mounted on the patient's head for validation. The Microtable was fabricated intraoperatively for cochlear implantation for the patient.