The AIM Frame
The AIM Frame is a bone-attached miniature parallel robot for minimally-invasive neurosurgical procedures, in particular cochlear implant (CI) surgery. The AIM Frame project of Vanderbilt's Computer-Assisted Otologic Surgery (CAOS) laboratory in cooperation with the MED Lab.

Cochlear implants are electronic devices that restore hearing to individuals who have severe or total hearing loss and cannot benefit from traditional hearing aids, which amplify external sounds. A cochlear implant bypasses non-functioning parts of the ear by directly stimulating the auditory nerve with electrical signals. The signals are transmitted to the auditory nerve through an electrode array implanted in the cochlea, a spiral-shaped structure of the inner ear. Surgeons currently gain access to the cochlea by performing a mastoidectomy, requiring tedious creation of a cavity in the temporal bone behind the ear using a hand drill. To avoid damaging sensitive structures such as the facial nerve, surgeons must rely on hand-eye coordination and spatial memory to execute the mastoidectomy procedure with submillimetric accuracy.

Cochlear Implant System
A Cochlear Implant. (Image: National Institutes of Health/ Department of Health and Human Services)

A new procedure, Percutaneous Cochlear Implantation (PCI) has been pioneered at the CAOS laboratory as a minimally-invasive alternative to traditional CI surgery. A rigid fixture called a "Microtable" is custom manufactured for each patient and attached to the skull using bone screws. The Microtable guides a drill and electrode insertion tool to the cochlea through a single drill hole behind the ear. The shape of the Microtable is automatically designed by custom software that calculates an optimally safe drill path from patient CT scans. By eliminating the mastoidectomy from CI surgery, PCI promises to reduce patient trauma, shorten procedure time, and reduce reliance on a surgeon's skill.

Microtables have been shown to be a safe solution for PCI surgery, but each surgery requires on-site machining. The purpose of the AIM Frame is to remove the need to machine a Microtable, by using a rapidly configurable parallel robot to perform the same targeting function as the Microtable but with a reduction in total procedure time. High accuracy and mechanical rigidity is achieved by use of a parallel robot design, the Gough-Stewart platform.

The AIM Frame system for Percutaneous Cochlear Implantation

PCI surgery with the AIM Frame begins with attaching a rigid platform called Pre-Positioning Frame (PPF) to the patient's head using bone screws and then taking a CT scan. Metal spheres on the PPF are automatically identified in a CT scan and allow planning software to automatically plan a safe drill trajectory to the cochlea. After the robot is adjusted to position, it is detached from its power source and  the spheres on the PPF. During surgery, the drill and electrode insertion tool attach to a coupling on top of the robot.

Drill tip
            placement with the AIM Frame
Two views from a CT scan of a drill tip (5/64" diameter) guided by the AIM Frame to the cochlea of a human cadaver. The AIM Frame successfully avoided all critical anatomy and placed the drill tip 0.38 mm from its planned target.

In addition to Percutaneous Cochlear Implantation surgery, the AIM Frame is being considered for other neurosurgical applications including electrode placement for deep brain stimulation and drainage of the petrous apex.


  1. The AIM Frame


  1. L. B. Kratchman, G. S. Blachon, T. J. Withrow, R. Balachandran, R. F. Labadie, and R. J. Webster III. Design of a Bone-Attached Parallel Robot for Percutaneous Cochlear Implantation. IEEE Transactions on Biomedical Engineering. (In Press).
  2. L. B. Kratchman, G. S. Blachon, T. J. Withrow, R. Balachandran, R. F. Labadie, and R. J. Webster III.  Toward Automation of Image-Guided Microstereotactic Frames: A Bone-Attached Parallel Robot for Percutaneous Cochlear Implantation.  Robotics, Science and Systems 2010 - Workshop on Enabling Technologies for Image-Guided Robotic Interventional Procedures. (Poster)