Exploring Frameless Stereotactic Image Guided Surgery

AORN Journal, March, 1999 by Charles Tessman

Image guided surgery (IGS) is a broad term referring to a number of radiographic modalities used in anatomic localization procedures. One of the most recent modalities is a technology called frameless stereotaxy--a term originating from the technology's initial use in cranial neurosurgical procedures. Frameless stereotactic IGS provides a new way to navigate three dimensionally without having to mount a frame to the patient's head. Many manufacturers produce this equipment, which is seen widely throughout neurosurgical ORs. Now this technology is broadening, and new applications in other areas and specialties are being implemented.

BACKGROUND

The idea of navigating three dimensionally in the skull has been around since the beginning of the century. The objective was to develop a method to define a specific point within the three-dimensional space of the cranium. At this time, the term stereotactus--based on the Greek word stereo, meaning three dimensional, and the Latin word tactus, meaning touch--was introduced.(1)

Framed stereotaxy. The first attempt to develop this method was the construction of a stereotactic frame in the early 1900s.(2) This technique--which was not actually tested on a human until the 1940s--worked by mounting the stereotactic frame to a patient's head using the exterior auditory canals and the inferior orbital rims as landmarks.(3) With these landmarks present on plain x-rays, neurosurgeons could calculate desired intracranial locations. This technique ultimately was abandoned because of the inability to calculate accurate adjustments when a patient's brain tissue had been shifted because of lesions.(4)

Modern advances. Stereotactic surgery was not practiced for many decades until the 1980s, when advances occurred in computed tomography (CT) and magnetic resonance imaging (MRI).(5) These radiographic modalities provided the ability to see abnormal shifting of the brain and determine a desired three-dimensional location in the cranium. Stereotactic neurosurgery quickly became Standard practice for assisting in lesion resections and collecting deep brain tissue for biopsy. This was a big step for neurosurgery, providing surgeons with greater confidence and patients with better outcomes and quicker recoveries.

Frameless stereotaxy. With continued advances in computer technology, the idea of frameless navigation developed. The first neurosurgical procedure using a frameless technique was performed in the early 1980s.(6) Since then, many frameless systems have been manufactured, and clinical trials for cranial surgery by the US Food and Drug Administration (FDA) have been completed and approved. The FDA next explored and approved a new application of the frameless technique in spinal surgery, which enabled surgeons not only to navigate to specific points but also to determine trajectories in the anatomy. This proved to be extremely useful for determining angle, length, and width of hardware placement. It is now common practice across the United States to use frameless stereotaxy for both cranial and spinal neurosurgical procedures.

FRAMELESS STEREOTAXY ADVANTAGES

Frameless stereotaxy in cranial and spinal procedures has many advantages over traditional methods for surgeons and, more importantly, for patients. Advantages for cranial procedures include

* real-time interaction with MRI images, allowing more precise surgical planning;

* smaller incisions and craniotomies;

* less invasive excisions, which may improve patient outcomes;

* less restriction of surgical access because of lack of stereotactic frame;

* less patient discomfort from having to wear a stereotactic frame to and from the CT or MRI unit and OR;

* less preparation time than framed stereotaxy because the frame does not need to be applied to the patient and calculations do not need to be made in the CT or MRI unit;

* easier use with pediatric patients, as less cooperation is needed.(7)

Advantages for spinal procedures include

* reduction and possible elimination of intraoperative radiation exposure;

* improvement of hardware placement accuracy, providing better patient outcomes;

* easier methods for surgical planning (eg, determining screw length and width for a particular vertebra preoperatively);

* reduction in surgical procedure time by making hardware placement decisions more efficient.

SYSTEM COMPONENTS

Although today several manufacturers produce different frameless stereotactic systems, the purpose and functions of the systems basically are the same. The main variations in the systems involve software and tools. Most systems have two separate pieces that can be rolled into the OR (ie, a cart, which houses the components, and a camera, which is mounted on a separate boom) (Figure 1). All frameless stereotactic systems include the following components:

[Figure 1 ILLUSTRATION OMITTED]

* a high-power computer that has the ability to instantly store and process MRI or CT images to provide real-time feedback;

*a high-resolution monitor that shows the necessary detail of an MRI or CT image;