8.10 Inspection of Stereotactic Sets

What a Stereotactic Set Does

Stereotaxis locates a target inside the body using a three-dimensional coordinate system rather than direct vision. In neurosurgery it is used for biopsies, electrode placement, catheter and shunt placement, and radiosurgery planning; comparable principles appear in breast localisation and elsewhere.

The workflow is: attach a reference frame to the patient, image the patient with the frame in place, calculate the target's coordinates in the frame's coordinate system, then set those coordinates on a targeting device that directs an instrument to the point.

The entire clinical value of the set is geometric accuracy, and that single fact determines how it is inspected.

---

Components of a Frame-Based System

Frameless (image-guided) stereotaxy replaces the rigid frame with navigation trackers and arrays, which are covered in Section 4.5. The inspection philosophy is identical: geometry is everything.

---

The Inspection Routine

1. Geometry and physical integrity

• No bends, dents, twists, or cracks anywhere on the ring, localizer, arc, or posts.
• Localizer rods straight, intact, correctly seated, and undamaged — they are the imaging reference and a bent rod produces a wrong coordinate.
• Mating surfaces clean, flat, and undamaged, so components seat in exactly the same relationship every time.
• Anything dropped is removed from service until the manufacturer's verification confirms it, because a small geometric change produces a confidently wrong target with no error indication.

2. Scales and markings

• Every graduation, vernier scale, and numeric marking must be legible. A worn or partially obscured scale is a removal-from-service finding, not a cosmetic one.
• Index marks and zero references present and undamaged.
• Any label identifying the component or its serial number legible for traceability.

3. Mechanical function

• Threads on posts, screws, clamps, and adjusters clean, undamaged, and running freely along full travel; galled or seized threads are a failure.
• Locking mechanisms engage positively and hold under load.
• Sliding and rotating adjusters move smoothly through full range and hold their set position without drift.
• Depth stops set and lock reliably.

4. Verification

• Use the phantom base or verification device per the manufacturer's procedure to confirm the assembled system targets a known point within specification.
• A set that will not verify is not released, regardless of how it looks.
• Verification is documented, and the facility's policy defines its frequency — commonly before use and on a defined schedule, plus after any suspected event.

5. Cleaning and processing

• Components are disassembled per IFU; threaded and sliding assemblies trap blood and bone.
• Method restrictions vary: some components are steam sterilizable, some are not, and imaging localizers may have specific restrictions.
• Store in the dedicated case with defined positions; loose storage is the usual cause of the bends that end a component's life.

---

Completeness

A stereotactic set is unusable if a single component is missing — the localizer, an arc adjuster, a depth stop, a specific probe holder, or the verification phantom. Counting is component by component against the manufacturer's list, and where pins or other items are single-use, the specialist confirms the correct type and quantity are available rather than assuming.

---

Disposition Summary

Why Dimensional Accuracy Is the Only Thing That Matters

A stereotactic system establishes a three-dimensional coordinate space over the patient so that a target seen on imaging can be reached by a probe or electrode along a calculated trajectory. Every component exists to make the relationship between the coordinate frame and the anatomy exact and reproducible.

The consequence is that ordinary inspection standards are insufficient. An instrument that moves smoothly, looks undamaged, and holds firmly can still be out of specification by a millimetre, and a millimetre at the frame becomes a significant error at depth. Because the surgeon is navigating by calculated coordinates rather than by direct vision, there is no intraoperative check that will reveal the error before the trajectory is taken.

Inspection therefore concentrates on geometry, graduations, and rigidity rather than on cleanliness and function alone — though those still apply.

The Specific Checks

Frame and arc components must be free of any bend, warp, or twist. Inspect the frame on a known flat surface, sight along the arc, and check that mating surfaces seat fully and evenly. Any component that has been dropped is suspect regardless of appearance and should be referred to the manufacturer for verification.

Graduations, scales, vernier markings, and index lines must be complete, crisp, and legible along their whole length. A worn or partially obscured scale is a removal criterion, because a misread coordinate is indistinguishable from a correct one at the time it is set. Do not attempt to re-mark a scale.

Locking mechanisms, micrometers, thumbscrews, and threaded posts are run through their entire travel in both directions. They must move smoothly, lock rigidly, and release cleanly. Any binding, slop, backlash, or point at which the mechanism jumps means the component cannot hold a setting reliably.

Probe guides, carriers, and electrode holders must be straight and unobstructed, with a lumen that is patent and undamaged.

Completeness, Verification and Processing

These systems are matched, numbered assemblies, and components from one system will often physically fit another while being dimensionally incompatible. Confirm every part carries the correct system identification and that the count matches the sheet exactly — including the small items, the pins, the wrenches, and the adapters, which are the ones that go missing.

Where the manufacturer supplies a phantom base or verification fixture, the system should be verified against it on the schedule specified, and that verification recorded. This is the only check that actually confirms accuracy rather than inferring it.

Process strictly according to the instructions for use: these assemblies frequently mix materials with different sterilization requirements, and some components are low-temperature only.