Navigation & Robotics in Spine Surgery

"Verify against the anatomy and do not trust the screen" is sound advice and useless without the checks themselves. There are four, and they are independent of one another, which is the point - each fails in a different way, so agreement between them is what provides confidence.

The triggered-EMG logic is a favourite trap because the intuition runs the wrong way: a low threshold is the worrying result, because current is escaping through thin or breached cortex to reach the nerve, while a high threshold means intact bone is insulating the screw. Modalities, alarm criteria and the rest of the monitoring picture are in Spinal Cord Monitoring and IONM.

The bail-out. Navigation and robotics fail intraoperatively in ways that are recoverable if anticipated - the array is knocked, line of sight is lost, registration will not hold at the caudal levels, the robot arm skives off a sloped facet, or the scan is degraded by artefact from existing metalwork. The response is a sequence, not a crisis: re-register and re-verify against a landmark; re-spin the intraoperative scan if the geometry has changed; move the reference array closer to the level being instrumented; and if accuracy still cannot be confirmed, convert to freehand or fluoroscopically guided placement with direct palpation. Any surgeon using navigation must remain able to place a screw without it. Losing the technology mid-case is an inconvenience for a surgeon who can do that and a genuine emergency for one who cannot, which is the strongest practical argument for continuing to teach and practise freehand technique alongside the machines.

An examiner who has heard the accuracy figures will ask the question that matters: a screw that is 2 mm better placed - does the patient notice? The evidence for accuracy is consistent. The evidence that it changes how patients do is much weaker, and a candidate who claims otherwise is easy to dismantle.

Why the two questions come apart. Most malpositioned pedicle screws cause no symptoms whatsoever. A lateral breach may sacrifice purchase without ever troubling the patient; even a modest medial breach is frequently tolerated. Symptomatic malposition requiring revision is uncommon, so the event that better accuracy would prevent is rare - and a technology that reduces a rare event has to be studied in very large numbers before any effect on that event becomes visible. Accuracy is a surrogate outcome: easy to measure, measured in every study, and only loosely coupled to what the patient experiences.

What the appraised evidence says. An umbrella review took 22 published meta-analyses of robot-assisted versus freehand technique and assessed them formally with AMSTAR-2 and GRADE, across 14 associations including "perfect" and "clinically acceptable" screw placement, complications, facet joint violation and radiation. Robot assistance came out favourably - but the certainty of the evidence for the majority of those associations was rated LOW to VERY LOW, and the authors' own conclusion was that the findings need cautious interpretation before being applied in practice. Much of the underlying literature is observational, subject to selection of straightforward cases into the new technology and of difficult ones away from it, and reported by enthusiasts during their own learning curves.

The randomised evidence is still arriving, and it is worth knowing what it is measuring: the ROBARTHRODESE trial randomises 300 patients to robot-assisted versus fluoroscopic freehand thoracolumbar fusion, and its primary outcome is the proportion of Grade A screws - with disability score, pain, complications, reoperation, radiation and a cost-utility analysis as secondary outcomes. The surrogate is still the primary endpoint even in the trials designed to settle the question.

How to say this in a viva without sounding either credulous or dismissive. The technology reliably does what it claims - it places screws more accurately and it takes the surgeon out of the radiation beam, and both are worth having. Its value is greatest where the anatomy makes freehand genuinely hazardous: severe deformity, revision with distorted landmarks, high thoracic and cervicothoracic levels, sacropelvic fixation, obesity, and percutaneous minimally invasive work where landmarks are not exposed at all. What it has not yet been shown to do is make an average lumbar fusion turn out better, and the case for buying one rests as much on radiation protection and on capability in complex cases as on outcomes data that does not yet exist.