The head clamp goes on at the start of the case, and after that almost nobody looks at it again.
That is usually fine. Three-point cranial fixation has been standard in neurosurgery for decades precisely because it works — it holds the skull rigid so the surgeon can operate under a microscope, or with navigation, without the field shifting by a millimetre. Most of the time it does its job silently and comes off at the end without anyone thinking about it.
But the force involved is not small, and the complications, though rare, are serious enough that OT teams should understand what is actually happening.
How much force are we talking about?
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In adults, published neurosurgical practice generally applies somewhere in the range of 60 to 80 pounds — roughly 267 to 356 newtons — across the three-point clamp.
That force is not distributed the way people assume. A single pin sits on one side. Two rocker-arm pins oppose it from the other. If the rocker arm is properly aligned, each of those two pins carries about half the load of the single pin. If it is not aligned, one pin takes more than its share.
Which is why rocker arm alignment is not a cosmetic detail. It is the difference between load being shared and load being concentrated on one point of the skull.
Too loose is a different problem from too tight
Both directions carry risk, and they fail differently.
Too little force and the head can slip mid-procedure. In a navigation case that invalidates your registration and costs time. In posterior cervical work it can mean losing the alignment the whole case depends on.
Too much force, or force applied to a skull that cannot take it, and the reported complications include depressed skull fracture, dural tear, epidural haematoma, cerebrospinal fluid leak and pin-site bleeding. These are documented in the literature — uncommon, but real, and several published cases involved patients whose skulls were thinner than expected.
That is the recurring theme. It is usually not the clamp. It is the skull.
Patients where extra caution applies
Some patients carry higher risk, and the OT team should know which ones before the clamp comes out of the box.
Children, obviously — the skull is thinner and the safe force is much lower. Patients with longstanding raised intracranial pressure or hydrocephalus, where the bone may be thinned. Patients with bone fragility from chronic disease, long-term steroid use or dialysis. Anyone with a previous craniotomy, where a pin might land on a burr hole, a plate or a thinned area.
In several of these situations the right answer is not a lower pin force. It is no pins at all.
Which is what the horseshoe headrest is for
A complete Mayfield neuro attachment kit ships with a horseshoe headrest, and it is not packaging filler.
For infants and very young children — generally under about two years — pin fixation is usually avoided entirely, and the headrest is the alternative. It also makes sense for short procedures where rigid fixation is not clinically necessary, and for adults where pinning is contraindicated.
The horseshoe shape is open at the face so the airway stays accessible. That matters to anaesthesia as much as it does to the surgeon. On the Ventek India kit the headrest is a silica pad on an adjustable base, so it can be wiped down properly between cases and sized to the patient rather than forced to fit.
If a supplier offers you a kit without a headrest, ask why. There is no good answer.
Paediatric pins are not just smaller pins
Worth saying plainly, because this is where avoidable injuries happen.
A complete kit includes a separate paediatric pin set, and paediatric fixation uses substantially reduced force. Using the adult set on a child, or applying adult torque to a paediatric skull, is exactly how the skull fracture cases in the literature occurred.
Practical suggestion: keep the two pin sets separately labelled in the CSSD tray. Not in the same pouch. Not “we know which is which”. Labelled.
Pins are consumables
They get treated as instruments in a lot of hospitals. They should not be.
A resharpened or fatigued pin can slip under load, and slipping is how a controlled fixation becomes an uncontrolled one. Most infection-control protocols have moved towards single-use pins for the same reason. Order them as a routine consumable line and keep stock, rather than sourcing them urgently when someone notices the tips are dull.
Before the clamp goes on
A short mental checklist helps. Confirm the patient is not in a higher-risk group. Check the planned pin sites against the surgical approach and against any previous craniotomy. Confirm the rocker arm is aligned before applying force. Confirm the adaptor lock is fully engaged before the drapes go on, because tightening it afterwards is awkward and often done badly.
And follow the instructions supplied with your specific unit. Different systems specify different values, and the surgeon assessment of the individual patient sits above any general figure — including the ones in this article.
For hospitals buying new, this is worth raising at enquiry stage rather than after delivery. Manufacturers who build neuro attachments in-house — Ventek India, for instance, which is CDSCO registered and ISO 13485 certified with CE and USFDA recognition — can tell you exactly how their tightening mechanism works and which pin sets ship with the kit.
None of this is complicated. It just needs to be deliberate, every single time.
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