Tied down. Drunk. Unconscious from the injury or consequences of the injury. Drugged.
The surgeon and his crew would render you immobile (or at least as immobile as possible) for the surgery they were performing, but obviously this is limited in where they can work on.
Tying an arm or a leg down is easy as these things go, so surgery to work on a damaged arm or leg is fairly easy. Stopping someone’s torso from moving around – or parts of it moving around – is much harder.
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