The median nerve runs through a tight tunnel at the wrist, walled by bone below and a thick ligament above, sharing the space with nine tendons. The tunnel has no give, so anything that swells the contents raises the pressure against the nerve. Resting pressure is near zero; a symptomatic wrist runs ten times that, enough that bending the wrist pinches off the nerve's blood supply ¹. At first the numbness comes only at night. Left alone, the insulation breaks down, then the nerve fibres themselves start to die. Early damage reverses fully once the pressure comes off. Late damage does not.

It hits three fingers, not five. Thumb, index, middle, and the thumb-side of the ring finger are median territory; a numb little finger is a different nerve at the elbow. Women get it about three times as often as men, mostly between forty and sixty, and the risk climbs with pregnancy, obesity ², diabetes, or an underactive thyroid. The confirming test is a nerve conduction study: electrical pulses timed down the nerve across the wrist, which also rules out a pinched nerve in the neck masquerading as the same thing ³.

The order is splint, then injection, then surgery — and the further you have to go, the better the result tends to be.

First night in the splint, most people sleep through: the wrist stays straight, the pressure stays flat, and the 3 AM wake-up does not come. A steroid injection clears the numbness for weeks to a few months, then it creeps back. Surgical release divides the ligament over the tunnel in ten to fifteen minutes under local anaesthesia; by two months, eight or nine in ten people with milder disease report full or near-full resolution ^{5 6}. A year out, the condition is over for the vast majority. The exceptions are the people who waited until the nerve was severely damaged; they keep some numbness and weakness for good ⁷.