The nerve is not squeezed so much as stuck. Fluid can free it.

HYDRODISSECTION FOR CARPAL TUNNEL

The median nerve is not compressed by the ligament so much as stuck to everything around it. Hydrodissection separates it with fluid rather than a blade — and the evidence for it is better than most people offering surgery will mention.

What the procedure actually does

Under ultrasound, a needle is placed alongside the median nerve inside the carpal tunnel and fluid is injected to physically separate the nerve from the tissue adhering to it — the flexor retinaculum above, the tendons and subsynovial connective tissue around it.

That subsynovial tissue is the part people are not told about. In chronic carpal tunnel it thickens and becomes fibrotic, and the nerve loses its ability to glide as the wrist and fingers move. A nerve that cannot glide gets tethered and stretched with every movement, which is a mechanical insult separate from being squeezed.

Hydrodissection restores that gliding plane. It is a mechanical intervention delivered through a needle, which is why the word “release” is accurate rather than marketing.

What is injected, and why the choice matters

Either 5% dextrose in water or a corticosteroid preparation, sometimes with local anesthetic. The choice is not cosmetic.

Dextrose is used where repeated treatment may be needed, where the patient is diabetic, or where steroid is undesirable — and its mechanism appears to be more than volume alone, with a described effect on sensitized nerve endings. Head-to-head comparison against corticosteroid has been done, and the picture is that dextrose performs comparably with a longer runway for repetition.

Steroid works faster in some hands and carries the usual constraints on repetition. We will tell you which we are using and why, and volume is chosen deliberately rather than by habit — injectate volume has been studied specifically and it changes the result.

What the evidence supports

Systematic review of hydrodissection in carpal tunnel syndrome supports meaningful improvement in symptoms and function, with more recent synthesis reaching the same conclusion. It is not an experimental technique and it is not a fringe one; it is a well-described ultrasound-guided intervention with a growing trial base.

What the evidence does not support is calling it a permanent cure. Benefit is measured in months in many series, and some people need it repeated. Anybody promising a single injection that ends the problem forever is overselling, and the honest version is that this is a genuine treatment with a defined duration rather than a substitute for every operation.

Who it suits

• Mild to moderate carpal tunnel on electrodiagnostic testing — the group with most to gain.
• Anyone wanting to avoid or defer surgery, including people who cannot take the recovery time off work.
• People in whom a steroid injection helped and wore off, which tells us the diagnosis is right.
• Diabetic patients, where repeated steroid is unattractive and dextrose is a reasonable alternative.
• People with a second lesion in the neck, where treating the wrist non-surgically first is a way of finding out how much of the problem it actually was.

Who it does not

Severe carpal tunnel with established denervation — thenar wasting, badly abnormal conduction studies — needs decompression rather than separation, and delaying that costs recovery that does not come back. What we do first is confirm that is genuinely what you have: severity graded on testing, the neck and elbow cleared as contributors, and the diagnosis refined before anybody discusses an operation. A surgical opinion is far more useful when it arrives with that work already done.

It is also not the answer where the hand symptoms are not actually coming from the wrist. That is the entire subject of carpal tunnel or the neck, and it is why we test before we treat.

What the appointment involves

• Ultrasound first, to confirm the nerve is enlarged where it should be and to see the anatomy. This is not a landmark procedure.
• Local anesthetic at the skin, then a fine needle placed alongside the nerve under continuous imaging.
• Fluid injected in stages while watching the nerve separate on screen. You will see it too if you want to.
• Ten to fifteen minutes. No sedation, no incision, no stitches, no splint, and you drive yourself home.
• Back to normal use the same day, with a limit on heavy gripping for forty-eight hours.

Compare that with an open release: an incision, two to six weeks of restricted use, and scar tenderness in the palm that can persist for months. The recovery difference is the main practical argument for trying this first in the right patient.

What people ask about hydrodissection

Is this the same as a cortisone shot?

No. A steroid injection puts medication near the nerve. Hydrodissection uses fluid volume under ultrasound to physically separate the nerve from what it is stuck to. Steroid can be the fluid used, but the mechanism being relied on is mechanical. What EMG and nerve conduction actually measure.

How long does it last?

Months rather than permanently in most series, and it can be repeated. That is the honest answer, and it is why established nerve damage is a reason to move toward decompression rather than to keep injecting. Double crush syndrome.

Will it get me out of surgery?

Sometimes, and the honest framing is that it buys a genuine trial without burning the surgical option. Nothing about having this makes a later release harder. Carpal tunnel, or the neck?.

Does it hurt?

A sting at the skin and a sensation of pressure and fullness as the fluid goes in. Over in about ten minutes, and you use the hand normally the same day. How the two are separated. How this compares with the other needle procedures.

Related reading

• Carpal tunnel, or the neck?
• EMG and nerve conduction studies
• Double crush syndrome
• Cervical radiculopathy
• When your hands are the problem
• What happens at the first visit