Ulnar Nerve Surgery: The Jumper Cable

My knees will be done. Now the nerve.

On July 13, 2026 I saw Dr. Alfred Yoon at UC Davis. The diagnosis is ulnar neuropathy of the left upper extremity. The surgical case request reads: TRANSFER, NERVE, UPPER EXTREMITY, RELEASE, CUBITAL TUNNEL.

That is two operations in one sitting. A cubital tunnel release at the elbow, to take the pressure off the ulnar nerve where it is being crushed. And a nerve transfer down near the wrist, where a healthy working nerve gets spliced into the failing one.

Dr. Yoon called it a jumper cable. He is exactly right, and the analogy is worth taking seriously, because it explains everything about why this operation exists and why it has to happen soon rather than eventually.

The ulnar nerve is the one that runs through the groove on the inside of your elbow. Hitting it is what people call the funny bone. It supplies sensation to the little finger and half the ring finger, and it drives almost every small muscle inside the hand. It is the nerve of grip and of pinch. It is the nerve you use to hold a winch handle, a chef’s knife, a tiller, and a control stick.

Mine is not working properly. This page is about the fix.

The Jumper Cable

The dead battery

The ulnar nerve is a long cable. It leaves the neck, runs the length of the arm, squeezes through a narrow tunnel of bone and ligament at the inside of the elbow called the cubital tunnel, and continues down to the hand.

When that tunnel compresses the nerve for long enough, the fibers downstream of the pinch degrade. Signal stops arriving at the hand. The small muscles inside the hand, the ones that spread the fingers and pinch and grip, stop getting told what to do.

Muscle that receives no signal does not simply wait patiently. It wastes. And past a certain point, it does not come back.

The cable

Running down my forearm, more or less parallel to the failing ulnar nerve, is a perfectly healthy motor nerve called the anterior interosseous nerve. Its final job in life is to run one small muscle near the wrist, the pronator quadratus, which helps rotate the forearm palm-down.

That job is redundant. A bigger muscle up near the elbow, the pronator teres, does the same thing. So the anterior interosseous nerve is a live, powered, expendable cable sitting right next to a dead one.

Dr. Yoon cuts it at the far end and splices it into the side of the ulnar nerve’s motor fibers, a few centimeters above the wrist. Live donor. Failing recipient. That is the jumper cable, and unlike a nerve graft, this one is actually carrying current.

Why there are two incisions

Incision one, at the elbow. This is the cubital tunnel release. The roof of the tunnel is opened and the ulnar nerve is freed. This stops the ongoing damage. It does not repair what is already gone.

Incision two, in the forearm above the wrist. This is the transfer. The anterior interosseous nerve is found, cut, and coapted into the ulnar motor fascicle. This is where the current gets restored.

The formal name for the technique is a supercharged end-to-side anterior interosseous to ulnar motor nerve transfer. In the literature it is abbreviated SETS. Surgeons also call it a babysitter procedure, and the next section explains why that name is the most honest one of the three.

The Race

Distance divided by rate, against a clock

Nerves regrow. Dr. Yoon puts the rate at about 2 millimeters per day. The published range for human peripheral nerve is roughly 1 to 3 millimeters per day, so 2 sits in the middle of it. Call it slow.

Here is the problem that the transfer exists to solve. If you only release the cubital tunnel, the nerve fibers have to regrow from the elbow all the way down to the muscles inside the hand. That is a long way. At 2 millimeters a day it takes months.

Meanwhile the hand muscles are starving for signal, and they have a shelf life. Denervated muscle degrades over roughly twelve to eighteen months and then the connection points are gone permanently. In advanced cases, the nerve loses that race. The wire arrives at a load that has already burned out.

The jumper cable moves the starting line. Instead of setting off from the elbow, the fibers set off from a splice a few centimeters above the wrist. Same speed. Far less distance. They get there in time. Run the numbers yourself below.

Two lane race calculator

Elbow to hand muscles, mm

Splice to hand muscles, mm

Growth rate, mm per day

Lane 1: release only

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Lane 2: jumper cable

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Distances are my own estimates until Dr. Yoon gives me real numbers. There is also a lag of a few weeks after surgery before the fibers begin advancing at all, which this calculator does not model. This is arithmetic, not a prognosis.

Why they call it a babysitter

The original theory was that the transferred nerve keeps the hand muscles alive, feeding them just enough signal to stay viable, until the real ulnar fibers finally complete the long crawl down from the elbow. A babysitter minding the house until the parent gets home.

More recent work suggests the babysitter may simply move in. There is evidence that the lasting reinnervation comes from the donor nerve itself rather than from the recovering ulnar nerve. Either way, the muscle keeps working, which is the point.

What I trade away

Nothing in surgery is free. Cutting the anterior interosseous nerve costs me the pronator quadratus, one of the two muscles that rotate my forearm palm-down.

The larger pronator teres up at the elbow does the same job and is untouched. The reported functional cost is close to nothing. That is precisely why this donor was chosen. It is the cheapest live cable in the arm.

Dashboard

Ulnar Surgery Countdown

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Estimated last week of September. Not yet scheduled.

Right Knee Countdown

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Tuesday August 25. This one comes first, and that is deliberate.

Why the knee goes first

After a total knee replacement you spend weeks putting your body weight through your arms into a walker. You cannot do that with a freshly operated elbow and a nerve splice that must not be loaded. So the right knee goes on August 25, and the ulnar surgery waits until the last week of September, by which time the walker is behind me. The sequence is not an accident and it is not negotiable.

Completed

✅ Left total knee replacement, June 2
✅ July 13 — Consultation with Dr. Alfred Yoon, UCDH Point West Surgery
✅ July 13 — Diagnosis: ulnar neuropathy, left upper extremity
✅ July 13 — Surgical case requested: nerve transfer plus cubital tunnel release
✅ July 13 — Pre-operative instructions reviewed with Joel Gontang, RN
✅ July 13 — Kenalog injection administered in office

Upcoming

⚪ August 14, 11:45 AM — Pre-op with Dr. Zachary Lum, 48X Total Joint Clinic
⚪ August 25 — Right total knee replacement
⚪ Last week of September — Ulnar nerve surgery, date to be confirmed

Medication Holds;

Do not take these medications, per doctor's detailed orders

🔴 Aspirin
🔴GLP-1, delays gastric emptying, aspiration risk under anesthesia.
⚠ The pre-op team calls two business days out to notify the time of day the surgery will be performed. The more complicated ones, such as this one, are generally scheduled toward the end of the day.

Immobilization Plan

🧵 Elbow sleeve — duration to be confirmed
🧵 Cast or splint, type to be confirmed — duration to be confirmed
⚠ A fresh nerve splice must not be put under tension. That is what the immobilization is protecting.
◯ Get the protocol and the durations in writing and update this block.

Open Questions

❓ Confirm the technique: supercharged end-to-side, anterior interosseous to ulnar motor?
❓ Is a transposition of the ulnar nerve being done, or decompression in place?
❓ Distance from the splice to the first target muscle, in millimeters?
❓ Expected time to first sign of reinnervation, and how is it measured?
❓ Exactly what am I giving up by sacrificing the pronator quadratus?

What the Ulnar Nerve Does

The nerve of grip and precision

The ulnar nerve carries sensation from the little finger and half the ring finger. It also drives most of the intrinsic muscles of the hand, the small ones that live inside the palm and between the fingers.

Those muscles are not about power. They are about control. Spreading the fingers. Pinching. Holding a grip steady while the wrist moves. When they go, the hand still closes, but it closes stupidly.

Advanced ulnar failure shows up as numbness in those two fingers, weak pinch, a hollow between the thumb and index finger where muscle used to be, and in bad cases a clawed posture of the ring and little finger.

I would like to keep using my hands. I have plans that involve knives, fishing rods, and eventually a tiller again.

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EMG Study

Vibe Updates

Monday July 13, 2026

Consultation with Dr. Yoon

Two incisions. One at the elbow to release the tunnel, one above the wrist to splice in a live donor nerve. He called it a jumper cable. I went home and read the literature and he is right.

Surgery date is still TBD, expected the last week of September. It has to wait until the right knee is done and I am off the walker, because a walker means putting my weight through my arms, and you do not do that to a fresh nerve repair.

Current vibe: two knees and a nerve in one calendar year. Everybody line up.

Sources

I am an engineer, not a physician. Nothing here is medical advice. These are the papers I read to understand my own operation.

Barbour J, et al. First description of anterior interosseous to ulnar motor fascicle supercharged end-to-side transfer, 2012.
Davidge KM, Yee A, Moore AM, Mackinnon SE. The supercharge end-to-side anterior interosseous to ulnar motor nerve transfer for restoring intrinsic function: clinical experience. Plast Reconstr Surg. 2015;136(3):344e-352e.
Dengler J, et al. Supercharge end-to-side anterior interosseous to ulnar motor nerve transfer restores intrinsic function in cubital tunnel syndrome. Plast Reconstr Surg. 2020;146(4):808-818.
Xie Q, Shao X, Song X, et al. Ulnar nerve decompression and transposition with versus without supercharged end-to-side motor nerve transfer for advanced cubital tunnel syndrome: a randomized comparison study. J Neurosurg. 2022;136(3):845-855.
Dunn JC, et al. Supercharge end-to-side nerve transfer: systematic review. Hand (N Y). 2021;16(2):151-156.
Exploring outcomes and mediating factors following supercharged end-to-side anterior interosseous nerve to ulnar nerve transfer: a scoping review with expert insight. J Hand Surg Glob Online. 2024.