There is a simple test you can do right now. Touch your thumb to your little finger and bend your wrist up toward you. One or two tendons will stand up in the middle of your wrist. The one closest to your thumb is the flexor carpi radialis, which everyone has. The next one over, toward the little finger side, is the palmaris longus. If you see two cords, you have one. If you see only the one nearest the thumb, you may not — and it matters far less than you would think.
What does the palmaris longus actually do?
Nothing. That is not an oversimplification. The palmaris longus is a vestigial tendon that contributes minimally to wrist flexion, and removing it costs you no grip strength, no wrist strength, and no function you will ever notice.
This is exactly why surgeons have used it as donor tissue for more than a century. In the polio era it was harvested routinely for tendon transfers to restore hand function in paralyzed patients — a tendon that did nothing where it was, put to work somewhere it was desperately needed. That is the same logic behind using it to rebuild your UCL.
How I harvest it, and why the technique matters
I take the tendon through three small stab incisions spaced up the forearm, and I do not use a tendon stripper.
The reason is anatomy. At the wrist, the palmaris longus lies immediately superficial to the median nerve — the nerve that carries sensation to most of your hand and powers your thumb. Down there the two structures are separated only by a thin layer of fascia. A nerve and a tendon can look similar enough to be confused: the nerve is whiter, softer and rounder and carries small vessels on its surface, while a tendon is more yellow, firmer and flattened. Those differences are real, but they are easy to miss through a single small opening.
Higher in the forearm the anatomy is entirely different. The median nerve runs deep to the flexor digitorum superficialis muscle while the palmaris longus lies on top of it, so at that level the two structures are not adjacent at all. Higher still, you can see muscle attaching to the tendon at the musculotendinous junction. That is the definitive confirmation, because a nerve has no muscle attached to it.
Why this matters: a documented complication
There is a rare but devastating complication in which the median nerve is harvested by mistake instead of the palmaris longus. Nineteen such cases were collected from members of the American Society for Surgery of the Hand over a thirty-year period.
The single most common operation during which it happened was ulnar collateral ligament reconstruction of the elbow — seven of the nineteen cases. This operation, more than any other.
Only seven of the nineteen errors were recognized during surgery. In the other twelve the nerve was used as the graft: passed through drill holes to recreate a ligament in seven cases, rolled up and sutured as a spacer in three, and used to reconstruct a tendon in two. The cause of the patient's numbness went unrecognized for three to four weeks in two patients, for months in several others, and for one year, three years and ten years in one patient each.
The method of harvest was documented in thirteen of those cases. A tendon stripper was used in ten of them.
A tendon stripper is a ring-shaped instrument advanced up the forearm from a single incision near the wrist. It strips the tendon free through tissue the surgeon cannot see. If the wrong structure has been loaded into it, nothing about the maneuver itself will reveal the error.
What the published analyses recommend
The authors of that study concluded that the surgeon should identify the tendon proximally before cutting it distally, and that confirming muscle is attached to the structure being harvested guarantees it is a tendon and not a nerve.
A second paper reviewing safe harvesting technique arrives at the same place. Its published checklist includes assessing the flattened shape of a tendon against the tubular shape of a nerve, checking for the absence of the small surface vessels a nerve carries, and adding incisions proximally — as many as are needed — until the palmaris longus is unequivocally identified.
Three incisions spaced up the forearm are how I build that confirmation into every case, rather than reserving it for cases where something has already started to look wrong.
One honest caveat
More incisions are not automatically safer. In three of the documented cases separate small incisions were used and the error still happened, and the study's authors noted that small incisions with limited visibility can themselves contribute, because they prevent the surgeon from comparing one structure against another.
The protection is not the number of openings. It is confirming the structure proximally, where the anatomy separates the nerve from the tendon and where the muscle attachment settles the question, before anything is divided.
What if I don't have one on my injured side?
The palmaris is absent in roughly 10 to 15 percent of people in most series, and reported rates vary widely by ethnic background, from about 2 percent to more than 25 percent.
Here is the useful part: absence on one side does not predict absence on the other. When the palmaris is missing from one forearm, the reported probability that it is also missing from the opposite forearm is about 28 percent. So if you do not have one on your throwing side, the odds are roughly three in four that you have one on the other side — which is the next place I look.
Taking the graft from your opposite arm costs that arm nothing, exactly as it would on the throwing side. The graft performs identically.
Some players ask me to take it from the other arm anyway
Over the years I have operated on ballplayers who were superstitious about it and asked me to harvest from the non-throwing arm even though they had a perfectly good palmaris on the surgical side.
I am happy to accommodate that. There is no functional difference, no difference in the quality of the reconstruction, and no reason to argue with an athlete about something that makes them more comfortable going into surgery. If it matters to you, tell me and we will do it that way.
What if I don't have one in either forearm?
Then I use the gracilis tendon from the hamstring of your landing leg. It is a longer and often thicker graft, and like the palmaris it can be removed without meaningful loss of function.
Don't worry about diagnosing yourself
The self-test is useful but not definitive. The tendon can be hidden in a thicker forearm, and not seeing it does not always mean it is absent. It is also worth knowing that finding it beforehand is not by itself a safeguard — in that series of nineteen cases, four of the patients had the presence or absence of the palmaris documented before surgery and the inadvertent harvest happened anyway.
I check for it in the office with you awake and participating, and I mark it on your forearm before the day of surgery. But the real protection happens in the operating room, not in the exam room.
The bottom line
Touch your thumb to your little finger and flex your wrist. The second tendon toward the little finger side is the palmaris longus. It does nothing, which is why it makes an ideal graft. If you do not have one on the injured side, there is a roughly three in four chance you have one on the other side. If neither forearm has one, I use a hamstring graft from your landing leg. In every one of those scenarios the reconstruction is the same — and in every one of them the tendon comes out through three incisions, under direct vision, confirmed proximally before anything is cut.
References
- Leslie BM, Osterman AL, Wolfe SW. Inadvertent harvest of the median nerve instead of the palmaris longus tendon. J Bone Joint Surg Am. 2017;99(14):1173-1182. doi:10.2106/JBJS.16.01218
- Choo J, Wilhelmi BJ, Kasdan ML. Iatrogenic injury to the median nerve during palmaris longus harvest: an overview of safe harvesting techniques. Hand (N Y). 2017;12(1):NP6-NP9. doi:10.1177/1558944716648313
- Thompson NW, Mockford BJ, Cran GW. Absence of the palmaris longus muscle: a population study. Ulster Med J. 2001;70(1):22-24.
