The soft fold of skin and muscle between your thumb and index finger has a proper name, used mostly by hand doctors and therapists. It also has an old everyday word and a name in acupuncture. Far from being spare skin, this small triangle is what lets the thumb swing wide enough to grip and pinch.
The Names for the Thumb Web
Hand surgeons and therapists call it the first web space, sometimes the thumb web space or thumb-index web. It is the first of the four webs of skin between the fingers, counting from the thumb. It is usually described as a triangle between the bones of the thumb and index finger, starting just past the thumb’s base joint at the wrist.1PubMed Central. Definition and measurement of functional first web space: A scoping review
The old everyday word is purlicue, sometimes spelled pirlicue. It was probably built within English by joining words together, and was first recorded in 1808 in a Scottish dictionary.2Oxford English Dictionary. purlicue, n. It is a real dictionary word but rare today, found mostly in word lists, crosswords or Scots dialect writing rather than in any medical setting.
Which name to use depends on who you’re talking to. With a doctor or physical therapist, “first web space” or “thumb web” will be understood. On an injury form, “web between thumb and index finger” works fine. Most clinicians won’t recognize purlicue.
The numbering in “first web space” starts at the thumb side, so the second, third and fourth webs lie between the fingers themselves. Of the four, the first is much the deepest and widest, which is why surgeons talk about it most.
A few nearby areas get confused with the web. The thenar eminence is the padded ball at the base of the thumb on the palm. The anatomical snuffbox is the hollow on the back of the wrist at the thumb’s base, beyond the web.
What Is Inside the Web Space
Two muscles fill the fold. The adductor pollicis, a two-part muscle, pulls the thumb toward the index finger.3American Massage Therapy Association. Muscles and Tendons of the Thumb The first dorsal interosseous lies between the thumb and index bones, mainly moves the index finger, and helps pull the thumb in.4American Massage Therapy Association. Muscles and Tendons of the Thumb The two lie in different layers: the first dorsal interosseous sits nearer the back of the hand, while the adductor pollicis lies deeper, on the palm side of the web.
The bulge you feel when you squeeze thumb and finger together is mostly these muscles tightening. Pinch the thumb against the side of the index and the mound rises on the back of the web.
Together the muscles round out the fold, so a web with wasted muscle looks hollowed rather than rounded. A noticeably flatter web compared with the other hand can be a sign that these muscles have weakened or shrunk, which is worth showing a clinician.
Arteries reach the web from both the palm side and the back side in about half of hands.5The Journal of Hand Surgery: British & European Volume. Arterial anatomy of the thumb A small branch of the radial artery, about 1.4 mm wide, feeds skin over the thumb base in every hand.6PubMed. Vascular and neural anatomy of the thenar area of the hand: its surgical applications That good supply helps cuts there heal, and surgeons value it when they need skin that survives being moved to a new position. The same richness means a deep cut in the web can bleed heavily and needs firm pressure and prompt care.
Feeling on the palm side of the thumb and index finger usually comes from the median nerve.7PubMed. Patterns of median nerve sensory innervation to the thumb and index finger: an anatomic study In about 7 in 10 hands a single nerve branch enters the web and then splits to supply the facing sides of thumb and index.8PubMed. Patterns of median nerve sensory innervation to the thumb and index finger: an anatomic study Skin on the back near the thumb base is supplied mainly by a branch of the radial nerve.9PubMed. Vascular and neural anatomy of the thenar area of the hand: its surgical applications
This also makes numbness informative. Tingling on the palm side of thumb and index often involves the median nerve, as in carpal tunnel syndrome. Numbness on the back of the web often involves the radial nerve, sometimes from tight watch straps or a wrist injury. When you see a doctor, describe which side is numb.
What the Web Space Does for Your Hand
The thumb accounts for about 40 to 50 percent of the hand’s function.10PubMed Central. Definition and measurement of functional first web space: A scoping review The web space is what lets the thumb make both the wide grasp around a cylinder and the narrow pinch.11PubMed Central. Definition and measurement of functional first web space: A scoping review It is also needed to bring the thumb across the palm to meet the other fingers, called opposition.12PubMed Central. First Web Space Reconstruction in Acquired Defects: A Literature-Based Review and Surgical Experience
The wide grasp is what you do around a jar or can: the web stretches open, and the thumb wraps one side while the fingers wrap the other. The pinch is the narrow version, where thumb and index fingertips meet and the web is only moderately open. Each needs a different web shape, so a web that opens well but cannot close smoothly, or the reverse, still causes trouble.
In opposition the thumb rotates as it crosses the palm, so its pad faces the fingertip pad rather than simply moving sideways. That rotation lets you touch the thumb to each fingertip in turn, as in picking up a coin, and the web has to give enough slack on the palm side for it to happen.
Doctors check three thumb motions: moving out flat in the plane of the hand, lifting up at right angles to the palm, and reaching across toward the little finger.13PubMed Central. Predictors of successful outcomes in first web space contracture release A web that is stiff or short can limit all three.
You can try a quick check at home. Lay the hand flat and swing the thumb out to the side. Lift the thumb straight up off the palm. Touch the thumb tip to the base of the little finger. Compare both hands; a clear difference is worth mentioning to a doctor.
Why Humans Have Such a Capable Thumb Web
More muscles go to the thumb in humans than in almost all other primates.14PubMed. Evolution and homologies of primate and modern human hand and forearm muscles, with notes on thumb movements and tool use Humans pair powerful thumb bending with a fingertip-to-fingertip pinch, unlike gibbons, whose thumb is set apart by a deep cleft.15PubMed. Evolution and homologies of primate and modern human hand and forearm muscles, with notes on thumb movements and tool use In gibbons the cleft suits swinging through trees, where the hand works like a hook, but it gives up the precise pinch a more open human web allows. This extra muscle gives the human thumb finer control over how hard and in what direction it presses, as in writing or threading a needle, not only more raw strength.
Our finger and thumb lengths changed only slightly from the common ancestor with chimpanzees, likely before regular stone toolmaking.16PubMed Central. The evolution of human and ape hand proportions Precise pinching depends on both joint flexibility and digit proportions together, not a long thumb alone.17PubMed Central. Estimating thumb-index finger precision grip and manipulation potential in extant and fossil primates
The LI4 Pressure Point
In acupuncture the point in the middle of the web’s muscle is called LI4 (Hegu). The labels don’t mean quite the same thing. The first web space is the whole fold of skin and muscle, while LI4 is a single point inside its muscle, a spot you could cover with a fingertip. Deep needling of LI4 raised pain thresholds at several body sites in healthy people.18PubMed. A comparison of effects on regional pressure pain threshold produced by deep needling of LI4 and LI11, individually and in combination Needling near the thumb also dampened the brain’s response to touch signals from the thumb in one study.19PubMed Central. What is the analgesic range of acupuncture stimulus for treating acute pain?
These are small, short-term studies, so LI4 may help a little rather than reliably treat pain. The needling was done in healthy volunteers, not in people with ongoing pain, and pressing with a thumb is not the same as a practitioner placing a needle deeply.
To find the point, press the thumb and index finger together. The muscle forms a mound on the back of the web, and the point sits near the highest part of it. Then relax the hand, because the muscle softens and the spot is easier to reach once it is no longer tensed. The point is found by feel, so a spot slightly off from where a chart shows is normal.
Use the opposite thumb, press firmly toward the index finger bone, and hold for a minute or two before switching hands. Expect a deep, dull ache or a sense of fullness; sharp or electric pain is the signal to ease off.
Traditional practice advises avoiding strong LI4 pressure during pregnancy. Don’t rely on it for severe or new pain that needs a diagnosis, and skip pressing over cuts, bruises or a swollen web.
Problems That Can Affect the Web Space
After serious hand injuries, burns or surgery, the web can scar and shrink, called a contracture.20PubMed. Prevention of Thumb Web Space Contracture With Multiplanar External Fixation This can be disabling because the thumb can no longer open wide.21PubMed. Prevention of Thumb Web Space Contracture With Multiplanar External Fixation Scar tissue shrinks as it matures, so the web can tighten gradually. You may first notice that the thumb won’t swing as far out as it used to, or that the fold looks like a taut band.
Treatment often begins with stretching and splinting, with surgery considered when the tightening of the web does not respond. Surgery releases the scar and adds skin or rearranges flaps so the thumb can open again. Surgeons may hold the thumb spread with a frame of pins and rods while tissue heals.22PubMed. Prevention of Thumb Web Space Contracture With Multiplanar External Fixation Success after release surgery depends on how well each thumb motion recovers.23PubMed Central. Predictors of successful outcomes in first web space contracture release Hand therapy afterward is a large part of the result, because regained range must be kept by using it.
Some children are born with a narrow thumb-index web. Surgeons widen it with skin flaps or Z-shaped skin cuts that lengthen the fold.24PubMed Central. Congenital Thumb-Index Web Space Deficiency Some need a repeat procedure if the web tightens again.25PubMed Central. Congenital Thumb-Index Web Space Deficiency
After an injury, follow splinting advice that keeps the thumb spread and do the hand therapist’s stretches regularly. Early gentle movement usually protects range better than long rest.
See a doctor if you can’t spread the thumb as far as on the other hand, or if skin in the web feels tight or pulls when gripping. Numbness or tingling in the thumb and index that lingers also deserves a visit, as does a deep cut in the web, which can reach nerves or arteries.