The ball of the thumb
Thenar muscles
Three short muscles that form the fleshy pad at the base of your thumb.
What it does
The thenar muscles form the mound at the base of the thumb. They swing the thumb across the palm, rotate it and bend it, giving the movement called opposition that lets the thumb tip meet each fingertip.
Surprising fact
Opposition is so important that losing it is one of the biggest disabilities a hand injury can cause, and surgeons have devised many tendon transfers to restore it.
Why it matters
In carpal tunnel syndrome the median nerve is squeezed at the wrist, and in long-standing cases the thenar muscles waste away, flattening the ball of the thumb.
Nearby
Read more
Sources
Drafted with AI help; awaiting a human fact-check against these sources.
Open in the 3D atlas · Suggest a correction · Not medical advice.
3D models: Z-Anatomy & BodyParts3D (CC BY-SA 4.0 / 2.1 JP). Card text CC BY 4.0.