A small thumb can be on one hand or both but most of the time the hands are not exactly the same (meaning one is worse than the other). There are 4 main parts to the small thumb: size, stability, and muscle, and motion.
1) As the name implies, the small thumb is small. It is short and can be thin.
2) It is also unstable at the MCP joint which is the joint (where motion happens) between the thumb and the hand. The problem with instability at this location is that it affects how you use your hand. An unstable thumb usually prevents good, strong pinch.
3) The muscles of the thumb are called the thenar eminence. These muscles are used to position the thumb to allow best function- things like holding a soda can or pinching. If these muscles are small or absent then the thumb-= the most important of the fingers- can't work correctly. If the thumb is not working correctly, the patient will have less use of the entire hand.
4) Lastly, a small thumb may have limited motion. This can be due to the limited muscles or it can be due to abnormal tendons from the forearm- tendons that can have abnormal connections. The thumb may not bend or straighten well.
The good news about the small thumb is that surgery can be helpful to correct it. Surgery can make it stronger and more stable and more mobile. Surgery can never make the thumb normal but it can make a better thumb. If a thumb is really small, sometimes the thumb may be best treated with pollicization, rather than reconstruction. http://congenitalhand.wustl.edu/2011/10/pollicization-creating-new-thumb.html
If the thumb is reconstructed without pollicization, there are 3 basic steps. 1) Give the thumb more muscle. There are choices for this step but both work well (flexor tendon to ring finger or muscle from pinky side of hand). 2) Make the MCP joint stable 3) Deepen the space between the thumb and index finger, the first web space. This makes the thumb longer and able to grab larger objects.
These pictures are unusual in that they are of an 11 year old with small thumb or hypoplastic thumbs on both sides.
|Small thumbs on both sides. The left hand (the one on the right side of the picture) is worse- smaller and with less muscle.|
|This picture is of the child with small thumbs trying to bring the thumbs up. Neither side does it well.|
|Another view of the small thumbs trying to lift the thumbs.|
|Yet another view of small thumbs, attempting to lift.|
|X-ray of small thumb (the left side) showing a small thumb with unstable joint.|
|Great x-ray of small thumb, unstable. Notice the bend in the thumb.|
|Last picture of small thumbs. Notice the the left thumb (on the right) is smaller or more angulated than the other one.|