The Big Thumb

The term ‘superdigit’ is utilized in congenital hand surgery to describe a digit that is larger than we expect. It is often related to the fusion of two digits into one and may be seen in cleft hand and central polysyndactyly among other conditions.  We also see large digits in other conditions such as Macrodactyly.  Occasionally, children may have a large thumb rather than large fingers.  Typically, these are very well tolerated and may not be obvious at a quick look at the thumb (whereas big fingers are almost always immediate noticeable as they are compared to the finger next door).  Additionally, the large thumb is unlikely to cause functional issues and will not block the motion of adjacent fingers.  Two children demonstrate some of the key issues.

The first example is that of a child with only two fingers- a thumb and a small finger.  This likely represents a cleft hand deformity with merging of two digits into the thumb.  This child has great function and motion of the thumb, but there is the concern of rotation- the thumb is more in the plane of the fingers compared to the location of the typical thumb (see previous Posts).  We plan to watch this child and only consider intervention if there is a functional problem.  The extra thumb is noticeable on clinical examination but the x-ray is especially helpful.  Also, compare the size of the thumb to the forearm bones and you can see how it is large.

Large thumb.  Note the size of the thumb compared to the only other digit and to the forearm.

Large thumb on x-ray.  Note the size of the thumb compared to the only other digit and to the forearm.

Another child has one thumb and 4 fingers which seem “normal.”  And the thumb at first glance is well developed also.  But it is a bit larger than expected and the nail is somewhat different.  In addition, the last joint of the thumb (the IP joint, near the nail) does not bend.  X- rays, shown below, tell the tale.  This is really an extra thumb.  However, the family is not interested in treatment as the child functions so well.

Large thumb with nail ridge suggesting the presence of two thumbs.  This child has radial polydactyly.

X- rays showing radial polydactyly as an explanation for the large thumb.

Charles A. Goldfarb, MD
My Bio at Washington University
congenitalhand@wudosis.wustl.edu