Names Matter: Radial Polydactyly vs Duplicated thumb

There are a number of terms for describing the patient with two thumbs including, ‘duplicated thumb’, ‘extra thumb’, ‘radial polydactyly’, and ‘split thumb’.  While the particular term may not seem to matter, it does have important implications. ‘Radial polydactyly’ is a medical term describing the location and anomaly- it is not controversial.  ‘Split thumb’ may be the best lay term as it accurately describes that neither thumb is full sized.   The terms ‘duplicated thumb’ and ‘extra thumb’ imply that each thumb is normal but there are simply two thumbs.   These terms are, therefore, inaccurate.

In reality, the thumbs are almost small.  But, there is widespread belief, as stated by my previous partner, Paul Manske, that a small thumb after reconstruction is almost always satisfactory both in appearance and function.  Others, including Tada, Ogino, and Baek have agreed.

I believe the terminology matters for two reasons.  First, the family needs to understand that after surgery, the reconstructed thumb will not be the same size as the contralateral thumb.  When viewed in isolation (i.e., not comparison to the normal thumb), the smaller thumb size may not be apparent.  But when directly compared to the opposite thumb (obviously, not something most people typically do), the size difference may be noticed.

Radial polydactyly.  Notice the size difference between the normal thumb and each of the extra thumbs on the other side.

The second implication of thumb size is for the surgeon and his/ her choice of reconstruction technique.  Most of the time, the outer thumb is removed and the inner thumb is stabilized and reconstructed.  However, there are techniques to combine the two thumbs- the Bilhaut technique and Dr Baek’s modification of this Technique.

The bottom line is that there are several factors affecting the appearance of the thumb after treatment for ‘radial polydactyly’.  In our research that the most commonly cited reason for dissatisfaction after surgery was a crooked thumb, not a thumb that was too small.

Crooked thumb after radial polydactyly reconstruction.

This reinforces the importance of surgical strategy as it will affect thumb alignment after surgery.  Importantly, a second surgery may be required to address joint deviation in children with radial polydactyly but often not until the child is much older (7-8 years of age)- this was recently confirmed in another study.

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