Radial polydactyly (duplicated thumb) is an uncommon condition in the general population- I have blogged about kids with extra thumbs a number of times. Those posts can be found HERE. Extra thumbs come in a wide variety of patterns, some of which are captured in the Flatt Classification (previously called the Wassel Classification) as shown in the this picture from orthobullets.com.
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| Flatt Classification for radial polydactyly from orthobullets.com |
Yet, this classification does not capture the extra thumbs in all kids with radial polydactyly. Many simply do not fit this pattern. As a result, the Rotterdam (in the Netherlands) group added a more complex classification system which is much more comprehensive. The publication abstract can be found HERE. It includes more specific patterns for triphalangeal thumbs (longer thumbs, more like a finger), triplicate thumbs (three thumbs, rather than the more common 2 thumbs), as well as adjustments for stiffness, deviation, and small size).
This is one example of a triplicate thumb. These are uncommon (even compared to the uncommon radial polydactyly).
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| Triplicate thumb |
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| Triplicate thumb, another view |
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| Final view of triplicate thumb |
And here are a few x- rays which show the complexity. This is a complex arrangement of bones and joints.
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| Triplicate thumb xrays |
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| Additional xrays for triplicate thumb |
The principles for treating the triplicate thumb are to create a stable, well aligned thumb. The thumb’s main role is to serve as a post and if stable and well- aligned, it can do just that. Ideally, we would love to have motion at the joints but motion is not mandatory for a great thumb. So, in reconstructing these three thumbs- the goal is to create the best single thumb. This requires excision of some parts, straightening of some bones, stabilizing joints (with new ligaments), and careful treatment of the skin and soft tissues (cosmetic surgery).
Here are images at about 3 months after surgery for the triplicate thumb. The child is starting to use his new thumb and will, over time, use it more and more. The thumb is stable. It is reasonably straight although not perfect. And he does have some motion. It may be that he will benefit from additional surgery down the road. If so, we try to perform that second surgery before kindergarden. Such surgery is needed in approximately 1/3 typical radial polydactyly patients but in notably more triplicate thumb patients like this one.
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| Top view of thumb after reconstruction for triplicate thumb |
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| Palm view after triplicate thumb reconstruction |
