Thumb Duplication (Pre-axial Polydactyly) - Children's Hospital Boston

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My Child Has:

Thumb Duplication (Pre-axial Polydactyly)

Programs that treat this condition

Hand and Upper Extremity Program

Hand Clinic

What is thumb duplication?

Thumb duplication

Also referred to as pre-axial polydactyly, radial polydactyly, or supernumerary thumbs, the term thumb duplication refers to a congenital condition of the upper extremity characterized by the presence of two thumbs on one hand. The thumbs may be separate or appear fused. (See Figure)

It is important to recognize that the term - thumb duplication is somewhat of a misnomer. Rather than having two normal thumbs, patients with thumb duplication typically have thumbs that are smaller and less developed than normal. Furthermore, the muscles, tendons, ligaments, blood vessels and nerves are often divided between each of the abnormal thumbs. For this reason, many believe that the term split thumb is more appropriate. For the purpose of this brief discussion, we will refer to this condition as pre-axial polydactyly.

What causes pre-axial polydactyly?

The exact cause of pre-axial polydactyly is unknown. Most cases occur sporadically during fetal development, without any defined inheritance pattern or known genetic association. In some instances, there may be a hereditary predisposition, particularly in the presence of a triphalangeal thumb, (i.e., a thumb with three bones instead of two).

How common is pre-axial polydactyly?

It is estimated that pre-axial polydactyly occurs in 1 out of every 1,000 live births. In general, males are more commonly affected than females. Usually the changes affect only one hand. Pre-axial polydactyly tends to occur more frequently in Caucasians, Asians, and Native Americans.

How is pre-axial polydactyly diagnosed?

Pre-axial polydactyly is diagnosed by physicians after a thorough medical history and careful physical examination. X-rays are used to confirm the diagnosis and to identify the pattern of bone involvement.

How is pre-axial polydactyly treated?

Surgery is necessary to create a single, functioning thumb. Typically this is performed around one year of age, before the development of pinch and fine motor function. As mentioned above, simply removing one of the two thumbs will not suffice, as each of the split thumbs has elements that need to be combined to recreate the best possible thumb.

As a result, surgical treatment usually entails removing the bony elements of the smaller thumb and reconstructing the remaining skin, tendons, ligaments, joints, and fingernails to form a new thumb. Even in the best of situations, the resulting thumb may smaller than the child's other, normal thumb. Furthermore, given the possibility of recurrent deformity in a small percentage of patients, additional operations may be needed later in life.



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