A duplicated thumb (preaxial polydactyly) is the presence of an extra thumb on one or both hands. The thumbs can be joined or separate. Learn more about the diagnosis of a duplicated thumb.
Key points
Thumb duplication is more common in individuals who are born male and in children of Asian descent.
Diagnosis of a duplicated thumb involves a physical examination and treatment decisions are made by a paediatric hand surgeon.
In most situations, the extra thumb can be safely removed through surgery. Each thumb duplication is different, and the surgical approach will depend on the structure and function of your child’s thumb.
Introduction
What is a duplicated thumb?
Thumb duplication (preaxial polydactyly)
A duplicated thumb is the presence of an extra thumb attached to the existing thumb on one or both hands. The thumbs can be joined or separate; they may move as a unit or independently from each other. The extra thumb can be well formed or floppy and connected by a thin skin stalk.
The level of thumb duplication varies. For example, the thumb may only be duplicated at the tip, or the entire thumb may be duplicated. Each thumb will have its own blood vessels and nerves. They may also have their own muscles, tendons and ligaments.
When a child has a duplicated thumb, both thumbs are smaller than had there been a single thumb. One of the duplicated thumbs may be much more underdeveloped than the other. Duplicate thumbs may be curved, have extra bones in them, and they may not bend and straighten at the joints.
Causes, Risk Factors, Prevalence
Causes of thumb duplication
The exact cause of thumb duplication is unknown. It is not caused by anything the mother did or did not do while pregnant.
Diagnosis
Diagnosis
A health-care provider can diagnose a duplicated thumb during a physical examination and treatment decisions are made by a paediatric hand surgeon. X-rays may be taken to evaluate the bony connection when there is a broad stalk. These X- rays will help the surgeon plan your child’s surgery.
An occupational therapist may also assess your child to evaluate the function of the duplicated thumb. This examination can provide insight into which thumb can be safely removed, and the way the thumb may function after surgery.
Treatment
Treatment
Surgery may be the recommended treatment for a duplicated thumb, depending on the structure and function of your child’s thumb. Families can choose not to have surgery to remove the extra thumb, if the extra thumb is not causing a problem with function.
Surgery may not be recommended if removing the extra thumb would be harmful to your child or worsen their hand function. However, it is rare that removal of an extra thumb causes functional problems.
