thumb duplication - congenital hand differences - Boston Children's Hospital 

childrenshospit...
The skilled experts in our Orthopedics and Sports Medicine Department's Hand and Orthopedic Upper Extremity Program and our Plastic Surgery Department's Hand and Microsurgery Reconstructive Program have treated thousands of babies and children with finger and hand problems, from simple to complex. We can provide your child with expert diagnosis, treatment and care-as well as the benefits of some of the most advanced clinical and scientific research in the world.
Thumb duplication is a form of polydactyly (an extra digit in the hand or foot) in which your child's hand (usually just one side) has more than one thumb.
The extra thumb can occur at the joint of the outermost bone (distal phalanx). The closer to the hand that the extra thumb occurs, the more complex the congenital difference is-such as bent or angular deformities, stiffness, limited range of motion and underdevelopment.