Congenital hand differences can affect both the shape and function of a child’s hand and arm. They occur in about 20 out of every 10,000 babies born and are more common in boys than girls.

Hand differences are not usually detected before birth. Occasionally, a difference such as extra fingers or missing bones can be seen on a prenatal ultrasound, but this is rare.

Congenital hand differences are often divided into two categories:

• Malformations—in which a certain part of the hand or arm fails to develop normally while the baby is in utero, and
• Deformations—in which the hand and arm begin to develop normally but are prevented from doing so in some way

Malformations occur about 4 to 8 weeks after conception—when the baby’s upper limbs are first developing. Deformations can occur later in pregnancy.

Syndactyly, the most common congenital hand difference, is an abnormal connection of the fingers to one another. In babies born with syndactyly, the fingers are “webbed” or fused together because they did not separate normally during development.

The condition can take a number of forms, including the following:

• Simple syndactyly. In this form, the fingers are joined either by skin or other soft tissue, which may appear webbed. The webbing may be either:
  • Complete—extending from the base of the finger all the way to the tip, or
  • Incomplete—stopping at any point before the tip
• Complex syndactyly. In this form, the bones of the fingers are fused together. This form of syndactyly is more difficult to treat because, in addition to bone, the fingers may also share a nail, nerves, muscles, blood vessels, and tendons.

Syndactyly often runs in families and can occur alone or as part of a medical condition such as Apert syndrome or Poland syndrome.

A baby with an upper limb deficiency may be born with hands or arms that are smaller than normal or are missing. Some of the more common limb deficiencies are described below:

• Radial Deficiency : In a radial deficiency, the radius bone and soft tissues of the forearm fail to develop properly. This causes the affected hand to be bent inward toward the thumb side of the forearm, giving it the appearance of a “club hand.”
  
  In a radial deficiency the hand is turned inward, giving it a club-like appearance.

  Courtesy of Shriners Hospital for Children—Northern California
  
  The forearm may also be shortened and the thumb may be smaller and weaker than normal or missing—a condition known as “thumb hypoplasia.”

  

  Thumb hypoplasia may cause a child’s thumb to be missing or underdeveloped.

  Courtesy of Shriners Hospital for Children—Northern California

  Some types of radial deficiency run in families, while others are related to congenital differences in the heart, kidneys, and blood system. To determine whether a radial deficiency is caused by an underlying medical condition, your doctor may recommend a thorough evaluation by a pediatrician and/or a geneticist.

• Transverse Deficiency

  In a transverse deficiency, all of the elements below a certain level in the patient’s arm are missing. The condition has an appearance similar to that of an amputation and is sometimes known as “congenital amputation.”

  Doctors believe that a transverse deficiency occurs when a vascular problem, such as a blood clot in the limb, causes the affected arm to stop developing. The most common type of transverse deficiency is one in which the elements below the elbow are missing.

  

  A child with a below-elbow deficiency, the most common type of transverse deficiency.
  Reproduced from Song K (ed): Orthopaedic Knowledge Update Pediatrics 4. Rosemont, IL. American Academy of Orthopaedic Surgeons, 2011, p. 149.

Nonsurgical treatment for hand differences often includes one or more of the following:

• Therapeutic recreation. Play, sports, and other activities can help build confidence and improve a child’s emotional well-being.
• Physical therapy. Specific exercises can strengthen the arm and hand and improve motion in the wrist and fingers.
• Occupational therapy. Exercise and training can prevent stiffness in the hand and improve handwriting and other skills necessary for daily activities.
• Assistive or adaptive devices. Using specialized devices can make eating, dressing and other daily activities easier.
• Prosthetics. Artificial devices can be used to replace missing parts or limbs.

Establishing peer contacts for both your child and your family is a very important part of treatment. Meeting other children with hand differences and their families will provide reassurance that you are not alone and can be an invaluable source of information and support.

You can find many support groups and discussion groups online. In addition, some children’s hospitals and other organizations sponsor “Hand Camps” for children with differences. These camps provide a safe and encouraging environment for children to socialize and participate in camp activities with other children who have congenital hand differences.