What are congenital upper limb differences?

A congenital upper limb difference is a variation in how a baby’s hand or arm has formed. You may also hear it called a congenital anomaly. Congenital means the baby has it at birth. This can be a challenge as a child grows and learns to interact with the world with their hands. The amount of difference (anomaly) varies. It may be a minor variation, such as unequal fingers. Or it may be a severe malformation, such as total lack of a bone.

Talk with a hand surgeon early about your child born with an upper limb difference. They may advise surgery for your child. Or they may advise prosthetic devices to help your child with limb function.

What are the kinds of congenital upper limb differences?

Congenital upper limb differences are grouped into 3 types. The types are malformations, deformations, and dysplasias. Examples include:

Malformations

A malformation is a difference or variation that occurred early in development when the limb was forming.

There are different kinds of malformations. They include:

Radial longitudinal deficiency. This involves all of the tissues on the thumb side (radial side) of the forearm and hand. The thumb-related forearm bone (radius) may be shortened bone or absent. The thumb may be small or not present at all.

Ulnar longitudinal deficiency. This is less common than a radial longitudinal deficiency. The bone in the forearm on the side of the little finger (ulnar bone) may be small or absent. The little finger or fingers nearby may be missing.

Polydactyly. This means more than 5 fingers on one hand. It’s one of the most common types of congenital upper limb differences. It often runs in families but it may not affect function.

Symbrachydactyly. This is when the hand has small or missing fingers.

Syndactyly. This is when 2 or more fingers are fused together. It often runs in families. The fusion can be partial with a bit of a web between fingers. Or it can be complete with the fingers fully fused together. There are 2 types of syndactyly:

Deformations

A deformation is a difference or variation that occurred after the limb formed. The typical shape and structures developed, but they were altered by some other internal or external force.

One example is constriction ring sequence . This is when a band of tissue within the uterus forms around tissue on the upper limb of a fetus. This can affect blood flow and normal growth. Why this happens is not known.

Dysplasias

A dysplasia is a variation in the shape or function of some cells within the limb. As with deformations, the typical shape and structures of the limb developed, but action by cells in the limb changed how the limb looks or works, or both.

One example is macrodactyly. This is an abnormally large finger. It’s caused by the overgrowth of the entire finger or thumb. It’s a rare condition. Surgery to treat this is complicated. New treatments may slow or stop the overgrowth process. However, the outcomes may be less than desirable. If the large finger or thumb is not functional, surgery to remove it (amputation) may be advised.