A congenital hand deformity (or congenital hand difference) is a hand that is abnormal at birth.
During fetal development in the mother’s womb, the upper limb is formed between four and eight weeks of pregnancy. Many steps are needed to form a normal arm and hand. If any of these steps fail, then a congenital hand difference can result. Some of these differences have genetic causes, but many of these differences occur without a known cause.
Some differences include missing parts (failure of formation), webbed or fused parts of the hand (failures of separation), extra parts in the hand (duplication), or parts that are larger (macrodactyly) or smaller (brachydactyly) than normal.
Syndactyly (Webbed fingers)
Before the child is born, the hand bud must separate into five fingers. Syndactyly is the failure of fingers to complete this normal process of separation during fetal development.
A complete syndactyly refers to the deformity in which the web between fingers extends to the tips of the fingers while in an incomplete syndactyly, the web between fingers longer than normal, but does not extend all the way to tips. A simple syndactyly refers to webbed fingers in which the skin and underlying tissues are involved while in a complex syndactyly, the bones of adjacent fingers are joined together too. Acrosyndactyly refers to deformity in which only the finger tips of adjacent fingers are joined together
The incidence is about 1 in every 2000 children. Webbed fingers can occur in any adjacent fingers or finger-thumb but the most common syndactyly involves the middle and ring fingers.
Syndactyly may just be an isolated incidence or it may occur as part of a syndrome such as Apert’s syndrome or Poland’s syndrome
Treatment is by surgical separation and is performed at any time after the age of approximately 6 months.
Polydactyly refers to extra fingers or toes (duplication). It ranges from an extra piece of soft tissue (skin) that has no bone inside to a complete duplication of a finger or toe.
The most common duplication is the thumb duplication (split thumb). It occurs in 1 in every 3000 births.
Consultation with a hand surgeon is required to determine the best possible treatment for thumb duplication. It can be left alone because majority of these hands are functional. Excision of the extra thumb requires additional reconstruction to stabilize the thumb.
Radial club hand (Radial Longitudinal Deficiency or Radial Ray Anomaly)
This deformity is the underdevelopment or total loss of the radius bone in the forearm. This condition often affects the development of the thumb resulting in hypoplastic thumb (small thumb) or a completely absent thumb.
The absent of radius (one of the two bones in the forearm) results in an unstable dislocated wrist joint. In some cases, there may also be problems with bending of the elbow.
The incidence is about 1 in 100,000 children. It is associated with several syndromes such as thrombocytopenia absent radius syndrome (TAR), Holt Oram Syndrome, VACTERL, and Fanconi’s Anemia.
Consultation with a hand surgeon is required to determine the best treatment options. The aim of surgery is to improve the function and perhaps the appearance of the hand. For children who can bend their elbow, centralization surgery, a procedure that stabilizes the wrist on the ulna bone, may be an option. Preparation for this surgery involves stretching and splinting of the wrist joint to straighten the wrist. Surgery may also be needed for hypoplastic thumbs. In absent thumb, a new thumb can be created using the index finger of the same hand (pollicization).
Amniotic Band Syndrome
Amniotic band syndrome or constriction ring syndrome is a condition that may cause amputation, webbing of tip of fingers or toes (acrosyndactyly) and constriction rings around the skin of the arms or legs.
The incidence is about 1 in 15,000 children.
It is postulated that this deformity is caused by a defect in the amnion (i.e. sac around the baby during pregnancy) which becomes loose and wrap around limbs or fingers/toes of the developing baby during pregnancy. It is not thought to be inherited.
Acrosyndactyly (fused tip of fingers) can be released surgically early to allow natural growth of individual fingers. Some tight rings that cause swelling of the limbs can be surgically removed.