Syndactyly is a condition wherein two or more digits are fused together. It occurs normally in some mammal

Mammal

Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...

s, such as the siamang

Siamang

The siamang is a tailless, arboreal, black-furred gibbon native to the forests of Malaysia, Thailand, and Sumatra. The largest of the lesser apes, the siamang can be twice the size of other gibbons, reaching 1 m in height, and weighing up to 14 kg...

 and kangaroo

Kangaroo

A kangaroo is a marsupial from the family Macropodidae . In common use the term is used to describe the largest species from this family, especially those of the genus Macropus, Red Kangaroo, Antilopine Kangaroo, Eastern Grey Kangaroo and Western Grey Kangaroo. Kangaroos are endemic to the country...

, but is an unusual condition in humans.

Classification

Syndactyly can be simple or complex.

• In simple syndactyly, adjacent fingers or toes are joined by soft tissue.
• In complex syndactyly, the bones of adjacent digits are fused. The kangaroo
  Kangaroo
  A kangaroo is a marsupial from the family Macropodidae . In common use the term is used to describe the largest species from this family, especially those of the genus Macropus, Red Kangaroo, Antilopine Kangaroo, Eastern Grey Kangaroo and Western Grey Kangaroo. Kangaroos are endemic to the country...
  
   exhibits complex syndactyly.

Syndactyly can be complete or incomplete.

• In complete syndactyly, the skin is joined all the way to the tip of the finger
• In incomplete syndactyly, the skin is only joined part of the distance to the fingertip.

Complex syndactyly occurs as part of a syndrome (such as Apert syndrome

Apert syndrome

Apert syndrome is a form of acrocephalosyndactyly, a congenital disorder characterized by malformations of the skull, face, hands and feet. It is classified as a branchial arch syndrome, affecting the first branchial arch, the precursor of the maxilla and mandible...

) and typically involves more digits and with complex syndactyly.

Fenestrated syndactyly means the skin is joined for most of the digit but in a proximal area there is gap in the syndactyly with normal skin. This type of syndactyly is found in amniotic band syndrome

Amniotic band syndrome

Amniotic band syndrome is a congenital disorder caused by entrapment of fetal parts in fibrous amniotic bands while in utero.-Epidemiology:Amniotic banding affects approximately 1 in 1,200 live births...

.

Simple syndactyly can be full or partial, and is present at birth (congenital). In early human fetal development, webbing (syndactyly) of the toes and fingers is normal. At about 16 weeks of gestation, apoptosis

Apoptosis

Apoptosis is the process of programmed cell death that may occur in multicellular organisms. Biochemical events lead to characteristic cell changes and death. These changes include blebbing, cell shrinkage, nuclear fragmentation, chromatin condensation, and chromosomal DNA fragmentation...

 takes place and an enzyme dissolves the tissue between the fingers and toes, and the webbing disappears. In some fetuses, this process does not occur completely between all fingers or toes and some residual webbing remains.

Genetics

Five types of syndactyly have been identified in humans. The corresponding loci

Locus (genetics)

In the fields of genetics and genetic computation, a locus is the specific location of a gene or DNA sequence on a chromosome. A variant of the DNA sequence at a given locus is called an allele. The ordered list of loci known for a particular genome is called a genetic map...

 associated with these types and their common phenotypical

Phenotype

A phenotype is an organism's observable characteristics or traits: such as its morphology, development, biochemical or physiological properties, behavior, and products of behavior...

 expression are as follows:

• type I: 2q34-q36; webbing occurs between middle and ring fingers and/or second and third toes.
• type II: 2q31; also involves long and ring fingers, but has a sixth finger merged in between.
• type III: 6q21-q23; small finger is merged into the ring finger.
• type IV: 7q36; involves all fingers and/or toes
• type V: 2q31-q32; similar to type I, but the metacarpals and metatarsals
  Metatarsus
  The metatarsus or metatarsal bones are a group of five long bones in the foot located between the tarsal bones of the hind- and mid-foot and the phalanges of the toes. Lacking individual names, the metatarsal bones are numbered from the medial side : the first, second, third, fourth, and fifth...
  
  may also be fused.

Treatment

Timing

Syndactyly of the border digits (thumb/ index finger or ring/ small fingers) is treated at early age to prevent the larger digit from curving towards the smaller digit with growth. Typically, syndactyly of these digits is treated at 6 months of age. The treatment of syndactyly of the other digits is elective and is more commonly performed when the digits have grown, at 18– 24 months of age.

Techniques

Because the circumference of the conjoined fingers is smaller than the circumference of the 2 separated fingers, there is not enough skin to cover both digits once they are separated at the time of surgery. Therefore, the surgeon must bring new skin into the area at the time of surgery. This is most commonly done with a skin graft (from groin or anterior elbow). Skin can also be used from the back of the hand by mobilizing it (called a "graftless" syndactyly correction), which requires planning over a period of months prior to surgery.

Complications

The most common problem with syndactyly correction is creeping of the skin towards the fingertip over time. This is likely due to tension at the site of the repair between the digits. Additional surgery may be required to correct this. One critique of using skin grafts is that the grafts darken in the years after surgery and become more noticeable. Also, if the skin grafts are harvested from the groin area, the skin may grow hair. Finally, the fingers may deviate after surgery. This is most commonly seen in complex syndactyly (when there has been a bony joining of the fingers).