Syndactyly is a condition wherein two or more digits are fused together. It occurs normally in some mammals, such as the

siamang The siamang (, ; ''Symphalangus syndactylus'') is an arboreal, black-furred gibbon native to the forests of Indonesia, Malaysia, and Thailand. The largest of the gibbons, the siamang can be twice the size of other gibbons, reaching in height, a ...

and

diprotodontia Diprotodontia (, from Greek "two forward teeth") is the largest extant order of marsupials, with about 155 species, including the kangaroos, wallabies, possums, koala, wombats, and many others. Extinct diprotodonts include the hippopotamus-sized ...

, but is an unusual condition in humans. The term is from Greek σύν, ''syn'' 'together' and δάκτυλος, ''daktulos'' 'finger'.

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 Kangaroos are four marsupials from the family Macropodidae (macropods, meaning "large foot"). In common use the term is used to describe the largest species from this family, the red kangaroo, as well as the antilopine kangaroo, eastern ...

exhibits complex syndactyly. Syndactyly can be complete or incomplete. * In complete syndactyly, the skin is joined all the way to the tip of the involved digits. * In incomplete syndactyly, the skin is only joined part of the distance to the tip of the involved digits. Complex syndactyly occurs as part of a syndrome (such as

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 (or pharyngeal) arch, the ...

) and typically involves more digits than simple syndactyly. Fenestrated syndactyly, also known as acrosyndactyly or terminal syndactyly, means the skin is joined for most of the digit but in a proximal area there are gaps in the syndactyly with normal skin. This type of syndactyly is found in

amniotic band syndrome Constriction ring syndrome (CRS) is a congenital disorder with unknown cause. Because of the unknown cause there are many different, and sometimes incorrect names. It is a malformation due to intrauterine bands or rings that give deep grooves in, ...

. 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 6 weeks of gestation, apoptosis takes place due to a protein named sonic hedgehog, also known as SHH, which 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 associated with these types and their common

phenotypical In genetics, the phenotype () is the set of observable characteristics or traits of an organism. The term covers the organism's morphology or physical form and structure, its developmental processes, its biochemical and physiological prop ...

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 In human anatomy, the metacarpal bones or metacarpus form the intermediate part of the skeletal hand located between the phalanges of the fingers and the carpal bones of the wrist, which forms the connection to the forearm. The metacarpal bones ar ...

and

metatarsals The metatarsal bones, or metatarsus, 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 me ...

may also be fused. Syndactyly type1 hands

Management

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 six 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 two 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 bone joining of the fingers).

History

The earliest appreciation of syndactyly as a birth anomaly or burn-trauma can be traced back to the Andalusian Muslim surgeon

Al-Zahrawi Abū al-Qāsim Khalaf ibn al-'Abbās al-Zahrāwī al-Ansari ( ar, أبو القاسم خلف بن العباس الزهراوي;‎ 936–1013), popularly known as al-Zahrawi (), Latinised as Albucasis (from Arabic ''Abū al-Qāsim''), was ...

(d. 1013 CE), known in the West as Abulcasis. The French barber surgeon Ambroise Paré also described syndactyly in the sixteenth century.

References

External links

{{Congenital malformations and deformations of musculoskeletal system Congenital disorders of musculoskeletal system