Syndactyly or webbed digits [fingers in the hand or toes in the foot] is a condition wherein two or more digits are fused together. It occurs due to the failure of differentiation in which the fingers fail to separate into individual appendages.
This separation usually occurs during the sixth and eighth weeks of embryologic development.
The condition can affect toes as well as fingers but syndactyly of the hand is much more challenging as hand-and-finger use is more complex than for the foot-and-toe use and if not treated, can significantly impairs finger and hand function.
In hand, the frequency of occurrence is
- Between the middle and ring fingers (57 %)
- Little and ring fingers (27 %)
- Middle and index fingers (14 %)
- Thumb and index fingers (3 %)
Males are affected twice as often as females.
Syndactyly is the most common congenital malformation of the limbs and has an incidence of 1 in 2000-3000 live births. It can occur in isolation but it is also found in many syndromes like Apert syndrome, Poland syndrome, band syndrome and many others.
It is also the most common congenital anomaly of the hand.
About 10-40% of cases are familial.
Types of Syndactyly
There are many different forms of syndactyly and classified on basis of severity of presentation.
Simple syndactyly refers to fingers joined only by soft tissue. This is called incomplete simple syndactyly when the union is partial and does not extend to the fingertips. When the soft tissue union extends to the fingertip, the condition is referred to as complete simple syndactyly.
Third web space between the long finger and the ring finger is the area most commonly involved in this type of syndactyly followed by the fourth, second, and (rarely) first web spaces. Bilateral involvement is found in 50% of patients.
When the fingers are completely joined together by bone or cartilaginous union, it is called complete syndactyly.
It is the most severe form and indicates fingers joined by bony fusion other than a side-to-side fashion such as extra, missing, or duplicated phalanges and abnormally shaped bones. In this type, abnormalities in the musculotendinous and neurovascular structures may also be present.
Once the child presents to the clinician, it is important to determine the type and severity of the syndactyly. In a simple complete or a complex syndactyly involving only the distal phalanx, the underlying tendon and neurovascular structures are usually normal.
However, in complicated syndactyly, neurovascular anomalies like bifurcation or absence in one side may be present.
Radiographs help to identify the severity of bony synostosis and any other bony abnormalities.
A minor incomplete syndactyly is not an indication for surgery but a syndactyly that prevents full range of motion would require a surgical release.
The surgery is not indicated in patients with complex syndactyly where if individual fingers separated would become hypoplastic.
The objective of surgery is to separate the webbed fingers so that they can be spread normally and to improve function and appearance.
Surgery can be done as early as 5 or 6 months of age.
The timing of surgery is important and depends on the fingers involved and the degree of completeness and complexity of the condition. Fingers of unequal length, such as thumb and index fingers or little and ring fingers, should be separated early in life because the longer finger will develop lateral deviation and flexion contracture.
As a rule, thumb-index finger syndactyly should be separated by six months of age, and that involving ring-little finger before one year of age.
It is best to separate the index and middle fingers at about one year of age. The middle and ring fingers are almost even in length and one can wait until the child is two or three years of age.
While awaiting the appropriate age for surgery, parents are instructed to do massage and stretching exercises to widen the skin web between the digits and keep up a range of motion of the interphalangeal joints.
When there are three digits involved, one should stage the operations and separate the webbed fingers at different sessions, preferably at intervals of 3-6 months. This is done to avoid circulatory insult to the finger in the middle.
Surgery aims at dividing the finger, resurfacing the surgical wound with flaps, and full-thickness skin grafts and reconstruction of the web with dorsal fasciocutaneous flap.
Complications of release include recurrence, finger ischemia, contracture, and skin-graft complications.