Syndactyly (sin-DAK-tuh-lee) (SD), originates from the Greek words Syn=together and Dactylos=digit, meaning it is a condition that causes webbing and joined fingers or and toes. It is a condition mostly shown in babies and newborns.

It is known to be one of the most common conditions affecting the limbs, affecting almost 3-10  in every 10,000 births worldwide, commonly in males than females, and affecting more Caucasians than Blacks and Asians.^1,2

Types of syndactyly

A few different types of SD can be classified and they will depend on which fingers and or toes are affected, and how much of their fingers and or toes are fused together:³

1. Simple Syndactyly - fusion of the fingers or toes by only the skin
   • Complete - the whole length of the finger or toe is fused by skin, base to nail bed
   • Incomplete - a fusion of the finger or toes only in certain parts
2. Complex Syndactyly - a fusion of bones, nerves and blood vessels, is rare than simple SD
3. Polysyndactyly - a combination of fusion of fingers and toes by webbing and also extra growth of fingers and toes
4. Complicated - abnormal development of extra bones, tendons and ligaments in the fingers or toes

Causes and risk factors

SD can be caused by the changes in the newborn’s genes when they are in gestation. These games are the building blocks which parents pass down to children and they contain information and instructions for the growth and the function of every cell of the body. Anything that affects and changes the gene when the foetus is in the developing stage may change their body in different ways. Sometimes these are not noticeable and other times they can cause disorders such as SD and other more complicated defects. It is known that genetic factors contribute to SD, but also environmental factors have been associated.³

A study from 2012 discusses that environmental factors can cause SD from maternal smoking, low nutrition, low socioeconomic status, and even having an increase in meat and eggs in the diet during pregnancy.⁴

Syndromes associated with syndactyly³

• Apert syndrome
• Down syndrome
• Poland syndrome

Familial inheritance

SD is a dominant trait, meaning that if one parent carries the genetic code in their DNA, then their baby is more likely to have the condition. Depending on the type of SD, the gene causing it may be different too, such as HOX, SHH and WNT genes.³

Clinical presentation⁵

Associated anomalies

Syndactyly can be easily found or it can also be found to be associated with other syndromes, such as Poland syndrome, and Apert syndrome, which are known to cause:²

• Cleft hands
• Craniofacial abnormalities
• Ring restrictions

Diagnosis and evaluation

Prenatal diagnosis

SD is commonly diagnosed at birth or during prenatal screening, using an ultrasound at around 8 weeks, because the limbs would form around this time. Therefore, the doctor would be able to check if there are any abnormalities with the baby.^3,6

Postnatal diagnosis

If there are any abnormalities with the baby’s hands or toes after birth, then the doctor may use X-rays to assess the bone structure of the fingers and or toes. They may also evaluate the arms, chest, head, face and feet to rule out any other syndromes.⁶

Differential diagnosis

SD is easy to diagnose upon physical examination, but there are other hand deformities and conditions that should be observed when evaluating the child:⁶

• Apert syndrome
• Poland syndrome
• Constriction band syndrome
• Carpenter syndrome
• Ectrodactyly (cleft hand)
• Oculodentodigital dysplasia 
• Synpolydactyly

Treatment

Non-surgical treatment

In some cases, children may never have surgery, however only if it affects the toes. Upon evaluation and the diagnosis, the doctor will advise the best option. It is rare for children to not need surgery on their fingers or toes, because if left untreated, it can affect the ability to move the digits and so the movement of the feet or  hands.⁶

Surgical intervention

When surgery is decided by the doctors, then there are a few things to take into consideration:⁷

• Timing of Surgery 

It is usually performed at the young age of 12 months, because it should be performed at an early age to allow for normal growth. Having  surgery at a later age could have further complications, such as scar contracture, that can be avoided at a younger age. If a repeat surgery is needed, then it can be done after 3 months of the initial surgery. 

• Surgical techniques:
  • Flap design - uses various geometrical designs, including triangular, rectangular and lobed shapes. This technique is dependent on the training of the surgeon and it can be easily adjusted to show a more natural anatomical space between fingers.
  • z-Pastly - used for mild simple SD, to lengthen the soft tissue and to increase movement.  
  • ZigZag pattern - Also known as Cronin's technique. The most used technique.

Rehabilitation and postoperative care

After surgery, the patient will have a bulky soft dressing, or a cast depending on the severity of the surgery. The dressing will  also be taken down 2 weeks after the surgery. When the incisions are healed, the patient can start to move the fingers slowly and gently, and also do a scar massage. Hand therapy can be provided by the doctor, to help with the scar massage and to help for movement of the fingers or toes. A follow-up session with the doctor is important in the future to avoid complications such as web creep.⁶

Prognosis and long-term outlook

The prognosis of SD depends on the treatment and how complex the SD is. Complicated and complex syndactyly do have less success and will require a repeat of the surgical procedure. Simple  syndactyly has shown more successful results with a long term outcome. However, studies also show that 10% of patients who undergo surgery will have to do a revision surgery in the future.^3,5

Recurrence and complications

With  any surgery, there are always complications, which includes:^2,6

1. Infections - It is rare, but there is always the potential to cause bad implications if not addressed properly and with care.
2. Scar formation - It can be due to the  use of split-thickness skin graft  or having growth in the surrounding bone. 
3. Web creep - This is when there is a defined webspace in the centre of the fingers attachment, which happens as the patient ages.  Proper monitoring is required in regards to web creep. 
4. Devascularisation - It requires a longer recovery time and rarely will require amputation.
5. Nerve injury - can result in complete or partial loss of digital sensation. 

Prevention and genetic counselling

Genetic conditions cannot be prevented, but SD linked to environmental factors that can be avoided, such as stopping alcohol, drugs and tobacco during pregnancy. Since it is a genetic condition,some steps can be taken:^3,6

Preconception genetic counseling

Doctors may advise this  if patients  are planning to have a child in the future, and if they already  know there is SD within the family’s genes . The counsellor would be able to guide in the right direction and also discuss other methods of having a child, such as adoption.

Summary

Syndactyly is  a genetic disorder affecting the hands and or the toes, causing the webbing or having an extra digit in hands and toes. It has been found to affect males more than females, and at younger months of their lives. It is important for the proper treatment and maintenance, because it can cause complications in the future affecting the function of the hands and toes. At present, corrective surgery is the most common treatment available.