Dactylosynostosis is a rare congenital condition in which two or more fingers (or toes) are abnormally fused together due to the bones being joined at birth. This fusion occurs not just at the skin or soft tissue level but at the bone level, making it different from syndactyly (which may involve just soft tissue).

What Happens in Dactylosynostosis?

In a typical hand or foot, each finger or toe develops separately during fetal development. In dactylosynostosis, however, the bones of adjacent digits don’t fully separate. This leads to a fusion of the bones, which can affect finger or toe movement and appearance.

Types of Dactylosynostosis

There are different variations, depending on which bones are fused:

• Metacarpal or metatarsal synostosis: Fusion of the bones in the palm (hand) or sole (foot)
• Phalangeal synostosis: Fusion of finger or toe bones
• It may involve just two digits or multiple digits in more complex cases.

This condition may occur as part of a genetic syndrome or on its own (isolated case).

Causes

Dactylosynostosis is usually congenital, meaning it’s present at birth. The causes may include:

• Genetic mutations – Some cases are inherited in families.
• Sporadic changes – In some children, the condition appears without a family history.
• Associated syndromes – It may be part of conditions like Apert syndrome, Pfeiffer syndrome, or other skeletal disorders.

Symptoms

The main symptoms of dactylosynostosis include:

• Visibly fused fingers or toes
• Shortened digits
• Limited movement or stiffness in the affected fingers or toes
• Abnormal hand or foot shape
• In some cases, there may be no pain, but function can be affected depending on severity

Diagnosis

Diagnosis usually involves:

• Physical examination – The fused digits are often obvious at birth
• X-rays – To confirm bone-level fusion and identify which bones are joined
• Genetic testing – If a syndrome is suspected

Early diagnosis helps in planning treatment to preserve hand or foot function.

Treatment

Treatment depends on the severity and whether the condition affects daily activities.

• Surgery is the main treatment for moderate to severe cases. It may involve:
  • Separating fused bones
  • Bone reshaping
  • Skin grafting or tendon adjustment if necessary
• Physical therapy may follow surgery to restore mobility and strength

In milder cases, if function is not affected, treatment may not be necessary.

Prognosis

With proper treatment, many children with dactylosynostosis can achieve good functional use of their hands or feet. Early intervention typically leads to better outcomes.