Syndactyly: Symptoms, Types, Causes and Treatment

Syndactyly is a fascinating yet complex congenital condition in which two or more fingers or toes are fused together. It is one of the most common anomalies affecting the hands and feet, and its variations range from simple webbing of the skin to complex bony fusions that can be part of broader syndromes. Understanding syndactyly is crucial not just for clinicians and surgeons, but for families navigating diagnosis, treatment, and the lifelong implications of this condition. In this article, we will explore the symptoms, types, causes, and treatment options for syndactyly, drawing on the latest clinical and genetic research.

Symptoms of Syndactyly

Syndactyly's symptoms can range from subtle to striking, depending on the severity and type. Some individuals may notice only mild webbing, while others experience complete fusion of digits, impacting both function and appearance. Early recognition of symptoms is key to timely intervention and optimal outcomes.

Manifestation	Description	Severity Range	Source(s)
Webbing	Skin joining between digits	Mild to severe	2 4 5
Bony Fusion	Bones fused between digits	Simple to complex	2 4
Digit Disarray	Disorganized finger/toe bones	Seen in syndromic cases	1 2
Functional Loss	Reduced movement/grip	Mild limitation to severe	3 11

Table 1: Key Symptoms

Understanding the Symptoms

Syndactyly presents with visible or palpable fusion of digits. This fusion can involve just the skin (simple syndactyly), or both skin and underlying bone (complex syndactyly) 2 4. In some cases, only a shallow web is present, while in others, the digits are entirely joined, sometimes even sharing nails or bones.

Visible and Functional Manifestations

• Webbing: The most common and recognizable feature is webbing of the skin between two or more fingers or toes. This can range from a slight increase in the normal web space to a complete fusion extending to the tips of the digits 2 4.
• Bony Union: In complex syndactyly, not only the skin but also the bones and sometimes nails are fused, making it difficult or impossible to move the affected digits independently 2 4.
• Digit Disorganization: Some syndromic forms, like Cenani-Lenz syndactyly, are associated with severely disorganized digits, shortening of limbs, and other skeletal anomalies 1.
• Functional Impact: Depending on the extent of fusion, patients may have limited hand or foot movement, affecting grip, dexterity, and walking 3 11. In mild cases, function may be almost normal, but severe cases can be quite disabling.

Associated Features

• Asymmetry: Syndactyly can be unilateral or bilateral, and symmetrical or asymmetrical, even within the same individual 2.
• Associated Anomalies: In syndromic forms, additional symptoms may include facial changes, short stature, or other organ involvement 1.

Types of Syndactyly

The types of syndactyly are as varied as the condition itself. Syndactyly can occur in isolation or as part of over 300 syndromic anomalies, and classification depends on the tissues involved, digits fused, and underlying genetics.

Category	Description	Example/Features	Source(s)
Simple	Fusion of skin only	No bone involvement	2 4 14
Complex	Fusion of skin and bone	Bones and possibly nails fused	2 4
Complete	Fusion extends to finger/toe tip	Full length of digits fused	2 4
Incomplete	Partial fusion, not reaching the tip	Web stops before fingertip	2 4
Syndromic	Occurs as part of syndrome (e.g., CLSS, EDSS)	Multiple malformations	1 7
Non-syndromic	Occurs alone	Limited to digits	2 3 6

Table 2: Syndactyly Types

Classification Details

Simple vs. Complex Syndactyly

• Simple: Only skin is involved; the digits are joined by a soft tissue web 2 4 14.
• Complex: Fusion includes bones, nails, and sometimes joints, making surgical correction more challenging 2 4.

Complete vs. Incomplete

• Complete: The webbing runs the entire length of the digit, sometimes involving the nail fold 2 4.
• Incomplete: The fusion stops short of the fingertip, with some separation visible 2 4.

Syndromic and Non-syndromic Forms

• Non-syndromic: Syndactyly occurs in isolation, typically inherited as an autosomal dominant trait, and is classified by which digits are fused (e.g., type I: third and fourth fingers fused) 2 3 6.
• Syndromic: Syndactyly as part of a broader syndrome, such as Cenani-Lenz syndactyly syndrome (CLSS), ectodermal dysplasia-syndactyly syndrome (EDSS), or as a feature of over 300 congenital syndromes 1 7 2.

Subtypes by Digit Involvement

Historically, syndactyly has been classified into multiple types (I–IX), each defined by specific patterns of digit involvement and inheritance 6. For example:

• Type I: Fusion of third and fourth fingers, second and third toes 6.
• Type II: Third and fourth fingers, often with duplication and involving fourth/fifth toes 6.
• Type IV: Complete syndactyly of all fingers 6.

Clinical Variability

• Phenotype can vary widely even within families, with differences in which digits are fused, degree of involvement, and symmetry 2 6.
• Some forms, such as those seen in CLSS, may include additional limb shortening, digit disorganization, and systemic anomalies 1.

Causes of Syndactyly

The causes of syndactyly lie at the intersection of genetics, embryology, and sometimes environmental factors. Advances in molecular biology have illuminated several pathways and genes, but many mysteries remain.

Factor	Description	Example/Genes/Pathways	Source(s)
Genetic	Inherited mutations, often autosomal dominant	HOXD13, LRP4, TP63, PVRL4, GJA1	1 2 3 7 9 10
Developmental	Disruption during limb formation	WNT-BMP-FGF8 pathway, interdigital cell death	8 10
Syndromic	Part of broader genetic syndromes	CLSS, EDSS, van der Woude syndrome	1 7 8 10
Unknown/Other	Etiology not fully understood	Many cases with unknown genetic basis	2 5 10

Table 3: Causes and Genetics

Genetic Underpinnings

Key Genes and Mutations

• HOXD13: Mutations in this gene are associated with several types of non-syndromic syndactyly, particularly types 1b and 1c 9.
• LRP4: Mutations cause severe forms of Cenani-Lenz syndactyly syndrome (CLSS), leading to complete syndactyly and additional skeletal and organ anomalies 1.
• TP63: Involved in syndromes featuring syndactyly and cleft lip/palate 9.
• PVRL4 (Nectin-4): Causes ectodermal dysplasia-syndactyly syndrome (EDSS) due to impaired cell adhesion during development 7.
• GJA1: Also linked to certain syndactyly types 9.

Patterns of Inheritance

• Most non-syndromic syndactylies are inherited as autosomal dominant traits, but some severe forms are autosomal recessive or X-linked recessive 2 3 6.
• Variable expressivity means that even within the same family, severity and affected digits can differ 2.

Developmental Biology

• Digit Separation: During embryonic development, digits are sculpted by programmed cell death (apoptosis) in the tissue between developing fingers and toes 10.
• Pathway Disruption: Disruption in the WNT-BMP-FGF8 pathway, as well as Notch and other signaling pathways, can prevent normal interdigital cell death, resulting in persistent webbing 8 10.
• Periderm Role: The periderm (a temporary embryonic skin layer) must be non-adhesive to allow proper digit separation; defects in periderm function can also cause syndactyly 8.

Environmental and Unknown Factors

• While genetics play the primary role, some cases of syndactyly have no identifiable genetic mutation, and environmental factors are not well established 2 5 10.

Treatment of Syndactyly

Syndactyly treatment aims to restore function, improve appearance, and prevent complications. Surgery remains the mainstay, but the approach depends on severity, type, and patient needs. Advances in technique and understanding of genetics may shape future therapies.

Approach	Description	Suitability/Outcome	Source(s)
Surgical Release	Separation of fused digits	Main treatment, timing varies	3 11 13 14
Skin Grafting	Covers skin deficit post-separation	Common, may have complications	11 12 13 14
Flap Techniques	Use of local tissue to reconstruct web space	Fewer complications than grafts	12 15
Genetics/Future	Gene-based, molecular therapies in future	Under research, not yet available	3 10

Table 4: Treatment Approaches

Surgical Management

Timing and Indications

• Early Surgery: In most cases, surgical separation is performed between 6 and 18 months of age, before school age to maximize functional development 14. Complex cases or those involving border digits may require earlier intervention 14.
• Assessment: Surgery is indicated when fusion impairs function, restricts growth, or causes significant cosmetic concerns 3 14.

Techniques

• Surgical Release: The fused digits are carefully separated. Reconstruction of the web space (commissure) is technically demanding and critical for function and appearance 14.
• Skin Grafting: Traditionally, a full-thickness skin graft is used to cover the area left after separation, often harvested from the groin or other sites 11 13 14.
  • Complications: Grafts can lead to web creep (recurrent webbing), scarring, contracture, or unwanted hair growth if donor skin comes from hair-bearing areas 11 12 13.
• Flap Techniques: Dorsal metacarpal advancement flaps or extended dorsal interdigital flaps can cover the deficit without skin grafts, reducing complications like scarring and web creep 12 15.
• Complex Cases: Syndactyly with bony fusion or part of syndromic conditions may require multiple surgeries and more extensive reconstruction 14.

Outcomes and Follow-up

• Long-term Results: Most patients have good functional and cosmetic outcomes, though some may need additional procedures for recurrence or contracture 11 13 14.
• Follow-up: Periodic examination is important until skeletal maturity, as late complications can develop 14.

Non-surgical and Future Therapies

• Genetic Counseling: Families benefit from genetic evaluation and counseling, especially in syndromic or familial cases 2 3.
• Gene-based Treatments: Future therapies may aim to correct or modulate the underlying genetic defects, but these are not yet available 3 10.

Conclusion

Syndactyly is a diverse and multifaceted congenital condition that impacts the lives of affected individuals and their families in various ways. From subtle webbing to complex fusions involving bone and multiple organ systems, the manifestations of syndactyly are as unique as the people who have it. Advances in genetics and surgical techniques offer hope for improved outcomes and understanding.

Key Takeaways:

• Syndactyly symptoms range from simple skin webbing to complex bony fusions, sometimes with functional loss or associated anomalies 1 2 3 4.
• The condition is classified by tissue involvement, extent of fusion, and whether it is part of a broader syndrome 2 3 4 6 14.
• Most cases are genetic, involving key developmental pathways and genes such as HOXD13, LRP4, and PVRL4; inheritance patterns can vary 1 2 3 7 9 10.
• Surgical treatment is the mainstay, with skin grafts and flap techniques offering good outcomes; genetic counseling and future gene-based therapies may further improve care 3 11 12 13 14 15.
• Early diagnosis and individualized management are essential to optimize function, appearance, and quality of life.

Understanding syndactyly requires an integration of clinical, genetic, and surgical perspectives—ensuring every patient receives care tailored to their unique presentation and needs.