Central Ray Synpolydactyly with Bilateral Medial Foot Polydactyly and Hydrocephalus: A Case Report

Summary:

Central ray synpolydactyly is a rare congenital anomaly that presents complex surgical challenges due to the combined presence of digit duplication and fusion. Early recognition and appropriate management are essential to preserve hand function and appearance. This case report describes the successful single-stage surgical management of a 3-year-old girl with right central ray synpolydactyly, a rare congenital hand anomaly combining features of polydactyly and syndactyly. The patient presented with an extra digit on the ulnar side of the middle finger, complete syndactyly with the middle finger, and incomplete syndactyly with the ring finger. Surgical correction involved excision of the extra digit and reconstruction of the third web space using an M-V flap, minimizing the need for skin grafting. Postoperative recovery was uneventful, with no complications, and at the 6-month follow-up, the patient demonstrated a full range of motion, functional independence, and a well-healed scar. This report highlighted the effectiveness of meticulous surgical planning and the M-V flap technique in achieving optimal functional and aesthetic outcomes in central ray synpolydactyly.

Synpolydactyly is a complex congenital hand anomaly that combines features of syndactyly and polydactyly. Polydactyly is a common congenital anomaly of the hands and feet.¹ It can be inherited in an autosomal dominant or recessive pattern and is associated with mutations in the HOXD13 gene.² However, multiple genetic and environmental factors also contribute to its development.³

Polydactyly is classified based on the affected digit: preaxial, postaxial, and central ray duplication.^1,4 Central ray duplications are frequently associated with syndactyly or split-hand deformities.^1,5

Syndactyly results from incomplete separation of digits during embryonic development. It most commonly affects the third and fourth digits. Risk factors include advanced maternal age, smoking, specific dietary factors, and low socioeconomic status.^5,6

Synpolydactyly most often affects the third and fourth digits and may present with additional complexities such as clinodactyly, abnormal tendon and neurovascular anatomy, and synostosis. A thorough evaluation is essential to rule out associated syndromes. Surgical reconstruction often requires multiple stages to achieve optimal function and aesthetics.⁷ We present a case of successful single-stage surgical management of a 3-year-old girl with a rare presentation of right central ray synpolydactyly.

CASE PRESENTATION

A 3-year-old girl presented to our clinic for evaluation of a right-hand deformity. Her medical history included obstructive hydrocephalus and previously corrected bilateral foot polydactyly.

Clinical examination revealed right central ray synpolydactyly, characterized by an extra digit on the ulnar side of the middle finger, with complete syndactyly to the middle finger and incomplete syndactyly with the ring finger. The extra digit was hypoplastic. Both duplicated digits showed good mobility at the proximal and distal interphalangeal joints. The metacarpophalangeal joint of the radial middle digit demonstrated a full range of motion, whereas movement of the extra digit was restricted.

Radiographic evaluation confirmed a diagnosis of right central ray synpolydactyly, and corrective surgery was planned (Fig. 1). Preoperative assessment included genetic testing for potential syndromic associations, which came back normal.

Fig. 1.

Radiographic evaluation of the affected hand showing a single, normally sized metacarpal bone shared by the duplicated middle digits, without any additional joint formation involving the ulnar-sided extra digit. No bony curvature (clinodactyly) is observed.

Surgical Procedure

The procedure aimed to optimize functional and aesthetic outcomes. A dorsal local skin flap incision was made on the extra digit, and the ulnar neurovascular bundle of the middle finger was carefully identified. The 3 phalanges of the extra digit were excised, whereas the skeletal structures of the middle finger remained intact. Intraoperative radiography confirmed complete excision of the extra digit.

The third web space was reconstructed using the M-V flap technique. The dorsal skin of the excised extra digit was repurposed to resurface the ulnar side of the middle finger, providing a natural, shallow web space. This technique was preferred over alternatives, such as the “jumping man” flap, which is typically used to deepen the web space between the thumb and index finger (Fig. 2). The skin was approximated with absorbable sutures (Fig. 3).

Fig. 2.

Intraoperative view following excision of the extra digit.

Fig. 3.

Intraoperative view postclosure.

Postoperative Course

The postoperative recovery was uneventful, and the patient was discharged home. During 6 months of follow-up, no contractures or functional limitations were observed, and the surgical scar healed well (Fig. 4).

Fig. 4.

Follow-up image demonstrating the hand grip function.

Occupational therapy was phase-based, focusing initially on wound care, edema control, and parent education with immobilization. Passive range of motion, scar management, and splinting were introduced between weeks 2 and 4, followed by active-assisted exercises and functional play from weeks 4 to 8.

Informed consent was obtained from the patient’s guardians for all aspects of this report. This study adhered to strict ethical guidelines.

DISCUSSION

Polydactyly and syndactyly are among the most common congenital hand anomalies, with an incidence ranging from 1.6 to 10.7 per 1000 individuals and a male-to-female ratio of approximately 2:1.2. Synpolydactyly is a rarer variant combining both anomalies, typically affecting the central hand, often bilaterally, and more frequently in men.²

Recent studies have identified a HOXD13 gene mutation (c.G917T: p.R306L) that disrupts interaction with phosphorylated Smad5, activating the Smad5/p65/c-Fos/RANK pathway and enhancing bone resorption. This provides insight into the molecular pathogenesis of synpolydactyly.⁸

Limb development is governed by tightly regulated signaling: FGF4, FGF8, and FGF10 drive mesenchymal proliferation and distal limb patterning via WNT3a and p63 signaling, whereas BMP2 modulates FGF activity through apoptosis and cartilage differentiation. Disruptions in these pathways may contribute to congenital anomalies such as polydactyly.⁸

According to the Oberg-Manske-Tonkin classification, synpolydactyly represents a complex failure of hand plate formation. In the Swanson and International Federation of Societies for Surgery of the Hand systems, syndactyly is categorized as type II (failure of differentiation), and polydactyly as type III (duplication), highlighting the embryological complexity of the combined anomaly.⁴

Although central ray duplication is often associated with syndactyly or split-hand deformities, involvement of the middle finger is rare. The coexistence of hand synpolydactyly, bilateral medial foot polydactyly, and hydrocephalus in this case is highly unusual and raises suspicion for a syndromic diagnosis.^1,4,5,9

Among the syndromic associations considered, megalencephaly-polymicrogyria-polydactyly-hydrocephalus syndrome appeared to be the closest match. However, this case was distinguished by the simultaneous presence of foot polydactyly and hand syndactyly, features not typically observed in megalencephaly-polymicrogyria-polydactyly-hydrocephalus, setting it apart from the classical presentation.^5,6,10

Early surgical intervention is recommended to optimize functional outcomes and prevent developmental motor impairments. In this case, surgery at age 3 was chosen to balance technical feasibility and developmental readiness. An M-V flap was used for web space reconstruction, avoiding the need for skin grafting while preserving function and aesthetics.⁷

Potential complications such as web creep, infection, and hypertrophic scarring were minimized through meticulous planning and use of local flaps.⁵ At 6 months, the patient demonstrated a full range of motion, no functional limitations, and a well-healed scar. Favorable outcomes in synpolydactyly repair depend on timely intervention, surgical technique, and structured rehabilitation.

CONCLUSIONS

This case report adds to the limited literature on central ray synpolydactyly. Despite the complexity of the deformity, careful surgical planning and execution, including using an M-V flap for web space reconstruction, resulted in excellent functional and aesthetic outcomes without complications. Although various techniques, such as V-Y advancement and jumping man flaps, have been described, the M-V flap proved a reliable and effective approach in this case.

DISCLOSURE

The authors have no financial interest to declare in relation to the content of this article.