Andrea Fabregas, BS
Gonzalo Del Rio, BS
Ana Ortiz, PhD
Sofia Jimenez, PhD

Department of Anatomy and Cell Biology, Universidad Central del Caribe, Bayamón, Puerto Rico

Introduction

Anatomical variation in musculoskeletal conditions are frequent and have major clinical implications. Polydactyly is a congenital malformation that presents with an extra digit in the hand, usually caused by improper differentiation of the hand plate along the anterior-posterior axis. Polydactyly is categorized as central, postaxial (ulnar), or preaxial (radial), with preaxial cases occurring in about 0.8–1.4 per 1000 live births. It often presents as an isolated abnormality (most frequent) or as part of a syndrome.

Methods

During a cadaveric dissection at Universidad Central del Caribe, a cadaver presented with two anatomically distinct thumbs on the right hand. A detailed anatomic evaluation documented variations in bones, muscles, tendons, and neurovascular structures. The polydactyly was classified according to the Wassel system and relevant structures were compared with established anatomical variations.

Results

The cadaver exhibited a duplicated thumb at the metacarpophalangeal joint, classified as Wassel Type VI polydactyly. Notable findings included previously unreported anomalies in both the flexor and extensor pollicis muscles. A webbing connection between the duplicated thumbs was observed, along with structural adjustments in the ligaments and joint surfaces.

Discussion

Thumb duplication, also called preaxial polydactyly, is a rare congenital defect often presenting with musculoskeletal variations. The independent function of the duplicated thumbs, facilitated by dual innervation and blood supply, highlights the complex nature of this case. These findings have critical clinical relevance for congenital hand surgery, as understanding the management and treatment for such variations is essential.

Keywords

Polydactyly; preaxial thumb duplication; Wassel classification; musculoskeletal variation; congenital hand anomalies

IRB Approval Number

2025-16