On-top plasty for atypical Wassel type VI thumb duplication: Timing and key points of surgery

Abstract Background: Thumb duplication is one of the most common congenital hand deformities, while atypical Wassel type VI thumb duplication is rare and challenging. This study aims to evaluate the clinical efficacy of on-top plasty for atypical Wassel type VI thumb duplication. Methods: The clinical data of 5 children with atypical Wassel type VI thumb duplication treated by on-top plasty from May 2018 to April 2021 were studied retrospectively. There were 4 males and 1 female with an average age of 28.6(11~47) months. During the surgery, the distal portion of the ulnar thumb was transposed onto the top of the radial thumb, accompanied by tendon transfer from the radial thumb to the ulnar thumb. The patients were followed up postoperatively for the assessment of thumb’s appearance and function by the modified Tada scoring. Results: All patients were followed up for an average of 29(16~51) months, and acquired good healing. No digit ischemic necrosis or bone nonunion occurred in all patients. The appearance of reconstructed thumbs was excellent, and the function was good and sufficient for patients to carry out activities of daily living. According to the modified Tada scoring, 4 thumbs were good, and 1 thumb was fair. Conclusions: The on-top plasty is a reliable method for atypical Wassel type VI thumb duplication. The good surgical timing is 1~3 years. The appropriate osteotomy, transposing of digit and transferring of tendons are key points of on-top plasty.