We present 3 cases of thumb polydactyly treated with a 2-stage “on-top plasty” technique. For all the 3 cases, the ulnar thumbs floated in the first web with a skin pedicle, and the radial thumbs presented hypoplasia of different degree. We designed a 2-stage “on-top plasty” technique. The first operation included transplantation of the ulnar floating thumb and construction of skin tube containing the neurovascular bundle. When followed up after the first operation, there was no vascular compromise, and all union was achieved. At the time of the second operation, the skin tube was opened up, the neurovascular bundle was transposed to the reconstructed thumb, and the first web plasty was performed. At the final follow-up, 3 cases showed acceptable results both cosmetically and functionally.

Ulnar polydactyly, a common congenital hand anomaly, exhibits significant phenotypic variability. Existing classification systems have limitations, particularly in categorizing rare variants. This study introduces a new classification system for ulnar polydactyly that addresses these limitations. We retrospectively reviewed the medical records of 35 patients with ulnar polydactyly treated at our institution between 2010 and 2022. Data collected included patient demographics, clinical presentation, radiographic findings, family history, associated anomalies, and surgical procedures. Based on detailed morphological and radiographic assessments, we developed a novel classification system comprising five main types (0–4) and associated subtypes. The 35 patients (23 males, 12 females) had a mean age of 3.2 years. Thirty patients had bilateral involvement, with 16 exhibiting symmetry. In total, 65 hands were affected, and one hand was excluded because the patient underwent surgery in another hospital. Type 0 was the most common (38 cases), followed by Type 4 (19 cases), Type 3 (4 cases), and Type 1 (3 cases). Our classification system effectively categorized all cases, including rare variants such as Type 1b (duplicated distal phalanx) and Type 4d (duplication originating from the deformed fourth metacarpal), which are not adequately addressed by previous classifications. Existing classification systems for ulnar polydactyly omit two key variants: Type 1b (duplicated distal phalanx) and Type 4d (duplication from the deformed fourth metacarpal). Our system specifically incorporates these types, providing a more comprehensive framework to guide diagnosis and improve surgical planning for these rare conditions. Retrospectively registered.

Background: Progressive osseous heteroplasia (POH) is an ultrarare disorder characterized by heterotopic ossification that progresses from the skin and subcutaneous tissues into deeper connective tissues. Most affected individuals harbor heterozygous inactivating variants in GNAS , whereas postzygotic mosaic variants have rarely been described. Evidence to guide surgical management remains limited. Methods: We retrospectively characterized two children with clinically diagnosed POH who underwent genetic testing and surgical treatment. Whole-exome sequencing was performed on peripheral blood and, when available, resected tissue, followed by PCR-Sanger sequencing and T-vector cloning. Case 1 underwent clinical and radiographic follow-up for 5 years; follow-up for Case 2 was limited to family-provided radiographs obtained at 2 years. Results: Case 1 harbored a possible postzygotic mosaic GNAS variant, NM_000516.7:c.-1_2del, with variant allele frequencies of 14.7% in peripheral blood and 40.56% in bone lesion tissue. The predominantly localized wrist lesion was macroscopically excised. A small radiographic recurrence appeared by the second postoperative year but progressed slowly thereafter; active wrist flexion was 5–10 ° at 5 years. Case 2 harbored NM_000516.7:c.565_568del (p. (Asp189MetfsTer14)), detected as a heterozygous variant in peripheral blood. The lesion diffusely involved neurovascular structures, tendon sheaths, the joint capsule, and adjacent bones, precluding complete excision. Family-provided radiographs at 2 years showed an extent of ossification broadly similar to that before surgery; no in-person clinical assessment was available. Conclusion: These cases provide additional clinical, molecular, and longitudinal information on POH and illustrate the importance of lesion distribution and resectability when interpreting surgical outcomes. The available postoperative findings cannot establish a causal relationship between variant status and prognosis because the patients differed in baseline disease extent, completeness of excision, follow-up duration, and outcome ascertainment. A possible association between mosaic burden and lesion distribution remains a hypothesis that requires evaluation in larger cohorts.