Thumb posterior rotation deformity: a neglected deformity in children with thumb polydactyly.

PURPOSE: To investigate the incidence and risk factors of thumb posterior rotation deformity in children with thumb polydactyly. METHODS: A retrospective analysis was conducted on the clinical data of 479 patients (521 thumbs, mean age 13.1 ± 12.7 months) with thumb polydactyly. Clinical data including gender, age, and affected side were collected. Clinical appearance photographs and x-ray images of all patients were obtained. Thumb posterior rotation deformity was determined on clinical appearance photographs. The ulnar deviation angle of the thumb was measured on anteroposterior thumb radiographs. RESULTS: According to the Wassel classification, 13 thumbs (2.5%) were Type I, 55 thumbs (10.6%) Type II, 92 thumbs (17.7%) Type III, 186 thumbs (35.7%) Type IV, 138 thumbs (26.5%) Type V, 34 thumbs (6.5%) Type VI, and 3 thumbs (0.6%) Type VII. According to the Wu classification, 222 thumbs (42.6%) were type A, 27 thumbs (5.2%) were type B, 121 thumbs (23.2%) were type C, and 151 thumbs (29%) were type D. A total of 35 hands (6.7%) presented with varying degrees of thumb posterior rotation deformity, with a mean rotational angle of 14.1°±9.0° (range, 5°-30°). Wassel classification and Wu classification were correlated with the incidence of thumb posterior rotation deformity. Patients with thumb posterior rotation deformity had a significantly larger ulnar deviation angle of the thumb (19.3°±17.5°) than those without (11.4°±15.7°). Logistic regression analysis demonstrated that both the level and the type of the bifurcation of the duplicated thumb and ulnar deviation angle of the thumb were independent risk factors for the occurrence of thumb posterior rotation deformity (P < 0.05). CONCLUSIONS: Thumb posterior rotation deformity is a common malformation in pediatric thumb polydactyly. The incidence of thumb posterior rotation deformity is significantly increased in patients with Wassel types IV, V, and VI thumb polydactyly, and thumb ulnar deviation also significantly elevates the risk of thumb posterior rotation deformity.