Association Between Thumb Hypoplasia, Radial Longitudinal Deficiency, and Radial Polydactyly.

Abstract

The expression of the sonic hedgehog protein has been associated with induction of both radial longitudinal deficiency (RLD) and radial polydactyly in animal studies. We sought to investigate the co-occurrence of thumb hypoplasia/RLD and radial polydactyly in a large registry patient cohort and to investigate the clinical presentations of such patients. The Congenital Upper Limb Differences (CoULD) registry was queried for all patients with contralateral diagnoses of thumb hypoplasia/RLD and radial polydactyly, as defined by the Oberg-Manske-Tonkin classification system, between June 2014 and January 2026. The demographic information, medical and musculoskeletal comorbidities, radiographs, and clinical images were collected. Ten patients were identified with contralateral diagnoses of thumb hypoplasia/RLD and radial polydactyly. The median age and interquartile range at time of enrollment was 1.67 (0.2-3.0), and 4 of the 10 were women. There was a wide range of diagnoses of thumb hypoplasia including type II, IIIA, IIIB, IV, V, and VII (unclassifiable), and two patients additionally had RLD (type 1 and type 3). There was a similarly a wide range of radial polydactyly classification, including type II, IV, V, VI, VII, and VIII (unclassifiable). Four had a syndrome diagnosis, four had medical comorbidities, and three patients had a history of other orthopedic conditions. This study demonstrated that with co-occurrence, there was no clear association in severity between thumb hypoplasia/RLD and radial polydactyly. There was minimal forearm involvement which has implications in timing of hand development. Additionally, there was a high degree of variability including syndromic conditions, as well as medical or orthopedic comorbidities. We recommend that clinicians are aware of this possible association and perform a thorough examination, as the identification of a mildly hypoplastic thumb would guide additional medical testing not typically performed in thumb polydactyly. Differential Diagnosis/Symptom Prevalence Study IV.