Defining Features of Hand Anomalies in Severe Thumb Hypoplasia: A Classification Modification

Purpose: To investigate morphologic hand anomalies in children with severe but unclassifiable forms of thumb hypoplasia and radial-sided hand deficiency. Methods: We identified 15 extremities in 13 patients with severe thumb hypoplasia and associated absent radial-sided digits through the Congenital Upper Limb Differences registry. All patients had forearm involvement. Medical records, clinical photographs, and radiographs were evaluated. Radial longitudinal deficiency (RLD) and thumb hypoplasia were classified according to the Bayne and Klug classification and modified Blauth classification, respectively. Unusual or defining associated hand characteristics were identified and categorized. Results: The most common type of forearm abnormality was absence of the radius (Bayne and Klug type IV), which was present in 10 extremities in the cohort. All 15 extremities had absent thumbs with loss of additional digits. In 6 patients, RLD was part of a syndrome (46%). Conclusions: Severe forms of thumb hypoplasia in RLD are uncommon. We propose a further modification of the Blauth classification of thumb hypoplasia, type VI, for improved communication regarding this severe type of radial deficiency involving the hand. Type of study/level of evidence: Diagnostic IV.