Humeroradial Synostosis: An Updated Classification and Differential Diagnosis Based on Genetic Aetiology

Humeroradial synostosis (HRS) is a rare congenital limb malformation, characterised by fusion of the humeral and radial bones, leading to functional disability of the elbow joint. HRS may be reported in familial or sporadic cases and observed either isolated or as part of a syndromic condition. According to an extensive review of the literature, a dozen known conditions may comprise an HRS. The present review aims to propose an updated classification based on molecular pathways (chondrogenesis and osteogenesis; limb development and patterning; genome regulation), combined with a concise overview of the conditions associated with HRS. This knowledge could guide molecular analyses, patient management and genetic counselling. As some cases remain unexplained, further genetic and epidemiological studies are required to evaluate the contribution of genetic and environmental factors in HRS physiopathology.