CONGENITAL PROXIMAL RADIOULNAR SYNOSTOSIS: RADIOGRAPHIC FEATURES IN TWO CASES WITH REVIEW OF THE LITERATURE.

Background: Congenital radioulnar synostosis (CRUS) is an uncommon developmental defect caused by failure of segmentation between the radius and ulna during early embryonic life. Despite its rarity, it is the most prevalent congenital functional abnormality affecting the elbow. Clinical presentation varies widely, ranging from subtle cosmetic concerns to significant restriction of forearm rotation with consequent limitations in activities of daily living. Case 1: A 4-year-old girl presented with inability to fully extend her left elbow since birth, accompanied by progressively worsening difficulty performing daily tasks involving the affected limb. There was also a history of absent left thumb noted at birth. Plain radiographs of the left forearm demonstrated symmetrical shortening of the radioulnar diaphysis, hypoplasia and posterior dislocation of the radial head, absence of the distal radial epiphysis, and osseous fusion of the proximal radius and ulna. Radiographs of both hands further revealed asymmetry of the left hand with aplasia of the first digit. Case 2: A 13-year-old girl was evaluated for lifelong inability to extend both elbows, with increasing functional impairment of her forearms during routine activities. Plain radiographs of both forearms showed bilateral, symmetrical osseous fusion of the proximal radius and ulna with posteriorly dislocated radial heads. Additional findings included symmetrical bowing of the radial and ulnar shafts, penciling of the distal ulnar metaphysis, and positive ulnar variance. Conclusion: These cases demonstrate the diverse clinical spectrum of CRUS and emphasize the critical role of radiographic assessment in accurate classification and detection of associated anomalies. Prompt diagnosis and comprehensive functional evaluation are vital for optimal management planning.