A 28-year-old female presents with a fracture of the distal third of the radius with dorsal angulation and an associated dislocation of the distal radioulnar joint (DRUJ). Neurovascular examination is normal. After initial closed reduction and immobilization in a long-arm cast, repeat X-rays at 1 week show loss of reduction with re-angulation of the radius fracture and DRUJ subluxation. What is the most appropriate next step in management?