Clinics in diagnostic imaging (225)

CASE PRESENTATION A 22-year-old Bangladeshi man who works as a manual worker attended the emergency department (ED) with right wrist pain following a fall. On examination, a bony ulnar prominence on the volar aspect of his right wrist was observed. The neurovascular status of his right hand was intact. Plain radiographs of his right wrist and radius/ulna are shown in Figure 1. What is the diagnosis?Figure 1: (a) Frontal and (b) lateral radiographs of the right wrist.IMAGE INTERPRETATION There is volar dislocation of the right distal ulna. No fractures are seen. DIAGNOSIS Distal radioulnar joint (DRUJ) volar dislocation. CLINICAL COURSE Closed manipulation and reduction of the right wrist was performed under sedation, using pronation and flexion. However, the wrist subsequently dislocated spontaneously. Manipulation was repeated using the same technique, and a plaster cast was applied with the wrist in pronation. Plain radiographs of the right wrist were repeated after reduction [Figure 2]. The distal ulna remained slightly subluxed, with a widened DRUJ. However, as the overall alignment had improved, the patient was discharged following consultation with the hand surgeons. The patient was reviewed at the Hand Surgery clinic four days later, at which point his plaster cast was replaced with a Muenster splint in 10° of pronation. Six weeks later, his DRUJ remained unstable, with spontaneous ulnar dislocation. Given the failure of conservative management, surgical repair with ligament reconstruction of the right wrist was offered, but the patient declined.Figure 2: (a) Frontal and (b) lateral radiographs of the wrist post reduction.DISCUSSION The forearm plays a significant role in the hand’s versatility and is essential for many activities of daily living (ADLs). The DRUJ stabilises the articulation of the radius around the stationary ulna during supination and pronation of the forearm.[1] Acute distal DRUJ dislocations usually occur in association with fractures of the distal radius or radial head secondary to trauma, as seen in Galeazzi fracture-dislocation and Essex-Lopresti injury, respectively.[2] Isolated dislocations and subluxations of the DRUJ are rare and commonly missed in up to 50% of cases during the acute period, often being treated as simple wrist sprains.[3] This proportion may be even higher in busy primary care settings or EDs. Failure to diagnose and treat an isolated DRUJ dislocation can result in chronic and persistent dislocation or subluxation, leading to subsequent instability.[4] This article reiterates the challenges in evaluating isolated DRUJ dislocations in primary care and emergency settings, as well as the considerations for subsequent management. Dislocations of the DRUJ can be either volar or dorsal. Volar dislocations, in which the ulna moves volarly relative to the radius following hyper-supination of the forearm, are less common than dorsal dislocations [Figure 3a].[2] Clinical signs of isolated volar dislocations include loss of forearm rotation, absence of the ulna styloid prominence, volar fullness at the ulnar aspect of the wrist, and narrowing of the wrist due to overlap of the volarly displaced ulna and the radius, caused by the pull of the pronator quadratus.[3] In dorsal dislocations, a prominent ulnar head is visible over the dorsal wrist [Figure 3b and c].[2] Paresthesia in the ulnar nerve distribution may also occur secondary to compression from the dislocated ulna.[1]Figure 3: A 36-year-old man presented with right wrist pain after falling while skateboarding. (a) Lateral radiograph of the right wrist shows an isolated dorsal distal radioulnar joint (DRUJ) dislocation with no fractures. (b & c) Clinical images of the right forearm show a prominent ulnar head over the dorsal wrist in the isolated dorsal DRUJ dislocation.On radiographs, isolated DRUJ dislocations can be mistaken for positional variations if a true lateral view is not obtained, where the palmar margin of the pisiform is projected midway between the palmar margins of the distal scaphoid pole and the capitate head [Figure 4].[4] To acquire these views, the forearm should be positioned in mid-pronation with a neutral wrist.[5] This can be challenging if forearm rotation is limited due to swelling or pain. Another suggestive feature of a DRUJ dislocation is widening of the radioulnar joint on the posterior-anterior view [Figure 5]. As such, if clinical suspicion is high, it is recommended that patients with no bony injury on plain radiographs be re-evaluated for adequacy of imaging.Figure 4: A 17-year-old female sustained dorsal subluxation of the right ulnar head with ulnar styloid fracture from a fall while skateboarding. (a) Lateral radiograph of a partially supinated wrist – dorsal subluxation is difficult to appreciate on this film when it is not a true lateral view of the wrist. (b) True lateral radiograph of the wrist – dorsal subluxation of the ulna is evident. (c) Annotated true lateral radiograph of the wrist – the anterior border of the pisiform should be between the anterior border of the scaphoid and capitate. C: capitate, S: scaphoid, P: pisiform, U: ulnaFigure 5: Same patient as described in Figure 4. (a) Frontal and (b) annotated frontal radiographs of the same wrist show a widened distal radioulnar joint and ulnar styloid fracture.In most reported cases, closed manipulation and reduction was successfully performed under general anaesthesia. The technique for reducing volar dislocations involves forcible pronation with dorsally directed pressure on the ulnar head, whereas reduction of dorsal dislocations is achieved with supination and extension of the wrist.[2] Our case of isolated volar DRUJ dislocation was succesfully reduced under procedural sedation in the ED on the second attempt, and an above-elbow plaster cast was applied with the forearm in pronation. Reduced DRUJ dislocations that remain stable may be immobilised in an above-elbow or sugar-tong plaster cast.[3] The ideal position for immobilisation depends on the direction of dislocation and the position of stability. For example, dorsal DRUJ dislocations should be immobilised in supination. However, as in our experience, these injuries are often unstable, with a risk of spontaneous re-dislocation or persistent subluxation. Wrist stability can be tested by rotating the wrist and observing the position of the ulnar head, and by checking for the piano key sign. Ballottement of the distal radioulnar joint, with comparison to the contralateral side, can also be performed to evaluate wrist stability.[3] Despite their instability, these injuries can still be managed on an outpatient basis. However, a hand or orthopaedic surgeon should be involved early during ED consultation to consider manipulation and reduction under anaesthesia and, if necessary, early surgical pinning of the radioulnar joint [Figure 6] when there is a block to reduction and the joint remains fully dislocated.[2] A block to reduction in these injuries may be caused by soft tissue interposition, which prevents successful closed reduction and necessitates open reduction in the operating theatre.[3]Figure 6: Same patient as described in Figure 4. (a) Frontal and (b) lateral radiographs of the same wrist following surgical pinning.In conclusion, isolated DRUJ dislocations are rare and often present with subtle clinical and radiological findings. Failure to manage these injuries appropriately may predispose patients to chronic instability and limitations in ADLs. It is important that primary care providers and emergency physicians maintain a high index of suspicion for DRUJ dislocations in patients presenting with significant tenderness and loss of forearm rotation, even in the absence of obvious bony fractures on plain radiographs. Most cases can be managed in an outpatient setting, provided there is early hand or orthopaedic follow-up. However, for DRUJ dislocations with a block to reduction, where the joint remains fully dislocated, emergent surgical intervention is required. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest. SMC CATEGORY 3B CME PROGRAMME Online Quiz: https://www.sma.org.sg/cme-programme Deadline for submission: 6 pm, 26 June 2026