Not-So-Simple Wrist Injury After Fall On Outstretched Hand: Dorsal Intercalated Segment Instability

Case Presentation

A middle-aged right-handed man presented with left wrist pain and swelling after falling onto his outstretched hand. Examination of his left wrist revealed tenderness over the anatomic snuffbox, scaphoid tubercle, and upon axial loading of the thumb. The range of movement of the left wrist was limited by pain. Plain radiographs of the left wrist and scaphoid showed no fracture or dislocation. Ascaphoid cast was applied, and a follow-up was arranged 10 days later.

At follow-up, his symptoms had shown minimal improvement. Repeat radiographs ( Fig. 1 ) demonstrated widening of scapholunate distance and increased scapholunate angle. The diagnosis of ligamentous dorsal intercalated segment instability (DISI) was made, and the patient was offered arthroscopic repair by the orthopaedics team. He opted for conservative treatment and received splintage for 6 weeks followed by rehabilitation and occupational training for 6 weeks.

Fig. 1 . More than 3 mm widening of the scapholunate interval (Terry-Thomas sign) on the posteroanterior view of the left wrist in ulnar deviation.

Discussion

DISI is a type of dissociative instability involving the proximal row of carpal bones with the lunate as the intercalated segment. This can either be bony or ligamentous in origin. 1 In ligamentous DISI, the primary ligament disrupted is the scapholunate interosseous ligament which comprises dorsal (strongest), volar, and proximal fibres. Disruption of secondary stabilizers such as the dorsal intercarpal, long radiolunate, and scaphotrapeziotrapezoid ligaments is also vital. 2 The typical mechanism of injury involves falling on an outstretched hand with the wrist in extension, ulnar deviation, and carpal supination.

A high index of suspicion is required to differentiate simple strain and sprain from carpal instability caused by ligamentous injury and avoid potential malpractice issues. Late diagnosis of perilunate lesions can occur in up to 30% of cases. 1 DISI should be suspected in patients with tenderness over the scapholunate joint, pain provoked by wrist extension and radial deviation with compatible history of injury.

The characteristic radiological finding is the widening of the scapholunate interval of more than 3 mm (“Terry-Thomas” or “David Letterman” sign) on the posteroanterior view. On the lateral view, DISI is defined by an increased scapholunate angle of more than 60°, radiolunateangle of over 15°, and capitolunate angle above 30° ( Fig. 2 ). As a result of disruption of the scapholunate ligament, the scaphoid “flexes” into volar flexion while the lunate “extends” into dorsal flexion.

Fig. 2 . The lateral view of the left wrist demonstrates a scapholunate angle greater than 60° and a radiolunate angle greater than 15°.

Treatment in the emergency department includes analgesics, anti-inflammatory medication and immobilization in a short-arm splint. An early orthopaedic referral is mandatory for the arthroscopic diagnosis of the scapholunate injury. Ligament repair is recommended within four to six weeks of the injury. 3

Improper management can result in abnormal force distribution in the wrist and natural progression to a specific pattern of degenerative arthritis, namely “scapholunate advanced collapse”. 4 In the first stage, the proximal scaphoid edges onto the posterior radial epiphysis, resulting in osteophytes at the radial styloid and scaphoid collapse. Subsequently, the entire scaphoid facet of the radius and scaphoid become involved. In the last stage, the enlarging gap between the scaphoid and lunate is replaced by the capitate, and arthritis of the capitolunate joint ensues. The radiolunate joint is spared.

This case illustrates the sequelae of a seemingly simple wrist sprain can be debilitating despite the absence of a fracture. Carpal instability must be in the differential diagnosis when a simple sprain cannot account for the clinical progress. Proper management which involves immobilization, prompt orthopaedic referral and ligament repair can avoid medicolegal issues.