A 30-year-old falls on an outstretched hand. He has marked swelling of the wrist and paraesthesiae in the thumb, index and middle fingers. Lateral radiograph shows a crescent-shaped bone lying anterior to the capitate, and on the anteroposterior film the carpus appears disrupted. The most likely diagnosis is:
- A Dislocation of the lunate with displacement into the carpal tunnel ✓
- B Perilunate dislocation with intact lunate alignment
- C Trans-scaphoid perilunate fracture-dislocation
- D Isolated fracture of the triquetrum
Correct answer: A. Dislocation of the lunate with displacement into the carpal tunnel
Explanation
In lunate dislocation, the lunate is extruded anteriorly and appears triangular or crescentic on the lateral view, classically described as the 'piece of pie' or tilted shape, while the capitate remains aligned with the radius. Anterior displacement compresses the median nerve, explaining the acute carpal tunnel symptoms. In perilunate dislocation the lunate stays aligned with the radius and the remaining carpus displaces dorsally, which contradicts option B.
Reference: Apley's System of Orthopaedics and Fractures, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.