FRCS Oral Exam Trauma Case: Master Perilunate Dislocation
Key Takeaway
Discover the latest medical recommendations for FRCS Oral Exam Trauma Case: Master Perilunate Dislocation. A common trauma case for FRCS involves perilunate dislocation, characterized by dorsal dislocation of the capitate and distal carpal row, with the lunate remaining in the radial lunate fossa. Diagnosis includes examining radiographs for gingival line disruption and utilizing Gilula's lines—three distinct curves assessing wrist alignment. Emergency management typically requires prompt reduction of this significant injury.
A 35-year-old male presents after a fall onto an outstretched hand (FOOSH) with the wrist in hyperextension and ulnar deviation. Radiographs reveal a complete dorsal dislocation of the capitate and other carpals relative to the lunate, which remains articulated with the radius.
Describe your systematic interpretation of this radiograph and the classification system used to grade this severity.
Candidate: "This is a perilunate dislocation. The lateral view shows the capitate is dislocated dorsally relative to the lunate, which maintains its position with the radius. I would use the Mayfield classification to stage the injury. I would also check for associated 'greater arc' injuries, such as a scaphoid or radial styloid fracture, on the PA view."
Failing to distinguish between a perilunate and a lunate dislocation (the 'spilled teacup' sign). Candidates often forget to mention the 'Greater Arc' vs. 'Lesser Arc' distinction or fail to address the high incidence of associated scaphoid fractures, which alters the surgical plan.
Systematically structure the response: 1. Alignment: State clearly that the lunate maintains its articulation with the radius (differentiating perilunate from lunate dislocation). 2. Mayfield Stages: Mention Stage I (SLIL injury), Stage II (capitolunate dissociation), Stage III (lunotriquetral injury), and Stage IV (lunate dislocation). 3. Injury Pattern: Categorize as 'Greater Arc' (involving bony fractures like the scaphoid/radial styloid) vs 'Lesser Arc' (purely ligamentous). 4. Clinical correlate: Immediately mention the status of the median nerve, as 30-50% present with acute carpal tunnel syndrome.
Following your assessment, the patient is found to have profound median nerve paresthesias in the thumb and index finger. How do you manage this in the acute setting, and what are the indications for open reduction?
Candidate: "I would perform an urgent closed reduction under sedation. If the median nerve symptoms resolve post-reduction, I would plan for elective ORIF. If they persist, I would perform an urgent carpal tunnel release."
Suggesting MRI before reduction or attempting reduction without adequate analgesia/sedation. Failing to recognize that if symptoms persist *after* successful closed reduction, immediate carpal tunnel release is mandatory, not "elective" follow-up.
Define the "Urgent Reduction" protocol: 1. Immediate Closed Reduction: To alleviate median nerve compression. 2. Decision Algorithm: Post-reduction status is key. If neurological symptoms persist or the reduction is unstable, open reduction is required. 3. Surgical Indication: Emphasize that closed reduction is rarely definitive; open reduction is standard of care to perform formal ligamentous repair (dorsal capsular repair and SLIL stabilization) and address associated 'Greater Arc' fractures with internal fixation (e.g., headless compression screw for scaphoid).
