Review Question - QID 219974

This 34-year-old male sustained a right wrist Mayfield stage IV lunate dislocation with an associated acute carpal tunnel syndrome. The most appropriate definitive treatment for this patient includes open reduction with internal fixation and carpal tunnel decompression (Answer 4).

Perilunate injuries are uncommon conditions, and due to their rather innocuous appearance on radiographic imaging, are missed up to 25% of the time. The injury stems from high-energy mechanisms where forces are imparted onto an outstretched hand with the wrist in extension and ulnar deviation. The sequence of injury has been described, with the force first disrupting the scapholunate ligament before progressing in a clockwise direction around the lunate (Illustration A). As this sequence was delineated, the Mayfield classification was developed, which functioned to characterize the degree of soft tissue injury in concordance with the sequence of injury (Illustration B). Mayfield Stage IV perilunate injuries, which involve dislocation of the lunate palmarly into the carpal tunnel, have been associated with the highest rates of acute carpal tunnel syndrome. Because of this displacement, the recommendation is for the patient to undergo open reduction of the lunate with ligamentous reconstruction/repair palmarly through the carpal tunnel in order to allow for decompression of the median nerve.

Stanbury and Elfar provide a review on perilunate dislocations, examining the anatomy, mechanism of injury, treatment, and techniques associated with the condition. These injuries commonly stem from high-energy mechanisms imparted onto an outstretched hand. The authors note 24-45% of patients experience acute carpal tunnel syndrome. When the presentation suggests acute carpal tunnel syndrome, the authors recommend immediate closed reduction, with definitive treatment including open reduction with ligamentous repair via a volar approach +/- dorsal approach in order to (1) decompress the carpal tunnel, and (2) allow for direct repair of the palmar extrinsic ligaments.

Muppavarapu and Capo similarly review perilunate injuries and illustrate the Mayfield classification. Interestingly, they note slower application of force to the wrist more often results in bony perilunate injuries (transradial styloid, transscaphoid, transcapitate), while rapidly applied force produces purely ligamentous disruptions. While the authors prefer a combined volar-dorsal approach, they recommend the inclusion of a volar approach in instances where there is palmar dislocation of the lunate or carpal tunnel symptoms.

Figures A and B represent AP and lateral views, respectively, of a right wrist exhibiting a Mayfield Stage IV lunate dislocation with a concomitant ulnar styloid fracture. Illustration A is a schematic representing the progression of injury in perilunate injuries. The green line represents the scapholunate ligament, which is injured in type I injuries. The yellow line represents the lunotriquetral ligament, which is injured in type III injuries. The black line represents the long radiolunate ligament, which is disrupted in type IV injuries. The red line represents a radioscaphocapitate ligament disruption or transcaphoid variants if they were to arise. Illustration B is a diagram summarizing the Mayfield classification.

Incorrect Answers:
Answer 1: closed reduction alone would not be sufficient, as this patient requires fixation to stabilize the carpus.
Answers 2 and 3: while these interventions would provide fixation and stability to the carpus, they would not address the patient's median nerve symptoms
Answer 5: proximal row carpectomy is reserved for chronic perilunate injuries greater than 8 weeks from dislocation.