Teaching Case

A 34-year-old woman self-presented to the emergency department with left wrist pain, swelling and limited dorsiflexion following a fall on outstretched hand (FOOSH) injury during football. Pain was localized on the volar ulnar side of the wrist. Finger mobility was normal. Past medical history was insignificant.

Radiographs of the wrist were obtained in both anteroposterior and lateral views. The lunate was volarly displaced and rotated relative to the rest of the wrist. A CT-scan the next day confirmed this lunate dislocation and furthermore detected small fractures in the palmar side of the lunate and triquetral.

A lunate dislocation involves volar displacement of the lunate in relation to the radius, predominantly caused by high-energy wrist trauma, commonly seen in FOOSH injuries, causing stretching and rupture of the volar joint capsule. FOOSH injuries are a common result of high-impact sports and slip-and-fall accidents in elderly patients, where reflexively straightening the arms to cushion a fall results in injury of the wrist [1-4].

Possible manifestations include tenderness, pain, swelling, restricted mobility, and acute carpal tunnel syndrome resulting from median nerve injury [1,3,4].

Two plain radiographs suffice to stage carpal instability following the Mayfield classification: I. Scapholunate disruption; II. Scapholunate disruption + Lunocapitate disruption; III.  Scapholunate disruption + Lunocapitate disruption + Lunotriquetral disruption; IV. Scapholunate disruption + Lunocapitate disruption + Lunotriquetral disruption + Radiolunate disruption. As the number of disrupted joints increases, each stage radiologically results in: I. scaphoid rotation; II. Capitate dislocation; III. perilunate dislocation; IV. Lunate dislocation [1-3,5-7].

In Mayfield stage IV, the 'piece of pie' sign on the posteroanterior view indicates a triangular instead of quadrangular shape of the lunate due to its projection over the capitate [1-3]. Other possible findings include disrupted carpal arcs (Gilula arcs), a rounded appearance of the scaphoid tubercle (signet ring sign) and scapholunate dissociation [1,2,6]. An abnormal scapholunate angle (<30° or >60°) and an abnormal capitolunate angle (>30°) suggest carpal instability [7]. Lateral views show disrupted axial alignment of radius, lunate, and capitate [1,6]. The lunate is angulated and volarly displaced relative to the capitate and radius (spilt teacup sign), in contrast to perilunate dislocation where the capitate is dorsally displaced relative to the lunate and radius [3,4,6]. CT and MRI are recommended preoperatively and when multiple fractures are suspected, as they can better identify occult fractures and bone misalignment [6].

Early closed reduction prevents pressure and damage on surrounding tissue [1,2,6]. However, closed reduction and immobilisation alone is successful in only 27% of cases [8]. As instability is often severe, open reduction with internal fixation and ligament repair is required [3,6,7]. In case of acute carpal tunnel syndrome, an emergency release is imperative. Unfortunately, complete recovery of range of motion is unlikely and after 6 years about 66% of patients show early signs of osteoarthritis after surgical repair [9].

Lunate and perilunate dislocations account for approximately 7% of all carpal injuries [10]. It is estimated that 16 to 25% of these injuries are missed on initial presentation [11]. Delayed or missed diagnoses, a scapholunate interval >3 mm or a scapholunate angle >70° after closed reduction are associated with a worse prognosis [2,3]. Severe complications are common and include chronic pain, osteoarthritis, carpal instability, avascular necrosis and scapholunate advanced collapse (SLAC). Long-term functional instability and diminished grip strength are frequently observed [2,3,5,7,12].

• Early diagnosis improves prognosis.
• Imaging is essential for diagnosis and injury staging, with conventional radiography being sufficient.
• Pay attention to specific radiological findings: disrupted Gilula arcs, piece of pie sign, spilt teacup sign, etc.
• CT and MRI provide valuable insights for further assessment (e.g., occult fractures) and treatment.
• Severe complications are common, despite adequate treatment.

All patient data have been completely anonymised throughout the entire manuscript and related files.