Transscaphoid Perilunate Dislocation
Updated: Oct 28, 2023
29M with right wrist pain and deformity after a motorcycle accident • Xray of the Week
Figure 1. Describe the wrist injury.
Figure 2. Transscaphoid perilunate dislocation. Frontal , lateral, oblique radiographs of the wrist. Red arrow points to scaphoid fracture and yellow arrow points to a normally positioned lunate bone. 2A. On the frontal view, the capitolunate joint space is obliterated as the bones overlap one another. 2B. On the lateral view the capitate (green arrow) is dislocated dorsal to the lunate (yellow arrow). Due to the fracture (red arrow), the proximal pole of the scaphoid has remained aligned with the lunate, whereas the distal pole has followed the capitate dorsally. The lunate and the distal radius remain normally aligned.
Discussion:
Of the eight carpal bones that make up the wrist, the scaphoid bone is fractured most often and accounts for 70% of all carpal fractures.[1] Less commonly, scaphoid fractures can be associated with perilunate dislocations. The injury mechanism in transscaphoid perilunate dislocations is typically “high energy” with wrist hyperextension (e.g. falling from a height, sports trauma, and motor vehicle accidents). These patients generally present with exquisite wrist pain and swelling, exacerbated by wrist motion.[2]
Figure 3. Mayfield Classification of Carpal Dislocations from https://wikem.org/wiki/Perilunate_and_lunate_dislocations
Carpal dislocations have been described to occur in 4 stages (Fig. 3) [3]. In a Stage I injury, the scapholunate joint is disrupted. A Stage II injury finds the capitolunate joint disrupted, and Stage III injury is disruption of the lunotriquetral joint. It is considered a Stage IV injury when there is complete lunate dislocation with volar displacement [2-4].
On PA radiographs, a Stage I scapholunate dissociation can be recognized by the ‘Terry-Thomas sign’ which refers to a gap greater than 2 mm between the scaphoid and lunate bones, and is due to scapholunate ligament rupture.
In normal lateral wrist radiographs, the capitate bone is aligned with the lunate bone and sits right above it. As seen in this case, with Mayfield Stage II when perilunate dislocation occurs, the capitate can be identified dorsally with respect to the lunate (Figs. 1B, 2B). This case also has a fracture through the scaphoid which is seen in 60% of cases.
With Mayfield Stage III, or midcarpal dislocation there is dislocation of the capitate from the lunate and subluxation of the lunate from the radius. A Stage IV lunate dislocation is characterized by the "spilled teacup" sign seen on lateral radiographs, indicating the volar displacement of the lunate bone resembling a teacup spilling forward [2,5]. (Fig. 4)
Transscaphoid perilunate dislocations can be treated with initial closed reduction and splint followed by surgical repair of injured ligaments after swelling has decreased. However, in cases where progressive median nerve dysfunction is noted, immediate open reduction with internal fixation (ORIF) is the preferred treatment [2,6].
Figure 4. Stage IV lunate dislocation. A. PA radiograph of lunate dislocation with triangular, “piece of pie” lunate appearance (green arrows), disruption of carpal arcs, increased radiolunate space, and overlap of lunate with other carpals.
B. Lateral radiograph showing the “spilled teacup” appearance of lunate dislocation (yellow arrows), with the concavity of the lunate facing anteriorly. The lunate has volar displacement and angulation, and has lost articulation with the radius and capitate.
References:
1. Papp S. Carpal Bone Fractures. Hand Clinics. 2010;26(1):119-127. doi:10.1016/j.hcl.2009.08.014 2. Kannikeswaran N, Sethuraman U. Lunate and perilunate dislocations. Pediatr Emerg Care. 2010;26(12):921-924. doi:10.1097/PEC.0b013e3181fe915b 3. Mayfield JK, Johnson RP, Kilcoyne RK. Carpal dislocations: Pathomechanics and progressive perilunar instability. Journal of Hand Surgery. 1980;5(3):226-241. doi:10.1016/S0363-5023(80)80007-4 4. Kennedy A, Allan H. In Brief: Mayfield et al. Classification: Carpal Dislocations and Progressive Perilunar Instability. Clinical Orthopaedics and Related Research. 2012;470(4):1243-1245. doi:10.1007/s11999-012-2275-x
5. Bashir WA, Aziz A, Jidaal I. Imaging of skeletal extremity trauma: A review. Trauma. 2014;16(4):300-317. doi:10.1177/1460408614542920 6. Kloss B, Patierno S, Sullivan A. Transscaphoid perilunate dislocation. International Journal of Emergency Medicine. 2010;3(4):501-502.doi:10.1007/s12245-010-0212-x
Nirali Dave is a medical student at Medical University of Lublin in Poland, currently doing clinical rotations in New York. Before that she completed her undergraduate education at Rutgers University, and worked as a medical scribe. Nirali was first exposed to basic radiologic imaging while scribing, and was very quickly taken by the field. Her passion for radiology comes from the bridging of anatomy, health technologies, and patient care. In the future, she hopes to complete a diagnostic radiology residency and stay committed to clinical research and patient education. UPDATE March 19, 2021: Nirali Dave is a resident in Radiology and Imaging Sciences at Indiana University School of Medicine.
Follow Nirali Dave on Twitter @ndave08
Kevin M. Rice, MD is the president of Global Radiology CME and is a radiologist with Cape Radiology Group. He has held several leadership positions including Board Member and Chief of Staff at Valley Presbyterian Hospital in Los Angeles, California. Dr. Rice has made several media appearances as part of his ongoing commitment to public education. Dr. Rice's passion for state of the art radiology and teaching includes acting as a guest lecturer at UCLA. In 2015, Dr. Rice and Natalie Rice founded Global Radiology CME to provide innovative radiology education at exciting international destinations, with the world's foremost authorities in their field. In 2016, Dr. Rice was nominated and became a semifinalist for a "Minnie" Award for the Most Effective Radiology Educator. He was once again a semifinalist for a "Minnie" for 2021's Most Effective Radiology Educator by AuntMinnie.com. He has continued to teach by mentoring medical students interested in radiology. Everyone who Dr. Rice has mentored has been accepted into top programs across the country including Harvard, UC San Diego, Northwestern, Vanderbilt, and Thomas Jefferson.
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