Trauma. Wrist pain. • Xray of the Week
Figure 1. What is the diagnosis?
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.
Lunate dislocations are typically a consequence of traumatic forces causing wrist hyperextension, such as a fall on an outstretched hand (1,2). Mayfield and colleagues described a progression of perilunate dislocation, with complete lunate dislocation representing the final stage of ligamentous and osseous failure with the greatest degree of carpal instability (Fig. 3) (2,3). Herzberg et al. further classified lunate dislocation according to volar displacement and rotation, with degree of rotation corresponding to increased probability of soft-tissue interposition and decreased likelihood of successful closed reduction (1,4). Patients may present with wrist swelling and pain, reduced range of motion, and symptoms of median nerve impingement (2).
Figure 3. Mayfield Classification of Carpal Dislocations. from https://wikem.org/wiki/Perilunate_and_lunate_dislocations
On plain radiographs, the PA view is useful for evaluating Gilula’s carpal arcs, three contours normally formed by the proximal and distal carpal rows that are interrupted by lunate dislocation (2,5). Figures 1A and 2A demonstrate this finding, along with overlapping of the lunate with the capitate, increased radiolunate distance, loss of total carpal height, and triangular “piece of pie” lunate appearance (1,2,5). The lateral radiograph is useful for detecting palmar dislocation and rotation of the lunate. Figures 1B and 2B show volar dislocation of the lunate from the lunate fossa, volar angulation of the lunate, loss of articulation and alignment with the radius and capitate, an abnormal scapho-lunate angle, and a “spilled teacup” appearance (1,2,5). The lateral view can also distinguish lunate dislocation from perilunate dislocation, in which the lunate remains articulated with the radius and the remainder of the carpal bones are displaced dorsally (1,2). Evaluation of wrist pathology can also be aided by CT, US, or fluoroscopy when radiographs are indeterminate (1,6).
Diagnosis of lunate and perilunate dislocation following wrist trauma is missed in up to 25% of cases, and reduction and ligament repair are necessary to prevent joint dysfunction (4). Late presentation can lead to avascular necrosis (2). Even with early treatment, however, over 50% of patients in a multi-center study experienced post-traumatic arthritis (4). Other complications include wrist pain and stiffness, median nerve injury, tendon rupture, and carpal instability (1,2,5). Closed reduction was previously the recommended treatment and is employed in the acute setting, though open reduction with fixation and ligament repair is now preferred (1,2).
1. Scalcione LR, Gimber LH, Ho AM, Johnston SS, Sheppard JE, Taljanovic MS. Spectrum of carpal dislocations and fracture-dislocations: imaging and management. AJR Am J Roentgenol. 2014;203(3):541-550. doi:10.2214/AJR.13.11680
2. Grabow RJ, Catalano L 3rd. Carpal dislocations. Hand Clin. 2006;22(4):485-vii. doi:10.1016/j.hcl.2006.07.004
3. Mayfield JK, Johnson RP, Kilcoyne RK. Carpal dislocations: pathomechanics and progressive perilunar instability. J Hand Surg Am. 1980;5(3):226-241. doi:10.1016/s0363-5023(80)80007-4
4. Herzberg G, Comtet JJ, Linscheid RL, Amadio PC, Cooney WP, Stalder J. Perilunate dislocations and fracture-dislocations: a multicenter study. J Hand Surg Am. 1993;18(5):768-779. doi:10.1016/0363-5023(93)90041-Z
5. Tucker A, Marley W, Ruiz A. Radiological signs of a true lunate dislocation. BMJ Case Rep. 2013;2013:bcr2013009446. Published 2013 Apr 23. doi:10.1136/bcr-2013-009446
6. Kim K, Kim MW. Ultrasonography Detected Missed Lunate Volar Dislocation Associated With Median Neuropathy: A Case Report. Ann Rehabil Med. 2017;41(4):709-714. doi:10.5535/arm.2017.41.4.709
Ian Rumball is a medical student and aspiring radiologist at the Zucker School of Medicine at Hofstra/Northwell in Hempstead, NY. He serves as chair for his school’s radiology interest group. Prior to medical school, he attended the University of Wisconsin - Madison and graduated with degrees in biology, history, global health, and African studies. As an undergraduate, he did research in the fields of oncology, hematology, and neuroendocrinology. He also published work in undergraduate journals of creative writing, history, and physiology. In his free time, Ian enjoys playing guitar, hiking his local state parks, and watching classic films.
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Kevin M. Rice, MD is the president of Global Radiology CME
Dr. Rice is a radiologist with Renaissance Imaging Medical Associates and is currently the Vice 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.
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