Optimal Oblique Radiographs to Identify Fifth Carpometacarpal Dorsal Subluxations: A Cadaveric Study.

Purpose Carpometacarpal (CMC) joint subluxations of the fifth finger are rare injuries and are notoriously difficult to diagnose due to severe swelling and overlapping of bones on radiographs. Various radiographic studies have been suggested to identify these injuries. We hypothesize that there will be no difference between various oblique radiographs for detection of a fifth finger CMC subluxation. Methods Using 4 cadaveric specimens, we took radiographs at various angles (0 degrees, 30 degrees, 45 degrees, and 60 degrees) with the fifth metacarpal in anatomic position, subluxated 25% and 50% dorsally. Radiology and orthopedic residents, fellows, and attending physicians viewed each image to determine whether a subluxation was present. Data were analyzed using area under the receiver operating curve, sensitivity, and specificity. Results A total of 36 responses were obtained from 9 radiologists (4 residents, 3 fellows, 2 attendings) and 27 orthopedic surgeons (16 residents, 8 fellows, 3 attendings). Radiographs taken at 60 degrees were more sensitive and specific (Sn 85, Sp 60) than at 0 degrees (Sn 64, Sp 33), 30 degrees (Sn 84, Sp 47), or 45 degrees (Sn 80, Sp 49). Area under the receiver operating curve was also higher for 60 degrees (0.87) than 0 degrees (0.59), 30 degrees (0.75), and 45 degrees (0.75). Conclusions Sensitivity, specificity, and area under the receiver operating curve were highest for 60 degrees radiographs. We recommend obtaining radiographs of the hand in 60 degrees of pronation from the lateral if there is suspicion for a fifth CMC subluxation or dislocation. Copyright (C) 2018 by the American Society for Surgery of the Hand. All rights reserved.