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

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.

Using 4 cadaveric specimens, we took radiographs at various angles (0°, 30°, 45°, and 60°) 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.

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° were more sensitive and specific (Sn 85, Sp 60) than at 0° (Sn 64, Sp 33), 30° (Sn 84, Sp 47), or 45° (Sn 80, Sp 49). Area under the receiver operating curve was also higher for 60° (0.87) than 0° (0.59), 30° (0.75), and 45° (0.75).

Sensitivity, specificity, and area under the receiver operating curve were highest for 60° radiographs. We recommend obtaining radiographs of the hand in 60° of pronation from the lateral if there is suspicion for a fifth CMC subluxation or dislocation.

This study suggests a simple radiographic view to enhance the diagnosis of fifth CMC subluxations.