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Theme: Inclusion and Collaboration Theme: Inclusion and Collaboration

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Optimal Oblique Radiographs to Identify Fifth Carpometacarpal Dorsal Subluxations: A Cadaveric Study
Julie E Johnson, MD1; John R. Fowler, MD1; Joanna Costello, MD2; Robert Kaufmann, MD1; (1)Department of Orthopaedic Surgery, University of Pittsburgh Medical Center, Pittsburgh, PA, (2)Department of Radiology, University of Pittsburgh Medical Center, Pittsburgh, PA

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

1) INTRODUCTION 

Carpometacarpal joint subluxations of the fifth finger are rare injuries, which are notoriously difficult to diagnose due to severe swelling and overlapping of bones on radiograph. Various radiographic studies have been suggested to identify these injuries. We hypothesize that a 30 degree pronated lateral will have the greatest diagnostic accuracy for detection of a 5th finger CMC subluxation.

2) METHODS 

Using four cadaveric specimens we took radiographs at various angles (0, 30, 45, and 60 degrees) with the fifth metacarpal in anatomic position, subluxated 25% and 50% dorsally (see Figure 1).  Radiology and orthopedic residents, fellows and attending physicians viewed each image to determine whether a subluxation was present. Data was analyzed using area under the curve (AUC), sensitivity and specificity.

(A)     (B)

(C)

Figure 1. Radiographs taken with the hand in 60 degrees of pronation from the lateral.  (A) no subluxation, (B) 25% subluxation and (C) 50% subluxation of fifth CMC joint.

3) RESULTS 

36 responses were obtained from 9 radiologists (4 residents, 3 fellows, 2 attending physicians) and 27 orthopedic surgeons (16 residents, 8 fellows, 3 attending surgeons). We found a statistically significant difference in using 30, 45 or 60-degree radiographs to identify a fifth CMC subluxation (P-values <0.017). 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).  AUC was also higher for 60 degrees (0.87) than 0 degrees (0.59) 30 degrees (0.75) and 45 degrees (0.75).  There was no statistically significant difference in accuracy between the orthopedists and radiologists (P-value = 0.14).

4) DISCUSSION and CONCLUSION 

Radiographs taken with the hand in 60 degrees of pronation from the lateral provided the most accurate diagnosis of fifth CMC subluxations compared to 0, 30 and 45-degree views.  Sensitivity, specificity and AUC were highest for 60 degree 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. 


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