Does Radiographic Beam Angle Affect the Radiocapitellar Ratio Measurement of Subluxation in the Elbow?

Abstract

Background Radial head alignment is the key to determine elbow reduction after treatment of subluxations or Monteggia fractures. The radiocapitellar ratio (RCR) quantifies the degree of subluxation, by evaluating radial head alignment with the capitellum of the humerus; this ratio is reproducible when measured on true lateral radiographs of nonsubluxated elbows. However, the impact of beam angulation on RCR measurement is unknown. Questions/purposes Our hypotheses were that the RCR of the nonsubluxated elbow would remain in the normal range as the beam angle changed and that the RCR variability would increase for the subluxated elbow with small deviations in the beam angle. Methods Radiographs were taken of six healthy cadaveric extremities using beam angles ranging from À20°to 20°a long the inferosuperior axis and from À20°to 20°along the dorsoventral axis. The same views then were taken of the six arms with anterior radiocapitellum subluxation followed by posterior radiocapitellum subluxation. RCRs were measured by one observer. As a reference value, the RCR was measured in the 0°to 0°position and the difference between each RCR in a nonreference position was subtracted from each RCR reference to obtain the delta-RCR. An ANOVA was performed to assess the main and interactive effects on the RCR measured in each C-arm position compared with the RCR measured on a true lateral radiograph. Results The RCR remained in the normal range even as the beam angle of the C-arm varied between À20°and 20°. The position of the beam did not affect the RCR in anteriorly subluxated elbows (p = 0.777), whereas RCR variation increased especially in the presence of posterior radial head subluxation when the C-arm position was 10°o r more out of plane (p = 0.006). The inferosuperior malposition of the C-arm had a greater impact on quantification of radial head alignment measurement. Despite that, the RCR measurement is reliable in reduced and subluxated elbows on lateral radiographs with a C-arm position deviation of as much as 20°.

Could sea wave-like sign be used in the diagnosis of adult simple elbow dislocations?

“…There are limited studies available in the literature, which evaluated the radiology of the elbow dislocation. Previous studies which have emphasized the importance of lateral radiography were defined some criteria about the reduction of elbow (10). There is not enough definition for evaluation of elbow dislocation on AP X-ray, except the relative articular congruity (1).…”

“…At that time, it is not easy to decide the reduction of the elbow joint with direct radiography. Some criteria were defined previously, but they were often insufficient (10). No consensus has been yet reached on a gold standard method.…”