Optimal Elbow Positions for Identification of the Radial Collateral Ligament Using Ultrasonography

Abstract

Background The standard position for examining the lateral elbow with ultrasonography is an "extended" or "slightly flexed" position. However, because the radial collateral ligament (RCL) is more deeply attached on the lateral epicondyle than the common extensor tendon, an anisotropic artifact of the RCL could be observed in the conventional positions, making it difficult to fully visualize the RCL. Objectives To determine optimal elbow positions for accurate identification of the RCL and to explore the relevant landmarks in ultrasonography. Design Prospective study. Setting Tertiary university hospital. Participants Forty healthy elbows of 20 participants. Methods The RCL was evaluated using ultrasonography in six elbow flexion positions (0 degrees, 30 degrees, 60 degrees, 90 degrees, 120 degrees, and 140 degrees). The relative depth, defined as the depth of the capitellum subtracted by the depth of the radial head under ultrasonography, was measured at each angle. The rates of successful identification of ultrasonographic landmarks for localizing the RCL were calculated. After ultrasonography, the optimal elbow position for identifying the RCL was determined by group consensus. Main Outcome Measurements Relative depth between radial head and capitellum, rates of successful identification of ultrasonographic landmarks, and consensus-based determination of the optimal angle. Results The relative depth significantly decreased with an increase in the flexion angle (P for trend <.001), approaching zero at the angles of 90 degrees and 120 degrees. The rates of successful identification of the superior tubercle, hyperechogenic line, and anterior and posterior tubercles were 100%, 100%, 90%, and 80%, respectively. In the group consensus, the 90 degrees and 120 degrees flexion angles were selected with the highest frequency (90%; 36/40). Conclusion Our findings suggest that elbow flexion at 90 degrees or 120 degrees is optimal for visualization of the RCL with the least possibility of anisotropy under ultrasonography, suggesting that the elbow should be flexed considerably beyond the conventional extended or slightly flexed position.