Examining the Elbow with Musculoskeletal Ultrasound
Examining the UCL of the elbow begins with the patient supine with the arm at 90 degrees of abduction, 30 degrees of elbow flexion, and maximum external rotation. Scanning can be done with and without a valgus force to show changes in the ligament under stress. Most commonly, the transducer is placed longitudinally on the inside of the elbow over the medial epicondyle Once the transducer is in place, it is up to the examiner to identify the structures and landmarks to perform a correct examination. Verifying the position of the transducer takes much practice and a skilled eye to identify all of the major structures of the elbow. The common flexor tendon should be visible in the image connecting to the medial epicondyle. Just deep to this larger structure is the ulnar collateral ligament, which is slightly more echoic than the flexor tendon. Under the UCL in the image is an anechoic space that represents the bone. The medial epicondyle is identifiable as the origin of the common flexor tendon. The trochlea and ulna are found more proximal, or further up the arm. The space between the medial epicondyle and the trochlea contains the UCL When the elbow is stressed with a valgus force the UCL becomes tight and forms a straight line over the trochlear notch.
To standardize the amount of stress placed on the elbow, some studies have used a Telos GA-II E stress device to provide consistent and variable force to the medial elbow The device uses three bars that stabilize the elbow and provide force outputs from the pressure applied to the elbow. This device is only designed to apply force to the elbow and is not used to assess the amount of joint laxity alone. Another study developed a new method for assessing medial elbow joint laxity. They compared the external rotation angle with the elbow at 90 degrees of flexion and with the elbow completely extended. Their method used gravity as the force and measured, with an inclinometer, the angle that the elbow dropped once in the two positions. The amount of laxity in the elbow correlates to the distance between the medial epicondyle and the trochlea. This space has been shown to be significant in terms of predicting elbow injury.