Identifying instability during EUA

The patients were placed in the supine position under general anesthesia. For valgus instability, the arm was positioned with the elbow in 30° flexion, humerus in full internal rotation, and forearm in pronation. Then, the manual valgus stress test was performed, and an anteroposterior (AP) image of the elbow was acquired using a fluoroscopic image intensifier [9]. A widening of more than 1 mm at the ulnohumeral joint was considered as subtle valgus instability [9]. For varus instability, the arm was positioned with the elbow in 15° flexion, humerus in full external rotation, and forearm in supination. Then, manual varus stress test was performed, and an AP fluoroscopic image was acquired. Since a previous study reported that the radiocapitellar joint is 0.47 mm more redundant compared with the ulnohumeral joint [10], a widening of over 1.5 mm at the radiocapitellar joint was considered as subtle varus instability (Fig. 1). In addition, a posterolateral pivot shift test was performed with the elbow in 90° flexion and forearm in supination [11]. If the longitudinal axis of the radius does not pass through the center of the capitellum, it was considered as a posterolateral instability [9]. Thereafter, a lateral image of the elbow was acquired to identify subtle posterolateral instability (Fig. 2a-c) [5]. If subtle instability was found, the contralateral asymptomatic elbow was examined to exclude underlying normal laxity of elbow joint.

a Intraoperative fluoroscopy image of a 53-year-old woman (patient #1). b Widening of the radiocapitellar joint was identified 2.3 mm in the varus stress view. c T2-weighted coronal magnetic resonance image showed rupture of the lateral collateral ligament and tear of the extensor tendon origin

a The 2.1 mm widening of the radiocapitellar joint was identified in the varus stress view of a 38-year-old man (patient #5). b The radial head was shifted posteriorly in the posterolateral pivot shift test. c T2-weighted coronal magnetic resonance image showed rupture of the lateral collateral ligament. d Intraoperatively, the definite lateral and lateral ulnar collateral ligaments were not found, except for thin fibrous tissue. e The lateral ulnar collateral ligament was reconstructed with a tibialis anterior allograft