Role of Dynamic Stabilizers of the Elbow in Radiocapitellar Joint Alignment: A Prospective In Vivo Study

Purpose: To investigate the effect of dynamic stabilizers of the elbow on radiocapitellar joint alignment, before and after the administration of regional anesthesia. Methods: At a single institution, 14 patients were prospectively enrolled in a study using a within-subjects control design. Before performing a supraclavicular regional block, 10 fluoroscopic images (1 anteroposterior and 9 lateral views) of the elbow were obtained for each patient. The lateral images were obtained with the forearm in maximal supination, neutral rotation, and maximal pronation, and these forearm positions were repeated for 3 elbow positions: (1) full extension; (2) flexion to 90°, with 0° of shoulder internal rotation; and (3) flexion to 90°, with 90° of shoulder internal rotation. After obtaining the 10 initial images, a block was performed to achieve less than 3/5 motor strength of the imaged extremity, followed by obtaining the same 10 images in each patient. Radiocapitellar ratio, defined as the minimal distance between the right bisector of the radial head and the center of the capitellum divided by the diameter of the capitellum, was measured in each image. Results: The 14 patients had a mean age of 47.8 ± 15.7 years, and 10 (71.4%) patients were women. A difference between radiocapitellar ratios measured before and after the regional block administration was observed for all lateral images (−1.0% ± 7.2% to −2.2% ± 8.0%), although this difference was less than the minimum clinically important difference. Conclusions: Paralysis of the dynamic stabilizers of the elbow produces a difference in the radiocapitellar joint alignment, but this did not reach the minimum clinically important difference. Clinical relevance: Paralysis of the dynamic stabilizers of the elbow via a supraclavicular nerve block produces no clinically relevant effect on the radiocapitellar alignment of uninjured elbows.