Smaller radioulnar window is associated with a distal biceps tendon rupture in patients with limited forearm rotation: a 3-dimensional computed tomography comparison study of proximal impingement caused by radial tuberosity hypertrophyda single-center case series

Background: It has been suggested that hypertrophy of the radial tuberosity may result in impingement leading to either a lesion of the distal biceps tendon or rotational impairment. Two previous studies on hypertrophy of the radial tuberosity had contradictory results and did not examine the distance between the radius and ulna: the radioulnar window. Therefore, this comparative cohort study aimed to investigate the radioulnar window in healthy subjects and compare it with that in subjects with either nontraumatic-onset rotational impairment of the forearm or nontraumatic-onset distal biceps tendon ruptures with rotational impairment of the forearm by use of dynamic 3-dimensional computed tomography measurements to attain a comprehensive understanding of the underlying etiology of distal biceps tendon ruptures. We hypothesized that a smaller radioulnar window would increase the risk of having a nontraumatic-onset distal biceps tendon rupture and/or rotational impairment compared with healthy individuals. Methods: This study measured the distance between the radius and ulna at the level of the radial tuberosity using entire-forearm computed tomography scans of 15 patients at the Amphia Hospital between 2019 and 2022. Measurements of healthy subjects were compared with those of subjects who had nontraumatic-onset rotational impairment of the forearm and subjects who had a nontraumatic-onset distal biceps tendon rupture with rotational impairment of the forearm. The Wilcoxon signed rank test was used for individual comparisons, and the Mann-Whitney U test was used for group comparisons.