In vivo assessment of the subacromial space during shoulder elevation following acromioclavicular joint reconstruction.

High-grade disruptions to the acromioclavicular joint (ACJ) significantly impair scapular function, which may compromise the subacromial space and increase the risk of impingement related pathology. Research has traditionally focused on the minimum distance between the humeral head and undersurface of the acromion, which may not accurately address the space above the supraspinatus footprint. This study aimed to quantify the subacromial space between the anterior acromion and the supraspinatus footprint, as well as the general humeral-acromial spacing during muscle-driven shoulder motion, in individuals who had undergone ACJ reconstruction. Twelve participants with acute unilateral ACJ disruptions, 1 to 3 years post-surgery, were recruited. Each underwent 3D computed tomography combined with biplane video-radiography during abduction, scaption, and flexion. Regions of interest (ROI) were applied to the scapula and humerus surface models representing the supraspinatus footprint and the inferior acromial surface. The minimum 3D Euclidean distances between respective ROIs were then calculated for each movement, along with its precise anatomical location. The surgical limb showed a 0.8 mm (23%) narrower subacromial space above the supraspinatus footprint during abduction compared to the contralateral limb, with the minimum location occurring 3.6 mm more medially on the acromion. Additionally, the minimum general humeral-acromial space was located up to 10.6 mm more posteriorly along the proximal humerus and 4.9 mm more medially on the acromion. These findings demonstrate that bone surface proximities and associated subacromial space can be significantly altered post-surgery following ACJ reconstruction, potentially increasing the risk of repetitive shear and compressive forces on the rotator cuff tendon.