Dynamic Acromiohumeral Bone Surface Proximity and Scapuloclavicular Kinematics in Nonoperatively Managed Acromioclavicular Joint Injuries
Jason Konrath, Sydney Wheaton, Alonso Figueroa, James Gregory, Payam ZandiyehBackground:
Abnormal scapular biomechanics after acromioclavicular joint (ACJ) disruption may increase susceptibility to secondary pathologies such as subacromial impingement and rotator cuff degeneration. Traditionally, nonoperative management is suggested for low-grade disruptions (Rockwood types ≤3). However, the effects of ACJ disruption on dynamic scapular mechanics and acromiohumeral bone surface proximity in patients managed nonoperatively remain unexplored.
Purpose:
To quantify in vivo scapuloclavicular and glenohumeral kinematics, as well as acromiohumeral bone surface proximity, during dynamic humeral elevation in patients with nonoperatively managed ACJ injuries, using subject-specific bone models and biplanar video-radiography (BVR).
Study Design:
Cross-sectional study; Level of evidence, 3.
Methods:
Ten participants (9 male, 1 female; mean age, 42 ± 10 years) with previous ACJ disruption classified as Rockwood type III-V were enrolled 1 to 3 years after injury. Participants underwent 3-dimensional (3D) computed tomography and BVR during abduction, scaption, and flexion. Patient-specific bone models were registered to the BVR data to quantify scapular, clavicular, and humeral kinematics. Regions of interest (ROIs) were defined on the scapular and humeral surface models to represent the supraspinatus footprint and inferior acromial surface. The minimum 3D Euclidean distance between ROIs and their anatomical locations was calculated for each movement.
Results:
The injured limb demonstrated greater scapular upward rotation and internal rotation relative to the clavicle during scaption and flexion. During forward flexion, the minimum bone surface proximity between the supraspinatus footprint and the inferior acromion also occurred at a more anterior location. Additionally, the injured limb reached minimum proximity earlier at lower elevation angles compared with the contralateral limb.
Conclusion:
Patients with nonoperatively managed ACJ disruption exhibit an anterior shift in acromiohumeral proximity during flexion, accompanied by increased scapular internal rotation. These findings suggest that subtle alterations in dynamic scapuloclavicular coordination may alter which regions of the coracoacromial arch are encountered by the supraspinatus tendon, potentially influencing localized mechanical loading and impingement mechanisms. Improved understanding of dynamic scapuloclavicular coupling may help refine rehabilitation strategies and inform treatment stratification.