Preliminary In Vivo Evaluation of Coracoclavicular Ligament Mechanics During Shoulder Elevation After Acromioclavicular Joint Reconstruction

Background: Persistent instability and altered scapular mechanics after acromioclavicular joint (ACJ) reconstruction may stem from inadequate replication of native coracoclavicular (CC) ligament function. However, in vivo data on postoperative CC ligament behavior during dynamic shoulder motion remain lacking. Purpose: To assess in vivo functional distance and timing characteristics of the conoid and trapezoid ligaments during active shoulder elevation after ACJ reconstruction, using dynamic stereo x-ray (DSX) imaging and patient-specific 3-dimensional (3D) models. Study Design: Cross-sectional study; Level of evidence, 3. Methods: Twelve participants (10 men and 2 women, mean age 39 ± 10 years, mean body mass 92 ± 17 kg) who had sustained an acute unilateral ACJ disruption (Rockwood classification of 3-5) and undergone anatomic ACJ reconstruction were recruited within 1 to 3 years after surgery. Participants underwent 3D computed tomography (CT) and DSX imaging to capture abduction, scaption, and flexion movements. Patient-specific bone models with digitized CC insertion points were then aligned within each frame of the biplanar radiograph images. From this, the peak functional distance, time at peak, and displacement were measured and compared with the uninjured limb. Results: Compared with uninjured limbs, the reconstructed limb demonstrated increased conoid and trapezoid peak distances of 23% and 17% between insertion points, respectively, across abduction, flexion, and scaption. Additionally, the conoid and trapezoid reached these peak distances at later stages of the movement cycle, and experienced increased displacement by 2.7 and 1.8 mm, respectively, in the reconstructed limb. Conclusion: This investigation established the methodological feasibility of using DSX combined with patient-specific CT models to quantify in vivo ligament behavior during functional shoulder motion. It further identified significant asymmetries in the functional distance between conoid and trapezoid ligament insertion points when comparing reconstructed and uninjured limbs across multiple shoulder elevation movements.