Dynamic function of coracoclavicular ligament at different shoulder abduction angles: a study using a 3-dimensional finite element model.

PURPOSE

The aim of this study was to determine the acromioclavicular (AC) motion and change in length and tension of the coracoclavicular ligament during different positions of shoulder abduction using a 3-dimensional finite element model based on computed tomography images from normal human shoulders.

METHODS

The right shoulders of 10 living subjects were scanned with a high-resolution computed tomography scanner at 0°, 60°, 120°, and 180° of shoulder abduction. Several modeling programs were used to simulate AC motion. Finite element models of the conoid and trapezoid ligaments were constructed based on each footprint. The tension and length changes of each ligament during shoulder abduction were assessed.

RESULTS

The distal clavicle exhibited internal rotation with respect to the medial acromion at 0°, 60°, 120°, and full abduction (3.2° ± 2.9°, 23.2° ± 10.8°, 20.6° ± 3.7°, and 37.1° ± 3.4°, respectively). With horizontal motion, the clavicle translated posteriorly at 60° of abduction (4.4 ± 3.4 mm) and then translated anteriorly at 120° and full abduction (0.4 ± 1.6 mm and 1.9 ± 0.4 mm, respectively). The lengths of the conoid ligament gradually increased at 60° to 180° of shoulder abduction whereas those of the trapezoid ligament remained relatively consistent at 60° to 120° of abduction compared with 0° of abduction.

CONCLUSIONS

The distal clavicle had a wide range of motion during shoulder abduction, which did not support the concept of synchronous motion with the scapula. The conoid and trapezoid ligaments functioned reciprocally during shoulder abduction. With increasing shoulder abduction, the length of the conoid ligament gradually increased; meanwhile, the trapezoid ligament was relatively consistent and then lax at full abduction. In particular, the conoid ligament may act as a key restraint to prevent excessive retraction of the scapula during shoulder abduction.

CLINICAL RELEVANCE

The data in this study have the potential to suggest that conoid and trapezoid ligaments should be reconstructed separately, and rigid AC fixation in patients with AC separation is not recommended based on the findings of this study.