The radiographic analysis allows one to classify the severity of an AC joint sprain. There is stretching of the AC joint capsule and ligaments of the regions with microscopic tears but no ligamentous disruption. There is no palpable instability. There is often moderate instability in the joint and there is a characteristic step between the clavicle and the acromion which is increased by holding a weight. The muscle attachments can also be compromised.
Pronounced instability is present.
This normally involves rupture of the AC joint capsule, the conoid and trapezoid ligaments. Formed by the relevant bones and the Mm that attach to both the scapula and the thoracic skeleton. The normal resting position of the scapula is 30 o anterior to the coronal plane and the medial border is rotated with the inferior aspect diverging away from the spine about 3 o . There are seventeen Mm that attach to the scapula. Scapular rotation-essential for full arm elevation.