This 1967 cadaveric study by Bearn investigated which structures of the sternoclavicular joint maintain clavicular position when the arm hangs at rest. Using 5 post-mortem specimens, each ligament was sequentially cut under graded loading to determine its contribution to clavicular support. The study directly addressed why trapezius EMG activity disappears when the shoulder is fully dependent.
Before this paper, Gray's Anatomy assigned clavicular support to the trapezius. Bearn's prior EMG work had already shown trapezius activity disappears when the shoulder is fully dependent — leaving no accepted explanation for how the clavicle stays elevated at rest.
This paper establishes that the SCJ capsule. Specifically its posterior-superior portion. Is the passive locking mechanism. When you see a patient with complete trapezius palsy (CN XI injury) and the clavicle is only slightly depressed, this is the reason: the capsule is holding it up.
For SCJ trauma, recognize that the posterior-superior capsule bears the greatest load and fails by bony avulsion at 30–40 lb. Anterior dislocations predominate because the anterior capsule is structurally weaker. The costoclavicular ligament limits elevation, not depression. A distinction that matters when interpreting SCJ instability patterns and planning reconstruction.
This 1967 cadaveric study by Bearn investigated which structures of the sternoclavicular joint maintain clavicular position when the arm hangs at rest. Using 5 post-mortem specimens, each ligament was sequentially cut under graded loading to determine its contribution to clavicular support. The study directly addressed why trapezius EMG activity disappears when the shoulder is fully dependent.
Before this paper, Gray's Anatomy assigned clavicular support to the trapezius. Bearn's prior EMG work had already shown trapezius activity disappears when the shoulder is fully dependent — leaving no accepted explanation for how the clavicle stays elevated at rest.
This paper establishes that the SCJ capsule. Specifically its posterior-superior portion. Is the passive locking mechanism. When you see a patient with complete trapezius palsy (CN XI injury) and the clavicle is only slightly depressed, this is the reason: the capsule is holding it up.
For SCJ trauma, recognize that the posterior-superior capsule bears the greatest load and fails by bony avulsion at 30–40 lb. Anterior dislocations predominate because the anterior capsule is structurally weaker. The costoclavicular ligament limits elevation, not depression. A distinction that matters when interpreting SCJ instability patterns and planning reconstruction.