What structures provides stability to the shoulder joint?
Most of the stability comes from the rotator cuff muscles, the joint capsule and ligaments, with some stability from the glenoid fossa.
The abnormality just visible on the chest x-ray, and better seen on the dedicated shoulder view, is a dislocated left shoulder.
The humeral head is inferiorly (technically antero-inferiorly) dislocated.
No fracture is currently evident.