This section is from the book "Applied Anatomy: The Construction Of The Human Body", by Gwilym G. Davis. Also available from Amazon: Applied anatomy: The construction of the human body.
The scapula is liable to be fractured more or less transversely through the body below the spine; the acromion and coracoid processes have been broken; it has also been fractured through the surgical neck, and the glenoid process has been chipped off.
The scapula has attached to its under surface the subscapularis muscle, along its posterior border is the serratus anterior (magnus) and rhomboids, to its dorsum and edge below the spine are attached the infraspinatus, teres minor, and teres major muscles. These are covered by a strong, tough fascia which dips between them to be attached to the bone.
Bearing these facts in mind it is readily appreciated why in many of these fractures, which usually traverse the bone below its spine from the axillary to the vertebral border, the displacement is slight, and why healing occurs with some appreciable deformity but with little disability.
If, however, the fracture is low down, breaking off the lower angle, then the teres major and lower portion of the serratus anterior (magnus) muscles displace the fragment toward the axilla, and this is to be borne in mind in treating the injury.
Fracture of the acromion process is more rare than would be expected. It is the result of direct violence, and the displacement and disability resulting from the injury are slight. The acromion is covered by a dense fibrous expansion from the trapezius above and the deltoid below, and these prevent a wide separation of the fragments.
Fracture of the coracoid process is also rare and may occur from muscular contraction or direct violence, as in luxation of the shoulder. It might be thought that owing to the action of the pectoralis minor, coracobrachialis, and short head of the biceps muscles, which are attached to it, it would be widely displaced, but this is not so, for the conoid and trapezoid ligaments still hold it in place.
Fractures through the surgical neck are not common. They pass down through the suprascapular notch and across the glenoid process or head, in front of the base of the spine and behind and parallel with the glenoid fossa. The tendency of the outer fragment to be dragged down by the weight of the arm is resisted by the coraco-acromial and coracoclavicular (conoid and trapezoid) ligaments as well as by the inferior transverse ligament, which runs from one fragment to the other from the base of the spine, on the posterior surface, to the edge of the glenoid cavity. These ligaments all remain intact.
Fracture through the glenoid process, chipping off a greater or less portion of the articular surface, is rarely diagnosed. It occurs sometimes in cases of luxation. The long head of the triceps muscle may be fastened to the detached fragment and is liable to pull it downward and therefore some interference with the functions of the joint would be apt to remain and prevent complete recovery.