The posterior scapular muscles are contained within fairly definite compartments, composed of deep fascia, which are attached round their origins to the bone, and accompany them to near their insertions. The sheath of the infraspinatus and teres minor muscles is more dense than that of the supraspinous. These facial sheaths tend to limit hemorrhagic and purulent effusions, and direct them forward toward the muscular insertions, and they also fix tumours growing from the fascia, and thus make them resemble tumours springing from the bone. The inferior angle of the scapula is crossed by the latissimus dorsi, and gives insertion to a slip of the muscle. When the angle slips out from under the latissimus, as it does in some injuries, especially when the muscular slip is torn, the angle of the scapula projects, and the upper limb is somewhat weakened. On the other hand, especially after carrying heavy weights on the shoulder, the posterior thoracic, or external respiratory nerve (of Bell) may be injured, causing paralysis of the serratus magnus. When this occurs, the vertebral border and inferior angle of the scapula project markedly from the posterior chest-wall (luxation). Projection of the angle of the scapula is also generally marked in lateral curvature of the spine, the scapula on the side of the convexity of the curve being affected. As already noted, the carrying of heavy weights on the shoulder may also lead to paralysis of the biceps, brachialis anticus, and supinator longus. Owing to its position between thick muscular pads, resting on the elastic chest, and its mobility, fracture, particularly of the body of the scapula, is not common. The part of the bone most frequently fractured is the acromion The acromion possesses two or three centres of ossification, ossification beginning about puberty, and junction with the rest of the bone about twenty-three ; but sometimes only a fibrous union occurs between process and spine. In such cases of fracture displacement is slight, owing to the dense periosteum and fibrous aponeurosis of the muscles. Occasionally the fracture may involve the acromioclavicular joint. The coracoid is rarely broken in dislocations of the head of the humerus inwards, and still less frequently by trauma or muscular violence. It may also be separated as an epiphysis up to the seventeenth year. Displacement is generally slight, being limited by the coraco-clavicular ligament, but may be considerable.
Fracture of the surgical neck of the scapula occurs rarely. The line of fracture is from the suprascapular notch to the upper part of the axillary border, nearly parallel to the glenoid cavity, and including the coracoid process. Displacement is generally slight, owing to the coraco-clavicular and acromio-clavicular ligaments ; but if these be torn, then the whole arm will be displaced downwards, the condition resembling a subglenoid dislocation, from which it may be distinguished by the ease with which reduction is obtained, but which is not maintained ; by the fact that the coracoid moves with the humerus ; by crepitus, etc. Fractures of the body of the bone generally affect the blade below the spine, little displacement occurring.
The scapula is not infrequently the seat of tumours, which generally grow from the neck, spine, or inferior angle. Sarcoma is generally of the periosteal type, and may necessitate removal of the whole bone, and sometimes of the arm as well, particularly if the joint be involved. The removal is done by making an elliptical incision, beginning over the clavicle, and ending over the angle of the scapula. The artery is tied before the vein, so as to empty the limb of blood, and the supra-, sub-, posterior, and dorsal scapular vessels and acromial branches of the acromio-thoracic artery require ligature.