Fractures of the humerus can occur proximally, at the shaft, or distally. The majority of both proximal and midshaft humerus fractures are nondisplaced and can be treated conservatively (nonsurgically).
Nonstress fractures of the midshaft (diaphysis) of the humerus will be reviewed here. Stress fractures of the humeral shaft and proximal humeral fractures are discussed separately. (See "Stress fractures of the humeral shaft" and "Proximal humeral fractures in adults".)
The humerus is the largest bone in the upper extremity. The proximal humerus articulates with the glenoid of the scapula to form the shoulder joint. The muscles and tendons of the rotator cuff, the acromion, and ligamentous attachments such as those between the coracoid process of the scapula and the acromion, serve to both stabilize the glenohumeral articulation and provide for a wide range of motion of the shoulder joint. The distal humerus articulates with the radius and ulna at the elbow.
The greater tuberosity, located lateral to the humeral head and on the superior aspect of the humerus, provides the attachment for three of the rotator cuff muscles: supraspinatus, infraspinatus and teres minor. The lesser tuberosity of the humerus is located on the anterior surface of the humerus and provides the attachment for the subscapularis muscle. For the purposes of fracture classification, the lesser tuberosity marks the boundary between the proximal humerus and the midshaft.
The humeral shaft supplies the attachment for a number of powerful muscles. The pectoralis major muscle inserts on the proximal shaft while the deltoid muscle attaches to the midshaft. The biceps brachii and triceps muscle groups attach further distally.