The humeral shaft extends from the insertion of the pectoralis major to the supracondylar ridges. Humeral shaft fractures are most frequently seen in patients older than 50 years of age and usually involve the middle third of the shaft. There are four basic patterns commonly seen with humeral shaft fractures.
The type of fracture is dependent on the mechanism of injury, the force of injury, the location of the fracture, and the muscular tone at the time of injury. Each of the above fracture patterns may be further classified based on the presence of displacement or angulation (Figs. 15–1 and 15–2).
Humeral shaft fractures—nondisplaced.
Humeral shaft fractures—displaced or angulated.
The extensive musculature surrounding the humeral shaft may result in distraction and displacement of the bony fragments after a fracture. The deltoid inserts along the anterolateral humeral shaft, whereas the pectoralis major inserts on the medial intertubercular groove (Fig. 15–3). The supraspinatus inserts into the greater tuberosity of the humeral head, resulting in abduction and external rotation. The biceps and the triceps insert distally and tend to displace the distal fragment superiorly.
In humeral shaft fractures, the muscles of the proximal humerus cause displacement of the fracture fragments. Five muscles play a major role in displacing fractures in this region: the deltoid, supraspinatus, pectoralis major, biceps, and triceps. A. In fractures between the rotator cuff and the pectoralis major, abduction and rotation of the proximal fragment occur. B. Fractures occurring between the pectoralis major insertion and the insertion of the deltoid are associated with adduction deformity of the proximal fragment. C. Fractures occurring below the deltoid insertion are associated with abduction of the proximal fragment.
A fracture proximal to the pectoralis major insertion may be accompanied by abduction and external rotation of the humeral head because of the action of the supraspinatus (Fig. 15–3A). A fracture between the insertion of the pectoralis major and the deltoid will usually result in adduction of the proximal fragment secondary to the pull of the pectoralis major (Fig. 15–3B). Fractures distal to the deltoid insertion usually result in abduction of the proximal fragment secondary to the pull of the deltoid muscle (Fig. 15–3C).
The neurovascular bundle of the upper extremity extends along the medial border of the humeral ...