*The views expressed in this chapter are those of the author(s) and do not necessarily reflect the official policy or position of the Department of the Navy, Department of Defense or the United States Government. Dominic L. Van Nielen, Nicholas J. Erdle, and Christopher S. Smith are military service members and this work was prepared as part of their official duties. Title 17 U.S.C. 105 provides that ‘Copyright protection under this title is not available for any work of the United States Government.’ Title 17 U.S.C. 101 defines a United States Government work as a work prepared by a military service member or employee of the United States Government as part of that person’s official duties.
Bony Anatomy1–3
- The distal humerus articulates with the sigmoid notch of the ulna (ulnohumeral joint) for flexion/extension at the elbow and the radius (radiocapitellar joint) to allow for pronation/supination.
- The highly congruent joint allows for excellent bony stability but also requires anatomic alignment of intra-articular fracture fragments to minimize early-onset traumatic arthritis.
- The ulnohumeral joint is positioned in 3 to 9 degrees of external rotation, 4 to 8 degrees of valgus in relation to the humeral shaft.
- The medial column is oriented 45 degrees from longitudinal axis of the humeral shaft, while the lateral column diverges at a more acute 20-degree angle.
- The medial epicondyle serves as attachment for both anterior and posterior bundles of medial collateral ligament as well as the origin of the flexor/pronator mass. Therefore, its anatomic reduction and fixation is paramount to joint stability. Inferiorly, the ulnar nerve courses from posterior to anterior under the bony sulcus of the medial epicondyle and is at risk for injury with fractures and surgical fixation.
- The posterior surface of the distal humerus is relatively wide and flat, making it easier to apply plate fixation.
- The anterior surface is more irregular and largely covered by articular cartilage with the convex capitellum laterally and the undulating trochlear joint surface medially. Both surfaces project approximately 45 degrees distal and anterior from the long axis of the humerus sharing a common center arc of rotation in the sagittal plane (thus directly influencing joint congruity and motion with malreduction of either column).
Radiographic Anatomy
1. AP View
- The AP view is obtained with the elbow fully extended and forearm supinated; this allows a clear view of the joint surface while minimizing overlap of the radius and ulna.
- The joint surface is best visualized on AP view. Ulnohumeral and radiocapitellar joints should be symmetric without any intra-articular step-off.
- The radial head should line up with the center of the capitellum in AP, lateral, and oblique views (Figs. 7-1 and 7-2).
Figure 7-1 AP view of elbow/distal humerus demonstrates a lateral condyle fracture with intra-articular extension but without step-off.
Figure 7-2 AP of distal humerus: bony detail is obscured by splinting material, but intra-articular involvement as well as the degree of articular displacement and fracture comminution are easily visualized.
2. Lateral View
- The lateral view is obtained with the elbow in 90 degrees of flexion.
- A “true” lateral radiograph demonstrates concentric overlap of three bony circles: the capitellum and the narrowest and widest portions of the trochlea (dashed yellow circle below).
- The “figure of 8” or “hourglass” (blue inset) is made from superimposition of bone forming the sagittal trochlear cortical surface and the distal termination of the humeral medullary canal. The narrow neck of the hourglass corresponds to the olecranon fossa.
- The radius should directly line up with the center of the capitellum (light blue arrow). Any subluxation should be critically evaluated for fracture or ligamentous injuries.
- A joint effusion, or “sail sign,” can be demonstrated radiographically. An anterior capsular lucency may be normal, but a posterior sail sign is always pathologic for an intra-articular process.
- The double-arc sign is pathognomonic for a coronal shear fracture (Figs. 7-3 and 7-4).
- The “figure of 8” or “hourglass” (blue inset) is made from superimposition of bone forming the sagittal trochlear cortical surface and the distal termination of the humeral medullary canal. The narrow neck of the hourglass corresponds to the olecranon fossa.
Figure 7-3 Lateral view of an intact elbow/distal humerus.
Figure 7-4 Rotation through fracture site can make obtaining “true lateral” difficult, but proximal extension is clearly visualized.
3. Oblique Views
- The patient is positioned with elbow extended and forearm supinated.
- Oblique views can be helpful to better visualize condylar fractures.
- Internal rotation (medial rotation) view is obtained with entire arm rotated medially 45 degrees to beam. This view better demonstrates medical epicondyle fractures (Fig. 7-5).
- External rotation (lateral rotation) view is obtained with entire arm rotated laterally approximately 45 degrees to beam; this view better visualizes lateral epicondyle fractures (Fig. 7-6).
- Internal rotation (medial rotation) view is obtained with entire arm rotated medially 45 degrees to beam. This view better demonstrates medical epicondyle fractures (Fig. 7-5).
Figure 7-5 Internal oblique.
Figure 7-6 External oblique.
4. Traction Views
- In severely comminuted or shortened fractures, traction views can be helpful in preoperative planning: plating orientation, surgical approach (i.e., olecranon osteotomy), or total elbow replacement (Fig. 7-7A and B).
- Distal humerus fracture with and without a traction view.
Figure 7-7 A: AP without traction. B: AP with traction.
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