Garet C. Comer
Julius A. Bishop

Bony Anatomy

The elbow is a complex structure arising from the articulations of the ulna, radius, and humerus.
- Ulna
  - The proximal ulna has two articular facets:
    - The greater sigmoid notch of the ulna articulates with the humeral trochlea along its 190-degree arc.
    - The radial notch is a groove along the proximal ulna that allows for articulation with the radial head.
  - The coronoid process projects anteriorly from the greater sigmoid notch and provides an anterior and varus buttress to the ulnohumeral joint. It consists of four parts:
    - The coronoid tip serves as an insertion point of the anterior capsule.
    - The coronoid base provides an anterior buttress.
    - The anteromedial facet, which contains the sublime tubercle on which the anterior bundle of the medial collateral ligament inserts.
    - The anterolateral facet along which sits the radial notch of the ulna and supinator crest on which the lateral ulnar collateral ligament inserts.
- Radius
  - The radial head is slightly elliptically shaped in the axial plane with a central convexity to allow for articulation with the concave capitellum.
  - The radial neck forms a 15-degree angle with respect to the radial shaft and is encircled by the annular ligament.
- The humerus
  - The distal articular surface of the humerus sits in 5 degrees of valgus and projects anteriorly 30 degrees relative to the humeral shaft.
  - The distal articular surface is composed of three convexities including the trochlea, the capitellum, and a central ridge between the two.
  - The center of rotation in the sagittal plane passes from the anteroinferior portion of the medial epicondyle to the center of the lateral surface of the capitellum where the lateral ulnar collateral ligament originates.

Radiographic Anatomy

AP View

The traditional AP view is performed in forearm supination to minimize overlap of the radius and ulna (Fig. 8-1).
Joint congruency
- The lines drawn along the distal humeral articular surface and along the anterior surfaces of the ulnohumeral and radiocapitellar articular surfaces should be perfectly parallel.
- Any divergence of these lines (indicating asymmetry of the ulnohumeral joint) is an indication that the elbow is not concentrically reduced or—in the case of radial head arthroplasty—may be “overstuffed” with too prominent an implant (Figs. 8-2 and 8-3).
The AP view should be examined for the extent of coronoid fracture with special attention toward evaluating for anteromedial facet involvement. Ultimately, though, CT is the most reliable modality for evaluating the coronoid.
Small avulsion fractures from the lateral ulnar collateral ligament footprint are frequently visible with proximal LUCL disruption much more common than midsubstance or ulnar avulsions.
The AP view is also useful to evaluate the radial head fracture morphology to determine if ORIF or radial head replacement is appropriate.

Gardner1e-ch008-image001 — Figure 8-1 A normal AP elbow x-ray.

Gardner1e-ch008-image002 — Figure 8-2 A normal AP elbow x-ray with concentric lines drawn along the articular surfaces.

Gardner1e-ch008-image003a — Figure 8-3 Intraoperative fluoroscopic views demonstrating divergence of the ulnohumeral lines due to an overstuffed radial component in the image on the left **(A)** and an appropriately sized implant in the right image **(B)**.

Gardner1e-ch008-image003b — Figure 8-3 Intraoperative fluoroscopic views demonstrating divergence of the ulnohumeral lines due to an overstuffed radial component in the image on the left **(A)** and an appropriately sized implant in the right image **(B)**.

Lateral View

The traditional lateral view is performed with the elbow flexed to 90 degrees and the forearm in neutral rotation (Fig. 8-4).
A true lateral view will produce three perfectly concentric circles over the distal humerus corresponding to the medial lip of the trochlea, the trochlear sulcus, and capitellum (Fig. 8-5).
Joint congruency
- The greater sigmoid notch and humeral surface should be concentrically aligned.
- On all projections, a line drawn through the radial head should bisect the capitellum, which is especially important on the lateral view given the posterolateral mechanism of terrible triad injuries.
- The radiographic landmark for the origin of the lateral ulnar collateral ligament is identified at the center of the three concentric circles of the distal humeral articular surface.
- The tip of the coronoid should lie just proximal to the radial head, which may assist in determining appropriate radial height.
The lateral projection is useful to estimate the depth of the coronoid fracture.
The lateral projection is also useful to evaluate the radial head fracture morphology to determine if ORIF or radial head replacement is appropriate.
Intraoperatively, the lateral view is utilized to confirm the correct location for suture button repair of the lateral ulnar collateral ligament to its origin. The origin is represented as the center point of the three concentric circles of the lateral image (Fig. 8-6).