Normal Variants

There are several normal osseous features of the elbow that are important to recognize because they may be more striking on MRI images than at arthros-copy. One of the most common is the pseudodefect of the capitellum, a normal anatomic feature that mimics an osteochondral lesion on MRI images [3]. The pseudodefect of the capitellum occurs posterolaterally where the normal articular surface of the capitellum ends abruptly giving a stepoff at the interface with the nonarticular portion of the distal humerus (Fig. 1). On MRI images with the elbow in full extension, the radial head is located at the posterior edge of the capitellar articular surface, just anterior to this nonarticular portion of the lateral condyle. Fortunately, pathologic osteochondral lesions of the capitellum typically occur in the anterior capitellum.

Two other normal anatomic variants occur in the trochlear groove at the junction of the olecranon and coronoid processes. In this location some

Pseudodefect The Capitulum

Fig. 1. Pseudodefect of the capitellum. (A) Sagittal T2-weighted image with the elbow in extension shows the normal nonarticular flat posterior aspect of the lateral condyle (arrow). (B) On a coronal T2-weighted image through the dorsal part of the radial head, the nonarticular portion of the lateral condyle (arrow) is adjacent to the articular surface of the radius simulating an osteochondral lesion.

Fig. 1. Pseudodefect of the capitellum. (A) Sagittal T2-weighted image with the elbow in extension shows the normal nonarticular flat posterior aspect of the lateral condyle (arrow). (B) On a coronal T2-weighted image through the dorsal part of the radial head, the nonarticular portion of the lateral condyle (arrow) is adjacent to the articular surface of the radius simulating an osteochondral lesion.

individuals have either a small focal absence of the articular cartilage, called a mid-trochlear notch, or a thin transverse line of ossification of the hyaline cartilage called a mid-trochlear ridge [4]. The mid-trochlear notch appears as a focal defect in the hyaline cartilage seen best on sagittal images, and is often filled with fluid mimicking a focal chondral defect (Fig. 2). It is most prominent at the medial and lateral margins of the trochlear groove. The transverse mid-trochlear ridge occurs more centrally in the trochlear groove at the junction of the olecranon and coronoid processes. This ridge is usually only 2 to 3 mm high and does not extend above the thickness of the adjacent hyaline cartilage

Fig. 2. Mid-trochlear notch. Sagittal T2-weighted image shows a small focal absence of cartilage (arrow) in the midportion of the trochlear groove consistent with the normal variant notch.

Flat Trochlear Groove
Fig. 3. Mid-trochlear ridge. (A) Sagittal T1-weighted image shows a small bump in the subchondral bone (arrow). (B) Sagittal T2-weighted image shows that the contour of the articular cartilage remains smooth over the ridge (arrow).

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