Case 20 - Pseudodefect of the trochlear groove versus fracture

Summary

Imaging description

The trochlear groove is the large curved depression that articulates with the trochlea of the humerus. At the junction of the olecranon and coronoid process there is an osseous ridge without cartilage in this trochlear groove. There is also a waist or inward tapering of the trochlear groove at the level of the trochlear ridge that produces both medial and lateral cortical notches on the trochlear groove (Figure 20.1). These cortical notches are seen as pseudodefects (apparent small cortical interruptions) on sagittal MR and can be mistaken for an osteochondral fracture (Figure 20.2). In order for this cortical notch to be identified as an incidental pseudodefect there should be no abnormal MRI signal in the adjacent bone marrow of the olecranon.

Importance

This pseudodefect can be mistakenly diagnosed as an osteochondral fracture resulting in unnecessary treatment. It is important for radiologists to be aware of this pseudodefect as it is a common finding and present in nearly 100% of the population.

Typical clinical scenario

A patient presents for MR imaging with a history of subacute or chronic elbow pain of unknown etiology. This pseudodefect of the trochlear groove should not be misconstrued as pathology and should not be reported as a possible cause of the patient’s elbow pain.

Differential diagnosis

There is no differential as the pseudodefect of the trochlear groove has a pathognomonic appearance and location in the olecranon.

Teaching point

A pseudodefect of the trochlear groove should not be confused with a fracture of the olecranon. The pseudodefect is present at the cortical notches on the trochlear groove that occurs at the junction of the olecranon and coronoid process. In addition, in order to identify the cortical notch as an incidental pseudodefect, the adjacent bone marrow signal on MR should be normal. A fracture would be expected to have abnormal MRI signal within the adjacent bone marrow.