Review Question - QID 211551

The double arc sign is considered a pathognomonic finding on the lateral elbow radiograph of a capitellar coronal shear fracture.

An axial compression force transmitted by the radial head to the capitellum with the elbow in a semi-flexed position can result in a shear fracture of the anterior portion of the capitellum. AP, lateral, and radiocapitellar radiographs are recommended to identify these injuries and one should have a low threshold for obtaining computed tomography scanning in patients with significant and/or complex elbow fractures.
The double-arc sign seen on the lateral radiograph is characteristic and represents the subchondral bone of the displaced capitellum and the lateral trochlear ridge.

McKee et al. investigated coronal shear fractures of the distal end of the humerus. They reported that all patients were treated with open reduction internal fixation, with early elbow motion allowed. They highlighted that all patients had a good/excellent functional results according to the elbow-rating scale of Broberg and Morrey.

Stamatis et al. retrospectively reviewed the treatment and functional outcome of coronal shear fractures of the distal humerus. They reported that all fractures healed within 6 to 9 weeks with a single case of osteonecrosis and post-traumatic arthritis, with preservation of muscle strength of the major muscle groups of the operated elbow compared to the uninjured elbow. They concluded that recognition of coronal capitellar fractures, prompt treatment with anatomic reduction and internal fixation, and early rehabilitation can lead to excellent functional outcomes.

Durakbasa et al. investigated the management, complications and outcomes after distal humeral coronal plane fractures. They reported that all patients were treated by open reduction and internal fixation either by lateral or posterior approach. They highlighted the complications including avascular necrosis (27%), degenerative arthritis (40%), joint step-off (40%), heterotopic ossification (47%), nonunion (7%), and implant failure (7%).

Figure A depicts the double arc sign which is seen on the lateral elbow radiograph and is created from the subchondral bone of the displaced capitellum and lateral trochlear ridge.

Incorrect Answers:
Answer 1, 2, 4, & 5: A sagittal or coronal shear lateral epicondyle fracture, transverse olecranon fracture, and transolecranon fracture-dislocation, respectively, would not cause the pathognomonic double arc sign.