Dynamic ultrasound assessment for insertional achilles tendinopathy: the COcco-RIcci (CORI) sign

To describe a novel, dynamic ultrasound assessment of the Achilles tendon at the calcaneal insertion taking advantage of the effusion within the deep retrocalcaneal bursa as a natural contrast agent.

Positioning the ultrasound transducer in a longitudinal plane over the Achilles tendon at the calcaneal insertion, manual compression of the deep retrocalcaneal bursa can be performed using the other hand. Dynamically shifting the anechoic effusion from the proximal to the distal compartment of the bursa, the undersurface of the Achilles tendon is lifted from the underlying cortical bone of the superior facet of the calcaneal tuberosity.

Pushing the anechoic effusion from the bursal cavity toward the undersurface of the Achilles tendon, an eventual focal injury of its deep fibers can be visualized dynamically during the maneuver as a "black crescent" within the tendon-i.e., the COcco-RIcci (CORI) sign. Otherwise, the gliding of the posteroinferior wedge of the Kager's fat pad inside the tendon-bone interface can be observed in normal conditions.

The CORI sign is a novel sonographic sign to further enhance the diagnostic accuracy of dynamic ultrasound imaging in patients with insertional Achilles tendinopathy especially to detect focal injury involving the deep fibers of the tendon.