Appearance of the weight-bearing lateral radiograph in retrocalcaneal bursitis

Abstract

Background and purpose: A retrocalcaneal bursitis is caused by repetitive impingement of the bursa between the Achilles tendon and the posterosuperior calcaneus. The bursa is situated in the posteroinferior corner of Kager's triangle (retrocalcaneal recess), which is a radiolucency with sharp borders on the lateral radiograph of the ankle. If there is inflammation, the fluid-filled bursa is less radiolucent, making it difficult to delineate the retrocalcaneal recess. We assessed whether the radiographic appearance of the retrocalcaneal recess on plain digital (filmless) radiographs could be used in the diagnosis of a retrocalcaneal bursitis.

Methods: Whether or not there was obliteration of the retrocalcaneal recess (yes/no) on 74 digital weight-bearing lateral radiographs of the ankle was independently assessed by 2 observers. The radiographs were from 24 patients (25 heels) with retrocalcaneal bursitis (confirmed on endoscopic calcaneoplasty); the control group consisted of 50 patients (59 heels).

Results: The sensitivity of the test was 83% for observer 1 and 79% for observer 2. Specificity was 100% and 98%, respectively. The kappa value of the interobserver reliability test was 0.86. For observer 1, intraobserver reliability was 0.96 and for observer 2 it was 0.92.

Interpretation: On digital weight-bearing lateral radiographs of a retrocalcaneal bursitis, the retrocalcaneal recess has a typical appearance.

Figure 1.

A. Kager's triangle with a normal appearance. B. The triangular lucency with sharp, smoothly curving borders is indicated with the dotted line. C. The arrowhead indicates the retrocalcaneal recess: the “bursal wedge” of Kager's fat pad, which normally forms a radiolucent corner posterosuperior to the calcaneus.

Figure 2.

A patient with a chronic retrocalcaneal bursitis. The retrocalcaneal recess has disappeared because of the less radiolucent fluid in the distended retrocalcaneal bursa.

Figure 3.

Clinical image (A) and radiograph (B) of a patient with a retrocalcaneal bursitis. The retrocalcaneal recess is obliterated by a chronic inflamed bursa (arrow). C. Endoscopic view of a patient with a retrocalcaneal bursitis.