The Kager's Fat Pad Sign

Diagnostic Value of Lateral Ankle Radiography in Achilles Tendon Rupture

INTRODUCTION

Achilles tendon rupture (ATR) is a common sports injury, but approximately 20% of acute ATR cases are misdiagnosed as ankle sprains at first presentation. This study aimed to investigate the diagnostic value of lateral ankle radiography in the diagnosis of acute ATR.

METHODS

This was a retrospective case-control study in which the lateral ankle radiographs of patients who presented to the emergency department between January 1, 2015 and December 31, 2019 were examined. The study included a total of 154 patients with acute ATR, who underwent lateral ankle radiography at the presentation and were surgically or magnetic resonance imaging (MRI) confirmed to have ATR in our hospital. The lateral ankle radiographs of the patients were examined by 2 clinicians blinded to clinical data for the following 3 findings: Kager's fat pad sign, tibio-first metatarsal angle, and tibiocalcaneal angle. The same procedure was repeated for 308 controls who underwent lateral ankle radiography and were diagnosed with ankle sprain.

RESULTS

Kager's fat pad sign was detected in 133 (86.4%) of the 154 patients with ATR and 26 (8.4%) of the 308 patients in the control group. The Kager's fat pad sign, tibio-first metatarsal angle, and tibiocalcaneal angle sensitivity values for the diagnosis of ATR were 86.4%, 61.7%, and 65.6%, respectively, and their specificity values were 91.6%, 78.9%, and 56.2%, respectively. Interobserver reliability was determined to be good for all 3 radiographic findings.

CONCLUSION

Clinicians should be particularly aware of Kager's fat pad sign when examining lateral ankle radiographs for ankle injury.

LEVELS OF EVIDENCE

Level IV: Case control study.

The Kager's fat pad radiological anatomy revised

Purpose

The aim of the study was to map connections within the Kager’s fat pad between the structures which limit it.

Methods

A retrospective re-review of 200 ankle magnetic resonance imaging (MRI) examination was conducted. Connections within the Kager’s fat pad between the superior peroneal retinaculum, the fibulotalocalcaneal ligament, the posterior talocalcaneal ligament, the flexor hallucis longus, the paratenon of the Achilles tendon, the flexor retinaculum and bones were studied and a model of the connections was constructed.

Results

The superior peroneal retinaculum was directly connected with the fibulotalocalcaneal ligament in 85.5% of cases, the lateral part of the paratenon in 82.5%, the processus posterior tali in 78.5%, the posterior talofibular ligament in 32%, the flexor retinaculum in 29.5% and the anterior talofibular ligament in 9%.

The fibulotalocalcaneal ligament was connected with the paratenon (on the medial side 88.5%, on the lateral side 68.5%), the flexor retinaculum in 70%, the posterior process of the talus in 79%, the osteofibrosus tunnel for the flexor hallucis longus in 53%, the posterior talofibular ligament in 43.5% and the calcaneofibular ligament in 10.5%.

The posterior talocalcaneal ligament was connected with the fibulotalocalcaneal ligament in 71%, with the osteofibrosus tunnel for the flexor hallucis longus in 76.5%, with the flexor retinaculum in 70%. The plantaris tendon showed projection to the crural fascia in 34 of % cases.

Conclusion

In the Kager’s fat pad there are present more connections than previously reported. All the connections unit at the level of the posterior process of the talus.