Arcuate Sign

Introduction

Fracture of the head of the fibula can indicate a serious knee injury. In some cases, the patient has sustained a complete knee dislocation which may be relocated at presentation to the Emergency Department. Radiographers should be aware of this sign and its significance.

Case 1

The fracture of the fibula head may appear trivial and incidental in the context of such a serious joint disruption. This is not the case. This patient had his fibula head fracture reduced and screwed back to the fibula to improve his outcome. Failure to re-attach the fibula fracture fragment (and associated soft tissue structures) may contribute to a varus deformity of the knee. Importantly, if the fracture has been reduced in the field, or reduced spontaneously, the fibula fracture known as arcuate sign is a significant finding. Avulsion fracture of the fibular head, referred to as the arcuate sign, indicates an injury to at least one of the posterolateral corner structures of the knee ...These ligamentous and tendinous structures have been variably termed the arcuate complex. Inserting from medial to lateral on the fibular head, they include the popliteofibular ligament (also known as the fibular insertion of the popliteus muscle), the arcuate ligament, and the conjoined tendon formed by the biceps femoris muscle tendon and fibular collateral ligament. The variably present fabellofibular ligament, posterolateral joint capsule, lateral gastrocnemius muscle, and popliteus muscle are also considered part of the complex .... we propose that the arcuate sign be considered not only as a marker of internal knee derangement, but also of potential knee dislocation. Jason T. Crimmins, M.D., and Robert D. Wissman, M.D. The Arcuate Sign: A Marker of Potential Knee Dislocation? A Report of Two Cases Radiology Case Reports,Vol 3, No 2 (2008). <a class="external" href="http://radiology.casereports.net/index.php/rcr/issue/view/13" rel="nofollow" target="_blank">Vol 3, No 2 (2008)</a>

Discussion

The trauma radiographer should be aware of the arcuate sign and its significance.

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