Clinical History
Frontal radiograph; coronal and sagittal PD MR images of the knee of a 38 year old man with knee injury.
Diagnosis: Posterolateral rotatory instability.
Comment
The Arcuate sign (on radiographs), signifies an avulsion fracture of the tip
of the fibular head by the arcuate complex. The arcuate complex consists of
the popliteofibular, arcuate, and fabellofibular ligaments. This avulsion
fracture therefore indicates posterolateral rotatory instability of this
patient's knee. Note that the biceps tendon inserts more laterally and
distally on the side of the femoral head rather than at the tip.
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