Arcuate sign (knee)
Updates to Article Attributes
The arcuate sign is often a subtle but important finding on knee x-rays and represents an avulsion fracture of the proximal fibula at the site of insertion of the arcuate ligament complex, and is usually associated with cruciate ligament injury (~90% of cases) 2. The fracture fragment is attached to the lateral (fibular) collateral ligament, the biceps femoris tendon, or both.
Clinical presentation
The fracture results most often from a direct blow to the anteromedial tibia when the knee is extended, resulting in posterolateral subluxation of the tibia in external rotation 1,3. Alternatively, sudden hyperextension of the knee with the tibia internally rotated may cause the same injury 1.
The importance of this injury is that if it is not diagnosed acutely, posterolateral instability may develop which is challenging to correct, and may result in failed cruciate ligament reconstruction 1,3.
Radiographic features
The shape and size of the avulsed fracture vary according to which ligaments are responsible.
Plain radiograph
The avulsion fracture is usually small, <1 cm in size, and involves the styloid process of the fibula. It is displaced superiorly and medially. Occasionally the fracture may be larger and extends to include the lateral aspect of the proximal fibula.
Slight internal rotation AP films are usually best to radiographically demonstrate this injury 3.
MRI
MRI can delineate the soft tissue component of the injury as well as to evaluate associated injuries that are common. Associated findings include 2:
-
cruciate ligament injuries
- especially posterior cruciate ligament 3
- bone bruises
- anteromedial femoral condyle: 50%
- anteromedial tibial plateau: 28%
-
meniscal tears
- medial meniscus: 28%
- lateral meniscus: 22%
- popliteus muscle injury: 33%
- medial collateral ligament injury: common 3
Differential diagnosis
-
Segond fracture
- avulsion is from the tibia
- fragment more medial and anterior
-<p>The <strong>arcuate sign</strong> is often a subtle but important finding on <a href="/articles/knee">knee</a> x-rays and represents an avulsion fracture of the proximal <a href="/articles/fibula">fibula</a> at the site of insertion of the <a href="/articles/posterolateral-ligamentous-complex">arcuate ligament complex</a>, and is usually associated with <a href="/articles/cruciate-ligaments">cruciate ligament</a> injury (~90% of cases) <sup>2</sup>. The fracture fragment is attached to the <a href="/articles/fibular-collateral-ligament">lateral (fibular) collateral ligament</a>, the <a href="/articles/biceps-femoris-muscle-1">biceps femoris</a> tendon or both.</p><h4>Clinical presentation</h4><p>The fracture results most often from a direct blow to the anteromedial tibia when the knee is extended, resulting in posterolateral subluxation of the tibia in external rotation <sup>1,3</sup>. Alternatively, sudden hyperextension of the knee with the tibia internally rotated may cause the same injury <sup>1</sup>.</p><p>The importance of this injury is that if it is not diagnosed acutely, posterolateral instability may develop which is challenging to correct, and may result in failed cruciate ligament reconstruction <sup>1,3</sup>.</p><h4>Radiographic features</h4><p>The shape and size of the avulsed fracture vary according to which ligaments are responsible.</p><h5>Plain radiograph</h5><p>The avulsion fracture is usually small, <1 cm in size, and involves the styloid process of the fibula. It is displaced superiorly and medially. Occasionally the fracture may be larger and extends to include the lateral aspect of the proximal fibula.</p><p>Slight internal rotation AP films are usually best to radiographically demonstrate this injury <sup>3</sup>.</p><h5>MRI</h5><p>MRI can delineate the soft tissue component of the injury as well as to evaluate associated injuries that are common. Associated findings include <sup>2</sup>:</p><ul>- +<p>The <strong>arcuate sign</strong> is often a subtle but important finding on <a href="/articles/knee-joint-1">knee</a> x-rays and represents an avulsion fracture of the proximal <a href="/articles/fibula">fibula</a> at the site of insertion of the <a href="/articles/posterolateral-ligamentous-complex">arcuate ligament complex</a>, and is usually associated with cruciate ligament injury (~90% of cases) <sup>2</sup>. The fracture fragment is attached to the <a title="Lateral collateral ligament of the knee" href="/articles/lateral-collateral-ligament-of-the-knee">lateral (fibular) collateral ligament</a>, the <a title="Biceps femoris muscle" href="/articles/biceps-femoris-muscle-1">biceps femoris</a> tendon, or both.</p><h4>Clinical presentation</h4><p>The fracture results most often from a direct blow to the anteromedial tibia when the knee is extended, resulting in posterolateral subluxation of the tibia in external rotation <sup>1,3</sup>. Alternatively, sudden hyperextension of the knee with the tibia internally rotated may cause the same injury <sup>1</sup>.</p><p>The importance of this injury is that if it is not diagnosed acutely, posterolateral instability may develop which is challenging to correct, and may result in failed cruciate ligament reconstruction <sup>1,3</sup>.</p><h4>Radiographic features</h4><p>The shape and size of the avulsed fracture vary according to which ligaments are responsible.</p><h5>Plain radiograph</h5><p>The avulsion fracture is usually small, <1 cm in size, and involves the styloid process of the fibula. It is displaced superiorly and medially. Occasionally the fracture may be larger and extends to include the lateral aspect of the proximal fibula.</p><p>Slight internal rotation AP films are usually best to radiographically demonstrate this injury <sup>3</sup>.</p><h5>MRI</h5><p>MRI can delineate the soft tissue component of the injury as well as to evaluate associated injuries that are common. Associated findings include <sup>2</sup>:</p><ul>
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