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Remote Fellowship – Foot & Ankle Fundamentals – 11/2/2020

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Diagnosis

Two-part High Ankle Sprain

Case Discussion

A high ankle sprain is an injury to the syndesmotic ligaments at the distal tibiofibular joint (tibiofibular syndesmosis) just proximal to the ankle joint.

The syndesmotic ligament complex consists of the interosseous ligament and the anterior and posterior tibiofibular ligaments.

The mechanism of injury is typically dorsiflexion of the ankle joint and/or external rotation of the leg.

MRI is both highly specific and highly sensitive in diagnosing syndesmotic injuries. Uninjured ligaments appear as hypointense and continuous band-like structures on all pulse sequences.  Injured ligaments may appear thickened, with irregular contour, and/or partial or complete discontinuity. The appearance of injured ligaments depends on whether the injury is acute versus chronic.

Acute ligament injuries appear hyperintense on T1-weighted images, and hyperintense with surrounding edema on T2. However, with chronic injuries the ligament appears thickened and hypointense on all pulse sequences (consistent with scarring/fibrosis) and/or disrupted, and without surrounding edema on T2.

Indirect signs of syndesmotic injuries include tibiofibular joint space fluid, prolapsed interspace fat, and syndesmotic diastasis.  Any ankle sprain accompanied by a posterior malleolar pattern of edema, posterior periosteal hemorrhage, or hypertrophic posterior malleolar tubercle (volkmann sign) should raise immediate suspicion for current or prior high ankle injury.

Key Images

Acute 2-part high ankle sprain of the anterior tibiofibular ligament and interosseous membrane, and a non-displaced fracture of posterior malleolus of the tibia in a 32-year-old man with left ankle pain following an injury at work. 

A. Axial PD FS image of the left ankle shows a tear of the anterior tibiofibular ligament (red arrow) and edema through the interosseous portion of the syndesmosis (yellow arrow, an indirect sign of high ankle sprain). Non-displaced fracture of the posterior malleolus (green arrow).
B. Axial T2 FS image shows disruption of the anterior tibiofibular ligament (red arrow) with surrounding hemorrhagic changes. There is also a non-displaced fracture of the posterior malleolus of the tibia (green arrow).
C. Sagittal T1 FS image shows a non-displaced fracture of the posterior malleolus of the tibia with a fragment measuring approximately 1.5 x 0.6 cm (green arrow).

References

  1. Perrich KD, Goodwin DW, Hecht PJ, Cheung Y. Ankle ligaments on MRI: Appearance of normal and injured ligaments. American Journal of Roentgenology 2009; 193:687-695
  2. Rosenberg ZS, Beltran J, Bencardino JT. MR imaging of the ankle and foot. RadioGraphics 2000; 20:S153-179
  3. Vogl TJ, Hochmuth K, Diebold T, et al. Magnetic resonance imaging in the diagnosis of acute injured distal tibiofibular syndesmosis. Invest Radiol 1997; 32(7) 401-409