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

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Diagnosis

Two-part Low Ankle Sprain

Case Discussion

A low ankle sprain is an injury to the lateral or medial ligament complexes of the ankle. There is both a lateral and a medial low ankle ligament complex. The lateral complex consists of the anterior talofibular ligament (ATFL), the calcaneofibular ligament (CFL), and the posterior talofibular ligament (PTFL). The ATFL is the weakest and most commonly injured, while the PTFL is the strongest and rarely injured (only injured with ankle dislocation). The CFL is an extracapsular ligament often injured in conjunction with ATFL injuries. The medial complex is made of the superficial deltoid and the deep deltoid.

MRI is both highly specific and highly sensitive in diagnosing low ankle injuries. Normal ligaments are hypointense and continuous band-like structures on all pulse sequences.  Injured ligaments may appear thickened, have an irregular contour, and/or be partially or completely discontinuous. The appearance of injured ligaments depends on whether the injury is acute versus chronic. Acute ligament injuries have increased signal on T1-weighted images, and are hyperintense with surrounding edema on T2. Chronically injured ligaments are thickened/fibrotic and/or disrupted, without surrounding edema on T2.

The anterior talofibular ligament tears with equal frequency along the middle of the ligament or at the attachment of the talar neck.  It rarely tears or avulses at the fibular attachment.

Key Images

Low ankle sprain in a 47-year-old man with medial and lateral left ankle pain since stepping in a hole 1 week prior.

A. Axial T2 image of the left ankle shows a rupture of the anterior talofibular ligament (ATFL) from the talar attachment (red arrow). There is also thickening and laxity of the calcaneofibular ligament (CFL), consistent with sprain and partial tearing distally (green arrow).
B. Axial T1 image shows a full thickness tear of the proximal calcaneofibular ligament at the fibular attachment (red arrows).
C. Coronal PD SPAIR image shows the ATFL ruptured distally and retracted from the talar insertion (red 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