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

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Diagnosis

Posterior Ankle Impingement

Case Discussion

Ankle impingement is the loss of full ankle range of motion secondary to an osseous and/or soft-tissue abnormality. Ankle impingement syndromes alter the biomechanics of the joint resulting in chronic ankle pain. These syndromes may be divided anatomically into anterolateral, anterior, anteromedial, posteromedial, and posterior impingement.

Anterolateral ankle impingement is usually secondary to fibrous soft tissue entrapment in the anterolateral ankle gutter, following a remote inversion injury with low ankle sprain. On MRI, an abnormal low signal fibrous soft tissue mass or fibrous band may be present in the anterolateral gutter.

Anterior ankle impingement is seen in athletes subjected to repeated ankle dorsiflexion. Findings of anterior ankle impingement include beaking at the anterior tibial plafond, osteochondral loose bodies within the anterior ankle joint capsule, anterior tibiotalar osteoedema “kissing lesions”, and synovitis in the anterior capsular recess.

Anteromedial ankle impingement is relatively uncommon and secondary to fibrous soft tissue entrapment. On MRI, a “meniscoid” lesion may be identified and appear isolated or stemming from a chronically torn thickened/fibrotic deltoid ligament complex.

Posteromedial impingement is relatively uncommon and typically follows a severe inversion injury, resulting in scar tissue or fibers from the deep posterior deltoid complex becoming entrapped between the medial wall of the talus and the medial malleolus. On MRI this may be seen as thickened low signal fibrous soft tissues and reactive bone marrow edema of both the medial talus and medial malleolus.

Finally, posterior ankle impingement is the result of repetitive or acutely forced plantar flexion of the foot. The presence of an os trigonum or Steida’s process may predispose someone to the condition.  However, soft tissue impingement of the flexor tendon sheaths may also be responsible. On MRI, bone marrow edema may be appreciated in the posterolateral talar tubercle, os trigonum, or both, indicating bone impaction or contusion. MRI may also show edema of the posterior synovial recess of the subtalar and tibiotalar joints and the flexor hallucis longus tendon sheath.  Chronic impingement posteriorly may eventually result in FHL rupture.

Key Images

14-year-old ballet dancer complaining of posterolateral ankle pain

A. Sagittal STIR image of the left ankle shows marked edema within the os trigonum or fractured Stieda process (red arrow), high signal edema extending into the lateral tubercle of the posterior talus (yellow arrow), and posterior subtalar recess synovitis (blue arrow).

References

  1. Cerezal L, Abascal F, Canga A, Pereda T, Garcia-Valtuille R, Perez-Carro L, Cruz A. MR imaging of ankle impingement syndromes. American Journal of Roentgenology 2003; 181:551-559