The tibiofibular syndesmosis is a fibrous joint essential for ankle stability, whence the classical comparison with a mortise. Syndesmosis lesions are quite frequent in ankle trauma. This is a key element in ankle stability and lesions may cause pain or instability and, in the longer term, osteoarthritis. The lesions are often overlooked due to diagnostic difficulties, but collision sport with strong contact is the main culprit. Diagnosis, whether in the acute or the chronic phase, is founded on an association of clinical and paraclinical signs. Cross-sectional imaging such as MRI is fundamental to confirming clinical suspicion. Absence of tibiofibular diastasis no longer rules out the diagnosis. Stress CT and the introduction of weight-bearing CT are promising future diagnostic tools. Exhaustive osteo-ligamentous ankle assessment is necessary, as syndesmosis lesions may be just one component in more complex rotational instability. Therapeutically, arthroscopy and new fixation techniques, such as suture buttons, are opening up new perspectives, especially for chronic lesions (>6months). The present anatomic, epidemiological, diagnostic and therapeutic review does not preclude further clinical studies of rotational ankle instability with its strong risk of osteoarthritis.