The posterior interosseous ligament (PIL) of the ankle syndesmosis remains a poorly recognized and inconsistently described structure, despite growing anatomical and biomechanical evidence supporting its relevance. Historically conflated with the deep component of the posterior inferior tibiofibular ligament (PITFL), the PIL has only recently gained attention as a potentially independent contributor to syndesmotic stability.

This review consolidates current anatomical, biomechanical, radiological, and surgical insights into the PIL, clarifies terminological inconsistencies, and evaluates its clinical significance.

A comprehensive synthesis of cadaveric studies, imaging research, and biomechanical models was undertaken to characterize the morphology, function, detectability, and surgical relevance of the PIL.

The PIL is identifiable in up to 80% of cadaveric specimens, though its morphology varies widely. MRI detectability varies depending on protocol and anatomical prominence, and current surgical techniques do not account for its presence. When present in robust forms, the PIL may contribute to rotational and posterior syndesmotic stability, especially in conjunction with PITFL insufficiency.

The PIL may represent a distinct deep posterior band in a proportion of ankles. However, its constancy, isolated biomechanical contribution and independent clinical relevance remain insufficiently established. Standardised terminology and targeted anatomical, imaging and biomechanical studies are needed.