Variations of anatomical elements contributing to subtalar joint stability: intrinsic risk factors for post-traumatic lateral instability of the ankle?

Ankle sprains are frequently followed by chronic lateral instability, often with talar hypermobility. This might be due to subtalar instability. Among intrinsic risk factors, anatomical variants are generally overlooked. In t he subtalar region, anatomical variation is particularly frequent. On the t alus as well as on the calcaneus, the anterior articular facets may be miss ing or fused with the medial facets, giving rise to three subtalar joint co nfigurations: a three-joint configuration, a fused configuration with a rel atively large anteromedial joint, and a two-joint configuration without ant erior joint. Osteometry was performed on these joint facets (134 calcanei, 122 tali), demonstrating significant differences in the surface of these co nfigurations and the existence of a supplementary supporting surface with g rossly transverse orientation in the three-joint configuration. There are a lso several variants of stabilizing ligaments within the sinus tarsi. Some of these configurations might expose to increased risk of associated subtal ar lesions, resulting in subtalar instability. A systematic look for these variants is recommended in order to evaluate the associated risk factors, e ventually resulting in a better understanding, prevention and cure of seque llae.