The posterior facet of the subtalar joint is the largest and most important of the three subtalar facets, accounting for over 70% of the talocalcaneal articular contact area. It is a biconcave-biconvex articulation between the posterior calcaneal articular surface (concave) and the posterior articular surface of the talus (convex). This facet is separated from the middle and anterior facets by the sinus tarsi and is the primary load-transmitting articulation of the hindfoot.
The posterior subtalar facet is the site of most subtalar osteoarthritis, which develops as a consequence of calcaneal fractures (malunion with loss of Bohler angle), talocalcaneal coalition, inflammatory arthritis, or primary degenerative disease. Clinical diagnosis requires subtalar stress testing and pain with hindfoot inversion and eversion. Selective anaesthetic injection into this isolated compartment under fluoroscopic guidance confirms the facet as the pain source before triple arthrodesis or isolated subtalar fusion is planned.
Comminuted intra-articular calcaneal fractures with posterior facet displacement produce progressive subtalar arthritis with hindfoot stiffness and pain on uneven terrain, the most common indication for subtalar fusion when conservative management fails.
Degenerative arthrosis of the posterior facet from cumulative hindfoot loading produces progressive restriction of inversion and eversion with sinus tarsi tenderness and characteristic subtalar sclerosis on X-ray, managed with orthotics, injection, and ultimately fusion.
