The anterior process of the calcaneus is the elongated anterior projection of the calcaneus that articulates with the cuboid at the calcaneocuboid joint anteriorly and gives attachment to the bifurcate ligament (Y ligament) on its superior surface. It forms the floor of the sinus tarsi medially and the posterior aspect of the calcaneocuboid articulation. The extensor digitorum brevis muscle arises from the anterolateral dorsal calcaneus near the anterior process.
The anterior process of the calcaneus is a frequently missed fracture site following forced plantarflexion and inversion (simulated sinus tarsi sprain on X-ray). The bifurcate ligament avulses the anterior process rather than tearing mid-substance, and plain radiographs in the internal oblique (Harris-Beath) view are required for diagnosis as it is hidden on standard lateral and AP views. CT confirms the fracture and assesses calcaneocuboid joint involvement. Missed fractures progress to non-union producing chronic lateral midfoot pain.
Forced inversion and plantarflexion avulses the bifurcate ligament from the anterior process calcaneus, producing a fleck fracture at the sinus tarsi level visible on oblique foot radiograph, frequently misdiagnosed as ankle sprain and resulting in painful non-union if treated with early mobilisation rather than a below-knee cast for 6 weeks.
Large anterior process fractures that extend into the calcaneocuboid joint produce post-traumatic arthrosis of the lateral column, causing lateral midfoot pain with weight-bearing managed with orthotics, injection, or calcaneocuboid arthrodesis.
