The Malleolar canal is formed by the flexor retinaculum together with the calcaneus.
It has four compartments and contents. The flexor retinaculum sends fibrous septa to the bone to form four separate osseofibrous tunnels for the following structures which are from anterior to posterior: the tendon and the synovial sheath of tibialis posterior, the tendon and synovial sheath of flexor digitorum longus, the posterior tibial vessels and their tibial nerves and the tendon and synovial sheath of flexor hallucis longus.
References
Malleolar canal Wikipedia(Text) CC BY-SA