Posterior ankle endoscopy/arthroscopy is a technique used to look at and treat problems in the back of the ankle. 

First, it’s important to understand ankle anatomy. The ankle joint is the joint between the lower leg bones (tibia and fibula) and the ankle bone (talus). The joint below the ankle joint is called the subtalar joint; it lies between the ankle bone and the heel bone (calcaneus). The talus has a bony prominence in the back next to the flexor hallucis longus (FHL) tendon. This is the tendon that moves the big toe downward toward the floor.

The bony posterior prominence might be the cause of ankle pain in some people if it is large (called a trigonal process) or it is not completely fused with the talar bone (called an os trigonum).