The posterior talus has a lateral and medial process. Three things about the lateral process

1. The lateral process is where the PTFL attaches.
2. If it is too long, it is called a Steida’s process.
3. It  forms from an accessory ossicle and if the ossicle doesnt fuse with the talus it becomes an os trigonum.

The lateral tubercle shouldnt project beyond a curve drawn along the talar dome ( Pink line and arrow). When the lateral process is enlarged it projects beyond the curve of the talar dome ( Blue arrow and line).

Two other bony causes can predispose to posterior impingement

1. Excessively downward sloping posterior tibial plafond
2. Haglund’s deformity