It can be tricky to differentiate between one of these synovial herniation pits and a Hill Sachs deformity. But the history helps a lot. Hill sachs is always associated with trauma and most often dislocation so in the absence of this history you can be sure it is a normal finding. If there has been a dislocation it is more difficult as both options are viable. The Hill Sachs tends to be a broader defect as it is a punch fracture of the posterior humeral head and it is usually not located exactly at the location where the hyaline cartilage ends and the enthesis begins.
It is this exact location that makes the synovial herniation pit a specific diagnosis.
There will be occasional times where i am faced with a history of trauma / dislocation and I am uncertain if I am looking at a herniation pit or a Hill Sachs.
In this occasional case cross sectional imaging like CT or MRI will come to my rescue.
Steve