No, the scapulothoracic joint is not a true synovial joint because the scapula is attached to the trunk by muscle only. The only true articulation with the trunk is indirectly through the clavicle.
The scapulothoracic joint is not a true joint in the sense in that it has no capsule or ligamentous attachments. It is more precisely identified as the scapulothoracic articulation. It is formed...