What could cause broken shoulder blade?

Chest trauma. The scapula is the medical name for the shoulder blade. The scapula bone is extremely thin & may fracture after any significant chest wall trauma. If the patient has multiple broken ribs, a clavicle fracture and a scapula fracture, one must be wary that the underlying lung has taken a significant injury as well.
Broken shoulderblade. I would think only trauma such as falling or direct blow. I doubt other causes.