Which fracture type cannot be immediately seen on an x-ray?

An occult fracture refers to a fracture that is not immediately visible on standard x-ray examinations. This type of fracture can occur in areas that are difficult to visualize with standard imaging, such as certain regions of the spine, pelvis, or joints. Because of this invisibility on x-rays, other imaging studies like MRI or CT scans are often required to identify these fractures.

In contrast, impacted fractures, torus fractures, and greenstick fractures are generally identifiable on x-rays. An impacted fracture involves one fragment of bone being driven into another, showing clear deformation. A torus fracture, often seen in children, presents as a buckling of the cortex of the bone and is also visible. A greenstick fracture, which is a partial fracture common in pediatric patients, reveals a characteristic bending and incomplete break of the bone visible on an x-ray.

Thus, the unique characteristic of an occult fracture being not immediately detectable with standard x-ray techniques solidifies its status as the correct answer in this context.