Bone fractures are classified in several ways. The most commonly used classification involves the severity of injury to the soft tissues surrounding the bone. An open fracture (formerly called compound) occurs when an open wound extends to the site of the fracture or when a fragment of bone protrudes through the skin. If the skin is not perforated, the fracture is called a closed fracture (formerly called simple). If the soft tissues around a closed fracture are damaged, the fracture is complicated.

Two other terms to designate fractures are incomplete, in which the fracture does not extend completely across the bone, and complete, in which the bone is broken into at least two fragments. An incomplete fracture that occurs on the convex side of the cure of the bone is a green-stick fracture. Hairline fractures are incomplete fractures in which the two sections of bone do not separate; they are common in skull fractures.

Comminuted (kom-i-nu'ted) fractures are complete fractures in which the bone breaks into more than two pieces--usually two major fragments and a smaller fragment. Impacted fractures are those in which one fragment is driven into the cancellous portion of the other fragment.

Fractures are also classified according to the direction of the fracture within a bone. Linear fractures run parallel to the long axis of the bone, and transverse fractures are at right angles to the long axis. Spiral fractures have a helical course around the bone, and oblique fractures run obliquely in relation to the long axis. Dentate fractures have rough, toothed, broken ends, and stellate fractures have breakage lines radiating from a central point.