Final answer:
Nonunion fractures occur when a bone fails to heal properly. Various fracture types like transverse, oblique, spiral, comminuted, and open fractures can lead to nonunion if not healed correctly. The healing process involves hematoma, callus formation, and remodeling by osteoblasts and osteoclasts.
Step-by-step explanation:
The classification of nonunion fractures pertains to scenarios where a fractured bone does not heal properly, leading to a persistent gap between fragments. Common types of fractures include transverse, oblique, spiral, comminuted, impacted, greenstick, open (or compound), and closed (or simple) fractures.
Although not explicitly listed in the information provided, nonunion fractures can be categorized based on the healing process and bone biology into categories such as hypertrophic, atrophic, and oligotrophic nonunions. Healing begins with a hematoma, followed by the formation of internal and external calli. Osteoblasts and osteoclasts then play roles in bone remodeling and repair, though in a nonunion, this process is disrupted, preventing proper healing.