American Board of Surgical Assistants (ABSA) Orthopedic Practice Test

The callus formation occurs at which stage of the bone healing process?

1. Initial stage

2. Early stage

3. Middle stage

4. Final stage

The correct answer is: Middle stage

Callus formation is a crucial part of the bone healing process and occurs during the middle stage of healing. This stage follows the initial inflammatory response to the injury, where blood supply increases and a hematoma forms at the fracture site. During the middle stage, the body starts to repair the broken bone by generating a soft callus, primarily composed of collagen and cartilage, which provides some stability to the fracture site. As healing progresses, this soft callus is then replaced with a hard callus formed by the mineralization of the newly formed tissue, which hardens it into new bone. This middle stage is characterized by significant osteoblastic activity, where bone-forming cells lay down new bone matrix, and the callus forms around the fracture to stabilize it, bridging the gap between the two ends of the fractured bone. Hence, understanding that callus formation signifies a transition from inflammation to active bone regeneration helps to clearly identify its occurrence in the middle phase of healing.