Which of the following factors can negatively affect fracture healing?

The choice indicating that big displacement negatively affects fracture healing is accurate because displacement refers to the distance and direction of separation between the fractured bone fragments. When there is significant displacement, the ends of the fracture may not align properly, leading to a disruption in the union process. Proper alignment is crucial for bone healing, as it allows for appropriate biomechanical stability and facilitates the formation of new bone tissue. If the fracture ends are not closely apposed, the healing process can be delayed, leading to complications such as nonunion or malunion.

Other factors, like having an immature skeleton or a single bone fracture, can affect healing but generally do not pose as significant a risk as displacement. The immature skeleton is often more amenable to healing due to the higher activity of the growth plate and cellular regeneration in younger patients. Additionally, a single bone fracture might heal well if the fragments are properly aligned, which contrasts with cases of severe displacement that complicate healing. A nearby unaffected support bone may provide some stability, thus not negatively impacting the healing of the fractured bone.