Which condition often results from an untreated fracture due to prolonged stress on the bone?

Delayed union is the correct answer because it refers to a situation where a fractured bone takes an unusually long time to heal. This condition can arise when a fracture is left untreated, particularly if there is ongoing stress or instability at the fracture site. The continued stress on an incompletely healed bone can disrupt the natural healing process, leading to a delay in the formation of new bone tissue and eventual union of the fracture.

In contrast, osteoporosis is a condition characterized by decreased bone density and increased fragility, not necessarily directly related to the stress from an untreated fracture. Ischemic bone necrosis occurs when there is a lack of blood supply to the bone, which is not a typical immediate consequence of untreated fractures. Complex regional pain syndrome is a chronic pain condition that can develop after an injury, but it does not specifically result from delayed healing of a fracture.