What is a key feature of spontaneous fractures?

The key feature of spontaneous fractures is that they arise in previously healthy bones, which is directly related to certain medical conditions or diseases that weaken the bone, such as osteoporosis or cancer. These fractures occur without significant trauma or injury and can happen during normal activities or even at rest.

The notion that spontaneous fractures result from healthy bones highlights their unexpected nature, since healthy bones typically withstand everyday stress. In contrast, the other choices suggest circumstances or conditions where fractures wouldn't be classified as spontaneous. Thus, understanding spontaneous fractures requires recognition of their occurrence in bones that appear normal but may have underlying pathologies leading to the fracture.