What type of fracture is characterized as unstable and is commonly associated with a lateral malleolus fracture?

The characteristic being described in the question points to an oblique fracture. An oblique fracture occurs at an angle across the bone, typically leading to instability, especially if it is located in a weight-bearing area such as the ankle. The instability comes from the way the fracture line traverses the bone; it can create a situation where the fracture fragments may not stay properly aligned or in place.

In the context of a lateral malleolus fracture, which occurs on the outside of the ankle, an oblique fracture can easily destabilize the ankle joint and disrupt the normal mechanics of the joint. This is particularly relevant because injuries to the ankle often involve ligamentous structures that can be compromised when bone stability is affected by the fracture type.

Other options do not align with the characteristics described in the question. For example, a widening joint space typically indicates ligamentous injury or dislocation rather than a specific type of fracture. Transversal fractures occur in a straight line across the bone and are generally more stable, while spiral fractures involve a twisting mechanism and may also suggest a different kind of stability based on the nature of the injury. Thus, the oblique fracture aligns well with the instability mentioned and its association with lateral malleolus fractures.