Which two sites are most commonly affected by stress fractures?

The tibia and fibula are indeed the most commonly affected sites for stress fractures, particularly among athletes and individuals engaging in repetitive weight-bearing activities. Stress fractures occur when there is an imbalance between bone resorption and bone formation, often exacerbated by high levels of physical stress without adequate recovery.

The tibia, being a weight-bearing bone in the lower leg, experiences significant forces during activities such as running and jumping. The fibula, while it bears less weight, is also subject to stress, especially during activities that involve lateral movements or pivoting. These factors contribute to the higher incidence of stress fractures in these bones compared to other options listed, which may not experience the same level of repetitive stress associated with physical activities.

In contrast, other options such as the patella and humerus, or pelvis and wrist, while they can experience stress fractures as well, are less commonly reported in clinical settings specifically in relation to stress-related injuries, making tibia and fibula the primary sites of concern.