If bone is placed under the excess stress, the rate of resorption will exceed the rate of bone replacement. This results in weakened cortical bone with buttressing by periosteal and endosteal new bone. If resorption continues to exceed replacement, a stress fracture will occur.

Stress fracture is a continuum of injury from an early remodeling reaction to overt fracture. If diagnosed and treated early, a discrete fracture line may never develop. Skeletal scintigraphy is very sensitive to the remodeling process and typically shows abnormalities 1-2 weeks or more before the appearance of radiographic changes in stress fractures.

Stress fracture can be graded as to its severity (Zwas criteria) in tibial bones: Grade 1 – small ill-defined cortical area of mildly increased activity; grade 2 – larger well defined elongated cortical area of moderately increased activity; grade 3 – wide fusiform cortico-medullary area of highly increased activity; grade 4 – extensive transcortical area of intensely increased activity.

MRI can provide more information in the evaluation of bone pain and does not expose the patient to ionizing radiation. MRI can identify marrow edema early in the stress response, making the technique competitive in early sensitivity. MRI can also differentiate the marrow edema of the stress reaction from the presence of a true fracture. Fractures are visualized as linear abnormalities on T1 scans.