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Remote Fellowship – Foot & Ankle Fundamentals – 11/2/2020

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Diagnosis

Stress Fracture

Case Discussion

Stress fractures are common overuse injuries and occur over time with repetitive microtrauma.

There are 2 different types of stress fractures: 1) fatigue fractures and 2) insufficiency fractures. Fatigue fractures occur in normal bone subject to abnormal forces, while insufficiency fractures occur in abnormal bone subject to normal forces.

The most common locations for stress fractures in the foot and ankle are the metatarsals (most commonly the 2nd and 3rd), calcaneus, navicular, tibia, and fibula.

MRI is both sensitive and specific for detecting stress fractures and allows detection much sooner compared with radiographs. On T1-weighted images, stress fractures appear as a hypointense fracture line. On T2-weighted images, periosteal and bone marrow edema may be seen.

Stress fractures in the forefoot may be graded on MRI according to the classification described by Fredericson:

– Grade 0: normal examination

– Grade 1: mild to moderate periosteal edema on T2-weighted images only, with no focal bone marrow abnormality

– Grade 2: more severe periosteal edema and bone marrow edema on T2-weighted images only

– Grade 3: moderate to severe edema of both the periosteum and marrow on both T1-weighted and T2-weighted images

– Grade 4: low-signal fracture line on all sequences, with changes of severe marrow edema on both T1-weighted and T2-weighted images.

Additional characterization can be achieved by ascertaining one of the following:

Intramedullary involvement, single cortical involvement, or transcortical involvement. 

Key Images

Stress fracture of the 2nd metatarsal in a 62-year-old man with pain in the right midfoot.

A. Coronal T2 image of the right foot shows a transverse linear area of decreased signal in the 2nd metatarsal diaphysis representing a fracture line (red arrow).
B. Sagittal STIR image shows intermediate signal intensity at the level of the fracture (red arrow), dorsal cortical disruption, and surrounding increased marrow signal intensity.
C. Sagittal T1 image shows decrease signal at the level of the stress fracture (red arrow)

References

  1. Brockwell J, Yeung Y, Griffith JF. Stress fractures of the foot and ankle. Sports Medicine and Arthroscopy Review 2009; 17(3):149-159