Radiology glossary

What does "stress fracture" mean on your scan?

Part of: General orthopedic findings, explained

A tiny crack has formed in the bone from repeated stress — not from a single injury, but from miles of accumulation. Bone constantly remodels itself, dissolving and rebuilding in response to load; when training ramps up faster than the rebuilding can keep pace — the classic story in runners, military recruits, and dancers — microdamage accumulates into a stress reaction and then a true stress fracture. The usual sites read like a map of impact: the metatarsals of the foot, the shin (tibia), the femoral neck, the sacrum, the spine's pars in young athletes. Early on, imaging shows only the bone's distress — marrow edema on MRI — before any crack is visible; later, a faint fracture line appears. The hallmark symptom is pain that starts with activity, worsens as the activity continues, and eventually aches even at rest. Stress fractures are sneaky precisely because there is no memorable injury — just a training log and a bone that could not keep up. The finding is a signal to unload the bone and let remodeling catch up.

What it means on MRI

MRI is the gold-standard test for stress fractures: it shows the bone's stress reaction — marrow edema — days to weeks before any crack appears, and later the fracture line itself, grading the injury from early reaction to complete break. It also shows the surrounding soft-tissue edema and rules out competing diagnoses. When an athlete has focal bony pain with a normal X-ray, MRI is the test that finds the stress fracture early, when rest alone usually suffices.

What it means on CT

CT can show a stress fracture line once it is established, with fine bony detail, but it is insensitive to the early stress reaction that MRI catches — and it adds radiation. CT is occasionally used when MRI is unavailable or when a fracture line needs precise delineation for management decisions. It is a second-line test here, not the first. CT’s niche is the established fracture line that needs precise delineation — occasionally used when MRI is unavailable or when a high-risk site needs exact mapping for management decisions. But CT misses the early stress reaction entirely, which is when the diagnosis matters most. Ordering CT first for a suspected stress injury risks false reassurance; MRI is the test that catches it early.

What it means on X-ray

Plain X-rays are usually normal in the first weeks of a stress fracture — the crack is too fine and the early reaction invisible — which is why “normal X-ray, still hurts” is the classic setup for MRI. Later, the X-ray may show a faint line or the fluffy callus of healing bone. X-ray's main early role is ruling out other causes of the pain; it cannot rule out a stress fracture.

What it means on Ultrasound

Ultrasound cannot see inside bone and cannot diagnose a stress fracture. It may show soft-tissue swelling over the painful spot, but the marrow reaction and fracture line are invisible to it. Persistent focal bony pain with a normal X-ray needs MRI, not ultrasound. Ultrasound may still be used around such injuries to assess the overlying soft tissues — swelling, bleeding, or associated tendon damage — which is useful context. But the bone’s interior, where both the marrow reaction and the fracture line live, reflects sound waves completely. Persistent bony pain with a normal X-ray is a job for MRI, not ultrasound.

What radiologists look at next

For a suspected stress fracture, the radiologist looks first for marrow edema on MRI — the earliest sign — then for a visible fracture line, periosteal reaction, or callus indicating a more established injury. They grade the severity from stress reaction to frank fracture, note the exact anatomic location (since some sites, like the femoral neck's tension side, are higher-risk), and measure the extent along the bone. The surrounding soft tissues are checked for edema, and the opposite limb is sometimes compared. The report distinguishes a low-risk injury that needs relative rest from a high-risk one needing aggressive protection.

Where it commonly shows up

• metatarsal
• tibia
• femoral neck
• foot
• sacrum

Questions to ask your doctor

• How advanced is the stress injury — reaction or true fracture?
• Is this a high-risk or low-risk location?
• How long do I need to rest from the offending activity?
• What caused the overload — training, biomechanics, nutrition?
• When should it be rechecked?

Common questions

What does a stress fracture feel like?

Typically pain that begins during activity and fades with rest, then progressively starts earlier in the workout and lingers afterward — eventually aching even at rest. The spot is often tender to touch. There is no single injury to remember, which is the clue: it is the pattern of pain tracking the training load that points to a stress injury.

Why didn't it show on my X-ray?

Early stress injuries are invisible on X-ray — the bone's distress exists only as marrow edema, which X-rays cannot see, and the crack itself is too fine. X-rays turn positive weeks later when healing bone reacts. This lag is well known, which is why MRI is ordered when the story fits despite a normal X-ray.

Will I need a cast or boot?

Many low-risk stress fractures heal with relative rest — stopping the offending activity — plus a gradual return guided by symptoms. High-risk locations (like certain hip or foot fractures) may need strict non-weight-bearing, a boot, or occasionally surgery because they heal poorly or can displace. Your doctor matches the protection to the site and severity.

Related conditions

• Fracture — What It Means on Your Report
• Bone Bruise — What It Means on Your Report
• Edema — What It Means on Your Report