Stress Fractures

For Medical Students

What It Shows

A stress fracture is a fracture through bone weakened by repetitive loading rather than by a single injury. 5.13.2 covers stress reactions.

Magnetic resonance imaging shows a low signal line inside an area of marrow change. 5.2.13 covers the T1 imaging.

It matters because the radiograph is normal in the early weeks, so a negative radiograph delays the diagnosis rather than excluding it. 5.3.1 covers the AP view.

How It Is Acquired

Image the symptomatic site with fluid sensitive and T1 weighted sequences. 5.2.16 covers the fat suppression.

Look for the line on the T1 weighted images, where it is clearest. 5.2.13 covers the T1 imaging.

Define the line's orientation and whether it reaches a cortex. 5.5.6 covers the bones.

Define the site, because risk varies between sites more than between appearances. 2.1.2 covers the distal femur.

Take the loading history and the metabolic history together. 4.2.9 covers the onset.

What Normal Looks Like

No low signal line within any marrow change. 5.13.1 covers bone marrow oedema.

An intact cortex on every plane. 5.3.2 covers the lateral view.

No periosteal new bone on the radiograph. 5.3.1 covers the AP view.

Marrow signal following fat away from the symptomatic area. 5.5.6 covers the bones.

What Abnormal Looks Like

A low signal line crossing the marrow with oedema around it. 5.13.1 covers bone marrow oedema.

A line reaching the subchondral plate, which raises collapse. 5.13.4 covers insufficiency fractures.

Periosteal new bone on a later radiograph, confirming the diagnosis in retrospect. 5.3.1 covers the AP view.

A complete fracture through a previously partial line. 5.3.11 covers tibial plateau fractures.

A line at a site known to progress rather than to heal. 2.1.2 covers the distal femur.

MRCS Level

How It Is Acquired

In a viva the expected answer finds the line and names the site.

The expected points are the two sequence types, the line on the T1 weighted images, the orientation, the site, and the loading and metabolic history.

Say that a negative radiograph does not exclude the diagnosis. 5.3.1 covers the AP view.

Say that computed tomography shows the line and carries a dose. 5.16.1 covers the fracture assessment.

Say that the site decides whether the fracture is treated by reducing load or by fixing it. 5.1.3 covers choosing the correct investigation.

What Abnormal Looks Like

The reasoning expected is that a stress fracture is a failure of the remodelling balance, so the treatment removes the load and corrects whatever tipped the balance. 3.4.10 covers the shock absorption.

A line perpendicular to the trabecular load direction behaves differently from one parallel to it. 3.5.3 covers the load distribution.

A line on the tension side of a bone progresses where one on the compression side often heals. 3.13.3 covers the varus alignment.

A fracture in an older patient with ordinary activity is an insufficiency fracture rather than a stress fracture, and the distinction is the bone rather than the load. 5.13.4 covers insufficiency fractures.

How Good It Is

Magnetic resonance imaging is the best available test for a stress fracture, and the radiograph remains the test that confirms healing.

Its best contribution is the line and its relation to the cortex and the subchondral plate. 5.5.6 covers the bones.

It is limited by signal that outlasts the healing, by lines hard to separate from vessels, and by giving no account of why the bone failed. 5.1.6 covers imaging pitfalls.

No figures appear for accuracy on this page, under decision 028, and no healing intervals or line dimensions appear either: those are published quantities from particular cohorts and this environment cannot check them.

FRCS Level

How Good It Is

At decision level the site and the side of the bone decide between load reduction and fixation. 2.1.2 covers the distal femur.

A line reaching the subchondral plate turns the question into one of joint preservation. 5.13.4 covers insufficiency fractures.

Alignment correction is part of the treatment when the fracture sits on an overloaded side. 5.16.5 covers osteotomy planning.

The metabolic assessment is part of the treatment rather than an afterthought. 5.1.3 covers choosing the correct investigation.

Serial radiographs rather than serial scans follow the healing. 5.3.1 covers the AP view.

Where It Misleads

The commonest error is excluding the diagnosis on a normal radiograph. 5.3.1 covers the AP view.

A nutrient vessel is read as a fracture line. 5.5.6 covers the bones.

A healed fracture with residual signal is reported as unhealed. 5.13.1 covers bone marrow oedema.

A subchondral line in an older knee is reported as a stress fracture rather than an insufficiency fracture. 5.13.4 covers insufficiency fractures.

An atypical site is reported without raising the pathological alternatives. 5.13.7 covers bone tumours.

Fellowship Level

Where It Misleads

At fellowship level the fracture has usually failed to heal once already and the question is why. 5.13.2 covers stress reactions.

The answer is rarely in the images: it is in the alignment, the load, the metabolism or the technique. 5.3.6 covers the long leg alignment films.

A line that persists with no oedema around it is a non-union rather than a healing fracture, and the two are reported alike. 5.20.8 covers common reporting errors.

A fracture at a site that does not fit the activity should be treated as pathological until proven otherwise. 5.13.7 covers bone tumours.

Repeat scanning across departments measures protocols alongside healing. 5.18.1 covers the quantitative MRI.

The useful report gives the line, its orientation, its relation to the cortex and the plate, the surrounding oedema, and the site's known behaviour. 5.20.1 covers structured reporting.