Suspected osteomyelitis (excluding spine)

ACR AC Suspected Osteomyelitis, Septic Arthritis or Soft Tissue Infection (2022 rev)

Radiographs first, MRI of the symptomatic region when they are normal or equivocal and infection is still suspected. MRI is the test because osteomyelitis begins in the marrow, and marrow is the one compartment radiographs and CT describe poorly.

A non-healing ulcer over a bony prominence, a discharging sinus, focal bone pain with fever, or a diabetic foot with a deep ulcer that probes to bone.

Referenced decision support — confirm against your local protocol.

Decision support, not a directive. Protocols and timings shown are typical published ones — your local protocol takes precedence, and the vetting radiologist decides.

The request in front of you

Everything is optional. Leave a field alone and the answer assumes nothing — the verdict updates as you go.

Study requested

What the referrer actually asked for. It is evidence of intent, not a constraint on the right answer.

Contrast as written

What the request form says, not what it should say.

Age

Pick a band, or type an exact age if it matters.

years

Pregnancy status

Fever or sepsis

Renal risk factors

The question a vetter can actually answer from the request. An explicit “none known” is a real answer, and it removes checks rather than deferring them.

Previous contrast reaction

The pathway — tap anything already done

Marking a study complete moves the answer on. A patient arrives partway through a pathway far more often than at the start of one.

Accept as requested

Limb radiograph — two orthogonal views

Limb radiograph

What we'd amend, and why

Radiographs are the cheap baseline that occasionally ends the pathway — cortical destruction, periosteal reaction or a sequestrum is diagnostic — and that provides the anatomical context every later study is read against, including the neuropathic deformity that will complicate the MRI. Radiographic change lags the infection substantially, so a normal early film is expected and is not an answer.

Nothing needs resolving before this goes ahead. Routine checks below are owned downstream.

How was this decided?

pathwayany — All patients
rulerule-paeds-dose — Child-sized technique and contrast dose; checked by Radiographer at the scanner

Decision support only. Local protocol takes precedence.

Handled at the scanner(1)nothing for you to do

Settled and owned downstream. Each returns to a radiologist only on the stated trigger.

Child-sized technique and contrast dose
Confirm that a size- or weight-based protocol is selected — child-sized kV and mAs against size-based diagnostic reference ranges — and that contrast volume is calculated by weight rather than taken from an adult default. Weight-based iodinated contrast volumes of roughly 1.5–2.0 mL/kg are widely used in paediatric CT.
Radiographer at the scannerAt the scanner
Flags back if: No paediatric or size-based protocol exists on the scanner for the requested examination, or the requested coverage or number of phases exceeds what the clinical question needs — for example a multiphase study where a single phase answers it, or whole-body coverage for a focal question.

Worth asking the referrer (1)

None of these hold the request up. They sharpen the protocol or the plan that follows.

Which bone or ulcer site, and is there orthopaedic metalwork nearby?
It sets the field of view, and metalwork both degrades MRI locally and shifts the pathway towards labelled white cell imaging.

Pathways

Big forks are separate pathways; the first whose conditions match is the one used.

Febrile or septic — suspected acute osteomyelitis

Role	Study & protocol	Why this answers the question
First line	Limb radiograph Limb radiograph — two orthogonal views usually appropriate	Radiographs remain worth taking in the febrile patient: cortical destruction, periosteal reaction or a sequestrum is diagnostic and occasionally ends the pathway, and they give the anatomical context — including neuropathic deformity — that the MRI will be read against. They are taken alongside the cross-sectional study rather than as a gate in front of it, because radiographic change lags the infection substantially and a normal early film in a septic patient is expected rather than reassuring.
First line	MRI Ankle and Hindfoot MRI Ankle and Hindfoot — routine usually appropriate	Equally endorsed once the patient is febrile, and the study that answers the question: osteomyelitis begins in the marrow, and confluent T1 marrow replacement with corresponding fluid-sensitive high signal is what distinguishes it from reactive oedema. It simultaneously maps the abscess, the sinus tract and the fasciitis or myositis that determine the operation, which is what a septic patient needs known today rather than after a normal film has been reported. The field of view must cover the symptomatic region — for the diabetic foot that means reaching the forefoot — and equivalent regional protocols apply elsewhere in the skeleton. The marrow diagnosis itself is made on unenhanced T1 and a fluid-sensitive sequence; gadolinium is added to delineate an abscess, a sinus tract and devitalised tissue for drainage, so it is a question about the operation rather than a default, and its absence never makes the study non-diagnostic for osteomyelitis.
Reasonable alternative	Bone scintigraphy Bone scintigraphy — whole body (± three phase)	Three-phase bone scintigraphy is the alternative when MRI is contraindicated, and labelled leucocyte imaging with a marrow study is the established route around orthopaedic hardware. Specificity is the weakness: in a neuropathic or recently operated foot, uptake is expected without infection.
Problem solving	CT Extremity / Musculoskeletal CT Extremity — Contrast-Enhanced Soft Tissue	CT is the study for cortical detail — a sequestrum, an involucrum, a cloaca — and for mapping an operation. It cannot exclude early osteomyelitis, because the marrow changes that come first are largely invisible to it, so it is not the way to answer a febrile patient quickly.

Fever plus focal bone pain and a normal radiograph is the classic presentation of acute haematogenous osteomyelitis, and it is the situation this arm exists for. It does not license a whole-limb request: the region still has to be named, or the study is centred on the wrong place.
Blood cultures and a surgical opinion do not wait for the scan. Nothing on this arm is a reason to defer sampling.

All patients

Matches your inputsDefault

Role	Study & protocol	Why this answers the question
First line	Limb radiograph Limb radiograph — two orthogonal views usually appropriate	Radiographs are the cheap baseline that occasionally ends the pathway — cortical destruction, periosteal reaction or a sequestrum is diagnostic — and that provides the anatomical context every later study is read against, including the neuropathic deformity that will complicate the MRI. Radiographic change lags the infection substantially, so a normal early film is expected and is not an answer.
Second line	MRI Ankle and Hindfoot MRI Ankle and Hindfoot — routine	MRI is the modality of choice for bone and soft-tissue infection because it shows marrow directly: confluent T1 marrow replacement with corresponding fluid-sensitive high signal is what distinguishes osteomyelitis from reactive oedema. It simultaneously maps the abscess, the sinus tract and the fasciitis or myositis that determine the operation. For the diabetic foot the field of view must reach the forefoot; equivalent regional protocols apply elsewhere in the skeleton. The marrow diagnosis rests on the unenhanced T1 and the fluid-sensitive sequence — gadolinium is added to delineate a collection, a sinus tract or devitalised tissue before drainage, not to make the diagnosis, which is why a patient whose kidney function stops the contrast still gets a study that answers the question asked.
Reasonable alternative	Bone scintigraphy Bone scintigraphy — whole body (± three phase)	Three-phase bone scintigraphy is the alternative when MRI is contraindicated, and labelled leucocyte imaging combined with a marrow study is the established route around orthopaedic hardware, where metal artefact makes MRI unreliable. Specificity is the weakness: in a neuropathic or recently operated foot, uptake is expected without infection.
Problem solving	CT Extremity / Musculoskeletal CT Extremity — Contrast-Enhanced Soft Tissue	CT is the study for cortical detail — a sequestrum, an involucrum, a cloaca — and for surgical planning when the operation is being mapped. It cannot exclude early osteomyelitis, because the marrow changes that come first are largely invisible to it.

Pitfalls

Reading reactive marrow oedema adjacent to an ulcer as osteomyelitis. The discriminator is confluent low T1 signal, not fluid-sensitive brightness alone.
Confusing neuropathic (Charcot) arthropathy with infection in a diabetic midfoot — they coexist, they look alike, and the distribution of the changes is the main clue.
Accepting a request for the wrong region: a study centred on the ankle will not show a forefoot ulcer.
Treating a normal radiograph as excluding infection in a patient with an ulcer that probes to bone.
Expecting MRI to work through orthopaedic hardware; metal artefact is where the nuclear medicine pathway earns its place.
Cancelling the MRI because gadolinium cannot be given. The marrow diagnosis is made on the unenhanced sequences; what is lost is the delineation of a collection and of devitalised tissue, and the honest response is to say so in the report rather than to abandon the study or to report it as complete.
Reaching for CT in a child because the MRI needs sedation. CT does not show the marrow, so it cannot exclude the diagnosis, and the dose is spent for nothing.

Priors — what to pull first

Previous radiographs of the same foot or limb are what make Charcot change interpretable; without them, deformity is easily read as destruction.
Retrieve prior surgery and amputation history — post-surgical marrow signal persists for a long time.

What makes a good request

Say which bone or which ulcer is in question. A whole-foot or whole-limb request produces a study centred on the wrong region.
This card covers peripheral bone. Suspected spinal infection is a separate pathway with whole-spine coverage, because contiguous and skip lesions change the field of view.
If amputation level or debridement extent is the real question, saying so changes the coverage and the reporting emphasis.
A child with suspected acute haematogenous osteomyelitis is not a small adult on this pathway. The radiograph is still taken, and MRI is still the cross-sectional study — CT is not the paediatric fallback, because it delivers dose without showing the marrow, and a normal CT in a child excludes nothing. Where the child cannot localise the pain, a whole-limb or whole-body fluid-sensitive screening sequence is the way to find the focus rather than a broader CT. Sedation or anaesthesia is planned alongside blood cultures, an orthopaedic opinion and antibiotics — it is a reason to organise the scan properly, never a reason to substitute a study that will not answer the question.

How these studies are acquired

Contrast, phases and timing for every study on the pathways above.

Limb radiograph — two orthogonal views MRI Ankle and Hindfoot — routine Bone scintigraphy — whole body (± three phase)CT Extremity — Contrast-Enhanced Soft Tissue

Confirm locally

Timings, contrast volumes and rates above are typical published values. Your department's protocol, scanner and patient population decide the actual numbers.
Safety thresholds and premedication policy follow local policy where it differs from the cited guidance.

References

Implemented from the cited published sources. Educational and workflow support only; confirm against current guidelines and local policy before clinical use.