01Purpose and principlesWhat the assessment is for and the core concepts behind it.
Bone infection and neoplasia overlap in symptoms and imaging. Both can cause pain, swelling, marrow replacement, cortical destruction, periosteal reaction and a soft-tissue mass. Age, anatomical site, tempo, systemic illness and prior surgery change the differential, but neither fever nor a dramatic radiograph alone is specific. The interpreter should describe the lesion and urgency before naming a diagnosis.
On radiographs, localise the lesion within the bone and along its length. Describe geographic, moth-eaten or permeative destruction; the width and definition of the transition zone; cortical thinning, scalloping or breakthrough; periosteal response; matrix mineralisation; soft-tissue mass; and pathological fracture. A narrow sclerotic margin often suggests slow growth, whereas an ill-defined transition and interrupted periosteal reaction suggest aggression, but infection remains a mimic.
MRI defines marrow and soft-tissue extent, joint involvement, abscess and relationships needed for surgery. Contrast can help distinguish devitalised or liquefied tissue from enhancing inflammation, but it is not a histological diagnosis. CT clarifies cortex and mineralised matrix and guides selected biopsy. Nuclear imaging can survey multifocal disease, while definitive sampling must follow the clinical context and specialist plan.
Key points
- Start with age, site, symptom duration, fever, cancer history, immune status, surgery or hardware and whether pain is focal, nocturnal or progressive.
- Radiographs assess location, pattern of destruction, cortex, periosteal response, matrix, fracture and joint involvement but may be normal early in infection.
- MRI is the preferred modality for marrow, abscess, soft-tissue extension, neurovascular relationship and skip lesions; protocol the whole relevant compartment.
- Infection can appear aggressive and tumour can cause systemic inflammation, so imaging narrows probability but tissue or microbiology establishes many final diagnoses.
- When tumour is suspected, refer before biopsy; the specialist team plans staging and a biopsy track that can be removed with definitive surgery.
- When the patient is septic or neurologically deteriorating, cultures and imaging proceed rapidly, but antimicrobial or decompressive treatment must not be withheld for diagnostic perfection.
02Indications, selection and cautionsWhen it is useful, when urgency changes and important limitations.
Marrow oedema and enhancement may precede radiographic change; adjacent soft-tissue inflammation, subperiosteal collection and abscess strengthen suspicion but require microbiological correlation.
Sclerosis, involucrum, sequestrum, cloaca and sinus formation suggest chronic osteomyelitis, particularly after surgery, trauma or retained hardware.
An ill-defined transition zone, permeative destruction, cortical breakthrough, interrupted periosteal reaction or soft-tissue mass requires urgent specialist assessment.
A sharply marginated lesion with a narrow transition and intact cortex may be indolent, but pain, growth, fracture risk and atypical features still determine referral.
Cloud-like osteoid, rings-and-arcs chondroid calcification and ground-glass or fibrous appearance can narrow the differential without replacing pathology.
A fracture through abnormal lucent, sclerotic or permeative bone should trigger assessment for tumour, metastasis, infection or metabolic disease before definitive fixation.
03Method and interpretationA systematic approach to the test and its findings.
Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.
- 01
Plain radiographyFirst step - Why
- Characterise lesion location, destruction, cortex, periosteal response, matrix and fracture as the initial structural examination.
- Interpretation and limitations
- Normal early films do not exclude osteomyelitis, and aggressive morphology is not specific enough to separate infection from malignancy.
- 02
Magnetic resonance imaging - Why
- Map marrow involvement, soft-tissue extension, abscess, neurovascular relations and intra-articular or spinal spread.
- Interpretation and limitations
- MRI is highly sensitive but can overestimate reactive oedema; protocol and reporting should answer the surgical or biopsy question.
- 03
Computed tomography - Why
- Show cortical destruction, sequestrum, subtle mineralised matrix and anatomy for selected image-guided procedures.
- Interpretation and limitations
- CT has less marrow contrast than MRI and does not establish organism or tumour grade.
- 04
Nuclear medicine imaging - Why
- Survey multifocal skeletal activity or stage selected cancers when conventional imaging is incomplete.
- Interpretation and limitations
- Tracer uptake reflects bone turnover or metabolic activity and may occur with tumour, infection, healing and degeneration.
- 05
Image-guided biopsy or aspiration - Why
- Obtain histology and microbiology from the planned target after multidisciplinary review.
- Interpretation and limitations
- Sampling error and contaminated biopsy tracks matter; suspected sarcoma biopsy must be designed by the treating specialist centre.
04Clinical next stepsHow the result changes management or prompts escalation.
01Infection pathwayMap and sample suspected osteomyelitisFirst stepA child has focal bone pain, fever or inflammatory markers raising concern for acute musculoskeletal infection.+
- 1Assess sepsis and limb or neurological threat, obtain blood cultures promptly when this does not delay emergency treatment.
- 2Obtain initial radiographs and use MRI to define marrow, joint and soft-tissue extent when available and appropriate.
- 3For a stable child, discuss aspiration, operative sampling and drainage with orthopaedics, radiology and microbiology before antibiotics.
- 4Start empirical treatment immediately for sepsis or deterioration, then tailor management to cultures, source control and response.
02Tumour pathwayRefer before biopsySymptoms or radiographs suggest an aggressive primary bone lesion or unexplained pathological fracture.+
- 1Protect the limb from further fracture and perform a careful neurovascular and systemic assessment.
- 2Describe the complete lesion and obtain appropriate initial radiographs without attempting local excision or unplanned biopsy.
- 3Refer urgently to the specialist bone-tumour service, which coordinates MRI of the whole compartment and staging.
- 4DefinitiveAllow the specialist multidisciplinary team to select the biopsy target and tract before definitive histological treatment.
03Uncertain lesionResolve infection-tumour overlapImaging is aggressive but history and laboratory findings do not distinguish infection from neoplasia.+
- 1Avoid declaring the diagnosis from periosteal reaction, enhancement or inflammatory markers alone.
- 2Review age, site, tempo, prior imaging, surgery, malignancy, immune status and antimicrobial exposure.
- 3Agree targeted MRI, CT or systemic imaging with musculoskeletal radiology and the receiving specialty.
- 4Plan tissue for both histology and microbiology when indicated, with a route that preserves future oncological surgery.
05Risks, monitoring and follow-upComplications, safety checks and further assessment.
- Follow temperature, pain, function and serial inflammatory markers alongside imaging when treating infection.
- Review culture and histology results through a named team and reconcile any result that conflicts with the imaging phenotype.
- For infection, repeat imaging only when deterioration, poor response or a management decision requires new anatomical information.
- For tumour, use specialist protocol surveillance matched to histology, treatment and recurrence pattern rather than generic intervals.
- After a pathological fracture or large lytic lesion, maintain weight-bearing restrictions until structural risk has been assessed.
06Special situationsVariants, exceptions and circumstances that change the usual approach.
Transition zone signals tempo
A narrow sharply defined interface implies slower growth than a broad indistinct margin, although exceptions and treated lesions occur.
Periosteum is reactive
Solid, laminated, spiculated and interrupted reactions describe growth rate and host response but do not uniquely identify a cause.
Oedema is not tumour margin
Reactive marrow signal may extend beyond viable neoplasm, so sequence interpretation and specialist staging are essential.
Abscess has anatomy
A rim-enhancing fluid collection may need drainage, while diffuse inflammatory signal alone does not prove drainable pus.
Biopsy is surgery
The path and compartment crossed by a needle can alter definitive resection, so suspected sarcoma sampling requires advance planning.
Normal early radiograph
Acute osteomyelitis may be radiographically silent because sufficient mineral loss and periosteal response take time to develop.
07Common pitfallsFrequent interpretation and management errors.
- 01
Equating aggressive periosteal reaction with malignancy alone.
- 02
Excluding acute osteomyelitis after normal early radiographs.
- 03
Using MRI signal as a substitute for microbiology or histology.
- 04
Biopsying a suspected sarcoma before specialist-centre planning.
- 05
Repeating surveillance imaging without a defined decision or response question.