Acute haematogenous osteomyelitis

01OverviewDefinition, clinical context and the essential points that orientate the chapter.

Acute haematogenous osteomyelitis is bone infection arising through the bloodstream, most often in a growing child's metaphysis. Presentation ranges from fever, limp and pinpoint metaphyseal tenderness to irritability or refusal to move a limb in an infant. Ask about preceding skin or respiratory infection, bacteraemia, recent antibiotics, travel, immunisation, sickle-cell disease, immune compromise and invasive procedures. A child can be afebrile, and antibiotics given before presentation can blunt both culture yield and inflammatory findings.

Assess physiological risk before pursuing anatomical certainty. Record a complete paediatric observation set, perfusion, mental state and urine output and use the current sepsis pathway when risk criteria are met. Examine every limb, the spine and skin for multifocal disease or a source. Localise maximal bony tenderness and inspect swelling, warmth and range of the joints above and below. Hip or shoulder disease can present as referred knee or arm pain, while infants may show only feeding change or pseudoparalysis.

BOASt specifies inpatient paediatric and orthopaedic care. Obtain FBC, CRP, blood cultures and ESR in that order of essential investigations and request enough blood for culture. Add renal and liver profiles before potentially prolonged treatment and a blood film when cytopenia or malignancy is plausible. Plain radiographs establish fracture, tumour, foreign material and a baseline but are commonly normal early because cortical and periosteal change takes time. Normal markers, especially early or after antibiotics, cannot independently clear a concerning child.

MRI maps marrow oedema, cortical breach, physeal and joint extension and subperiosteal or muscle abscess and is BOASt's preferred second-line imaging, ideally within 48 hours unless clinical urgency demands sooner. Ultrasound within the same timeframe can detect joint fluid or a superficial collection and guide aspiration but cannot exclude marrow disease. Sedation or anaesthesia planning must not create an unsafe delay. If MRI is unavailable and the child is worsening, senior radiology and surgical teams select the fastest study that answers the immediate source-control question.

Blood culture may identify the organism without bone puncture and should precede antibiotics when doing so does not delay sepsis treatment. Aspirate an effusion or collection and obtain deep tissue at surgery using sterile, separately labelled samples. Send microscopy, aerobic and anaerobic culture and additional tests for age, exposure or immune status after microbiology discussion. Superficial swabs do not represent bone microbiology. If malignancy or an unusual inflammatory lesion remains possible, coordinate biopsy so culture and histology are both protected.

Treatment depends on stability and anatomy. High-risk sepsis requires immediate empirical intravenous antibiotics after blood cultures if cultures are rapidly obtainable. A stable child going promptly to theatre may have antibiotics deferred by the senior team until deep sampling. Uncomplicated acute osteomyelitis begins with intravenous antibiotics chosen from the local paediatric bone-and-joint policy and adjusted for weight, allergy, renal function, local resistance and cultures. Clinical improvement and falling inflammatory indices support conversion to an active oral agent; a calendar alone should not decide the switch.

Drainage is indicated when septic arthritis accompanies bone infection and considered for abscess, necrotic tissue, pressure-related compromise, diagnostic uncertainty needing biopsy or failure to improve. Surgery should evacuate pus, protect the physis and neurovascular structures, obtain representative samples and avoid unnecessary damage to viable bone. Persistent fever or CRP rise after apparently appropriate therapy triggers a new search for missed abscess, wrong organism, inadequate dose, another focus, thrombosis or a non-infective diagnosis rather than reflexively extending the same plan.

At discharge, document the exact drug, formulation, dose, timing, stop or review date and missed-dose plan. Confirm oral tolerance, family capability and laboratory surveillance. Provide return instructions for fever, recurrent pain, swelling, drainage, medication toxicity or declining function. BOASt recommends at least 12 months of clinical and radiographic follow-up because growth arrest and deformity can emerge after infection appears cured. Rehabilitation restores range, strength and gait while activity advances around pain, bone integrity and any operation.

Key points

A limping, non-weight-bearing or pseudoparalysed child with focal bone tenderness and fever has osteomyelitis until a safer explanation is established; early skin and radiographs may look normal.
Admit all children with suspected acute musculoskeletal infection for combined paediatric and orthopaedic care and examine the whole child, spine and adjacent joints.
Initial investigations are FBC, CRP, blood cultures and ESR in the BOASt sequence, plus plain radiographs of the relevant bone and joint; no single result excludes disease.
MRI is the preferred second-line modality, ideally within 48 hours, and sooner when deterioration or a deep collection is suspected; ultrasound helps identify an effusion or superficial collection.
Give empirical intravenous antibiotics immediately in high-risk sepsis. If stable and surgery is planned promptly, senior teams may defer antibiotics briefly to obtain deep samples.
First-line treatment of uncomplicated acute osteomyelitis is intravenous antibiotics; abscess, septic joint, necrotic tissue or poor response creates a drainage or debridement question.
Use clinical recovery and serial temperature, CRP, ESR and white-cell trends to decide intravenous-to-oral switch and total course with microbiology, not an isolated normal value.
Follow clinically and radiographically for at least 12 months with expertise able to recognise recurrent infection, physeal arrest, deformity and functional loss.

02AetiologyUnderlying causes, associations and risk factors, with why each one matters.

Transient bacteraemia

Organisms seed the richly perfused metaphyseal circulation during bacteraemia from skin, respiratory or other mucosal sites, often without an obvious portal.

Staphylococcus aureus

S. aureus is the principal pathogen across age groups; age, immunisation, sickle-cell disease, exposure and local resistance alter the probability of other organisms.

Host susceptibility

Infancy, immunodeficiency, haemoglobinopathy, indwelling vascular access, chronic skin disease and recent infection increase susceptibility or change the expected microbiology.

Direct or contiguous spread

Trauma, surgery, puncture and nearby soft-tissue infection can mimic a haematogenous presentation but imply different organisms, anatomy and source-control needs.

03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.

1
Metaphyseal trapping
Slow flow and hairpin capillary loops near the growth plate permit circulating bacteria to adhere, multiply and provoke local marrow inflammation.
2
Pressure and cortical escape
Purulent marrow exudate raises intraosseous pressure, compromises perfusion and tracks through cortex to form a subperiosteal abscess or adjacent soft-tissue collection.
3
Joint extension
In anatomical regions where metaphysis is intracapsular, infection can enter the joint directly and produce simultaneous osteomyelitis and septic arthritis.
4
Growth-plate injury
Inflammation, vascular compromise or surgical damage near the physis can cause partial growth arrest, angular deformity or limb-length discrepancy.
5
Chronic transition
Inadequate source control or delayed effective therapy permits devitalised bone and bacterial persistence, evolving into sequestrum, sinus or recurrent chronic infection.

04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.

Infant pseudoparalysis

Reduced spontaneous limb movement, crying with handling or poor feeding may be the only localising features before fever or swelling develops.

Metaphyseal tenderness

Focal deep pain near the end of a long bone with limp or refusal to bear weight supports a bone-centred process.

Associated septic joint

An effusion and severe passive-range pain adjacent to metaphyseal infection signals joint contamination and an urgent drainage decision.

Subperiosteal abscess

Increasing swelling, focal fluctuance, persistent fever and MRI fluid outside cortex indicate cortical escape and a source unlikely to resolve with drugs alone.

Multifocal disease

Tenderness at more than one site, spinal pain or pulmonary and cardiac findings suggests widespread bacteraemic seeding.

Atypical course

Night pain, mass, cytopenia, recurrent sterile lesions or failure despite susceptible therapy should reopen malignancy and inflammatory differentials.

Red flags requiring action

Shock, altered behaviour, mottling, oliguria, rising lactate or rapidly worsening limb pain indicates systemic danger and requires parallel sepsis treatment and orthopaedic source-control planning.
A painful immobile joint beside the affected metaphysis, especially the hip or shoulder where the metaphysis may lie within the capsule, raises concern for associated septic arthritis requiring urgent drainage.
Fluctuance, marked swelling, persistent fever or failure of CRP and symptoms to improve after appropriate therapy suggests a subperiosteal, soft-tissue or intraosseous collection.
Back pain, neurological deficit, multifocal tenderness, chest symptoms or a new murmur suggests vertebral, multifocal, pulmonary or endovascular spread and widens imaging and specialist assessment.

05InvestigationsWhat to request, why it matters and how to interpret it.

Investigation order

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
Initial FBC and CRPFirst step
Why
Assess inflammation, cytopenia and a baseline for response.
Interpretation and limitations
A normal early result does not exclude infection; serial direction is more useful, while cytopenias or blasts require urgent alternative-diagnosis review.
02
Blood cultures before antibiotics when safe
Why
Identify bacteraemia without invasive bone sampling.
Interpretation and limitations
Take promptly and do not defer antibiotics in high-risk sepsis; repeat persistent S. aureus bacteraemia and investigate metastatic foci.
03
ESR
Why
Provide a slower inflammatory baseline and recovery marker.
Interpretation and limitations
It changes more slowly than CRP and may remain raised during clinical improvement, so it should not alone prolong intravenous therapy.
04
Initial plain radiographs
Why
Exclude fracture, tumour and foreign body and document a skeletal baseline.
Interpretation and limitations
Early films may be normal; later periosteal reaction or lucency supports but does not date or prove infection.
05
Preferred second-line MRIPreferred
Why
Map marrow, cortex, physis, joint and soft-tissue extension.
Interpretation and limitations
Arrange ideally within 48 hours and urgently for deterioration; marrow oedema is sensitive but must be interpreted against trauma, tumour and inflammatory disease.
06
Ultrasound
Why
Detect joint effusion or accessible subperiosteal and soft-tissue fluid.
Interpretation and limitations
A positive collection guides aspiration; a negative scan cannot exclude medullary osteomyelitis.
07
Deep aspirate or operative samples
Why
Recover the organism and distinguish infection from tumour or sterile inflammation.
Interpretation and limitations
Send separately labelled microbiology samples before antibiotics when stable, with histology when the diagnosis is uncertain; avoid superficial swabs.

06Differential diagnosisRealistic alternatives and the features that help distinguish them.

Septic arthritis

Joint-centred pain with severe restriction and effusion may occur alone or coexist, so apparent bone tenderness does not remove the need for joint assessment.

Trauma or occult fracture

A witnessed injury and focal bony pain can resemble infection, but fever, inflammatory trajectory or pain progression demands reassessment even with a plausible injury.

Malignancy

Leukaemia and primary bone tumours can cause night pain, fever, cytopenias or destructive imaging and require blood-film and imaging review when features are atypical.

Inflammatory disease

Juvenile idiopathic arthritis and chronic recurrent multifocal osteomyelitis produce sterile inflammation, usually with a different tempo or distribution and negative cultures.

Cellulitis or pyomyositis

Superficial or muscle infection may dominate examination and coexist with bone disease; MRI defines the anatomical centre and any drainable extension.

07ManagementImmediate care, first-line treatment, alternatives and escalation.

01UnstableTreat sepsis while defining sourceFirst stepHigh-risk sepsis, organ dysfunction or rapid clinical decline accompanies suspected bone infection.

1Call paediatrics, orthopaedics, anaesthesia and microbiology and apply the current sepsis pathway without waiting for imaging.
2Take blood cultures and essential tests immediately, then give empirical intravenous antibiotics with no avoidable delay.
3Image urgently enough to find septic joint, abscess or another focus and move directly to drainage when indicated.
4Reassess perfusion, lactate, urine output, pain and all potential metastatic sites through resuscitation and source control.

02StablePreserve culture and map anatomyDefinitiveThe child is physiologically stable and definitive sampling or surgery can occur promptly.

1Complete paediatric and orthopaedic examination, FBC, CRP, blood cultures, ESR and plain radiographs.
2PreferredArrange preferred MRI and ultrasound within 48 hours or sooner according to pain, site and clinical trajectory.
3If theatre is planned, make an explicit senior decision whether a short antibiotic delay safely improves deep-sample yield.
4Start policy-based intravenous therapy after samples and tailor promptly to culture, allergy, weight and organ function.

03ReviewProve response and protect growthTreatment has started and the child requires a switch, source-control or discharge decision.

1Track fever, focal tenderness, limb use, CRP, ESR and white count alongside culture and imaging results.
2Investigate failure to improve for missed abscess, septic joint, resistant organism, inadequate exposure or a mimic.
3Convert to an active oral agent only when clinical and laboratory direction, absorption and adherence are satisfactory.
4Continue specialist clinical and radiographic surveillance for at least 12 months and rehabilitate strength and movement.

Key medicines and prescribing safety2 treatments · regimens, roles and cautions

Covers likely bloodstream organisms while cultures and MRI define the pathogen and anatomical source.

Empirical intravenous therapy for paediatric bone infection

Use the trust's current paediatric bone-and-joint infection regimen at the full weight-based dose immediately after blood cultures in high-risk sepsis; in a stable child, start immediately after planned deep sampling and record dose, interval and review time.

Selection varies with age, allergy, renal function, local MRSA prevalence, sickle-cell disease, water or animal exposure and prior antibiotics; involve paediatric infection specialists early and never let drug preparation delay drainage of a septic joint or abscess.

Completes treatment without unnecessary intravenous-line exposure once systemic and local response makes oral therapy dependable.

Culture-directed oral continuation

When the child is clinically improving, inflammatory trends are favourable, oral absorption is reliable and an active formulation is available, prescribe the exact weight-based oral agent and frequency agreed with microbiology for the documented remaining course and review date.

Check palatability, maximum adult dose, interactions, allergy, renal or hepatic adjustment and family ability; recurrence of fever, pain or poor use requires urgent reassessment rather than automatic extension.

08ComplicationsImportant consequences, why they occur and why they matter clinically.

Sepsis and metastatic infection

Persistent bacteraemia can cause shock, multifocal bone infection, endocarditis, pneumonia or distant abscesses and requires repeated systemic assessment.

Abscess and necrotic bone

Subperiosteal, intramuscular or intraosseous pus prevents reliable antimicrobial penetration and may need image-guided or operative drainage.

Growth disturbance

Physeal injury may appear months later as limb-length inequality or angular deformity, supporting prolonged clinical and radiographic surveillance.

Chronic osteomyelitis

Residual devitalised bone can harbour biofilm, causing recurrent pain, drainage and future reconstructive surgery after apparent early recovery.

Functional loss

Pain, immobilisation and joint involvement cause stiffness, weakness and delayed return to school or sport without protected mobilisation and rehabilitation.

09Monitoring and follow-upTreatment response, safety checks and longer-term review.

Record temperature, perfusion, pain, sleep, appetite, limb use and adjacent-joint movement at least daily during acute treatment.
Trend CRP, ESR and white count at clinically meaningful intervals and interpret them with examination rather than pursuing complete biochemical normality in isolation.
Review blood, aspirate and operative cultures with microbiology and verify weight-based dose after every weight, organ-function or route change.
Inspect any surgical wound and reassess for fluctuance, effusion, spinal symptoms, new focal pain or signs of metastatic infection.
Monitor renal, liver, marrow and line complications according to the selected antimicrobial and outpatient intravenous plan.
Follow growth, alignment, limb length, radiographs, gait, joint range and return to activity for at least 12 months.

10Special situationsVariants, exceptions and circumstances that change the usual approach.

Normal early radiographs are expected

Radiographic bone destruction lags behind marrow infection, so a normal film is a baseline rather than a discharge test.

Blood culture can spare bone puncture

A convincing clinical and MRI pattern plus a matching bloodstream organism may identify therapy, but persistent uncertainty still needs tissue.

Hip anatomy matters

Intracapsular metaphyseal anatomy in young children permits direct spread into the joint and lowers the threshold for urgent effusion assessment.

CRP direction beats one value

A falling CRP with restored limb use supports response, whereas renewed rise with pain prompts a source search even during susceptible therapy.

Sickle-cell disease changes probability

Salmonella becomes more relevant but S. aureus remains possible, so exposure and cultures should guide rather than a single association.

Recovery precedes surveillance completion

Symptoms can settle long before a physeal bar declares itself, explaining the minimum year of growth-aware follow-up.

11Common pitfallsFrequent interpretation and management errors.

01
Explaining refusal to bear weight as minor trauma without repeating examination and inflammatory assessment when symptoms progress.
02
Using a normal temperature, CRP or early radiograph as a stand-alone exclusion test.
03
Ordering MRI routinely while failing to assess the adjacent joint or resuscitate a septic child.
04
Giving antibiotics before obtainable deep samples in a stable child already booked for prompt surgery without documenting the trade-off.
05
Persisting with the same treatment despite ongoing fever and pain without searching for abscess or another focus.
06
Stopping follow-up once antibiotics end and missing late growth arrest or deformity.