Educational draft · awaiting clinical reviewThe full textbook explains uncertainty but does not replace live national or local guidance, specialist advice, or current prescribing information.
Septic arthritis and osteomyelitis
Paediatrics and child health · UK scope · Sources checked 27 Aug 2026 · Clinical review pending
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Suspected septic joint with sepsis
A febrile child with severe joint pain, non-weight-bearing, painful passive movement and abnormal perfusion may have destructive septic arthritis with bacteraemia.
Action: Use ABCDE and paediatric sepsis care, obtain blood cultures and urgent blood tests when this does not delay treatment, give age- and risk-appropriate intravenous antibiotics and contact orthopaedics immediately for aspiration and drainage. Keep fasting for likely theatre while maintaining glucose, analgesia and circulation.
Overview
Recognise haematogenous bone and joint infection before cartilage, physis or blood supply is damaged, obtain high-yield cultures and MRI or ultrasound promptly and combine age-appropriate intravenous antibiotics with urgent aspiration, drainage and safe response-guided oral transition.
Most childhood osteoarticular infection is haematogenous. Bacteria lodge in metaphyseal bone or vascular synovium, with Staphylococcus aureus the leading organism. Kingella kingae is important in preschool children and can produce mild fever and modest markers. Neonates have broader Gram-positive and Gram-negative risk; sickle cell disease increases Salmonella as well as staphylococcal infection. Trauma often draws attention to a limb but does not itself exclude infection.
History establishes speed, fever, preceding infection, skin wound, surgery, puncture, animal exposure, travel, immunisation, antibiotics and comorbidity. Ask infants about feeding and limb movement; pseudoparalysis may be the only local sign. Examine the whole child for sepsis, rash, murmurs, multiple painful sites and infection source. Palpate every bone and move adjacent joints gently. Hip infection may present as knee pain, and pelvic osteomyelitis as abdominal, buttock or back pain.
Aetiology
01
Haematogenous Staphylococcus aureus
Transient bacteraemia seeds metaphyseal capillary loops or vascular synovium, making S. aureus the dominant childhood pathogen.
02
Age-specific organisms
Kingella affects young children, while neonates have group B streptococcal and Gram-negative risk from immature immunity and healthcare exposure.
03
Comorbidity-linked infection
Sickle cell disease, immunodeficiency, indwelling lines and recent surgery alter organisms, dissemination risk and empirical antimicrobial coverage.
04
Contiguous or inoculation spread
Puncture, open fracture, pressure injury or adjacent soft-tissue infection directly introduces organisms into bone or joint.
Pathophysiology
1
Metaphyseal bacterial seeding
Slow turbulent blood flow permits bacterial adherence, inflammation and pus formation within poorly collateralised growing bone.
2
Joint pressure injury
Purulent effusion raises intracapsular pressure, compromises epiphyseal blood flow and directly exposes cartilage to destructive enzymes.
3
Subperiosteal abscess formation
Cortical spread lifts the vascular periosteum, creating a local pus collection and further impairing bone perfusion.
4
Physeal and systemic spread
Infection can cross growth structures in infants, seed adjacent joints or enter blood and produce metastatic sepsis.
Clinical features and red flags
Septic joint pattern
Acute fever, severe joint pain, non-weight-bearing and painful restriction in every direction strongly suggests septic arthritis.
Focal osteomyelitis
Local metaphyseal tenderness, swelling, warmth and reduced limb use develops with fever or rising inflammatory markers.
Infant pseudoparalysis
A baby cries with handling or stops moving one limb despite little redness or localised swelling.
Pelvic or spinal infection
Back, buttock or abdominal pain, refusal to sit or walk and painful spinal movement can conceal deep osteomyelitis.
Indolent preschool infection
Kingella can cause a limp and modest markers with little fever, so reassuring appearance does not exclude infection.
Septic deteriorationRed flag
Shock, altered consciousness, rapidly worsening pain or organ dysfunction requires immediate antibiotics and critical-care support.
Red flags requiring action
Shock, altered consciousness or organ dysfunction with bone or joint pain requires immediate sepsis treatment.
A painful immobile hip is time critical because pressure can compromise femoral-head blood supply.
Pseudoparalysis in a neonate or infant may be the only sign of osteoarticular infection.
Back pain with weakness, bladder change or epidural collection features requires urgent spinal MRI and specialist care.
Investigations
01First-line blood cultures and inflammatory profileFirst stepFirst line
Why
Obtain organism and baseline full blood count, CRP, ESR and organ function before antibiotics when safe.
Interpretation and limitations
Blood culture can be diagnostic; normal early markers or a modest Kingella response do not exclude infection.
02Plain radiography
Why
Exclude fracture and tumour and document baseline anatomy before bony changes or surgery.
Interpretation and limitations
Normal early films are expected in many infections and must not delay ultrasound, MRI or source control.
03Urgent joint ultrasound
Why
Detect effusion and guide aspiration in hip and other accessible joints when septic arthritis is possible.
Interpretation and limitations
Effusion confirms fluid but not infection; aspiration and the clinical context determine management.
04Preferred MRI with appropriate contrastPreferred
Why
Map osteomyelitis, pelvic or spinal infection, abscess, pyomyositis and adjacent-joint involvement.
Interpretation and limitations
Marrow oedema is sensitive but interpreted with timing and differential; abscess or necrosis changes surgical planning.
Differential diagnosis
01
Transient synovitis
A well child with modest hip restriction after viral illness improves rapidly and lacks progressive sepsis or destructive microbiology.
02
Trauma or occult fracture
A plausible injury and focal tenderness can mimic infection, while fracture and haematogenous infection occasionally coexist.
03
Juvenile idiopathic arthritis
Longer morning stiffness, multiple joints, rash or uveitis pattern favours sterile inflammation but infection must be excluded first.
04
Leukaemia or bone tumour
Night pain, mass, constitutional symptoms, cytopenias or atypical imaging requires urgent oncology-aware investigation and tissue diagnosis.
05
Discitis or pyomyositis
Spinal refusal, abdominal pain or focal muscle tenderness can reflect infection adjacent to rather than within a joint.
Management
01Initial emergencyCulture and treat without harmful delayFirst stepA child is febrile, non-weight-bearing or has severe joint or focal bone pain with infection concern.+
1Use ABCDE, give analgesia, obtain blood cultures and baseline tests and call orthopaedics and paediatrics immediately.
2Start IV antistaphylococcal treatment through the age- and risk-specific local pathway, adding broader coverage where indicated.
3Keep fasting for possible theatre and arrange ultrasound for joint fluid or MRI for bone, pelvis, spine and abscess questions.
02Septic arthritisDrain the pressurised infected jointClinical, imaging or aspirate findings support purulent joint infection.+
1Aspirate for microbiology and proceed to arthroscopic, open or selected repeat aspiration drainage according to joint and child.
2Continue organism-directed intravenous antibiotic and monitor pain, temperature, perfusion, range and CRP response.
Complications
01
Cartilage destruction and avascular necrosis
Delayed joint drainage can permanently damage articular surface and epiphyseal blood flow, especially in the hip.
02
Growth arrest and deformity
Physeal infection or ischaemia can produce angular deformity, joint incongruity and limb-length difference during later growth.
03
Abscess and chronic osteomyelitis
Devitalised bone and undrained pus can sustain infection, sinus formation, later relapse and repeated surgical intervention.
04
Sepsis and metastatic infection
Persistent bacteraemia can cause shock, endocarditis, pneumonia, venous thrombosis and multiple secondary bone or joint foci.
05
Functional and psychological harm
Pain, immobilisation, repeated operations and prolonged therapy can impair mobility, school participation, sleep and family wellbeing.
Monitoring and follow-up
Record temperature, pain, joint range, focal tenderness, weight bearing or infant limb use and analgesic need at least daily initially.
Trend CRP at clinically useful intervals and use it with examination rather than requiring an arbitrary normal value before oral switch.
Follow every blood, aspirate and operative culture and narrow or broaden therapy promptly with microbiology.
Repeat blood cultures for persistent fever or S. aureus bacteraemia and assess heart, veins and additional painful sites.
Review IV access, renal and hepatic function and medicine adverse effects throughout prolonged antimicrobial treatment.
After discharge monitor recurrence, gait, range, limb length, angular growth and femoral-head integrity when the hip was involved.
Confirm written duration, dose, supply and responsible outpatient team so treatment is not accidentally shortened or duplicated.
Special situations
Infants may stop moving
Pseudoparalysis can be the only local sign because babies cannot report deep bone or joint pain.
Ultrasound sees fluid, not bacteria
A hip effusion requires clinical and aspirate interpretation and cannot by itself distinguish transient synovitis.
MRI maps the operation
Defining marrow extent and abscess changes drainage and duration rather than simply confirming that inflammation exists.
Cultures remain worth taking
Blood may identify the organism even when a small joint aspirate or antibiotic-exposed sample is sterile.
Response tests source control
Persistent fever and CRP after active antibiotic often means undrained pus, multifocal disease or a wrong diagnosis.
Common pitfalls
01
Using fever absence to exclude infection in an infant or Kingella disease.
02
Calling a hip effusion transient synovitis without aspiration when the child is high risk.
03
Waiting for MRI while a clinically septic hip needs urgent drainage.
04
Delaying antibiotics in shock to preserve culture yield.
05
Using one empirical regimen regardless of neonatal age, sickle cell disease or MRSA risk.
06
Assuming a negative post-antibiotic culture disproves infection.
07
Switching to oral medicine before source control and objective improvement.
08
Failing to investigate persistent bacteraemia or non-response for abscess and endocarditis.
Practice
Two practice questions
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Question 1 of 2
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Paediatrics and child healthOriginal SBA
Septic hip management
A febrile 5-year-old is unable to bear weight and has a hip held flexed with severe pain on every passive movement. Ultrasound shows an effusion. What is the best next management?
Sources and review status4 sources · checked 27 Aug 2026 · clinical review pending+
Sources
Sources and review status
National guidance is shown before implementation-dependent detail. Typical adult dose examples remain subject to patient factors, contraindications and the live BNF or specialist protocol. Source check completed 27 Aug 2026; clinical approval remains outstanding.
Septic arthritis usually causes an acutely painful joint held in a position of maximal volume, with severe restriction in all directions and refusal to bear weight. Hip, knee and shoulder are important sites. Osteomyelitis produces focal bony tenderness, swelling or warmth, but deep pelvis and spine may have little visible change. Fever can be absent after antipyretic, in infants or indolent organisms, so function and focal findings remain important.
Take blood cultures, full blood count, film, CRP, ESR, electrolytes, liver and renal function before antibiotics when rapidly achievable. If the child has shock, organ dysfunction or transfer delay, antibiotics and resuscitation take priority. Blood culture can identify the organism even when joint aspirate is sterile. CRP changes more quickly than ESR and supports treatment response, but neither value can rule infection in or out alone.
Plain radiography is useful for fracture, tumour and baseline anatomy but early bone infection may show only soft-tissue swelling. Ultrasound identifies hip or other superficial joint effusion and guides aspiration; it cannot determine whether fluid is infected. MRI with appropriate contrast is the preferred imaging for osteomyelitis extent, pelvic or spinal disease, abscess and adjacent joint involvement. Do not allow sedation logistics to delay drainage of a clinically septic joint.
Joint aspirate should be obtained urgently for Gram stain, culture, cell count and molecular testing when available. A high synovial white-cell count supports infection but overlaps with inflammatory arthritis. Prior antibiotic reduces culture yield, yet withholding necessary antibiotic from a septic child to protect a sample is unsafe. Operative tissue and pus should also go to microbiology. Consider tuberculosis or fungal culture in chronic, epidemiologically relevant disease.
Empirical intravenous therapy follows local resistance, age and syndrome and must cover S. aureus. Many UK pathways use an antistaphylococcal beta-lactam such as flucloxacillin, with broader cephalosporin or additional coverage for young infants, Gram-negative risk, sickle cell disease or severe sepsis; add MRSA-active therapy when risk or microbiology supports it. Record dose in mg/kg, frequency, maximum and renal adjustment from the current BNFC and local guideline.
A septic joint needs source control. Hip infection usually undergoes urgent operative washout or specialist drainage; knee and other joints may be managed by serial aspiration, arthroscopy or open drainage depending on pus, age, site and response. Drain a bone or subperiosteal abscess and remove infected material when medical therapy alone will not control it. Keep the child fasting once surgery is likely while maintaining glucose and fluids safely.
Treatment duration is not one fixed number. Uncomplicated infection with rapid clinical and CRP response can move early from IV to an active oral agent, while MRSA, bacteraemia, abscess, pelvic or spinal disease, neonates and slow response need longer therapy. The multidisciplinary team defines total course and end point. Oral choice must have adequate bioavailability, susceptibilities and a formulation the child will reliably take.
Review non-response after 48 to 72 hours or sooner if deterioration occurs. Repeat cultures, check dose and administration, search for abscess, venous thrombosis, adjacent joint seeding, endocarditis, multifocal disease or an incorrect diagnosis such as malignancy or inflammatory arthritis. After cure, monitor range, gait, pain, limb length and growth because physeal injury, avascular necrosis and chronic osteomyelitis can emerge later.
Key points
Septic arthritis is an orthopaedic emergency because purulent pressure and inflammation rapidly damage cartilage and blood supply; osteomyelitis can form subperiosteal or intraosseous abscess and injure the growth plate.
Suspect infection in any febrile child with new non-weight-bearing, pseudoparalysis, severe joint pain, focal bony tenderness or painful restriction, especially infants who may show only irritability or poor feeding.
Use sepsis ABCDE and contact paediatrics and orthopaedics immediately. Obtain blood cultures before antibiotics when this causes no delay; give prompt intravenous therapy if the child is septic or transfer is prolonged.
Full blood count, CRP and ESR support and monitor the diagnosis, but normal values early, in young infants or with Kingella infection do not safely exclude disease.
Plain radiographs assess fracture and baseline bone but are commonly normal early. Ultrasound detects a joint effusion and guides aspiration; MRI is preferred for osteomyelitis, pelvic infection, abscess and multifocal disease.
Joint aspiration provides cell count, Gram stain, culture and molecular tests, but a negative culture after prior antibiotics does not exclude septic arthritis.
Begin age- and risk-specific intravenous antibiotics covering Staphylococcus aureus through the local antimicrobial pathway; extend for neonates, MRSA risk, sickle cell disease, immunocompromise or penetrating injury.
Drain a septic joint urgently by aspiration, arthroscopy or open washout as selected by site, organism, response and surgical team; antibiotics alone are not reliable source control for a pressurised infected joint.
Switch to oral treatment only when the child is clinically improving, afebrile, able to take medicine, blood culture and organism issues are addressed and CRP is falling, with a documented total course and follow-up owner.
Persistent fever, rising CRP, ongoing bacteremia or pain after 48 to 72 hours requires repeat examination and imaging for abscess, adjacent joint infection, endocarditis, resistant organism or another diagnosis.
Persistent bacteraemia, murmur or multiple painful sites suggests endocarditis or metastatic infection.
Sickle cell disease changes the organism differential and requires Gram-negative and Salmonella-aware antimicrobial advice.
Failure to improve after 48 to 72 hours suggests undrained abscess, resistant organism, thrombosis or alternative diagnosis.
05Joint aspirate
Why
Send cell count, Gram stain, aerobic and anaerobic culture and molecular testing before or during drainage.
Interpretation and limitations
Purulence or positive microbiology supports infection; antibiotics can sterilise culture without removing the need for treatment.
06Operative bone and tissue samples
Why
Obtain multiple deep cultures and histology when abscess, debridement, chronicity or tumour mimic is present.
Interpretation and limitations
Deep samples outperform superficial swabs and allow targeted antimicrobial narrowing and diagnostic correction.
3Repeat drainage or imaging when fever, effusion, bacteraemia or pain persists despite appropriate treatment.
03OsteomyelitisMap extent and drain collectionsFocal bone findings and MRI or microbiology support acute osteomyelitis.+
1Define adjacent joint, subperiosteal abscess, physis, spine or pelvic involvement and obtain deep cultures when surgery occurs.
2Treat with targeted antibiotic and drain abscess, remove devitalised tissue or stabilise bone when the surgical indication is present.
3Review clinical and CRP trajectory and search for multifocal or cardiac infection if bacteraemia persists.
04Oral transitionSwitch only after objective improvementThe child is stable, afebrile and improving after source control and intravenous treatment.+
1Confirm pain, weight bearing or limb use and CRP are improving and organism, susceptibilities and abscess issues are addressed.
2Choose a reliably absorbed active oral formulation the child can take and document total duration and missed-dose advice.
3Arrange orthopaedic and paediatric review for recurrence, range, gait, growth and limb-length complications.
Key medicines and prescribing safety2 treatments · regimens, roles and cautions+
Covers the dominant S. aureus pathogen promptly while cultures and drainage identify a narrower definitive agent.
Empirical intravenous antistaphylococcal therapy
Use the current local paediatric bone-and-joint regimen at the exact weight-based BNFC dose and frequency, commonly IV flucloxacillin with additional age-, sepsis-, Gram-negative- or MRSA-directed coverage when risk requires it.
Obtain cultures first only when this is immediate, review allergy and renal or hepatic function, and broaden for neonates, sickle cell disease, immunocompromise or penetrating injury.
Completes eradication outside hospital once intravenous therapy and drainage have controlled acute disease.
Targeted oral step-down antibiotic
Select an active high-bioavailability oral agent at the exact current child weight-based dose after clinical and CRP improvement; define total course individually from site, source control, organism, bacteraemia and complications.
Do not switch for convenience alone, confirm formulation can be taken and absorbed, and extend or reassess for MRSA, abscess, spine, neonate or slow response.