Paeds · rheumatology-musculoskeletal-and-sports
Acute monoarthritis and septic arthritis
Also known as septic arthritis · pyogenic arthritis · suppurative arthritis · acute monoarthritis · hot joint · Kocher criteria
A fellowship approach to the child with an acutely hot, swollen joint: the Kocher clinical prediction rule that separates septic arthritis from transient synovitis, the urgent joint aspiration that confirms pus in the synovial fluid, the empiric intravenous antibiotics stratified by age and organism, and the surgical emergency that a septic hip represents because intracapsular pressure threatens the femoral head blood supply within hours.
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Red flags
- Never reassure away a febrile child with a swollen joint held rigidly flexed — septic arthritis destroys cartilage within hours to days and the septic hip is a surgical emergency that will not wait for the morning
- A septic hip must be drained in theatre by arthrotomy and washout — intracapsular pus under pressure obliterates the femoral head blood supply and causes avascular necrosis that no antibiotic can reverse
- The Kocher criteria are a probability tool, not a rule-out — a child with zero predictors still carries a small but real risk of septic arthritis, and clinical judgement, CRP, and ultrasound override any reassuring score
- Kingella kingae is the commonest organism in children under four years and is easily missed because it grows poorly on routine culture and produces a deceptively mild, low-fever, low-inflammatory picture — request blood-culture-bottle inoculation or oropharyngeal PCR
- Always draw blood and aspirate synovial fluid for culture before giving the first antibiotic dose — an antibiotic given before sampling sterilises the diagnostic specimen and forces blind management
- A neonate with septic arthritis may show no localising signs at all — the presentation is sepsis, pseudoparalysis of a limb, or irritability, and multiple joints may be involved
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- Musculoskeletal medicine - recognise and investigate the hot swollen joint
- Acute presentations - the febrile child with a limp
- Renewed curriculum for first-year trainees from 2027 - Learning goal 6: Clinical management - essential general paediatrics
- Rheumatology - diagnose and manage acute monoarthritis and septic arthritis
- Orthopaedics and musculoskeletal medicine - apply the Kocher criteria and plan urgent aspiration and drainage
- Acute presentations - the limping febrile child and the septic hip
- Rheumatology 10-12
- Acute presentations 10-12
- Clinical Applications
- Long Cases
- Short Cases
- 9. Musculoskeletal medicine - septic arthritis and the hot joint
- 11. Child health and immunisation - antimicrobial stewardship
- 4. Professional skills and knowledge: Patient management
- Foundation of Practice (FOP)
- Theory and Science (TAS)
- Applied Knowledge in Practice (AKP)
- Clinical
- History
- Communication
- Video
- General Pediatrics Content Outline - Musculoskeletal disorders
- General Pediatrics Content Outline - Universal Task 4: Management and Treatment
- General Pediatrics Content Outline - Infectious Diseases
- Patient Care 4: Clinical Reasoning
- Patient Care 5: Patient Management
- Medical Knowledge 1: Infectious diseases and musculoskeletal disorders
- Systems-Based Practice 2: Antimicrobial stewardship
- Medical Expert
- Pediatrics: Foundations EPA - Acute care of the febrile limping child
- Pediatrics: Rheumatology and orthopaedics applied domain
A three-year-old boy is carried into the emergency department refusing to walk, holding his right hip flexed and externally rotated, with a fever of thirty-nine degrees and a knee that screams when anyone touches it; or a toddler presents with a swollen red ankle and a limp that came on over a day; or a neonate in the nursery is irritable and febrile with a swollen shoulder and will not move the arm. In each, the question is the same — is this joint infected, and if there is any doubt, aspirate it, drain the hip, and treat. [5] [1]
Run the pathway as five moves. Score the probability of sepsis with the Kocher criteria — fever over thirty-eight point five, unable to bear weight, ESR over forty, white cell count over twelve — and add CRP over twenty from the Caird study. Sample the joint urgently with needle aspiration before any antibiotic, sending synovial fluid for cell count, Gram stain, and culture. Scan with ultrasound to detect a joint effusion and guide the tap when the joint is deep, like the hip. Strike with empiric intravenous antibiotics the moment cultures are drawn — flucloxacillin plus a third-generation cephalosporin in the under-four to cover Staphylococcus aureus and Kingella kingae. Sweep the septic hip to theatre for arthrotomy and washout, because intracapsular pus threatens the femoral head and antibiotics alone cannot relieve that pressure. [1] [3] [7]
Overview & Definition
Acute monoarthritis is inflammation of a single joint presenting over hours to days, and septic arthritis is the bacterial, pus-forming subset that is the orthopaedic and infectious-disease emergency within it. The two are framed together because the hot swollen joint is a single clinical problem whose first task is always the same — exclude infection — and because the other causes, from transient synovitis to juvenile idiopathic arthritis, reveal themselves only once sepsis has been ruled out. [1] [5]
The fellowship framing rests on a single pathological truth. The synovium is a highly vascular membrane that produces the fluid lubricating the joint, and bacteria reach it most often by the haematogenous route, seeding the synovial membrane and multiplying within the synovial fluid where host defences and antibiotics penetrate poorly. The resulting neutrophilic inflammation raises the intra-articular pressure, erodes the articular cartilage, and — in the hip, where the capsule is tight and the femoral head blood supply is intracapsular — chokes the circulation to the epiphysis. This is why septic arthritis is measured in hours, not days. [9]
The clinical importance comes from what happens if the joint is drained late or treated inadequately. Permanent cartilage destruction, avascular necrosis of the femoral head, growth arrest with leg-length discrepancy, recurrent infection, and progression to chronic osteomyelitis are the sequelae of a delayed or partial response. In the neonate and the immunocompromised child the presentation is occult, multiple joints may be involved, and the diagnosis is even more easily missed — which is why a low threshold to aspirate any suspicious joint is the safeguard. [5] [6]
References10ShowHide
- [1]Kocher MS, Zurakowski D, Kasser JR. Differentiating between septic arthritis and transient synovitis of the hip in children: an evidence-based clinical prediction algorithm. J Bone Joint Surg Am, 1999.PMID 10608376
- [2]Kocher MS, Mandiga R, Zurakowski D, Barnewolt C, Kasser JR. Validation of a clinical prediction rule for the differentiation between septic arthritis and transient synovitis of the hip in children. J Bone Joint Surg Am, 2004.PMID 15292409
- [3]Caird MS, Flynn JM, Leung YL, Millman JE, D'Italia JG, Dormans JP. Factors distinguishing septic arthritis from transient synovitis of the hip in children. A prospective study. J Bone Joint Surg Am, 2006.PMID 16757758
- [4]Li SF, Cassidy C, Chang C, Gharib S, Torres J. Diagnostic utility of laboratory tests in septic arthritis. Emerg Med J, 2007.PMID 17251607
- [5]Lavy CB. Septic arthritis in Western and sub-Saharan African children - a review. Int Orthop, 2007.PMID 16741731
- [6]Smith SP, Thyoka M, Lavy CB, Pitani A. Septic arthritis of the shoulder in children in Malawi. A randomised, prospective study of aspiration versus arthrotomy and washout. J Bone Joint Surg Br, 2002.PMID 12463664
- [7]Ceroni D, Dubois-Ferriere V, Cherkaoui A, Gesuele R, Combescure C, Lamah L, Manzano S, Hibbs J, Schrenzel J. Detection of Kingella kingae osteoarticular infections in children by oropharyngeal swab PCR. Pediatrics, 2013.PMID 23248230
- [8]Yagupsky P. Diagnosing Kingella kingae in Pediatric Chest Wall Infections. Pediatr Infect Dis J, 2023.PMID 36729685
- [9]Autore G, Bernardi L, Esposito S. Update on Acute Bone and Joint Infections in Paediatrics: A Narrative Review on the Most Recent Evidence-Based Recommendations and Appropriate Antinfective Therapy. Antibiotics (Basel), 2020.PMID 32781552
- [10]Font A, Agüera M, Ríos-Barnés M, et al. Impact of paediatric antimicrobial stewardship program in haematogenous bone and joint infections. Eur J Pediatr, 2025.PMID 40527966