Joint-infection management and Perthes disease

Diagnostic & Surgical Management Pathways

• Ultrasound of the Hip: The initial imaging modality of choice. Demonstrates capsular distension and joint effusion with high sensitivity ($> 95\%$). However, ultrasound cannot reliably distinguish sterile reactive fluid (transient synovitis) from purulent septic exudate.
• Urgent Synovial Fluid Aspiration: Indicated whenever there is high suspicion of septic arthritis ($\ge 3$ Kocher criteria or significant effusion with systemic toxicity). Performed under ultrasound guidance or image intensifier using sterile technique.
  • Synovial Fluid Findings in Septic Arthritis: Frank purulence; white blood cell count $> 50,000 \times 10^6\text{/L}$ ($> 50\text{ G/L}$) with $> 75\%\text{ to }90\%$ polymorphonuclear neutrophils; low glucose ($< 50\%$ of blood glucose); positive Gram stain and bacterial culture (along with universal Kingella kingae PCR).
• Emergency Surgical Arthrotomy & Washout: Mandatory definitive therapy for confirmed septic arthritis of the hip. Formal open arthrotomy (or skilled arthroscopy) provides complete evacuation of purulent debris, division of loculations, and decompression of intracapsular pressure, protecting the femoral head blood supply. Repeated washouts may be required.
• Empirical Intravenous Antibiotic Therapy:
  • Commenced immediately following synovial fluid aspiration (never delay surgery to await culture results).
  • First-line in Australia (Therapeutic Guidelines: Antibiotic): Intravenous flucloxacillin ($50\text{ mg/kg}$ up to $2\text{ g}$ IV 6-hourly) or intravenous cefazolin ($50\text{ mg/kg}$ up to $2\text{ g}$ IV 8-hourly) to cover methicillin-susceptible Staphylococcus aureus (MSSA) and Group A Streptococcus.
  • Add intravenous ceftriaxone or cefotaxime in children $< 3\text{ months}$, unimmunized children (Haemophilus influenzae type b), or when Kingella kingae is suspected.
  • Substitute vancomycin or clindamycin if community-acquired MRSA is prevalent.
  • Transition to high-dose oral antibiotics (e.g., cephalexin) once the child is clinically afebrile, weight-bearing, and CRP is consistently normalizing, completing a total antibiotic course of 3 to 4 weeks.
• Management of Transient Synovitis:
  • Conservative outpatient management.
  • Strict bed rest and non-weight bearing until acute pain abates.
  • Regular oral non-steroidal anti-inflammatory drugs (NSAIDs, e.g., ibuprofen $10\text{ mg/kg}$ TDS with food) for 3 to 7 days.
  • Mandatory safety-netting and review in 48 to 72 hours: Symptoms must progressively improve. Any development of high fever, worsening pain, or failure to resolve within 7 to 10 days mandates re-investigation to exclude septic arthritis, Perthes disease, or osteomyelitis.

Perthes Disease (Legg-Calvé-Perthes)

Perthes disease is idiopathic, self-limiting avascular necrosis (osteochondrosis) of the femoral head epiphysis, accompanied by subsequent resorption, revascularization, collapse, and remodeling.

Clinical Presentation & Examination

• Demographics: Boys are affected four to five times more frequently than girls (male-to-female ratio 4:1 to 5:1). Typical age of presentation is 4 to 8 years (range 3 to 12 years). Bilateral involvement occurs in 10% to 15% of patients (typically asynchronous).
• Symptom Complex: Insidious onset of a fluctuating, mild, antalgic limp. Pain is often mild or intermittent, characteristically aggravated by physical activity and relieved by rest. Many children experience pain referred to the groin, anterior thigh, or medial knee (leading clinicians to examine only the knee and miss the underlying hip pathology!).
• Physical Examination Findings:
  • Antalgic gait.
  • Disuse muscular atrophy of the ipsilateral thigh and calf muscles.
  • Marked, asymmetrical reduction in hip range of motion, characteristically with loss of internal rotation and abduction in both flexion and extension.
  • Trendelenburg test may be positive in advanced disease.

Radiographic Stages (Waldenström Classification)

Initial imaging requires bilateral anteroposterior (AP) and frog-leg lateral pelvic radiographs:

1. Initial / Necrotic Stage: Widening of the medial joint space (cartilage hypertrophy); smaller, denser femoral head ossification centre; subchondral radiolucent fracture line along the anterior-superior margin of the epiphysis ("crescent sign" on frog-leg view).
2. Fragmentation Stage: Resorption of dead bone resulting in patchy radiolucencies, sclerosis, and flattening of the femoral head epiphysis.
3. Re-ossification / Healing Stage: Ingrowth of new woven bone and vascular mesenchymal tissue; radiodense bone covers the epiphysis.
4. Remodeling / Residual Stage: Final healing. The femoral head may heal with a normal spherical contour or with permanent deformity: a flattened, enlarged femoral head (coxa plana) and enlarged femoral head (coxa magna), predisposing to early adult secondary osteoarthritis.

Management Principles

• The overarching clinical goal is "containment"—ensuring the deformable, necrotic femoral head remains centered deeply within the spherical acetabulum so it molds into a round shape during the re-ossification phase.
• Children Aged $< 6\text{ Years}$ (Good Prognosis): High remodeling capacity. Managed conservatively with observation, activity modification, avoidance of high-impact sports, physiotherapy to maintain abduction, and temporary crutches during symptomatic flare-ups.
• Children Aged $\ge 6\text{ to }8\text{ Years}$ or Severe Lateral Pillar Collapse (Poor Prognosis): Surgical containment procedures, including femoral varus derotation osteotomy (VDRO) or pelvic innominate osteotomy (Salter osteotomy) to redirect the acetabulum over the femoral head.

Slipped Upper Femoral Epiphysis (SUFE / SCFE)

Slipped Upper Femoral Epiphysis (SUFE, known as SCFE in North America) is a true paediatric orthopaedic emergency. It represents a Type 1 Salter-Harris shear fracture through the hypertrophic zone of the proximal femoral growth plate (physis), resulting in displacement of the femoral neck anteriorly and superiorly relative to the epiphysis (which remains seated in the acetabulum, meaning the femoral head slips posteriorly and medially).

Primary references (checked 7 October 2026): RCH limp assessment.