# CIM Case: Transient Synovitis vs Septic Hip ## Clinical Scenario **Patient:** 4-year-old boy **Presentation:** Sudden onset right hip pain and limp since this morning, crying with movement, refusing to walk **Relevant history:** Mild upper respiratory tract infection 1 week ago, no trauma, no recent vaccinations, previously well, fully immunised, no sick contacts **Examination findings:** - Temperature 37.8°C - Right hip held in flexion, abduction, external rotation (position of comfort) - Refuses to weight-bear on right leg - Log roll positive (pain with any hip rotation) - Severely limited internal rotation and extension - Mild fullness in groin - No skin changes, no erythema - Left hip and knee examination normal - Abdomen soft, non-tender --- ## Investigations Provided ### Laboratory Results | Test | Result | Normal Range | Interpretation | |------|--------|--------------|----------------| | WCC | 14.5 ×10⁹/L | 5-15 ×10⁹/L | Upper normal | | CRP | 45 mg/L | <5 mg/L | ↑ Elevated | | ESR | 55 mm/hr | <10 mm/hr | ↑ Elevated | | Blood culture | Pending | - | Sent | | Hb | 118 g/L | 110-140 g/L | Normal | | Platelets | 350 ×10⁹/L | 150-400 ×10⁹/L | Normal | ### Imaging **Image 1: AP Pelvis Radiograph** **Radiological features:** - No bony abnormality - Widening of right hip joint space (suggests effusion) - Soft tissue swelling lateral to right hip - No femoral head abnormality (no Perthes changes) - Physes normal - Left hip normal **Image 2: Ultrasound of Right Hip** **Ultrasound findings:** - Moderate hip effusion present (8mm fluid collection) - Synovial thickening - No organised collection - No bony erosion visible ## Questions & Model Answers **Differential Diagnosis for Paediatric Irritable Hip:** | Diagnosis | Key Features | Concern Level | |-----------|--------------|---------------| | **Septic arthritis** | Fever, refuses to weight-bear, elevated CRP/ESR | **HIGHEST - surgical emergency** | | **Transient synovitis** | Viral prodrome, low-grade/no fever, less unwell | Common, self-limiting | | **Perthes disease** | Older (4-8), insidious onset, X-ray changes | Important to exclude | | **SUFE** | Adolescent, obese, physeal slip | Wrong age group | | **JIA** | Prolonged symptoms, other joints | Less acute | | **Osteomyelitis** | Point tenderness, may have adjacent joint effusion | Possible | **Most Concerning Diagnosis: SEPTIC ARTHRITIS** **Why It Must Be Excluded:** - Destroys articular cartilage within 6-8 hours - Permanent joint damage if untreated - Can lead to sepsis and death - Requires urgent surgical washout **This Patient's Concerning Features:** - Refusing to weight-bear - Temperature 37.8°C (borderline febrile) - Elevated CRP (45) and ESR (55) - Hip effusion on ultrasound - Very limited ROM **Golden Rule:** Assume septic arthritis until proven otherwise > **Consultant Tip:** Never miss septic arthritis. When in doubt, aspirate the hip. A negative aspiration is far better than missing a septic joint. **Kocher Criteria (Original 1999):** | Criterion | Definition | Points | |-----------|------------|--------| | Non-weight-bearing | Unable or refuses to walk | 1 | | Temperature >38.5°C | Oral or rectal | 1 | | ESR >40 mm/hr | Westergren method | 1 | | WCC >12 ×10⁹/L | Total white cell count | 1 | **Probability of Septic Arthritis:** | Score | Predicted Probability | |-------|-----------------------| | 0 | 0.2% | | 1 | 3% | | 2 | 40% | | 3 | 93.1% | | 4 | 99.6% | **This Patient's Score:** | Criterion | This Patient | Score | |-----------|--------------|-------| | Non-weight-bearing | Yes | 1 | | Temperature >38.5°C | No (37.8°C) | 0 | | ESR >40 | Yes (55) | 1 | | WCC >12 | Yes (14.5) | 1 | | **Total** | | **3** | **Kocher Score 3 = 93% probability of septic arthritis** **Limitations of Kocher Criteria:** | Limitation | Implication | |------------|-------------| | Derived from referral population | May overestimate probability | | Original study had high septic arthritis rate | Not generalisable to all settings | | CRP not included | CRP is often more discriminating | | Binary cutoffs | Misses borderline cases | | Low scores don't exclude | 3% at score 1 still means some cases missed | **Modified Kocher (with CRP):** - CRP >20 mg/L added as 5th criterion - Improves specificity - This patient: CRP 45 → positive > **Consultant Tip:** Use Kocher as a guide, not a rule. Score of ≥2 warrants aspiration. Score of 1 with high clinical suspicion still needs aspiration. **Immediate Management:** **Decision:** This patient requires urgent hip aspiration **Rationale:** - Kocher score 3 = 93% probability of septic arthritis - Even with lower probability, consequences of missing septic arthritis are severe - Aspiration is diagnostic AND therapeutic (decompresses joint) **Preparation for Aspiration:** | Step | Details | |------|---------| | **Consent** | Explain procedure and need for possible surgery | | **Fasting** | NBM in case theatre required | | **IV access** | For fluids and antibiotics | | **Blood cultures** | Before antibiotics if time allows | | **Theatre availability** | Book emergency theatre | **Aspiration Technique:** **Setting:** Theatre or ED with ultrasound guidance preferred **Approach Options:** - **Anterior (preferred):** 2cm distal and lateral to ASIS, direct to femoral head-neck junction - **Lateral:** Through greater trochanter (more painful) **Procedure:** 1. Aseptic technique 2. Ultrasound guidance improves success 3. Aspirate joint - note volume and appearance 4. Send for: Gram stain, culture, cell count, crystals (if older child) **Fluid Interpretation:** | Parameter | Septic | Transient Synovitis | |-----------|--------|---------------------| | Appearance | Purulent, turbid | Serous, yellow | | WCC | >50,000/μL | <50,000/μL | | Polymorphs | >90% | <75% | | Gram stain | May be positive | Negative | | Culture | Positive (50-80%) | Negative | **If Aspiration Confirms Septic Arthritis:** - Immediate surgical washout - IV antibiotics after cultures taken > **Consultant Tip:** Don't wait for culture results. If the aspirate looks purulent or WCC is very high, proceed to washout immediately. **Diagnosis Confirmed:** Septic arthritis of right hip **Surgical Washout:** **Timing:** URGENT - within 6 hours of diagnosis **Approach Options:** | Approach | Advantages | Disadvantages | |----------|------------|---------------| | **Anterior (Smith-Petersen)** | Direct access, between sartorius and TFL | May need to extend | | **Medial (Ludloff)** | Good for infants, minimal dissection | Risk to medial circumflex | | **Arthroscopic** | Minimally invasive, thorough lavage | Requires expertise | **Surgical Technique (Anterior Approach):** 1. **Incision:** Bikini line or anterior approach 2. **Interval:** Between sartorius and TFL (or rectus femoris) 3. **Capsulotomy:** Incise capsule longitudinally 4. **Debridement:** - Drain all pus - Lavage with copious saline (3-6 litres) - Remove fibrin and debris - Assess articular cartilage 5. **Drain placement:** Consider leaving drain for 24-48 hours 6. **Closure:** Loose closure or leave capsule open, close wound **Postoperative Care:** | Aspect | Management | |--------|------------| | **Antibiotics** | IV flucloxacillin 50mg/kg QID (if Staph suspected) | | **Duration** | IV 2-4 weeks, then oral to complete 4-6 weeks total | | **Microbiology** | Adjust antibiotics based on culture/sensitivities | | **Immobilisation** | Hip spica in young children, gentle ROM in older | | **Monitoring** | Daily review, CRP trending down | **Common Organisms by Age:** | Age | Common Organisms | Empiric Antibiotics | |-----|------------------|---------------------| | Neonate | Group B Strep, Staph, Gram-negatives | Fluclox + gentamicin | | 1-5 years | Staph aureus, Kingella kingae | Flucloxacillin | | >5 years | Staph aureus | Flucloxacillin | | IVDU/immunocompromised | MRSA, Pseudomonas | Vancomycin + ciprofloxacin | > **Consultant Tip:** Don't delay surgery waiting for culture results. Empiric antibiotics after intraoperative cultures are taken. Adjust based on sensitivities. **Interpretation:** Consistent with TRANSIENT SYNOVITIS **Findings Suggesting Transient Synovitis:** - Clear/serous aspirate - WCC <50,000/μL (often <10,000) - Polymorphs <75% - Negative Gram stain - Cultures negative (await final result) **Management of Transient Synovitis:** **Admission vs Discharge:** | Consideration | Management | |---------------|------------| | **If confident diagnosis** | May discharge with close follow-up | | **Any uncertainty** | Admit for observation 24-48 hours | | **This patient (Kocher 3)** | Admit and observe initially | **Conservative Treatment:** | Aspect | Approach | |--------|----------| | **Analgesia** | Paracetamol, ibuprofen | | **Rest** | Bed rest until comfortable | | **Weight-bearing** | As tolerated | | **Traction** | Not routinely needed | | **Duration** | Resolves within 7-10 days | **Follow-up Protocol:** | Time | Assessment | |------|------------| | 24-48 hours | Clinical review, repeat CRP | | 1 week | Clinical and inflammatory marker review | | 6-8 weeks | X-ray pelvis (exclude early Perthes) | **Why Follow-up X-ray at 6-8 Weeks?** - Perthes disease can initially present like transient synovitis - Early X-ray changes may not be visible - Screen at 6-8 weeks to exclude Perthes **Red Flags During Observation:** - Worsening symptoms - Rising CRP/ESR - Persistent fever - Unable to weight-bear after 48-72 hours → **Consider re-aspiration or MRI** > **Consultant Tip:** Always follow up transient synovitis with an X-ray at 6-8 weeks. Early Perthes can masquerade as transient synovitis. **Complications of Paediatric Septic Arthritis:** **Early Complications:** | Complication | Mechanism | Prevention/Management | |--------------|-----------|----------------------| | **Sepsis** | Untreated infection | Early surgery, IV antibiotics | | **Adjacent osteomyelitis** | Spread through metaphysis | Look for on MRI, treat aggressively | | **Repeat washout** | Inadequate initial debridement | Low threshold for re-look | | **Wound infection** | Contamination | Aseptic technique | **Late Complications:** | Complication | Mechanism | Incidence | |--------------|-----------|-----------| | **AVN of femoral head** | Vascular disruption, increased pressure | 10-15% | | **Growth disturbance** | Physeal damage | 5-10% | | **Joint stiffness** | Cartilage damage, fibrosis | 10-20% | | **Leg length discrepancy** | AVN, physeal arrest | Variable | | **Early osteoarthritis** | Cartilage destruction | 10-30% | | **Septic hip sequelae** | Severe: destruction, dislocation | 5-10% | **Prognostic Factors:** | Factor | Better Prognosis | Worse Prognosis | |--------|------------------|-----------------| | **Time to treatment** | <24 hours | >4-5 days | | **Age** | >2 years | Neonates | | **Organism** | Gram-positive, sensitive | MRSA, Gram-negative | | **Joint** | Knee, ankle | Hip, shoulder | | **Initial WCC** | Lower | Very high (>100,000) | **Long-term Outcomes:** | Outcome | Approximate Rate | |---------|------------------| | Full recovery | 60-70% | | Mild sequelae (stiffness, mild LLD) | 15-25% | | Moderate sequelae (significant LLD, OA) | 10-15% | | Severe sequelae (destroyed joint) | 5% | **Follow-up Protocol:** | Time | Assessment | |------|------------| | 2 weeks | Wound, clinical, CRP | | 6 weeks | X-ray, ROM, completing antibiotics | | 3 months | X-ray, clinical assessment | | 6 months | X-ray for AVN/growth disturbance | | 12 months | Final assessment | | Long-term | Annual until skeletal maturity if any sequelae | > **Consultant Tip:** Time is cartilage. Early diagnosis and treatment gives the best chance of full recovery. Delayed treatment (>4 days) has much worse outcomes. --- ## Key Teaching Points ### Pattern Recognition **This pattern suggests Septic Arthritis:** - Acute onset, unwell child - Refuses to weight-bear - Fever (even low-grade) - Elevated CRP/ESR/WCC - Hip held in flexion, abduction, external rotation - Effusion on ultrasound **Distinguish Septic Arthritis from Transient Synovitis:** | Feature | Septic Arthritis | Transient Synovitis | |---------|------------------|---------------------| | Onset | Acute, hours | Gradual, 1-2 days | | Fever | Usually present | Absent or low-grade | | General health | Unwell, toxic | Well-appearing | | CRP | >20-40 mg/L | <20 mg/L | | ESR | >40 mm/hr | <40 mm/hr | | Aspirate WCC | >50,000 | <50,000 | | Treatment | Surgical washout | Conservative | **Kocher Criteria Quick Reference:** - 0 criteria: <1% risk - 1 criterion: 3% risk - 2 criteria: 40% risk - 3 criteria: 93% risk - 4 criteria: 99.6% risk ### Critical Management Points 1. **Never miss septic arthritis** - assume it until proven otherwise 2. **Kocher ≥2 = aspirate** - err on the side of aspiration 3. **Aspiration is diagnostic AND therapeutic** - decompresses the joint 4. **Surgery within 6 hours** - delays cause permanent cartilage damage 5. **Staph aureus is commonest organism** - flucloxacillin empirically 6. **Follow up transient synovitis** - X-ray at 6-8 weeks to exclude Perthes --- ## Common Examiner Follow-ups **Q: "What is Kingella kingae and why is it important?"** Kingella kingae: - Gram-negative coccobacillus - Increasingly recognised as cause of paediatric septic arthritis (age 6 months - 4 years) - May be culture-negative on standard media (needs special techniques) - Often preceded by URI or stomatitis - Usually good prognosis - Treated with cephalosporins or penicillin Consider Kingella if: young child, culture-negative septic arthritis, less unwell than expected for Staph. --- **Q: "When would you get an MRI?"** MRI indications in paediatric irritable hip: - **Diagnostic uncertainty** after aspiration - **Poor response to treatment** (to look for abscess, osteomyelitis) - **Adjacent osteomyelitis suspected** (proximal femoral metaphysis is intra-capsular) - **Multifocal disease** suspected - **Iliopsoas abscess** suspected MRI is NOT first-line but helpful when diagnosis unclear or complications suspected. --- **Q: "This child has a draining sinus at follow-up. What now?"** A draining sinus indicates: - **Chronic infection** - inadequately treated - **Osteomyelitis** - may have developed - **Sequestrum** - dead bone harbouring infection Management: 1. MRI to assess extent 2. Inflammatory markers 3. Surgical debridement (possibly multiple) 4. Prolonged antibiotics (6-12 weeks) 5. Consider bone biopsy/culture 6. MDT discussion (paediatric ID, orthopaedics) --- **Q: "How do you manage neonatal septic hip?"** Neonatal septic arthritis is different: - **Organisms:** Group B Strep, Staph, Gram-negatives - **Presentation:** May be subtle - pseudoparesis, irritability, poor feeding - **Kocher criteria don't apply** - neonates often afebrile - **High index of suspicion** needed - **Urgent aspiration and washout** if suspected - **Antibiotics:** Flucloxacillin + gentamicin (cover Gram-negatives) - **Prognosis:** Worse than older children due to physeal damage --- ## Related Topics - Paediatric Osteomyelitis - Perthes Disease - Hip Aspiration Technique - Paediatric Sepsis - Antibiotic Therapy in Bone and Joint Infection