Transient Synovitis (Irritable Hip)
Summary
Transient Synovitis, commonly known as "Irritable Hip", is the most common cause of acute hip pain in children (aged 3-10). It is a benign, self-limiting sterile inflammation of the hip synovium, often following a recent viral Upper Respiratory Infection (URI). However, it is a Diagnosis of Exclusion. The clinician's primary duty is to exclude Septic Arthritis, which is an orthopaedic emergency. This differentiation is guided by the Kocher Criteria (Fever, Non-weight-bearing, ESR, WCC). Management is rest and NSAIDs. [1,2,3]
Key Facts
- The "Monday Morning Hip": Often presents after a weekend of jumping castles or activity, but the viral link is stronger.
- Prognosis: Excellent. Resolves spontaneously in 3-7 days.
- Recurrence: 4-15%.
- Differential: Septic Arthritis is the "Wolf" masked by the "Sheep" (Transient Synovitis).
Clinical Pearls
"The Ibuprofen Test": Give a dose of NSAID. If the child is running around happily 40 minutes later, it is likely Transient Synovitis. If they are still miserable and guarding, think Sepsis/Perthes.
"Knee Pain is Hip Pain": Always examine the hip.
"Frog Leg Position": The child will lie with the hip flexed and externally rotated. This maximizes joint volume (capsular capacity) and minimizes intracapsular pressure.
Demographics
- Incidence: 0.2% of children per year.
- Age: 3-10 years (Mean 6).
- Gender: Male > Female (2:1).
Mechanism
- Post-Viral: Immune complex deposition in the synovium following a URI or viral illness (Epstein-Barr, Adenovirus).
- Post-Traumatic: Minor trauma initiating inflammation.
- Sterile Effusion: The joint fills with fluid (reactive arthritis), stretching the capsule and causing pain.
Symptoms
Signs
The Kocher Criteria (Differentiation from Septic Arthritis)
Used to calculate the probability of Septic Arthritis.
- Non-weight-bearing.
- Temperature >38.5°C.
- ESR >40 mm/hr (or CRP >20 mg/L in modified Caird criteria).
- WCC >12,000.
Probability of Septic Arthritis:
- 0 factors: <0.2%
- 1 factor: 3%
- 2 factors: 40%
- 3 factors: 93%
- 4 factors: 99%
Imaging
- Ultrasound:
- Detects Effusion. (Often present in both Transient Synovitis and Septic Arthritis, so it doesn't differentiate well, but confirms pathology is in the hip).
- X-Ray AP/Frog:
- Usually Normal.
- Rules out Perthes / Fracture.
Procedures
- Joint Aspiration:
- Indicated if Kocher Criteria suggest Sepsis (>2 factors) or if symptoms persist.
- Septic: Pus, WCC >50,000, Positive Culture.
- Transient Synovitis: Clear/Straw fluid, WCC <50,000, Sterile.
CHILD WITH LIMPING HIP
↓
HISTORY + EXAM + VITALS (TEMP)
┌──────────┴──────────┐
FEBRILE / TOXIC AFEBRILE / WELL
KOCHER SCORE ≥2 KOCHER SCORE 0-1
↓ ↓
FULL WORKUP PRESUMED TRANSIENT
(Bloods, Urgent US) SYNOVITIS
↓ ↓
ASPIRATION? NSAIDs + REST
↓ (Safety Net)
SEPTIC ARTHRITIS ↓
↓ RESOLVED 48H?
IV ABX + WASHOUT ┌─────┴─────┐
YES NO
↓ ↓
DISCHARGE RE-EVALUATE
(Perthes?)
1. Conservative (Transient Synovitis)
- Analgesia: Ibuprofen (Anti-inflammatory) + Paracetamol.
- Rest: Absolute bed rest/Couch potato mode for 48 hours.
- Safety Netting: "If fever develops or pain gets worse, come back immediately."
2. Management of Septic Arthritis (The Differential)
- Emergency: Cartilage destruction occurs within 8 hours of pus contact.
- Surgical: Arthroscopic or Open Washout (Arthrotomy).
- Medical: IV Antibiotics (Flucloxacillin/Ceftriaxone) for 4-6 weeks.
Missed Septic Arthritis
- The only major risk. If missed, leads to destruction of the femoral head and permanent disability.
Recurrence
- Transient synovitis can recur.
Perthes Disease
- 1% of "Transient Synovitis" cases turn out to be early Perthes disease on follow-up. All cases should have a follow-up X-ray at 3 months if symptoms were atypical.
Kocher et al. (1999)
- The landmark paper defining the 4 predictors.
- Later validated and modified (Caird et al.) to include CRP (>20) as a strong predictor.
AAOS Guidelines
- Recommend Ultrasound as the decision-making tool for aspiration.
What is Irritable Hip?
It is like having a "runny nose" inside the hip joint. After a viral cold, the lining of the hip gets inflamed and produces extra fluid. This creates pressure, making it painful to walk.
Is it serious?
No, it is harmless and goes away by itself in a few days. However, we have done tests to make sure it isn't an infection in the bone (Septic Arthritis), which is very serious.
What should I do?
Give them Nurofen (Ibuprofen) regularl for 48 hours and keep them resting. No sports or running around until they are completely pain-free.
When to come back?
If they get a high fever, get decidedly worse, or if they are still limping in 3 days.
- Kocher MS, et al. Differentiating septic arthritis from transient synovitis of the hip in children: an evidence-based clinical prediction algorithm. J Bone Joint Surg Am. 1999.
- Caird MS, et al. Factors distinguishing septic arthritis from transient synovitis of the hip in children. J Bone Joint Surg Am. 2006.
Q1: What are the Kocher Criteria? A: 1. Fever >38.5. 2. Non-weight-bearing. 3. ESR >40. 4. WCC >12. Used to predict Septic Arthritis.
Q2: What is the significance of "Internal Rotation" in hip pathology? A: Loss of Internal Rotation is the earliest and most sensitive sign of intra-articular hip pathology (Synovitis/Effusion). The capsule is tightest in extension/IR, so patients avoid this position (holding the hip in Flexion/Abduction/ER).
Q3: How does the aspiration result differentiate Septic Arthritis from Transient Synovitis? A: Septic: Turbid/Purulent, WCC >50,000/mm³, >75% Neutrophils, Positive Gram Stain. Transient: Clear/Yellow, WCC <50,000, Sterile.
(End of Topic)