Transient Synovitis of the Hip

Procedure

Check four predictors: a history of fever, refusal or inability to bear weight, an ESR of at least 40 mm/h, and a serum white cell count above 12,000 cells/mm³ (12.0 × 10⁹/L). Count how many are present.

Positive Finding

Each criterion present increases the probability of SEPTIC ARTHRITIS. Predicted probability of septic arthritis by number of predictors (Kocher 1999): 0 → <0.2%, 1 → 3.0%, 2 → 40.0%, 3 → 93.1%, 4 → 99.6%.

Interpretation

A clinical prediction rule for distinguishing septic arthritis from transient synovitis in a child with an irritable hip. IMPORTANT: more criteria met means HIGHER probability of septic arthritis, not transient synovitis. Two criteria already carry roughly a 40% probability of septic arthritis and warrant urgent paediatric orthopaedic assessment — this is not a reassuring finding. Three or four criteria indicate high probability (93.1% and 99.6% respectively) and require emergency referral for aspiration. Only zero predictors meaningfully argues against septic arthritis (<0.2%). Note that later external validation studies have reported lower probabilities than Kocher's original cohort (e.g. ~59% for four predictors), so the rule supports — but does not replace — clinical judgement and joint aspiration where suspicion exists. The probabilities above come from Kocher's original study (1999; children seen 1979–1996). In Kocher's own follow-up in a new group of children (2004; 51 with septic arthritis, 103 with transient synovitis) the same four predictors still worked well, though less accurately than before (area under the curve 0.86, down from 0.96). At another hospital (Luhmann 2004; 165 hips), all four predictors gave only a 59% probability of septic arthritis, and the authors concluded the rule did not transfer well to their setting.

Procedure

Perform high-frequency ultrasound in longitudinal plane over anterior hip joint. Measure anterior joint capsule distension from femoral neck surface to anterior capsule wall.

Positive Finding

Anterior joint capsule distension >7 mm (some guidelines use >6 mm); echo-free or hypoechoic fluid within joint space

Interpretation

Confirms a hip joint effusion consistent with synovitis; greater than 7 mm, or marked asymmetry compared with the other side, supports the diagnosis. An effusion alone does NOT distinguish transient synovitis from septic arthritis — both produce one. Where septic arthritis is suspected, aspiration remains the definitive investigation.

Procedure

Child supine. Bend the hip and knee to 90° and gently turn the hip in, comparing with the other side. Stop at the first sign of pain.

Positive Finding

Painful or reduced internal rotation compared with the other side.

Interpretation

Shows the hip joint is irritable, as seen in transient synovitis, septic arthritis, Perthes disease and slipped capital femoral epiphysis. It does not separate them. A child with fever, inability to bear weight or who looks unwell needs same-day medical assessment.

Procedure

Watch how the child lies and holds the hip before you touch it.

Positive Finding

The hip is held bent, turned out and slightly apart (flexion, abduction, external rotation), and the child resists moving it.

Interpretation

This position gives the joint the most room and suggests a joint effusion. It occurs in both transient synovitis and septic arthritis, so it does not separate them.

Procedure

Gently move the child's hip into bending, bringing the knee across the body and turning it in. Stop at the first sign of pain.

Positive Finding

Pain or guarding when the hip is moved into this position.

Interpretation

This position squeezes the joint capsule, so it is painful when there is an effusion. It shows hip joint irritability but does not identify the cause.

Procedure

Blood tests arranged by the doctor, usually with a white cell count and temperature, when a septic joint needs to be ruled out.

Positive Finding

Raised inflammatory markers.

Interpretation

Markedly raised markers, with fever and refusal to bear weight, raise concern for septic arthritis, which is an emergency. The Kocher criteria combine these findings to estimate the risk. Mild or normal results fit transient synovitis.