Kocher, J Bone Joint Surg Am 1999 - Differentiating between Septic Arthritis and Transient Synovitis of the Hip in Children: An Evidence-Based Clinical Prediction Algorithm - Article Summary

Differentiating between Septic Arthritis and Transient Synovitis of the Hip in Children: An Evidence-Based Clinical Prediction Algorithm

Kocher, Kasser, et al.·J Bone Joint Surg Am·1999·618 citations·Retrospective cohort

Kocher and colleagues set out to build a clinical prediction rule that separates septic arthritis from transient synovitis in a child with an irritable hip.

Retrospective review of 168 children with an acutely irritable hip at one tertiary children's hospital from 1979 to 1996, 82 with septic arthritis and 86 with transient synovitis.

Methods

Design: Retrospective review
Multivariate logistic regression prediction rule
Patients: 168 children
82 septic arthritis vs 86 transient synovitis
1979 to 1996
Index test: History of fever
Non‑weight‑bearing
ESR
Serum WBC
Reference standard: Joint fluid WBC ≥50,000 cells/mm³
Joint and blood cultures
Clinical course
Outcomes: Predicted probability of septic arthritis
ROC area

Key Findings

Predicted probability of septic arthritis climbed with each added predictor, from under 0.2% with none present to 99.6% with all 4.
Mean ESR and serum WBC differed between groups (p < 0.001), but intermediate values overlapped too much for either test to separate them alone.
The 4 predictors combined gave an area under the ROC curve of 0.96.
Cultures were positive in only 46% of septic hips (38 of 82), the rest diagnosed by joint fluid WBC of at least 50,000 cells/mm³.
Staphylococcus aureus was the most common organism, isolated in 22 of 38 culture‑positive cases (58%).
The rule was derived retrospectively at one hospital, and the authors called for prospective validation in new settings.

Board pearl

The 4 Kocher predictors are fever history, inability to bear weight, ESR of at least 40 mm/hr and serum WBC above 12,000 cells/mm³, and 3 of 4 gave a 93.1% predicted probability of septic arthritis.

Kocher predictors of septic arthritisKocher, J Bone Joint Surg Am 1999

History of fever (oral temperature >38.5 °C in the prior week)
Non‑weight‑bearing (by history)
ESR ≥40 mm/hr
Serum WBC >12,000 cells/mm³

Predictors present	Probability of septic arthritis	Suggested workup
0	<0.2%	Observe without aspiration
1	3.0%	No recommendation given
2	40.0%	Aspirate under fluoroscopy or ultrasound
3	93.1%	Aspirate in the OR, ready for arthrotomy
4	99.6%	Aspirate in the OR, ready for arthrotomy

Authors' conclusion

Although several variables differed significantly between the group that had septic arthritis and the group that had transient synovitis, substantial overlap in the intermediate ranges made differentiation difficult on the basis of individual variables alone. However, by combining variables, we were able to construct a set of independent multivariate predictors that, together, had excellent diagnostic performance in differentiating between septic arthritis and transient synovitis of the hip in children.