1. Is the lab useful to distinguish Septic Arthritis versus Transient Synovitis? Laboratory rounds Jan 30, 2003 Rob Hall PGY3

2. Case  3yo  Refuses to weight bear on left hip  No hx of trauma or fever  URTI recently  T 38.0  Painful ROM right hip  Kid looks well  What is your differential?  What tests would you order?  How useful are your tests going to be?

3. Differential of Limp  Trauma –fracture, sprain, strain, contusion, abuse  Infection –Septic arthritis, osteomyelitis, cellulitis, fascitis, myositis  Inflammation –Toxic synovitis, JRA, HSP, serum sickness, rheumatic fever  Other –AVN, SCFE, tumor, leukemia, sickle cell

4. Are a wbc, ESR, or CRP useful for distinguishing septic arthritis vs transient synovitis?  Small retrospective studies with poor design –Molteni 1978 –McCarthy1980  Potentially meaningful studies –Kunnamo 1987 –Del Beccaro 1992 –Kocher 1999

5. Kunnamo 1987 American Journal of the Diseased Child  Prospective study of all kids referred to a tertiary pediatric referral center with arthritis  N = 278, only 18 with septic arthritis  Gold standard was based on follow up if joint not tapped and no follow up data given

6. Kunnamo 1987 American Journal of the Diseased Child  Variable Sensitivity Specificity –CRP > 20 94% 92% –ESR > 20 94% 68% –WBC > 12 59% 95% –T > 38.5 77% 95% –T>38.5 or 100% 87% CRP >20

7. Kunnamo 1987 American Journal of the Diseased Child  Small study  Method problems  Wide confidence intervals –CRP > 20: sensitivity 94% (95%CI 72 – 99%)  Doesn’t answer the question

8. Del Beccaro 1992 Annals of Emergency Medicine  Retrospective chart review  Method problems  N = 132 –Septic arthritis 38 –Transient synovitis 94  Gold standard problems –Transient synovitis defined based on clinical course but 13% lost to follow up

9. Del Beccaro 1992 Annals of Emergency Medicine  Statistically significant differences –Variable Septic Arthritis Transient synovitis –Temp38.137.2 –ESR 4419 –WBC13.211.2

10. Del Beccaro 1992 Annals of Emergency Medicine VARIABLESENSITIVITYSPECIFICITY ESR > 2079%72% T > 37.566%68% T > 38.045%85% WBC > 1526%84% ESR > 20 and/or Temp > 37.5 97%50%

11. Del Beccaro 1992 Annals of Emergency Medicine  Wide confidence intervals  Huge overlap between groups with each variable  How can we use this information? –ESR, CBC, temp not that helpful in isolation –Combinations may be useful

12. Kocher 1999 Journal of Bone and Joint Surgery  Retrospective chart review of 282 patients  Same metholodogical problems  Found statistical differences b/w septic arthritis and transient synovitis for…… –Hx of fever –Ability to weight bear –Joint effusion on Xray –Temp –ESR –WBC

13. Kocher 1999 Journal of Bone and Joint Surgery  Multivariant analysis found four predictors of septic arthritis –History of fever –Non-weight bearing –ESR > 40 –WBC > 12  Developed an algorithm based on above 4 variables

14. Kocher 1999 Journal of Bone and Joint Surgery PredictorsTransient Synovitis Group Septic Arthritis Group Probability of septic arthritis (%) 022%0%0.2% 15413.0% 2191440% 355393% 403099.6%

15. Kocher 1999 Journal of Bone and Joint Surgery  This is NOT a validated prediction rule  Again suggests that combination of information is useful

16. Approach to the Irritable Hip

17. Surprise! The lab alone is NOT the answer…………