Septic Arthritis
Septic Arthritis
Nongonococcal Septic Arthritis
- Destroys cartilage within days
- Staph and strep are most likely isolates
- 50% cases involve knee joint
- No history or exam finding can rule out nongonococcal septic arthritis
Risk Factors
| Factor | Sensitivity % | Specificity % | (+) LR | (-) LR |
|---|---|---|---|---|
| Age >>0 | 19 | 95 | 3.5 (1.8-7.0) | 0.86 (0.83-1.00) |
| Diabetes Mellitus | 12 | 96 | 2.7 (1.0-6.9) | 0.93 (0.83-1.00) |
| Rheumatoid arthritis | 68 | 73 | 2.5 (2.0-3.1) | 0.45 (0.32-0.72) |
| Recent joint surgery | 24 | 96 | 6.9 (3.8-12.0) | 0.78 (0.64-0.94) |
| Hip or knee prosthesis | 35 | 89 | 3.1 (2.0-4.9) | 0.73 (0.57-0.93) |
| Skin infection | 32 | 88 | 2.8 (1.7-4.5) | 0.76 (0.60-0.96) |
| Hip or knee prosthesis and skin infection | 24 | 98 | 15.0 (8.1-28.0) | 0.77 (0.64-0.93) |
| HIV-1 infection | 79 | 50 | 1.7 (1.0-2.8) | 0.47 (0.25-0.90) |
Physical Exam
| Factor | Sensitivity % | Specificity % | (+) LR | (-) LR |
|---|---|---|---|---|
| Fever | 46 | 31 | 0.67 (0.43-1.00) | 1.7 (1.0-3.0) |
Serum Laboratory Values
| Factor | Sensitivity % | Specificity % | (+) LR | (-) LR |
|---|---|---|---|---|
| Elevated WBC (> 10 k/mcL) | 90 | 36 | 1.4 (1.1-1.8) | 0.28 (0.07-1.10) |
| Elevated ESR (> 30 mm/h) | 95 | 29 | 1.3 (1.1-1.8) | 0.17 (0.20-1.30) |
| Elevated CRP (> 100 mg/L) | 77 | 53 | 1.6 (1.1-2.5) | 0.44 (0.24-0.82) |
Synovial Fluid Laboratory Values
| Factor | Sensitivity % | Specificity % | (+) LR | (-) LR |
|---|---|---|---|---|
| WBC >100,000/hpf | 29 | 99 | 28.0 (12.0-66.0) | 0.71 (0.64-0.79) |
| WBC >50,000/hpf | 62 | 92 | 7.7 (5.7-11.0) | 0.42 (0.34-0.51) |
| WBC >25,000/hpf | 77 | 73 | 2.9 (2.5-3.4) | 0.32 (0.23-0.43) |
| PMN ≥90% | 73 | 79 | 3.4 (2.8-4.2) | 0.34 (0.25-0.47) |
Fagan Nomogram
Likelihood ratios
- Positive LR = How strongly a positive result increase the odds of disease
- Negative LR = How well a negative result decreases the odds of disease
