Septic Arthritis

Alan R. Blackburn II

John R. Fowler

INTRODUCTION

Pathoanatomy

Septic arthritis is an infection of the joint space resulting from traumatic inoculation, hematogenous seeding, or contiguous spread.
Cartilage destruction is rapid by the action of proteolytic enzymes and bacterial toxins, necessitating prompt diagnosis and management to prevent eventual osteomyelitis.

Mechanism of Injury

Epidemiology

Staphylococcus aureus and Streptococcus are the most common causative organisms, accounting for 91% of septic arthritis cases, regardless of site, although Gonococcus should always be high on the differential. If a clenched fist injury has occurred, polymicrobial infections are typical, and Eikenella corrodens may be involved in up to 30% of cases.

EVALUATION

Physical Examination

Signs and symptoms include erythema, edema, warmth, and painful range of motion both actively and passively.
Fluctuance may be present.
Systemic signs such as fever, chills, or tachycardia may be present; however, these systemic signs may be absent when small joints are affected.

Laboratory Evaluation

White blood cell count, ESR, and CRP should always be obtained; however, these studies may or may not be elevated when dealing with small joints of the hand.
Blood cultures should always be sent, especially when systemic symptoms are present.
Definitive diagnosis is made with synovial fluid analysis; however, aspiration of small joints can be challenging and may yield only minimal amounts of fluid.
- Aspirate should be sent for Gram stain, aerobic and anaerobic culture, and crystal analysis.
- Additional fluid may be sent for cell count, fluid protein and glucose levels, and fungal and mycobacterial cultures.
A diagnosis of joint sepsis is supported by a synovial fluid WBC count of higher than 50 000/mL (>75% neutrophils), glucose 40 mg less than fasting blood glucose, and a positive Gram stain or culture.
The presence of crystals does not exclude the possibility of coexisting infection.