summary Septic Arthritis is the inflammation of the joints secondary to an infectious etiology, most commonly affecting the knee, hip, and shoulder. Diagnosis is made with an aspiration of joint fluid with a WBC count > 50,000 being considered diagnostic for septic arthritis. Lower counts may still indicate infection in the presence of positive gram stains or cultures results. Treatment is usually urgent surgical irrigation and debridement followed by culture directed IV antibiotics. Epidemiology Anatomic location most commonly affected joints in descending order login to view 10 more bullets Risk factors age > 80 years medical conditions login to view 4 more bullets history of crystal arthropathy endocarditis or recent bacteremia IV drug user recent joint surgery Etiology Pathophysiology pathoanatomy login to view 6 more bullets cellular biology login to view 3 more bullets microbiology login to view 2 more bullets Associated conditions prosthetic implant infection Classification By organism staphylococcus species login to view 4 more bullets neisseria gonorrhea login to view 5 more bullets gram-negative bacilli login to view 10 more bullets streptococcus login to view 4 more bullets propionibacterium acnes login to view 1 more bullet salmonella or streptococcus pneumoniae login to view 1 more bullet bartonella henselae login to view 1 more bullet pseudomonas aeruginosa login to view 1 more bullet pasteurella multocida login to view 1 more bullet eikenella corrodens login to view 1 more bullet fungal/candida login to view 1 more bullet Presentation Symptoms pain in affected joint fevers (only present in 60% of cases) may appear toxic Physical exam inspection login to view 4 more bullets palpation login to view 2 more bullets motion login to view 2 more bullets Imaging Radiographs recommended views login to view 1 more bullet findings login to view 2 more bullets Ultrasound indications login to view 2 more bullets MRI indications login to view 1 more bullet Studies Serum labs WBC >10K cells/mL with left shift ESR >30 mm/hr login to view 2 more bullets CRP >1 mg/dL login to view 2 more bullets Joint fluid aspirate gold standard for treatment and allows directed antibiotic treatment should be analyzed for login to view 6 more bullets characteristic findings login to view 7 more bullets Saline load test utilized to determine if wound near a joint communicates with the joint for the knee login to view 2 more bullets Differential Crystal arthropathy gout pseudogout Cellulitis Bursitis prepatellar bursitis Treatment Operative IV abx, operative irrigation and drainage of the joint login to view 11 more bullets Nonoperative gonococcal septic arthritis can be treated with antibiotics and aspiration login to view 2 more bullets Technique Operative irrigation and drainage of the joint approach login to view 1 more bullet irrigation login to view 1 more bullet debridement login to view 1 more bullet cultures login to view 1 more bullet Complications Arthritis Fibrous ankylosis Osteomyelitis Prognosis Delayed diagnosis can lead to profound, extensive cartilage damage within 8 hours