Snapshot A 52-year-old man presents to his emergency department for worsening knee pain. He reports that his symptoms began approximately 10 days ago and is unable to bear weight on the affected knee. Medical history is significant for poorly controlled type II diabetes mellitus. On physical exam, the right knee is erythematous, swollen, and tender to palpation. There is decreased range of motion on the affected joint. Laboratory testing demonstrates an elevated erythrocyte sedimentation rate and C-reactive protein. An athrocentesis is obtained and demonstrates a white blood cell count of 65,000 cells/μL and gram-positive organisms. Introduction Clinical definition login to view 4 more bullets Epidemiology Risk factors login to view 8 more bullets Etiology Staphylococcus aureus login to view 1 more bullet Streptococci login to view 1 more bullet Neisseria gonorrhoeae login to view 1 more bullet Pseudomonas aeruginosa login to view 1 more bullet Borrelia burgdorferi login to view 1 more bullet Mycobacterium tuberculosis Staphylococcus epidermidis login to view 1 more bullet Pathogenesis login to view 5 more bullets Presentation Symptoms login to view 2 more bullets Physical exam login to view 6 more bullets Imaging Radiography login to view 2 more bullets Studies Labs login to view 1 more bullet Arthrocentesis login to view 1 more bullet Synovial fluid culture login to view 6 more bullets Differential Gout Pseudogout Inflammatory arthritis (e.g., rheumatoid arthritis) Viral arthritis (e.g., hepatitis B and C and parvovirus B19) Treatment Medical login to view 14 more bullets Operative login to view 8 more bullets Complications Osteomyelitis Sepsis Prognosis Dependent on a number of comorbid conditions (e.g., age and immunosuppresion) login to view 1 more bullet