Septic Arthritis

51 year old male with history of alcohol abuse and bilateral previous knee surgeries presented with sudden onset right knee pain of 2 days duration and fever for two days.  No known trauma.  Patient febrile to 100.6 in PCP’s office.  On arrival to hospital knee exam shows erythema, warmth, suprapatellar edema, knee effusion, pain with active and passive range of motion.  WBC 23.

Patient’s with new knee pain, swelling, erythema, fever and leukocytosis should be evaluated for septic arthritis.  His risk factors included: alcohol abuse and previous knee surgery. Known RFs for septic arthritis: age >80 years old, Diabetes mellitus, rheumatoid arthritis, prosthetic joint, previous joint surgery, IVDU, alcohol abuse, and recent skin infection.

Most common route of infectious is hematogenous, but could also include spread from bone infection, spread from skin infection, or direct innoculation (bites/trauma).

Most common bacteria: staph aureus, then strep, and minority are gram negatives (consider in elderly, immunosuppressed, GI infections, trauma).  Treatment is vancomycin, unless gram negative infection is suspected.  If so, treat with ceftriaxone or ceftazidime. 

Synovial fluid tap is important for diagnosis and treatment.  WBC in fluid should be >50,000 and >75% polys but may be lower in immunosuppressed or partially treated infection.  Always send gram stain and cultures (cultures from blood and synovial fluid).

According to a recent article in the American Journal of Medicine it is safe to perform a joint tap on a patient that is therapeutically anticoagulated.  http://www.ncbi.nlm.nih.gov/pubmed/22340924