Snapshot A 26-year-old man presents to his primary care physician with pain in his knee, elbow, and wrist and reports subjective fever. He is sexually active with two partners and uses condoms inconsistently. On physical examination, there is tenderness of the tendon sheath upon palpation and a warm mildly swollen joint with asymmetric involvement of the knee, wrist, and elbow. (Gonococcal arthritis) Introduction Clinical definition osteomyelitis infection of the bone and marrow septic arthritis infection of the joint Pathophysiology pathoanatomy osteomyelitis hematogenous spread more common in children occurs in the metaphysis usually monomicrobial contiguous spread from adjacent infection can be polymicrobial and monomicrobial direct micro-organism inoculation e.g., surgery and trauma septic arthritis hematogenous spread most common direct micro-organism inoculation e.g., trauma and iatrogenically (surgery and arthrocentesis) Select Microbes Causing Osteomyelitis Select Microbes Causing Osteomyelitis Microbe Comments Staphylococcus aureus Most common overall Vertebral involvement Intravenous drug use Another common cause includes coagulase-negative staphylococci Salmonella enteridis Sickle cell anemia can also be due to S. aureus Pseudomonas aeruginosa Trauma (e.g., puncture wound to foot), diabetics, and intravenous drug users Neisseria gonorrhoeae Sexually transmitted infections can lead to osteomyelitis, although septic arthritis is more common Staphylococcus epidermidis Prosthesis Mycobacterium tuberculosis Vertebral osteomyelitis (Pott's disease, also known as Tuberculous spondylitis) Pasteurella multocida Animal bites/scratches Group B Streptococcus Infants younger than 3 months Select Microbes Causing Infectious Arthritis Select Microbes Causing Infectious Arthritis Microbes Comments Staphylococcus aureus Most common arthritis can be mono- or poly-articular can be accompanied with cellulitis, abscess, intravenous drug use, osteomyelitis, or endocarditis Streptococci and other gram-positive organisms Second most common cause Pseudomonas aeruginosa Can be seen in intravenous drug users Neisseria gonorrhoeae Seen in sexually active young adults presents with polyarticular arthritis Disseminated gonococcal infection