Osteomyelitis vs Septic arthritis
How to tell Osteomyelitis and Septic arthritis apart when a board question makes them look alike.
Osteomyelitis is infected bone/marrow; septic arthritis is infected joint fluid with painful passive motion.
Side by side
Osteomyelitis is bone infection with focal bone pain, fever, elevated ESR/CRP, contiguous spread from ulcers/trauma or hematogenous seeding, and MRI marrow involvement.
Septic arthritis is infected joint space with acute painful swollen joint, fever, severe pain with passive range of motion, and purulent synovial fluid.
Bacteria infect bone through blood, direct inoculation, or contiguous soft-tissue spread, causing marrow inflammation and bone destruction.
Microbes infect synovium, where limited host defenses allow rapid cartilage destruction without urgent drainage.
MRI marrow edema, bone biopsy/culture, elevated ESR/CRP, probe-to-bone in diabetic ulcers, and chronic draining sinus support osteomyelitis.
Arthrocentesis with high synovial WBC/neutrophils, positive Gram stain/culture, low glucose, and severe passive-motion pain supports septic arthritis.
The trap
Adjacent bone and joint infections can coexist, so localize the pain and image/tap the correct compartment.
The repair move
For focal limb infection, decide whether the infected compartment is bone or joint.
Try a free question
CoreA patient with a chronic diabetic foot ulcer has focal metatarsal pain, exposed bone on probe, elevated ESR, and MRI showing marrow edema. Which diagnosis is most likely?
Show answer and explanation
Answer: A. Osteomyelitis. Chronic ulcer with probe-to-bone finding and MRI marrow edema supports osteomyelitis.
Why the other choices are tempting
- B. Septic arthritis is infected joint fluid with painful passive motion.
- C. Cellulitis is dermal/subcutaneous infection without marrow involvement.
- D. Reactive arthritis is sterile post-infectious arthritis.
- E. Erysipelas is superficial sharply demarcated skin infection.
Flashcards
Tap a card to flip it.
What imaging test is sensitive for osteomyelitis?
MRI is sensitive for osteomyelitis because it shows marrow involvement.
What sample best identifies the organism in osteomyelitis?
Bone biopsy/culture best identifies the organism in osteomyelitis.
Quick answers
What is the fastest way to tell Osteomyelitis from Septic arthritis?
Osteomyelitis is infected bone/marrow; septic arthritis is infected joint fluid with painful passive motion.
What is the key clue for Osteomyelitis?
Osteomyelitis is bone infection with focal bone pain, fever, elevated ESR/CRP, contiguous spread from ulcers/trauma or hematogenous seeding, and MRI marrow involvement.
What is the key clue for Septic arthritis?
Septic arthritis is infected joint space with acute painful swollen joint, fever, severe pain with passive range of motion, and purulent synovial fluid.
What is the common trap with Osteomyelitis vs Septic arthritis?
Adjacent bone and joint infections can coexist, so localize the pain and image/tap the correct compartment.