Osteomyelitis

Osteomyelitis is an infection inside a bone. It's almost always caused by bacteria (most often Staphylococcus aureus) and rarely by fungi or other germs. Bacteria reach the bone three main ways: through the bloodstream (most common in kids and older adults), from a nearby infection or open wound spreading inward, or after surgery on the bone. Once it becomes chronic, the infection produces a chunk of dead bone (sequestrum) wrapped in a shell of new reactive bone (involucrum) — and antibiotics alone usually can't eradicate it. The dead bone has to be cut out surgically.

You're more likely to develop osteomyelitis if you have diabetes, poor circulation in your limbs, a weakened immune system (from medication or disease), a history of IV drug use, or a recent fracture or bone surgery.

• Deep bone pain that worsens and won't settle — a constant ache in one spot that gets worse over days rather than better, and doesn't respond to typical pain relievers.
• Fever and chills — your body's systemic response to the infection, sometimes with night sweats.
• Redness, warmth, and swelling over the bone — the overlying skin may look inflamed even though the infection is inside the bone.
• Draining wound (sinus tract) if chronic — in long-standing cases, a small hole in the skin opens and drains pus intermittently, sometimes for months.

Two blood markers of inflammation (ESR and CRP) are usually elevated, though those numbers can rise from many things. Blood cultures and any wound cultures are drawn before antibiotics start so we can identify the exact bug. X-rays often look normal in the first week or two — bone changes lag behind the infection. An MRI is far more sensitive: it shows fluid in the bone marrow and any abscess in the surrounding tissue. A nuclear medicine scan is a backup when MRI isn't an option. The gold-standard test is a bone biopsy (taken with a needle under CT guidance or in the OR) — that tells the lab exactly which germ is involved and which antibiotics will kill it.

Surgery is needed for chronic osteomyelitis, infections that have grown around prior hardware (plates, screws, joint replacements), or acute infections that aren't getting better on antibiotics. The operation has three parts: cut out the dead, infected bone and any infected hardware; fill the empty cavity with antibiotic-loaded cement or bone graft so it doesn't collapse; and cover the wound with healthy soft tissue (often with a plastic surgeon) to give the bone a clean blood supply.

External patient-education references and related OSI pages for additional background:

• Britannica — Human skeleton
• AAOS OrthoInfo — patient education library
• OSI glossary — orthopedic terminology in plain language