When bone gets infected, the body builds a new shell around the dead part
Hippocrates described bone infection in the 300s BC, and before antibiotics it often killed. Osteomyelitis is still stubborn: bacteria can hide inside bone cells and in microscopic channels where drugs struggle to reach, while the skeleton responds by growing fresh bone around the dying section like a sleeve.
The culprit is usually bacterial, most often Staphylococcus aureus, though fungi occasionally cause it in regions where species such as Histoplasma are common. Germs arrive in three main ways. The commonest is through the bloodstream from somewhere else in the body, which in children tends to seed the long bones and in adults the vertebrae. Infection can also spread in from nearby soft tissue, surgery, implants or deep wounds, or develop where circulation is poor, as in diabetic foot ulcers. About 1 to 3 percent of people with lung tuberculosis develop it in bone, and spinal tuberculosis has its own name, Pott's disease.
Anatomy explains the favourite targets. Blood slows in looping vessels near the growing ends of long bones, giving bacteria a place to settle, so the tibia, femur and humerus are especially vulnerable, along with the jaw. Within 48 hours the resulting inflammation can kill bone cells and marrow. In children, whose outer bone membrane is loosely attached, pus may collect beneath it. After about a week, fragments of dead infected bone called sequestra appear, and the body lays down a new bony casing, the involucrum, around them.
Chronic cases are hard to clear because Staphylococcus aureus can form biofilms and invade the tiny network of channels housing bone cells, where it tolerates antibiotics. Symptoms are often vague, such as pain, swelling, fatigue and night sweats; fever is more typical of the acute form, which develops over days rather than months. Plain x-rays come first but miss early changes, so MRI usually follows, and a positive culture from a bone biopsy is needed to name the organism with confidence.
Treatment involves antibiotics, typically for four to six weeks, and sometimes surgery to remove dead bone and drain abscesses. Hyperbaric oxygen has helped in resistant cases. In the most extreme pelvic infections, surgeons have resorted to removing the lower half of the body. Outcomes are generally good when the infection is caught early.
Source: Osteomyelitis
