Bone infections, known medically as osteomyelitis, happen when bacteria reach bone tissue through one of three routes: spreading from a nearby wound or infection, traveling through the bloodstream from another part of the body, or entering directly during surgery or a fracture. About 80% of cases come from that first route, where an infection in surrounding tissue gradually works its way into the bone beneath it. The condition has become more common over the decades, rising from roughly 11 cases per 100,000 people in the 1970s to about 24 per 100,000 by the 2000s.
Spread From Nearby Tissue
The most common way bacteria reach bone is by migrating from an infection right next to it. This happens frequently in people with diabetic foot ulcers, pressure sores over the hips or tailbone, or wounds from previous surgery. In these cases, bacteria don’t need to travel far. A deep ulcer on the bottom of the foot, for example, can erode through soft tissue until it contacts the bone underneath. Once bacteria reach bone, they colonize tiny channels within the bone’s structure called the lacuno-canalicular network. These channels are so dense and narrow that antibiotics struggle to reach effective concentrations inside them, which is a major reason bone infections are notoriously stubborn to treat.
Gum and tooth infections can also spread this way, reaching the bones of the skull. Bones near surgical sites or areas that have received radiation therapy are similarly vulnerable because the tissue around them is already compromised.
Spread Through the Bloodstream
Bacteria circulating in your blood can settle in bone even when the original infection is somewhere else entirely. This route, called hematogenous spread, tends to involve a single type of bacterium rather than a mix. It behaves differently depending on age. In children, bloodborne bacteria typically land in the long bones of the legs and arms, particularly near the growth plates of the thighbone, shinbone, or upper arm bone. In adults, bloodborne infections favor the vertebrae of the spine.
The original source of bacteria varies. Urinary tract or gastrointestinal infections can seed bone with certain gram-negative bacteria. A dental extraction has been linked to bone infections caused by a type of streptococcus normally found in the mouth. People who inject drugs face a heightened risk of a specific bacterial strain reaching their bones through contaminated needles and repeated bloodstream exposure.
Direct Entry Through Wounds or Surgery
The third route is the most straightforward: bacteria enter bone directly through an opening. Open fractures, where a broken bone pierces the skin or a deep wound exposes it, create a direct path for environmental bacteria. Bone surgery carries the same risk. Any procedure that physically opens or drills into bone can introduce bacteria, especially if a metal plate, screw, or artificial joint is implanted. Hardware gives bacteria a surface to cling to and form protective clusters called biofilms, making the resulting infection harder to eliminate.
The Bacteria Behind It
Staphylococcus aureus causes the majority of bone infections. It’s found on the skin or in the nose of virtually everyone, which means the bacteria responsible are usually already living on your body. Staph has specific traits that make it effective at infecting bone: it adheres well to bone tissue, resists immune defenses, and breaks down surrounding tissue with enzymes. Both standard staph and its antibiotic-resistant form (MRSA) are common culprits. Staph is present in over 50% of bone infection cases from nearby tissue spread.
When an infection spreads from adjacent tissue, it often involves multiple bacterial species at once, including streptococci and anaerobic bacteria that thrive without oxygen. Bloodborne bone infections, by contrast, almost always involve just one species.
Who Is Most at Risk
Certain conditions make bone infections far more likely. Diabetes and peripheral vascular disease top the list because both impair blood flow and wound healing, particularly in the feet and lower legs. A small cut or blister that would heal quickly in a healthy person can linger for weeks, deepening until it reaches bone. People with weakened immune systems, whether from medication or illness, have less ability to fight bacteria before they establish themselves in bone.
Pressure sores are another significant entry point, especially for people with limited mobility. Sustained pressure on skin over bony areas like the hips and tailbone breaks down tissue layer by layer. Sickle cell disease alters the risk profile too, predisposing people to bone infections from less common bacterial species. Anyone with implanted hardware, from joint replacements to spinal fusion rods, carries an ongoing risk because bacteria can colonize metal surfaces months or even years after surgery.
What It Feels Like
Bone infection typically causes deep, persistent pain at the affected site. Unlike a surface wound that hurts when touched, the pain from osteomyelitis often feels like it’s coming from inside the bone and may ache constantly. The area over the infected bone is usually warm, swollen, and red. Fever and fatigue are common, especially in acute cases where the infection develops over days to weeks. In children, the onset can be sudden, with a high fever and refusal to use the affected limb. In adults with vertebral osteomyelitis, the main complaint is often persistent back pain that worsens over weeks and doesn’t respond to typical treatments.
Chronic bone infections, which develop when acute infections aren’t fully cleared, can be subtler. Pain may come and go, and a draining wound that never quite heals is a hallmark sign. Some people go through cycles of improvement and flare-ups for months before the underlying bone infection is identified.
How It’s Diagnosed
Standard X-rays can reveal bone damage, but only after the infection has been present for several weeks. Earlier infections won’t show up on a plain X-ray. MRI is far more sensitive and can detect changes in bone and the surrounding soft tissue much sooner, making it the preferred imaging tool when osteomyelitis is suspected.
Identifying the exact bacteria responsible usually requires a bone biopsy. This can be done with a needle guided by imaging, using local numbing, or through a small surgical procedure under general anesthesia. Knowing the specific organism matters because it determines which antibiotic will actually work. Blood tests can show signs of infection and inflammation but can’t confirm osteomyelitis on their own.
What Treatment Looks Like
Bone infections require prolonged antibiotic treatment, typically six to eight weeks. That duration reflects how difficult it is to get antibiotics into bone tissue at concentrations high enough to kill bacteria hiding in the bone’s internal network. Treatment often starts with intravenous antibiotics and may transition to oral medications once the infection is responding. Infections involving prosthetic joints generally require about 12 weeks of antibiotic therapy.
In many cases, antibiotics alone aren’t enough. Surgery may be needed to remove dead bone tissue, drain abscesses, or take out infected hardware. For chronic infections where bacteria have formed biofilms deep within bone, surgical cleaning of the infected area is often the only way to give antibiotics a chance at working. Recovery can take months, and some infections require multiple rounds of treatment. The bacteria’s ability to hide in the tiny channels of bone and form protective colonies is the central reason bone infections are so much harder to resolve than infections in soft tissue.