Chronic osteomyelitis is a persistent infection of the bone that resists the body’s immune defenses and standard short-term antibiotic treatments. It arises when an infection is not fully eradicated, allowing bacteria to establish a stronghold within the bony architecture. Characterized by its recalcitrant nature, chronic osteomyelitis requires specialized, prolonged care involving both surgical and medical intervention.
Understanding Chronic Bone Infection
The difficulty in treating chronic osteomyelitis stems from specific pathological changes that occur within the bone structure itself. When a bone infection becomes chronic, the body attempts to contain the spreading infection by forming new bone around the infected site. This dense, new bone growth is known as the involucrum, which walls off the infection from the surrounding healthy tissue.
Inside this protective shell, fragments of dead, infected bone called the sequestrum become isolated from the blood supply. Because antibiotics travel through the bloodstream, they cannot effectively reach the bacteria within the sequestrum, rendering systemic drug therapy ineffective. The involucrum also creates an environment with reduced blood flow and low oxygen tension, decreasing the ability of immune cells to fight the infection.
Biofilms are protective matrices secreted by bacteria that adhere to surfaces, particularly when foreign materials like internal fixation hardware are present. These biofilms shield the organisms from both antibiotics and the host immune system. This makes the infection extremely difficult to clear without physically removing the contaminated tissue or foreign object.
How Bone Infections Originate
Bone infections can reach the skeletal system through three main pathways. The first is hematogenous spread, where bacteria travel through the bloodstream from a distant source of infection to settle in the bone. This route is more common in children, often affecting the long bones, but in adults, it frequently involves the vertebrae.
Contiguous spread, the most frequent cause in adults, occurs when an infection enters the bone directly from adjacent soft tissue or an open wound. This can follow a traumatic open fracture, a deep penetrating injury, or be a complication of orthopedic surgery.
Osteomyelitis associated with vascular insufficiency is commonly seen in individuals with diabetes or peripheral artery disease. Poor blood circulation in the extremities, especially the feet, allows minor trauma or a skin ulcer to become severely infected. Compromised blood flow prevents the body’s defenses from reaching the area, permitting the infection to spread rapidly into the underlying bone.
Identifying Symptoms and Confirming Diagnosis
The symptoms of chronic osteomyelitis are often less dramatic than an acute infection, frequently presenting as persistent or recurring issues. Patients commonly experience localized bone pain that may wax and wane over time. A hallmark sign of the chronic state is a draining sinus tract, a fistula extending from the infected bone to the skin surface, allowing pus and debris to escape.
Localized signs also include swelling, warmth, and tenderness over the affected bone. Physicians rely on a combination of imaging and laboratory tests to confirm the diagnosis. Initial evaluation typically includes plain X-rays, which may reveal characteristic findings like bone sclerosis, cortical thickening, or the presence of a sequestrum.
Magnetic resonance imaging (MRI) is used due to its high sensitivity for identifying bone marrow edema and soft tissue involvement. Laboratory tests, such as the C-reactive protein (CRP) level and the erythrocyte sedimentation rate (ESR), are often elevated, reflecting the ongoing inflammatory process.
The definitive diagnosis requires a bone biopsy and culture, which involves surgically obtaining a tissue sample from the infected site. This procedure is necessary to accurately identify the specific pathogen, allowing for culture-specific antibiotic selection, as Staphylococcus aureus is the most common organism.
Comprehensive Treatment Approaches
Treatment for chronic osteomyelitis requires a combined surgical and medical approach. The surgical procedure, known as debridement, is primary for resolving the infection. During debridement, the surgeon removes all infected, non-viable tissue, including the sequestrum, surrounding soft tissue, and any contaminated orthopedic hardware.
The goal is to reach healthy, bleeding bone tissue, ensuring no remnants of the infection remain. This often leaves a significant cavity or ‘dead space’ in the bone, which must be managed to prevent fluid accumulation and relapse. Surgeons may fill this space temporarily with antibiotic-impregnated polymethylmethacrylate beads or cement, releasing high local concentrations of antibiotics directly into the area.
Following successful debridement, medical treatment involves administering antibiotic therapy tailored to the specific pathogen identified by the bone biopsy. This therapy is typically initiated intravenously for four to six weeks or longer, before transitioning to a prolonged course of oral antibiotics. The extended duration is necessary to ensure adequate drug penetration into the bone and surrounding tissue.
Hyperbaric oxygen therapy, which involves breathing pure oxygen in a pressurized chamber, can be utilized to increase oxygen levels in the affected tissues. Increased oxygenation enhances the effectiveness of the body’s immune response and promotes bone healing.