osteomyelitis

osteomyelitis
Field	Orthopedic surgery, Infectious disease (medical specialty)

osteomyelitis is a serious infection of the bone, typically caused by bacteria such as Staphylococcus aureus, but can also result from fungi or other pathogens. The condition can be classified based on duration, mechanism of infection, and the specific bone involved, with the tibia, femur, and vertebra being common sites. It poses significant diagnostic and therapeutic challenges across medical specialties including orthopedic surgery and infectious disease (medical specialty).

Definition and classification

Osteomyelitis is formally defined as an inflammation of the bone marrow and surrounding bone structures due to an infectious process. Classification systems are used to guide management, with the Cierny-Mader classification being a prominent staging system for long-bone infections in adults. The Waldvogel classification categorizes the disease based on the duration as either acute or chronic, and the route of infection as hematogenous, contiguous, or associated with vascular insufficiency. Pediatric cases are often described using classifications that consider the unique anatomy of the growth plate in children.

Causes and risk factors

The most common causative organism is Staphylococcus aureus, including Methicillin-resistant Staphylococcus aureus strains. Other frequent pathogens include Streptococcus pyogenes, Pseudomonas aeruginosa, and Escherichia coli, with Mycobacterium tuberculosis being a cause in regions where tuberculosis is endemic. Major risk factors include open fractures, surgical procedures like joint replacement, the presence of diabetes mellitus with foot ulcers, sickle cell disease, and the use of intravenous drug use. Conditions that compromise the immune system, such as HIV/AIDS or therapies for organ transplantation, also increase susceptibility.

Pathophysiology

The pathophysiology typically begins with microbial inoculation, which can occur via the bloodstream, as seen in hematogenous osteomyelitis often originating from a distant site like pneumonia, or by direct extension from a contiguous focus of infection such as a traumatic wound. Bacteria adhere to bone matrix and cartilage, forming a biofilm that is highly resistant to antibiotics and host defenses. The ensuing inflammatory response leads to increased intraosseous pressure, vascular compromise, and subsequent bone necrosis, forming a characteristic sequestrum. This process can involve adjacent structures like the periosteum and synovial joint.

Signs and symptoms

Clinical presentation varies with acuity and patient age. Acute hematogenous osteomyelitis in children often presents with rapid onset of fever, localized bone pain, and reluctance to use the affected limb, commonly the femur or tibia. In adults, particularly with vertebral osteomyelitis, symptoms may include insidious back pain and tenderness. Chronic osteomyelitis is characterized by persistent or recurrent pain, draining sinus tracts, and overlying erythema. In diabetic foot infections, signs may be masked by peripheral neuropathy. Systemic signs like sepsis can occur in advanced cases.

Diagnosis

Diagnosis relies on a combination of clinical assessment, laboratory studies, and imaging. Key laboratory tests include complete blood count, C-reactive protein, and erythrocyte sedimentation rate, though blood cultures are positive in only about 50% of cases. Imaging begins with plain radiographs, which may show periosteal reaction or lytic lesions after 10-14 days. Advanced imaging modalities are crucial; magnetic resonance imaging is highly sensitive for detecting early marrow edema, while computed tomography is superior for visualizing bone destruction. The definitive diagnostic standard is bone biopsy for culture and histopathology, often guided by fluoroscopy.

Treatment

Treatment is multidisciplinary, involving orthopedic surgery and infectious disease (medical specialty) specialists. The cornerstone is prolonged antibiotic therapy, often initiated intravenously with agents like vancomycin or cefazolin, tailored to culture results. Surgical intervention is frequently required for chronic cases to debride necrotic bone, drain abscesses, and remove infected hardware from prior procedures like internal fixation. Adjunctive strategies include the use of antibiotic-impregnated beads or spacers, and in severe cases, reconstruction with bone graft or techniques like the Ilizarov technique. Management of underlying conditions, such as glycemic control in diabetes mellitus, is essential.

Prognosis and complications

Prognosis depends on the infection's chronicity, the causative organism, patient comorbidities, and the timeliness of intervention. Acute osteomyelitis in otherwise healthy individuals often resolves with appropriate treatment. Chronic osteomyelitis, however, has a high recurrence rate and can lead to devastating complications including pathologic fracture, septic arthritis, and the development of squamous cell carcinoma in long-standing sinus tracts. Systemic complications can progress to sepsis and multiorgan dysfunction syndrome. Long-term sequelae may include chronic pain, limb length discrepancy in children, and significant functional impairment requiring further surgical procedures like amputation. Category:Infectious diseases Category:Orthopedic surgery