Osteomyelitis is an infection of bone tissue affecting cortex, marrow, and periosteum, with potential progression to chronic disease, sequestrum (devitalized infected bone), involucrum (new bone around infected area), and sinus tract formation. Lew-Waldvogel etiologic classification: hematogenous (bloodstream seeding, common in children's metaphyses and adult vertebrae); contiguous focus with or without vascular insufficiency (post-trauma, post-surgical including hardware, diabetic foot, pressure ulcers); chronic. Cierny-Mader anatomical-physiological classification combines anatomic stage (medullary, superficial, localized, diffuse) and host class (A: normal, B: systemically/locally compromised, C: treatment morbidity exceeds disease) to guide treatment.
Pathogens vary by route and host: hematogenous in children—Staphylococcus aureus (most common), Streptococcus pyogenes, Streptococcus pneumoniae, Kingella kingae (especially under 4); hematogenous in adults—S. aureus, gram-negatives in elderly/IV drug users (Pseudomonas, Serratia), Mycobacterium tuberculosis (Pott disease in spine), Brucella in endemic areas; contiguous post-traumatic/surgical—S. aureus including MRSA, coagulase-negative staphylococci (hardware), gram-negatives, anaerobes; diabetic foot—polymicrobial including S. aureus, streptococci, gram-negatives, anaerobes (Bacteroides, Peptostreptococcus); vertebral osteomyelitis (discitis-osteomyelitis)—S. aureus most common, also gram-negatives, TB, Brucella; sickle cell anemia—Salmonella distinctively common.
Diagnosis combines clinical (pain, tenderness, fever, drainage, exposed bone with positive probe-to-bone test in diabetic foot, neurologic deficits in vertebral), laboratory (CBC, ESR, CRP—elevated and trended; blood cultures), imaging (plain X-ray initially, lytic changes appear after 2 weeks; MRI is gold standard with high sensitivity/specificity; CT for cortical detail, sequestrum; nuclear medicine—bone scan, WBC scan, FDG-PET for hardware), and bone biopsy with culture (essential before antibiotics for non-hematogenous; multiple deep biopsies; histology shows acute inflammation, necrosis). Treatment requires multidisciplinary approach: empiric antibiotic coverage (vancomycin + cefepime/ceftazidime or piperacillin-tazobactam covering MRSA + gram-negatives; consider MRSA-only if hospital MRSA prevalence high; add anaerobic coverage for diabetic foot/sacral ulcer); narrow to targeted therapy based on culture; duration 4-6 weeks IV-then-oral typical for hematogenous, often longer (8-12 weeks or until biomarkers normalize) for chronic/hardware-associated; oral step-down with high-bioavailability agents (fluoroquinolones, clindamycin, doxycycline, linezolid) increasingly used per OVIVA trial. Surgical debridement: aggressive removal of necrotic bone, drainage of abscesses, hardware retention vs removal (early <4-8 weeks may attempt retention with prolonged antibiotics; chronic infection requires removal with staged reimplantation), local antibiotic delivery (PMMA cement beads, calcium sulfate). Negative pressure wound therapy and hyperbaric oxygen as adjuncts. Address underlying issues: glycemic control, vascular insufficiency revascularization, nutrition, smoking cessation.