The most appropriate management for this patient is bone biopsy and culture. He has classic signs of long-bone osteomyelitis related to his previous fracture. The presence of chronic or intermittent drainage from a demonstrable sinus tract overlying an area of previous trauma, along with consistent clinical findings and radiographic evidence of a bone sequestra (dead bone) or involucrum (new bone formation), are hallmarks of chronic osteomyelitis. Other than local signs of ongoing infection, patients with chronic osteomyelitis rarely manifest systemic symptoms. Laboratory studies are generally not diagnostically helpful because leukocyte counts are almost always normal and inflammatory markers (erythrocyte sedimentation rate and C-reactive protein), although supportive of chronic infection when elevated, are very nonspecific for focal infection. Bone biopsy for histopathologic assessment and full microbiologic studies is important for diagnosing osteomyelitis, excluding other entities (such as neoplasm), and isolating the causative pathogen(s).

With the exception of Staphylococcus aureus, microorganisms from the surface of wounds or draining sinus tracts rarely correlate with cultures obtained from bone specimens and should not be acted upon. However, when S. aureus is isolated, it may be considered the causative pathogen, and therapy may be initiated without bone biopsy when the clinical picture is consistent with osteomyelitis. This patient's bone infection likely resulted from the introduction of bacteria at the time of his military injury. Although osteomyelitis resulting from hematogenous entrance of bacteria most often involves a single organism (such as S. aureus), infection that arises from a contiguous focus of infection or open trauma may comprise a multitude of potential pathogens alone or in combination.

Initiating empiric antimicrobial therapy without an attempt at confirming a histologic and microbiologic diagnosis is strongly discouraged and best delayed until more information is available to best select specific antimicrobial agent(s), route of administration, and duration of therapy.

MRI is the most sensitive and specific imaging modality for diagnosing osteomyelitis but is unnecessary in the presence of a chronic draining sinus. The demonstration of microorganisms coupled with characteristic features of osteomyelitis eliminates the need for MRI confirmation of the diagnosis.