Diagnostic Tests to Help Determine Osteomyelitis: an Analysis and Comparison of Clinical Signs, Microbiology, Pathology and Radiology.

Osteomyelitis is present in approximately 20% of cases of foot infection in persons with diabetes [1, 2] and greatly increases the likelihood that the patient will require a lower-extremity amputation [3, 4]. Early diagnosis and treatment drastically improves prognosis. While there are multiple modalities through which osteomyelitis is diagnosed, unfortunately there is no definitive method. Bone biopsy with histopathological and microbiological analysis has been deemed the gold standard for diagnosing osteomyelitis [3, 5].

Osteomyelitis is considered proven if one or more pathogens are cultured from a reliably obtained bone specimen that shows bone death, acute or chronic inflammation and reparative responses on histological examination. However, histological analysis can also produce falsely positive results based on sampling error or if there are other causes of inflammation [6]. Furthermore, a recent study done by Meyr et al. has highlighted a discrepancy amongst pathologists that leaves the medical community questioning the validity of some pathological diagnoses.

Microbiological analysis can differ based on specimen processing and is also dependent on sampling technique. Often results can be falsely negative because of sampling error, prior antibiotic therapy, or inability to culture fastidious organisms; likewise, they may be falsely positive because of contamination by wound-colonizing flora [6].

Also, cultures of superficial swab samples from diabetic ulcers and sinus tracts may not adequately identify the true bacteriological characteristics of diabetic foot osteomyelitis because of bacterial colonization of the wound surfaces with microorganisms that are typically not considered to be pathogenic (such as enterococci and coagulase-negative staphylococci) [7]. Senneville et al. attempted to define the true correlation between cultures of swab samples and cultures of bone biopsy specimens obtained from areas of osteomyelitis in the diabetic foot. It was found that swab cultures are inaccurate and unreliable indicators of the pathogenic organism in chronic diabetic foot osteomyelitis and there was overall poor concordance between the superficial swab culture and bone biopsy culture results for all microorganisms [8].

Other methods for diagnosing osteomyelitis include radiographic analysis. On plain film, osteomyelitis is suspected when one or more of the following radiographic signs is observed: periosteal elevation, cortical disruption, medullary involvement, osteolysis, and sequestra (segments of necrotic bone separated from living bone by granulation tissue) [9]. Signs of osteomyelitis only show up on plain film 10-20 days after infection, [10, 11]. Dinh et al, in their meta-analysis on radiographic modalities, found 54% sensitivity and 68% specificity in detecting osteomyelitis with plain film versus 90% sensitivity and 79% specificity with MRI [12].