Session VIII - Reconstruction
Comparison of a Bone Protocol versus Quantitative Cultures Used to Diagnose Osteomyelitis
Dolfi Herscovici, Jr, DO; Julia M. Scaduto; Roy W. Sanders, MD; Florida Orthopaedic Institute, Tampa General Healthcare, Tampa, Florida, USA
Purpose: Bone infections can lead to destruction of bone. Although radiography, nuclear medicine, and serological studies are used to make a diagnosis of infection, accurate identification requires the acquisition of bony tissue. However, use of culture mediums and demineralizing bony specimens may delay the diagnosis. Quantitative cultures can be returned within 1 to 2 hours and may allow for earlier diagnosis, provided they are as accurate in making the diagnosis of osteomyelitis. The purpose of this study was to compare costs and effectiveness of quantitative cultures versus bone biopsies in diagnosing osteomyelitis.
Methods: From July, 2001 through February, 2003, patients were evaluated for the study if they had active signs of a deep infection; had previous surgery resulting in a nonunion, with or without a history of infection or drainage; or had a history of osteomyelitis, requiring further surgery. The protocol consisted of obtaining, from the site of nonunion or suspected infection, 1 gram of tissue for quantitative culture and five pieces of bone (bone protocol) sent for a gram stain, aerobic and anaerobic cultures, evaluation for acid-fast bacilli, and demineralization for microscopic pathologic examination. Serial debridement was performed as necessary, infectious disease consultations were obtained, and definitive skeletal fixation or repair of nonunions was delayed until results were negative for any growth of organisms. A positive (+) quantitative culture was defined as any study demonstrating more than 105 organisms per high-powered field. Any (+) studies (positive cultures or pathologic report) identified in the bone protocol were compared with the findings of the quantitative culture. Accuracy in diagnosing infections and costs of the two methods of evaluation were then compared.
Results: Fifty-one patients were evaluated, and 35 (68.6%) had positive signs of infection. Overall, no patient was reported to have acid-fast bacilli, 6 of 51 (11.8%) patients had (+) positive results for anaerobic organisms, and only 9 of 51 (17.7%) patients had (+) reports for gram stains. The cost of these three studies was $254, $440, and $85, respectively. All 35 patients (+) for infection had (+) aerobic cultures, and osteomyelitis was identified in only 13 of 51 (25.5%) patients. The cost of these two studies was $179 and $271, respectively, and did not include the pathologist's fee for interpreting the specimens. The cost of the quantitative culture was $336 and was (+) in only 13 of 51 (29.4%) patients. No patient had a (+) quantitative culture without (+) aerobic or anaerobic cultures. Five of six patients with (+) anaerobic cultures had (+) quantitative cultures, but these five also had (+) aerobic cultures. In the 35 (+) patients with aerobic cultures, only 13 of 35 (37.1%) had (+) quantitative cultures. Finally, in 13 of 51 patients with (+) pathologic reports, 11 had (+) aerobic or anaerobic cultures, and only 4 had (+) quantitative cultures.
Discussion: Different modalities are used during the differential diagnosis of osteomyelitis. They should not be excessive and should produce useful information. The gold standard, however, is the result of a biopsy of the bone. In this study, the cost of the work-up for each patient was $1565, and, although only 35 patients had (+) study results, some of the patients evaluated did not have overt signs of infection, such as nonunions. All (+) 35 were treated for infection, regardless of the pathologic findings or gram stain, and although quantitative cultures were returned within 1 to 2 hours, only 13 of 35 (37.1%) were positive.
Conclusions: Quantitative cultures, pathology, acid-fast studies, and gram stains were all used during the work-up but provided little useful information and did not affect the overall treatment of the patient. By using aerobic and anaerobic cultures of the bone as the primary work-up for osteomyelitis, a savings of $946 per patient can be realized. If other studies are necessary, they should be used only when indicated rather than as a general screening tool.