Bone biopsies required for proper treatment of chronic osteomyelitis

Researchers found no microbiologic correlation between nonbone and bone specimens.

Cultures of specimens taken from biopsies of nonbone tissues do not reliably identify the infectious cause of chronic osteomyelitis, a prospective study shows.

Because the successful treatment of patients with the disease depends on targeting treatment to the underlying cause, “only bone cultures should be used to guide antibiotic treatment in patients with COM (chronic osteomyelitis), including those infected by S. aureus,” the study authors said. “Choosing nonbone cultures for this purpose will lead to incorrect etiologic COM diagnosis and, therefore, inappropriate therapy.”

Andres F. Zuluaga, MD, MSc, and colleagues at the University of Antioquia Medical School and Hospital Universitario San Vincent de Paul in Medellín, Columbia, conducted the study. The researchers evaluated the concordance of microbiologic cultures of specimens taken from both bone and nonbone biopsies of 100 patients with COM. They defined COM as a bone infection that did not improve, or worsened clinically or microbiologically after one month of evolution, independent of surgical or antibiotic treatment.

The location of the COM involved mainly the tibia (34%) and femur (33%), followed by the fibula (8%), iliac crest (7%), vertebra (3%) humerus (3%) and other medullar bones (12%). In 93 of the 100 cases, bacteria reached the bone through local spread of an infection, according to the study.

The researchers used special biopsy protocols to reduce the risk of specimen contamination. Orthopedic surgeons performed all bone and nonbone biopsy procedures and chose the biopsy site based on macroscopic signs of infection. They also noted whether incisions were made through intact skin or infected soft tissue. All patients had ceased antibiotic treatment for 48 hours before specimens were taken, according to the study.

Of the 100 patients, 94 bone cultures allowed for isolation and identification of the infecting organism and yielded 150 isolates, most frequently S. aureus (43 of 150 isolates; 29%). Nonbone cultures from 89 patients yielded 116 isolates, with S. aureus again the most common organism identified (44 of 116 isolates; 38%).

However, “Cohen kappa values computed for COM caused by S. aureus or any other cause were all close to 0, indicating no microbiologic correlation of nonbone with bone specimens,” the study authors said.

“The diagnostic accuracy of nonbone specimens, as determined by the rate of microbiologic agreement with bone cultures, was 30%. The Cohen kappa value was lower than 0 (–0.0092 ? 0.0324; P>.99), confirming that the observed agreement of 30% was the same as that expected by chance,” they said.

“In other words, the results from cultures of nonbone specimens are completely independent from bone specimens, without regard for the group analyzed,” they added.

The study was published in Archives of Internal Medicine.

For more information:
Zuluaga AF, Galvis W, Saldarriaga JG, et al. Etiologic diagnosis of chronic osteomyelitis. Arch Intern Med. 2006;166:95-100.