Issues And Answers In Diagnosing Diabetic Foot Osteomyelitis
The “unlikely” category of osteomyelitis is defined as the probability of osteomyelitis being less than 10 percent with no need for further investigation or treatment. In order to be classified in this category, one of the following three criteria must be satisfied: (1) normal MRI; (2) normal bone scan; or (3) a superficial ulcer present for less than two weeks with no signs/symptoms of inflammation and normal X-rays.
Possible osteomyelitis is defined as the probability being 10 to 50 percent with future treatment and investigation usually advised. A diabetic foot wound falls into this category if it meets one of the following criteria: (1) plain radiographs demonstrating cortical destruction; (2) a MRI with bone edema or cloaca; (3) a positive probe to bone test; (4) visible cortical bone; (5) an ESR > 70 mm/hr; (6) a non-healing wound despite adequate offloading and perfusion for greater than six weeks; or (7) an ulcer present for greater than two weeks with clinical evidence of infection.
Probable osteomyelitis is defined as a probability between 51 to 90 percent with a foot that you should consider treating, but further investigation may be needed. In order to satisfy this category, one must meet one of the following criteria: (1) visible cancellous bone in clinical evaluation of the ulcer; (2) a MRI showing bone edema with other signs of osteomyelitis; (3) a bone sample with positive culture (but negative histology); or (4) a bone sample with positive histology (but negative culture).
Definite (“beyond a reasonable doubt”) osteomyelitis is defined as having a probability of osteomyelitis greater than 90 percent that clinicians should treat as osteomyelitis. The criteria for this category includes: (1) a bone sample with both positive culture and histology; (2) definite purulence identified in bone intraoperatively; (3) an intraosseous abscess on MRI; or (4) an atraumatically detached bone fragment removed from the ulcer.
Unfortunately, clinicians should no longer consider the bone biopsy, as a stand-alone test, to be the “gold standard” for diagnosing osteomyelitis in the diabetic foot. Although it will certainly remain an important tool to help assist in the diagnosis, recent studies show that this may not be the gold standard as we originally thought. Both the microbiologic and histopathologic analyses of bone present with their own intrinsic problems.
Therefore, physicians should use a more comprehensive approach when attempting to reach the diagnosis. At our facility, we utilize the consensus guidelines of the International Working Group on the Diabetic Foot and encourage everyone to examine their own practices relative to this protocol.
Dr. Pirozzi is a resident within the Temple University Hospital Podiatric Surgical Residency Program at Temple University Hospital in Philadelphia.
Dr. Meyr is an Assistant Professor in the Department of Podiatric Surgery at the Temple University School of Podiatric Medicine in Philadelphia.