188 - The Role of Bone Pathology in the Management of Residual Osteomyelitis After Amputation for Diabetic Foot Infections

Background: Diabetic foot osteomyelitis is a common infection often treated by a combination of antibiotic therapy and limb-sparing amputation. During amputation, IDSA guidelines recommend histopathological analysis of the proximal resection margin, but there are few studies evaluating the prognostic value of such analysis. We did a retrospective cohort study to evaluate whether histopathologic findings predict the clinical outcomes of further proximal amputation or death.  

Methods: We conducted a retrospective cohort study at a VA hospital reviewing 84 patients. We evaluated patients who had a diagnosis of diabetes mellitus with diabetic foot osteomyelitis who were treated with limb-sparing amputations. All cases that were included had adequate histopathological description of the proximal margin of the amputation site. We also collected relevant clinical data including comorbidities, labs, culture data and pre-op and post-op antibiotics. The primary outcome was defined as the need for further proximal resection at the amputation site within six months of the original amputation or death from all causes within three months of the original amputation. Categorical variables were compared using Fischer’s exact test or the Chi-Square test. Continuous variables were compared using the t-test.

Results: We found a statistically significant difference (p=0.0003) of the primary outcome with 10 of 19 (53%) patients with positive margins needing further surgical resection and 1 of 19 (5%) patients dying. Of the patients with negative margins, 9 of 55 (14%) patients needed further surgery and none died. Positive proximal bone margin significantly increases risk of further proximal surgery


Conclusion: Our study showed that patients with residual osteomyelitis at the proximal margin were more likely to need further proximal amputation or die. We did not have adequate power to assess whether extended antibiotic therapy improved outcomes for patients with positive margins, but there was no suggestion that it did. Further research will be needed to elucidate what the ideal duration of antibiotic therapy is for residual osteomyelitis after amputation for diabetic foot osteomyelitis.