The aim of this study was to improve the appropriateness of imaging requested and performed for diabetic foot osteomyelitis by physicians in our institution. We aimed to reduce needless simultaneous imaging examinations and to decrease the overall cost to the healthcare system. This study demonstrates that this is achievable in an uncomplicated manner, even in a large university-based healthcare center with two distinct Radiology and Nuclear Medicine departments.

Our study specifically targeted diabetic foot osteomyelitis, as it is a significant cause of mortality and morbidity. It also represents a significant cost to the healthcare system, where imaging plays a crucial role in the diagnosis and contributes to tailoring patient management.

Following the intervention, nuclear medicine examinations, mostly bone scan and Gallium scintigraphy, have significantly decreased by 25%. On the other hand, MRI examinations were only increased by 7%. We were able to achieve a post-intervention adherence of 78% compared to our pre-intervention cohort which was 43%, therefore increasing the adequate adherence to our algorithm by 35% (p < 0.001). This intervention has reinforced the adherence to the ACR and IDSA appropriateness criteria, emphasizing the use of MRI rather than the use of nuclear medicine examinations as a first-line investigation for suspected foot osteomyelitis in diabetic patients with pedal ulcers. In a recent metanalysis, Llewellyn et al. reported a higher diagnostic accuracy with MRI (95.6% sensitivity; 80.7% specificity) when compared to conventional scintigraphy examinations (83.6% sensitivity; 70.6% specificity). However, WBC scintigraphy had a higher diagnostic accuracy (87.3% sensitivity; 94.7% specificity), similar to MRI. Therefore, can be osteomyelitis reliably diagnosed by MRI and WBC scintigraphy. Nonetheless, the wider availability of MRI machines, the lack of exposure to ionizing radiation, the higher spatial resolution allowing surgical planning if needed, and the higher costs related to WBC scintigraphy make MRI the preferred modality in most cases [18]. In the absence of a foot ulcer, however, nuclear medicine examinations such as 18F-FDG PET/CT may be appropriate, as per the ACR appropriateness criteria, in diagnosing deep soft-tissue infection and differentiating osteomyelitis and from Charcot neuro-arthropathy, especially for patients with metallic implants, for whom MRI examination would be limited [12]. Interestingly, a recent study by Diez et al. has shown that 18F-FDG PET/CT was the most accurate technique for differentiation of Charcot neuro-arthropathy from diabetic foot OM [19]. To our knowledge, this is the first study that focuses specifically on the application of the appropriateness criteria, whereas other studies have focused on the diagnostic hallmarks of osteomyelitis.

During our meeting with the clinicians, they reported a subjective impression of MRI inaccessibility due to limited access in the past, as well as the cost, and time constraints. Their impression could be used as a hypothesis to explain the initial underutilization of MRI versus nuclear medicine examinations. This could also explain the simultaneous request of different imaging modalities with the intent to expedite a diagnosis for patient management. However, our study demonstrated that the timing between an entered requisition and execution was similar for an MRI (mean: 3.5 days, median 2 days) and for scintigraphy (mean: 3.5 days, median 3 days) in the post-intervention cohort. Additionally, we noted a decrease from 7 to 4% in the number of simultaneous requested and performed MRI and scintigraphy. Although not statistically significant (p = 0.36), the decrease in the needless simultaneous examinations allows for cost and time reduction. Thus, our study has demonstrated that the time of request completion should not be a factor that motives requesting multiple examinations simultaneously.

Furthermore, to assess the repercussions of our intervention, we assessed how our findings impacted the overall cost to the healthcare system. There was a 22% (p = 0.002) net decrease in hospital imaging-associated fees per patient. In public healthcare systems, this is a major factor that allows for a more appropriate fund allocation and improving cost-effectiveness.

There are a few limitations to our study. The first limitation is related to the retrospective nature of the study. Although most of the data was collected on our PACS system, some patients may have had imaging or follow-up imaging performed in other institutions, which would not have been available to review. Moreover, we had a smaller post-intervention cohort with 73 patients for an 8-month period versus 223 patients over a 24-month period in the pre-intervention cohort. However, our cohorts did not significantly differ in demographic constitution and results were found to be statistically significant.

Another limitation is that our algorithm includes bone scintigraphy with Gallium scintigraphy, as opposed to WBC scintigraphy, as is generally recommended in the literature. This is due to our local reality and expertise. WBC tagging is not performed locally in our institution, therefore the blood samples need to be transported to another facility and then returned in order to be injected into the patient. This implies significant costs, and limited slots are available. In contrast, the local nuclear medicine team has extensive experience and a strong expertise in the interpretation of Gallium examinations. It should also be noted that most studies investigating the accuracy of Gallium scintigraphy in OM are older, and most used only planar images. In contrast, the local practice involves triple-phase bone scan, with planar ± SPECT-CT acquisitions, followed when required by Gallium scintigraphy with planar ± SPECT-CT acquisitions. WBC scintigraphy is reserved for equivocal or very complex cases.

As a confounding factor, the post-intervention data acquisition was performed between November 1, 2019, and June 30, 2020, during the COVID-19 pandemic. However, we estimate that this factor did not play a significant role as our study targeted only emergency patients and not out-patients. These patients were mostly treated by the same doctors as the pre-intervention cohort and both radiological examinations were as available as in the pre-pandemic cohort.

The validity of our results could potentially be strengthened by a longer post-intervention follow-up. It would be particularly interesting to explore what will happen two to three years after the intervention, when new clinicians, residents or attendings, join our institution. This assessment will be the true measure of whether we managed to implant a long-lasting change in diabetic foot osteomyelitis investigation.

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