Predictive Value of 99mTc DPD Bone SPECT/CT Uptake Ratio for Culture Results in Lower Limb Osteomyelitis

Background/Objectives: The diagnosis of osteomyelitis is typically based on clinical suspI icion supported by imaging and lab findings. Various nuclear medicine imaging, including bone SPECT/CT, is emerging as an effective tool to guide the diagnosis of osteomyelitis. This study investigates whether the preoperative 99mTc DPD bone SPECT/CT uptake correlates with intraoperative tissue culture positivity in patients with suspected lower extremity osteomyelitis. Methods: We retrospectively reviewed 46 patients who underwent surgery for suspected osteomyelitis of the lower extremity between February 2020 and May 2025. Bone SPECT/CT was performed using 99mTc DPD, and uptake values were measured using Syngo.via software. Lesion-to-Background Ratio (LBR) was calculated by comparing uptake in the lesion with the contralateral bone. Intraoperative culture was conducted at the region with high uptake in SPECT/CT. Results: Among the 46 patients who underwent surgery, 28 had positive tissue cultures, and 18 were negative. The mean LBR was significantly higher in culture-positive cases (14.5 ± 4.5) than in culture-negative cases (6.8 ± 8.0, p = 0.0002) Inflammatory markers (WBC, ANC, ESR, CRP) and the antibiotic-free interval before surgery did not significantly differ between groups or correlate with LBR. ROC analysis identified an LBR threshold of 9.44, yielding a sensitivity of 71.4% and specificity of 88.9% for predicting positive cultures (AUC = 0.81). Conclusions: 99mTc DPD bone SPECT/CT uptake ratio may serve as a useful tool for the preoperative assessment of suspected lower extremity osteomyelitis, providing a more reliable prediction of intraoperative microbial culture results compared to serum inflammatory markers or the duration of antibiotic-free intervals. High tracer uptake may also be observed in various other conditions and thus should be interpreted in a multidisciplinary context in conjunction with other modalities.