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 \ratio 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.