The research, conducted at Loghman Hakim Hospital, a tertiary referral centre affiliated with Shahid Beheshti University of Medical Sciences in Tehran, was published in Health Science Reports. It followed the Standards for Reporting of Diagnostic Accuracy Studies (STARD 2015) and enrolled 127 adults with diabetes and clinically suspected foot infection, each of whom underwent both ultrasound and magnetic resonance imaging (MRI) as part of routine care. The stakes are considerable: diabetic foot ulcers affect an estimated 19 to 34 percent of diabetic patients over their lifetime, and people with these ulcers face roughly an eight-fold higher risk of lower extremity amputation compared with non-diabetics. Osteomyelitis is present in 10 to 15 percent of moderate infections and in about half of severe ones, making early and reliable detection a decisive factor in whether a limb is saved.

The technical logic of the study is straightforward but demanding. MRI, performed on a 1.5 Tesla scanner with a full protocol of T1-weighted, T2-weighted, proton-density fat-saturated, diffusion-weighted and contrast-enhanced sequences, served as the reference standard for osteomyelitis and deep abscess, in line with Infectious Diseases Society of America and International Working Group on the Diabetic Foot guidance. On MRI, osteomyelitis was defined by bone marrow oedema appearing dark on T1-weighted images and bright on fluid-sensitive sequences, restricted diffusion, and cortical destruction adjacent to the ulcer. Ultrasound criteria included periosteal elevation or thickening, subperiosteal abscess, and cortical erosion with fluid in direct contact with bone. Ultrasound was always performed first, and each modality was interpreted by a different experienced radiologist blinded to the other’s findings, preserving the independence of the two readings.

The headline result is stark. MRI identified osteomyelitis in 106 of the 127 participants, or 83.5 percent, yet ultrasound detected only 17.9 percent of those MRI-positive cases, with a confidence interval of 11.2 to 26.6 percent. In other words, more than four out of five bone infections visible on MRI were invisible to ultrasound. Specificity was high, at 95.2 percent, meaning that when ultrasound did suggest bone infection it was usually right, with a positive predictive value of 95 percent. But the negative predictive value collapsed to just 18.7 percent overall, and in severe ulcers it fell to an almost meaningless 1.1 percent. A clean ultrasound scan in a severely affected foot, the data show, provides almost no reassurance whatsoever that the underlying bone is healthy.

The severity subgroup analysis sharpens the clinical message. Among the 19 patients with moderate ulcers, classified as Wagner grades 1 and 2, MRI found no osteomyelitis at all, and ultrasound correctly agreed in every case. But among the 108 patients with severe ulcers, grades 3 through 5, MRI confirmed bone infection in 98.1 percent, and ultrasound missed the overwhelming majority of them. Overall accuracy for osteomyelitis detection in severe ulcers was a mere 18.5 percent. The authors argue that these figures quantify the danger of false reassurance: a clinician who relies on a negative ultrasound to exclude bone infection in a severely ulcerated foot risks delayed diagnosis, inadequate surgical debridement, and ultimately amputation.

The picture changes dramatically when the target shifts from bone to soft tissue. For abscess detection, ultrasound achieved perfect sensitivity of 100 percent in both moderate and severe ulcers, meaning a negative scan reliably rules out a drainable collection. Specificity, however, was poor, at 30.4 percent overall and as low as 22.6 percent in severe ulcers, producing a flood of false positives and a positive predictive value of only 46.6 percent overall. The practical implication is that ultrasound works well as a rule-out tool for abscess but should not be used alone to confirm one before committing a patient to surgical drainage. For cellulitis, ultrasound identified the condition in 126 of 127 cases, agreeing with both the clinical diagnosis and MRI in 99.2 percent of participants, although the authors caution that because every participant had clinically diagnosed cellulitis, these concordance figures describe detection rather than true discriminative accuracy.

Why does ultrasound fail so badly at bone? The physics and anatomy offer an explanation. Ultrasound sound waves reflect strongly at soft tissue interfaces and cannot penetrate cortical bone, so the modality can only infer infection from secondary signs at the bone surface, such as periosteal reaction or cortical irregularity. Early marrow infection, which MRI captures through signal changes deep within the bone, produces no visible surface change for the ultrasound probe to detect. The study’s authors also note operator dependence and probe quality as limiting factors, and they contrast their findings with earlier literature: a 1999 study by Enderle and colleagues reported ultrasound sensitivity of 78.6 percent for chronic osteomyelitis, and paediatric studies have shown better performance in acute haematogenous osteomyelitis, where accessible affected areas and different disease biology may favour surface detection.

The study is candid about its limitations. Bone biopsy with histopathology and microbiology remains the definitive gold standard for osteomyelitis, but subjecting every participant to an invasive bone procedure was not ethically justifiable, so MRI served as the reference standard, and MRI itself is imperfect. Charcot neuroarthropathy, with its reactive marrow oedema, can mimic infection on MRI and may have inflated apparent disease in some cases. Each modality was read by a single radiologist, so interobserver reproducibility could not be assessed. Requiring contrast-enhanced MRI excluded patients with advanced kidney disease, a group in whom chronic renal impairment is common and in whom ultrasound may in practice be the only feasible option. Patients with indeterminate MRI bone findings, described as osteitis without confluent marrow replacement, were excluded rather than adjudicated, a recognised source of optimistic bias in diagnostic accuracy studies. The predominance of severe ulcers in the cohort also introduces spectrum bias toward the very patients in whom ultrasound performed worst.

Microbiological data from the cohort add epidemiological texture. Staphylococcus aureus was the most prevalent pathogen at 25.2 percent, followed by Escherichia coli at 18.1 percent, Staphylococcus epidermidis at 14.2 percent, Enterococcus species at 13.4 percent, Pseudomonas aeruginosa at 9.4 percent, Klebsiella pneumoniae at 8.7 percent and Acinetobacter baumannii at 7.9 percent. Most ulcers were severe: 37 percent were Wagner grade 3, 31.5 percent grade 4 and 16.5 percent grade 5, with the forefoot the most commonly involved region at 48 percent and the plantar surface the most frequent site of surface involvement at 40.9 percent. No imaging-related complications were recorded for either modality.

The authors propose a tiered diagnostic protocol as the study’s practical takeaway. Ultrasound, cheap, portable and radiation-free, earns its place as a first-line triage tool for soft-tissue complications, rapidly identifying abscesses that need drainage and confirming cellulitis at the bedside. But its diagnostic ceiling at the bone surface is now quantified, and it is low. Where osteomyelitis is clinically suspected and ultrasound is negative, MRI remains a mandatory next step, consistent with current IWGDF guidance that recommends plain radiography first, followed by MRI when suspicion persists. In a condition where every day of delay narrows the window between debridement and amputation, the message for clinicians is unambiguous: trust ultrasound to map the soft tissues, but never let a negative scan silence suspicion of infection in the bone.

Subject of Research: Diagnostic accuracy of ultrasonography versus MRI for detecting osteomyelitis and soft-tissue infections in diabetic foot ulcers

Article Title: Ultrasonography Cannot Exclude Osteomyelitis in Diabetic Foot Ulcers: A Cross‐Sectional Diagnostic Accuracy Study Against Magnetic Resonance Imaging

Article References: Haghighi‐Morad, M., Vahedi, H., Fard, A. Y., Pordanjani, B. M., & Mahmoudi, S. T. S. (2026). Ultrasonography Cannot Exclude Osteomyelitis in Diabetic Foot Ulcers: A Cross‐Sectional Diagnostic Accuracy Study Against Magnetic Resonance Imaging. Endocrinology, Diabetes & Metabolism, 9(5), Article e70320. https://doi.org/10.1002/edm2.70320

Image Credits: AI Generated

DOI: 10.1002/edm2.70320

Keywords: diabetic foot ulcer, osteomyelitis, ultrasonography, MRI, diagnostic accuracy, amputation, abscess, cellulitis, diabetes complications, medical imaging, Wagner classification, IWGDF guidelines