Conventional Radiography: Radiographs are the first-line imaging modality for evaluating DFI due to their availability and cost-effectiveness. Key findings in DFI include soft tissue swelling, gas formation in necrotizing infections, and cortical irregularities suggestive of OM. However, radiographic sensitivity is limited (43–86%), as bone changes in OM may not be apparent until 10–14 days after infection onset. Radiography also has low specificity (27–83%) due to overlap with neuropathic changes, particularly in Charcot arthropathy.

Fig 4: Patient with type 2 diabetes mellitus and a history of lesions in the plantar and interdigital regions. Initial plain radiograph (A) shows osteopenia in the head of the fifth metatarsal, as well as osteopenia and early signs of lysis in the proximal phalanx. On follow-up plain radiograph after one week (B), the findings in the proximal phalanx (arrow) show progression, while those in the head of the fifth metatarsal (arrowhead) remain stable . In this case, a false positive is observed on the plain radiograph, highlighting the critical importance of the clinician specifying the exact location of the ulcer. Osteomyelitis was confirmed and surgical treatment was decided.

Fig 5: Patient with type 2 diabetes mellitus and a history of left first-ray transmetatarsal amputation, presenting with a plantar ulcer in the third metatarsal región of the right foot. Neuropathic arthropathy in 2 and 3 MTC (A) . MRI reveals findings consistent with infectious tenosynovitis with abscess formation (star) at this level (B-C), with no diffusion restriction (F) . Contrast enhancement (E) and edema is observed in 3 MTC the contrast-enhanced Dixon sequence (D-E). No restricción in Difusion ruling out osteomyelitis and arthritis suggesting reactive osteitis (G star blue) The images correspond to sagittal STIR sequence (A), coronal STIR sequence (B), coronal T1-weighted sequence (C), sagittal contrast-enhanced Dixon sequence (D), coronal contrast-enhanced Dixon sequence (E), and diffusion-weighted sequences (F and G ). Follow-up plain radiographs show no progression of the findings (H) after after percutaneous osteotomy.

Fig 8: Patient with type 2 diabetes mellitus, a history of prior amputation, and Charcot arthropathy with surgical fixation causing artifact in the región (A-F) . The patient presents with an ulcer in the weight-bearing area of the cuboid, with suspicion of superinfection. MRI reveals inflammatory and infectious changes at the cutaneous level, bursitis, and extension to the cuboid, with mild bone marrow edema and subtle contrast enhancement. The findings suggest a differential diagnosis between mechanical and infectious pathology. The disruption of anatomical planes, clinical evaluation, and plain radiographs (showing newly developed cuboid osteopenia) (arrows in A-F) contributed to the diagnosis, which was surgically confirmed.

Magnetic Resonance Imaging (MRI) MRI is the most sensitive modality for detecting OM and differentiating soft tissue infections from bone involvement. Conventional MRI sequences demonstrate marrow edema, cortical destruction, and perilesional soft tissue inflammation. T1-weighted images show hypointense marrow signal in OM, while T2-weighted and STIR sequences enhance visualization of inflammatory changes. Contrast-enhanced MRI further delineates infected tissue, aiding in surgical planning.

Advanced MRI Techniques

1. Diffusion-Weighted Imaging (DWI): This technique measures the Brownian motion of water molecules, providing insight into tissue cellularity and integrity. Restricted diffusion, reflected by decreased apparent diffusion coefficient (ADC) values, suggests OM. DWI has been shown to improve diagnostic accuracy in differentiating OM from reactive marrow changes.

2. Dixon Sequences: Dixon-based fat-water separation imaging enhances soft tissue contrast, improving visualization of edema, abscess formation, and marrow involvement. The ability to generate in-phase, out-of-phase, fat-only, and water-only images increases the specificity of infection detection.

3. Dynamic Contrast-Enhanced (DCE) MRI: This technique evaluates tissue perfusion by assessing contrast kinetics. Increased vascular permeability and prolonged contrast retention are indicative of infection. DCE-MRI can be particularly useful in monitoring treatment response, as reductions in perfusion parameters correlate with therapeutic success.

4. Diffusion Tensor Imaging (DTI): DTI extends conventional DWI by providing information on the directionality of water diffusion, which can be particularly useful in evaluating microstructural integrity. This technique allows for the assessment of nerve involvement in DFI, differentiating between infection-related neuropathy and non-infectious neuropathic changes. Fractional anisotropy (FA) and mean diffusivity (MD) are key parameters in DTI, with decreased FA and increased MD values indicative of neural degradation. DTI may also help differentiate between OM and neuropathic bone marrow changes by analyzing the integrity of bone trabeculae. Recent studies suggest that DTI can enhance diagnostic accuracy in complex DFI cases, particularly when combined with other advanced MRI sequences.

Fig 1: Patient with poorly controlled type 1 diabetes mellitus. Chronic plantar ulcers with recent worsening. MRI reveals findings consistent with osteomyelitis of the third toe, with an initial focus of interphalangeal arthritis and secondary osteomyelitis involving the proximal and middle phalanges.Osteomyelitis of the F1 and metacarpophalangeal arthritis are ruled out. The images correspond to perfusion curves (A), axial and coronal T1-weighted sequences (B), and sagittal STIR sequence (C). Restriction Difussion b800 and dADC (D).

Fig 2: Figure 2. Patient with type 2 diabetes mellitus and a chronic ulcer on the right foot. MRI shows extensive inflammatory changes in the third and fourth toe, with fracture and/or osteolysis of the distal third of the proximal phalanx of the fourth toe, accompanied by bone marrow edema and dorsal dislocation. The findings are consistent with osteomyelitis (Marked hypointensity in T1 yellow arrowhead ) and osteitis in the third toe (Very mild hypointensity in T1 blue star). These changes are also evident on serial radiographs, along focal osteopenia with initial signs of osteomilietis in the second phalanx of the hallux and the third toe (arrows). Hypodensity of the head of the 3rd MTT does not reflect pathology on MRI (star). Images correspond to STIR coronal and sagital sequence (A), T1 (B), and serial plain radiographs (C and D). Image E shows a photograph of the ulcer on the fourth toe.

Fig 3: Patient with poorly controlled type 2 diabetes mellitus and a history of prior transmetatarsal amputation. Presents with an extensive ulcerated lesion in the posterior talar region. Plain radiography reveals osteopenia at the calcaneus, visible only in oblique projections (circles) (A). MRI demonstrates an extensive and deep ulcerated cutaneous lesion in the posterior talar region, with cortical and medullary bone erosion, as well as bone signal alterations consistent with contiguous localized infectious osteomyelitis (dixon T1 and opposite fase B, linear T1 signal drop at the periphery of osteomyelitis indicating reactive edema ), and diffusion restriction (C). Postoperative radiographs show antibiotic-loaded cement at this level (arrow) (D).

Fig 6: Patient with type 2 diabetes mellitus presenting with dactylitis of the second toe of the left foot. Plain radiograph shows soft tissue enlargement at the level of the distal phalanx of the second toe, with mild osteopenia and subtle presence of air (arrows) (A and B). MRI reveals thinning of the cutaneous and subcutaneous tissues at the distal end of the third phalanx of the second toe, associated with ulceration, along with bone marrow edema in the third phalanx and, to a lesser extent, in the second phalanx, consistent with osteítis (D and E). Findings are suggestive of osteomyelitis in the third phalanx. The ‘ghost bone’ sign is observed on T1-weighted sequences (C and F).

Fig 7: Plantar skin ulcer and subcutaneous collection at the level of the second metatarsal head and the first interdigital space, extending to the first intermetatarsal space adjacent to the second metatarsophalangeal joint. Synovitis of the second metatarsophalangeal joint, suggesting an infectious origin. A sinus tract is identified at this level on contrast-enhanced Dixon sequences (A-B), suggestive of chronic osteomyelitis. The images correspond to sagittal contrast-enhanced Dixon sequence (A), coronal contrast-enhanced Dixon sequence (B), sagittal T1-weighted sequence (C), and sagittal STIR sequence (D).

Fig 9: Patient with type 2 diabetes mellitus and an infected ulcer in the plantar region of the left foot. MRI reveals bone marrow edema and cortical irregularity in the second and third metatarsophalangeal joints, consistent with osteomyelitis. These findings are associated with inflammatory/infectious changes in the plantar region at the level of the third metatarsal head, as well as a soft tissue collection containing air-like signal abnormalities, suggestive of gas formation (star). Contrast suppressed T1 sequence shows a linear hypoperfused area translating to a zone of tissue ischemia/devitalization (arrows) (F). The images correspond to sagittal T1-weighted sequence (A) and axial T1-weighted sequence (E), sagittal STIR sequence (B) and axial STIR sequence (D), and sagittal (C) and coronal (F) fat-suppressed T1-weighted TSE sequences.