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Background: Dorsoproximal osteochondral defects commonly affect the proximal phalanx, but information about diagnosis on computed tomography (CT) and magnetic resonance imaging (MRI) is limited. Objectives: To assess CT and MRI diagnoses of osteochondral defects, describe the lesions and compare sensitivity and specificity of the modalities using macroscopic pathology as gold standard. Study design: Cross‐sectional study. Methods: Thirty‐five equine cadaver limbs underwent standing cone‐beam CT (CBCT), fan‐beam CT (FBCT), low‐field MRI and pathological examination. CT and MR images were examined for proximal phalanx dorsomedial and dorsolateral eminence osteochondral defects. Defect dimensions were measured. Imaging diagnoses and measurements were compared with macroscopic examination. Results: Fifty‐six defects were seen over 70 potential locations. On CBCT and FBCT, osteochondral defects appeared as subchondral irregularity/saucer‐shaped defects. On MRI, osteochondral defects were a combination of articular cartilage defect on dorsal images and subchondral flattening/irregularity on sagittal images. Subchondral thickening and osseous short tau inversion recovery hyperintensity were found concurrent with osteochondral defects. Compared with pathological examination, the sensitivity and specificity of diagnosis were 86% (95% confidence interval [95% CI] 75%–93%) and 64% (95% CI 38%–85%) for FBCT; 64% (95% CI 51%–76%) and 71% (95% CI 46%–90%) for CBCT; and 52% (95% CI 39%–65%) and 71% (95% CI 46%–90%) for MRI. Sensitivity of all modalities increased with defect size. Macroscopic defect dimensions were strongly correlated with CBCT (r = 0.76, p < 0.001) and moderately correlated with FBCT and MRI (r = 0.65, p < 0.001). Macroscopic measurements were significantly greater than all imaging modality dimensions (p < 0.001), potentially because macroscopy included articular cartilage pathology. Main limitations: Influence of motion artefact could not be assessed. Conclusions: Osteochondral defects could be visualised using both CT and MRI with sensitivity increasing with defect size. Diagnostic performance was best using FBCT, followed by CBCT then MRI, but CBCT‐measured defect size best correlated with macroscopic examination. MRI provided useful information on fluid signal associated with defects, which could represent active pathology. [ABSTRACT FROM AUTHOR]

Simple Summary: Fractures of the third metacarpal/tarsal parasagittal groove and proximal phalanx sagittal groove are common in racehorses. It is important to detect precursor pathologies including fissures to prevent the propagation to fracture. This study aims to identify the imaging features and compare the diagnosis of fissures on cone-beam (CB) computed tomography (CT), fan-beam (FB) CT, and low-field magnetic resonance imaging (MRI) to histopathology associated with fissures. Fissures were characterised on CBCT and FBCT as hypoattenuating linear defects, striated hypoattenuating lines, or subchondral irregularity. Fissures were characterised on MRI as subchondral hypo-/hyperintense defects. The diagnostic sensitivity was highest in CBCT, followed by FBCT and MRI, while specificity was highest in MRI, followed by FBCT and CBCT. Fissures identified on CT were associated with histopathology of subchondral bone sclerosis, microcracks, and collapse. In conclusion, all modalities were able to identify fissures with sensitivity higher in CT and specificity higher in MRI. CT-identified fissures were associated with histopathological indications of fatigue bone injuries. Imaging features and histopathological features of fissures characterised in this study may help clinical identification and image interpretation of fissures in horses. Fissure in the third metacarpal/tarsal parasagittal groove and proximal phalanx sagittal groove is a potential prodromal pathology of fracture; therefore, early identification and characterisation of fissures using non-invasive imaging could be of clinical value. Thirty-three equine cadaver limbs underwent standing cone-beam (CB) computed tomography (CT), fan-beam (FB) CT, low-field magnetic resonance imaging (MRI), and macro/histo-pathological examination. Imaging diagnoses of fissures were compared to microscopic examination. Imaging features of fissures were described. Histopathological findings were scored and compared between locations with and without fissures on CT. Microscopic examination identified 114/291 locations with fissures. The diagnostic sensitivity and specificity were 88.5% and 61.3% for CBCT, 84.1% and 72.3% for FBCT, and 43.6% and 85.2% for MRI. Four types of imaging features of fissures were characterised on CT: (1) CBCT/FBCT hypoattenuating linear defects, (2) CBCT/FBCT striated hypoattenuated lines, (3) CBCT/FBCT subchondral irregularity, and (4) CBCT striated hypoattenuating lines and FBCT subchondral irregularity. Fissures on MRI appeared as subchondral bone hypo-/hyperintense defects. Microscopic scores of subchondral bone sclerosis, microcracks, and collapse were significantly higher in locations with CT-identified fissures. All imaging modalities were able to identify fissures. Fissures identified on CT were associated with histopathology of fatigue injuries. [ABSTRACT FROM AUTHOR]