A detailed radiographic description and correlated magnetic resonance imaging findings of an infrequently identified articular indentation of the articular margin of the distal phalanx

Summary Background Equine veterinarians frequently obtain lateromedial radiographs of the feet. During assessment, one infrequently encounters a triangular‐shaped articular indentation of the articular surface of the distal phalanx (P3). To the authors’ knowledge, there are no detailed radiographic or MRI descriptions of this specific articular indentation in the literature so far. Objectives The main purpose of this study was to give a detailed morphological description of this radiographical identified articular indentation. Study design Descriptive study. Methods All LM and DP radiographs of the feet of horses presented at our hospital between August 2016 and August 2019 were retrospectively reviewed for presence of an articular indentation. Following selection, patient information, patient history, clinical findings, MRI‐finding and surgical details were retrieved. In total, 30 horses were included of which 12 underwent magnetic resonance imaging. Radiographs and MRI results were evaluated for the precise location, shape and extent of the articular indentation and for signs of degenerative joint disease of the DIPJ. Results Four different indentation types were identified radiographically. Concomitant low field MRI proved to be a useful and excellent imaging modality for evaluation of this rare articular indentation and its surrounding subchondral bone. MRI findings were various and ranged from slight subchondral contour deviations to obvious OCLL (Osseous Cyst Like Lesions). Furthermore, MRI identified some additional indentation related OCLLs that were not noted on plain radiographs. Main limitations The limited number of horses that were included and the absence of complementary histopathology. Conclusions Articular indentations are typically identified in the third quarter of the articular margin of P3 and may have underlying OCLLs. Since OCLLs are known to be a potential cause of future unsoundness, careful radiographic assessment is advised if an indentation is encountered. If needed, Standing Low‐Field MRI can give additional and detailed information.