Evaluating the Etiology of Osteochondritis Dissecans of the Knee: The Role of the Articular-Epiphyseal Cartilage Complex

Introduction: In pathologic form, osteochondritis dissecans (OCD) is a focal end-stage disease of articular cartilage. Comparative anatomy studies have demonstrated that injury to epiphyseal anlage cartilage leads to development of OCD in many species, whereas in humans, the exact etiology is suspected but remains unknown. A potential candidate is the articular-epiphyseal cartilage complex, and our hypothesis is that injury at the junction between the epiphyseal anlage cartilage and the articular cartilage results in childhood OCD. Methods: A retrospective, two-institution assessment of children with magnetic resonance imaging (MRI) of the affected knee before the onset of an OCD lesion was performed. Demographics were recorded, including the history of why each initial pre-OCD MRI (Index-MRI) was obtained. MRI measurements were made on the Index-MRI as well as the subsequent OCD-MRI of the epiphyseal ossification length (Growth), marrow edema, the distance of lesion from physis (Lesion Position), and the distance from articular surface (OCD Depth). Comparisons over time were then calculated. Results: Six children (seven knees) were identified with an Index-MRI (Pre-OCD development) obtained at median age 11.6 years and OCD-MRI obtained at a median of 1.9 years later. ‘Growth’ occurred in at least one dimension for all children (sagittal MRI, p=0.018). As a group, the ‘Lesion Position’ did not change significantly in any plane but two demonstrated continued ossification of the epiphysis and one demonstrated bone necrosis. As a group, the ‘OCD Depth’ was significantly different (coronal plane, p=0.029 and sagittal plane, p=0.026) over time, with all lesions increasing their depth (since none existed on the Index-MRI). Discussion: Even though the articular-epiphyseal cartilage complex appeared to be involved with the etiology of knee OCD in this limited series, we found significant variation in the response to a presumed injury with either halted progression, continued ossification, or even regression of ossification adjacent to the OCD. This variation either indicates that there is a multimodal etiology, or that the articular-epiphyseal cartilage complex inconsistently responds to injury. This may explain the inconsistent response to management and calls for further basic science studies to ascertain the exact location of injury in the human articular-epiphyseal cartilage complex.