I read with great interest the article ‘‘Mucoid degeneration of the posterior cruciate ligament: a case report’’, by Shoji et al. [5]. However, in spite of finding this work instructive and enlightening, there are some observations I would like to make. The authors state that, to their knowledge, ‘‘clinically symptomatic posterior cruciate ligament (PCL) mucoid degeneration has never been reported’’ [5]. In fact, this is not true. Even though they have cited in their references an article written by our group [2], dealing with mucoid degeneration of the anterior cruciate ligament (ACL), another work of our team, even more relevant in this setting, was not mentioned. In this work, we suggest that diffuse intrasubstance signal abnormalities of the PCL seen at magnetic resonance imaging (MRI) were the counterpart of the mucoid degeneration of the ACL [7]. This conclusion was based on several evidences, namely: (1) the structural changes of the PCL seen at MRI were very similar to the already classic appearance of the mucoid degeneration of the ACL, especially in the coronal and axial planes (although somewhat different in the sagittal images); (2) six out of the seven patients studied had concomitant signs of degeneration of the ACL and the PCL, supporting the possibility of a common origin for these changes; (3) it is already established that degeneration of the ACL and PCL often coexist and that the former is a predictor of the latter [1, 6]; and (4) Hodler et al. [3] showed that focal signal abnormalities of the cruciate ligaments seen at MRI in the knees of cadavers were the result of degenerative changes. As far as I know, ours is the first work to describe such findings in vivo. It is probable that Shoji et al. were not aware of our article, given that their manuscript was received for evaluation on October, 2008, and our work was published on the November–December issue of the same year, in a different journal. This unawareness makes the similarities between their patient and our first case even more striking. Both subjects were young, presented with limited range of articular motion and without imaging signs of degeneration of the ACL. The appearance of the PCL in both patients was quite similar, ‘‘tram track’’-like (with a core of high signal intensity in T2-weighted images surrounded by a rim of low signal in sagittal images, mostly posterior and superior). MRI is superior to arthroscopy for diagnosing intraligamentous abnormalities [4], although biopsy, which can be carried out via arthroscopy, remains the gold standard to establish a definitive diagnosis. The work of Shoji et al. [5] made me happy in many ways. First of all, this excellent article confirmed definitively, through surgery and biopsy, the hypothesis that we made based on imaging, lending credit to our own work. Furthermore, it was once more emphasized the role of MRI as a non-invasive tool in the diagnosis of purely intrasubstance ligamentous abnormalities, which can be missed even at arthroscopy in some patients [4]; MRI allows a precise preoperative staging and can alert the surgeon that the affected ligament is not normal, even if it does not look altered externally during arthroscopic inspection. The point to be learned here is to avoid the erroneous diagnosis of a partially torn LCP in a patient who has a clearly abnormal ligament on imaging but lacks a history of trauma or clinical signs which may suggest a ruptured ligament. S. L. Viana (&) Department of Magnetic Resonance Imaging, Clinica Vila Rica, SHLS 716, W423-431, CEP 70390-907 Brasilia, DF, Brazil e-mail: radiolog@uol.com.br