Magnetic resonance imaging of degenerative changes of the posterior cruciate ligament

Background Mucoid degeneration and ganglia reflect a continuum of degenerative changes within the posterior cruciate ligament (PCL). Purpose To assess the prevalence of and radiologists' familiarity with PCL mucoid degeneration and ganglia. Material and Methods Knee magnetic resonance imaging (MRI) from July 2013 to June 2015, excluding patients who had a preceding trauma or MRI findings indicative of a prior injury, were retrospectively reviewed, with the specific request to assess degenerative changes of the PCL, by the same musculoskeletal radiologists who previously reported these examinations, and one fellow. Results A total of 692 patients entered this study. The radiologists and the fellow together identified mucoid degeneration in 34 patients (4.9%), ganglia in 14 patients (2.0%), and both in four patients (0.6%). Several patterns of PCL mucoid degeneration were identified: diffuse thickening in seven patients, partial thickening in 16 (four associated with a ganglion), longitudinal intraligamentous PCL signal-intensity abnormalities resembling a "tram track" in 15. In all cases there was increased signal intensity on fluid-sensitive sequences. In the previous reports, only three cases of PCL mucoid degeneration out of 38 (7.9%) were described, with intraligamentous PCL signal-intensity abnormalities. In the reports of the patients with degeneration and ganglia, only ganglia were described. In the previous reports, ganglia were correctly diagnosed. Conclusion Mucoid degeneration of the PCL is much more common than previously assumed and is underestimated by radiologists.