Mucoid degeneration of the anterior cruciate ligament: frequently under-diagnosed entity in MRI *

ObjectiveThe purpose of our study was to describe the MR appearance of mucoid degeneration of the anterior cruciate ligament and to address its clinical significance.Patients and methodsA database search of 2000 knee MRI examinations revealed 32 examinations (Chart 1) with reported mucoid degeneration of the anterior cruciate ligament.ResultsOf 32 examinations that met imaging criteria, all patients (100%) had different degrees of mucoid degeneration. Associated ganglia were seen in eight patients; located in the proximal ligament in four examinations (12.5%) and the distal ligament in two (6%) and involved the mid-portion of the ligament in two (6%).Intra-osseous cysts were noted distally in 15 examinations (47%), proximally in four (12.5%) and on both sides in six (19%). All our patients had accessible medical records; no clinical evidence of instability was reported.Four patients who underwent arthroscopy had an intact anterior cruciate ligament at that time.ConclusionAnterior cruciate ligament mucoid degeneration has specific MRI features and should not be misdiagnosed as partial or total tear, and typically not associated with ligament instability.