Mucoid metaplastic-degeneration of anterior cruciate ligament.

Mucoid degeneration of the anterior cruciate ligament (ACL) is a pathological state not yet well morphologically defined, involving people without history of knee instability or significant trauma, and causing important pain. The aim of this study was to define the histopathological and radiographic features of this pathological condition.Analysis of 1 215 knee magnetic resonance (MR) examinations found 64 cases (5.3%) of ACL mucoid metaplastic-degeneration (MMD), subsequently all subjects underwent surgical and arthroscopic validation. MR examinations have been performed using a dedicate system provided with a permanent magnet of 0.18 T and with a dedicate coil of 12 cm of field of view (FOV) or an high field instrument with 1.5 T. Radiological criteria to define ACL MMD were based essentially on increased signal intensity in T2W sequences and in STIR ones, as in T1W scans the ligament showed an intermediate signal.ACL MMD was diagnosed in 36 males and 28 females, with a mean age of 44 years. ''Segmentary MMD'' was found in 11 subjects (17.2%) commonly affecting the postero-lateral bundle of the ligament without femoral or tibial spongious mucoid intrusion. ''Total MMD'' (involving the entire ligament and accompanied with femoral or tibial intrusion) was found in 53 subjects (82.8%).The comparison between histopathological and MR findings suggests that the commonly called ACL mucoid degeneration (ACL MD) should be better defined as mucoid metaplastic degeneration (MMD).