Medial Synovial Fold of the Posterior Cruciate Ligament on Knee Magnetic Resonance Imaging and Arthroscopy: Retrospective Investigation of Impingement.

OBJECTIVE: The purpose of this study was to classify the types of medial synovial fold of the posterior cruciate ligament (PCL) on magnetic resonance imaging (MRI) and to identify the relationships between fold type and impingement of the PCL on arthroscopy.

SUBJECTS AND METHODS: Ninety-nine patients who underwent knee MRI and arthroscopy were included. All MRIs were retrospectively and independently assessed by 2 radiologists. Medial synovial folds of the PCL on MRI were categorized into 3 types. Type A showed no medial synovial fold. Type B showed a small synovial protrusion that did not extend beyond an imaginary line drawn from the medial tibial spine to the lateral aspect of the medial femoral condyle. Type C had a long enough fold to extend beyond the imaginary line. The presence of a tear in the anterior cruciate ligament, PCL, or menisci and impingement of the PCL were obtained from arthroscopic records.

RESULTS: Intraobserver agreement in the classification of medial synovial folds was nearly perfect (κ = 0.850). Interobserver agreement was substantial (κ = 0.759). Of 99 cases, 34 were type A, 41 were type B, and 24 were type C folds on MRI. Thirty-nine impingements of the PCL (39.4%) were identified on arthroscopy. Multivariable analysis revealed that type C folds were 40.60 times more likely to have impingement than type A folds (odds ratio, 40.60; 95% confidence interval, 8.73-188.93; P < 0.001).

CONCLUSIONS: Of the 3 types of medial synovial folds, type C was significantly associated with impingement of the PCL on arthroscopy. Therefore, type C folds may be a cause of internal derangement of the knee.