Medial collateral ligament injury of the knee. Correlations between MRI features and clinical gradings

To evaluate the degree of correlation between MRI and clinical gradings of medial collateral ligament (MCL) injuries and assess for associated structures on MRI which may influence the clinical perception of MCL laxity. All knee MRIs with acute MCL injuries between 2016 and 2020 at our centre were retrospectively reviewed by two blinded musculoskeletal radiologists. The clinic notes were reviewed for clinical gradings. One hundred and nineteen MRIs included. Forty-eight percent (57/119) agreement between MRI and clinical gradings ($\kappa$ = 0.21, standard error (SE) 0.07). MRI grades: I 29% (34/119), II 50% (60/119), III 21% (25/119). Clinical grades: I 67% (80/119), II 26% (31/119), III 7% (8/119). In patients with clinical grade III MCL injury, there was waviness of the superficial MCL on MRI in 100% (8/8), deep meniscofemoral ligament tear in 75% (6/8), anterior cruciate ligament (ACL) partial or complete tear in 75% (6/8) and posteromedial corner (PMC) injury in 100% (8/8); compared with 0% (0/111), 34% (38/111), 44% (49/111) and 41% (46/111) respectively in clinical grade I or II injuries (p < 0.05). Agreement between MRI and clinical gradings of MCL injuries was only 'fair', with MRI almost always overestimating the grade of the injury when there was a mismatch. Waviness of the superficial MCL and injuries to the deep MCL, ACL and PMC correlate with clinical instability.