The International Society of Arthroscopy, Knee Surgery and Orthopaedic Sports Medicine classification of knee meniscus tears: three-dimensional MRI and arthroscopy correlation.

OBJECTIVES: To introduce MRI-based International Society of Arthroscopy, Knee Surgery and Orthopaedic Sports Medicine (ISAKOS) classification system of meniscal tears and correlate it to the surgical findings from arthroscopy. We hypothesized that the ISAKOS classification will provide good inter-modality and inter-rater reliability for use in the routine clinical practice of radiologists and orthopedic surgeons.

METHODS: In this HIPAA-compliant cross-sectional study, there were 44 meniscus tears in 39 patients (26 males, 16 females). Consecutive arthroscopy-proven meniscal tears (March 2017 to December 2017) were evaluated by two board-certified musculoskeletal radiologists using isotropic three-dimensional (3D) MRI user-defined reconstructions. The surgically validated ISAKOS classification of meniscal tears was used to describe medial meniscus (MM) and lateral meniscus (LM) tears. Prevalence-adjusted bias-adjusted kappa (PABAK) and conventional kappa, and paired t test and intra-class correlation coefficient (ICC) were calculated for categorical and numerical variables, respectively.

RESULTS: For the MM, the PABAK for location, depth, length (ICC), pattern, quality of meniscus tissue, and zone was 0.7-1, 0.65, 0.57, 0.67, 0.78, and 0.39-0.7, respectively. For the LM, the PABAK for location, depth, length (ICC), pattern, quality of meniscus tissue, zone, and central to popliteus hiatus was 0.57-0.95, 0.57, 0.74, 0.93, 0.38, 0.52-0.67, and 0.48, respectively. The mean tear lengths were larger on MRI than on arthroscopy (mean difference MM 9.74 mm (6.66 mm, 12.81 mm; p < 0.001), mean difference LM 4.04 mm (0.31 mm, 7.76 mm; p = 0.034)).

CONCLUSIONS: The ISAKOS classification of meniscal tears on 3D MRI provides mostly moderate agreement, which was similar to the agreement at arthroscopy.

KEY POINTS: • There is a fair to good inter-method correlation in most categories of ISAKOS meniscus tear classification. • The tear lengths are significantly larger on MRI than on arthroscopy. • The inter-reader correlation on 3D MRI is moderate to excellent, with the exception of lateral meniscus tear patterns.