Medial meniscus tears are most prevalent in type I ACL tears, while type I ACL tears only account for 8% of all ACL tears.

PURPOSE: This study aimed to assess the distribution of different anterior cruciate ligament (ACL) tear locations in different magnetic resonance imaging (MRI) planes, and to explore the relationships of ACL tear types with both meniscus injuries and bone bruising. METHODS: A retrospective study was performed in patients under 60 years old who underwent MRI scans in the sagittal and coronal oblique planes of the knee for ACL tears between 2014 and 2020. Patients with reports of chronic tears, partial tears, or prior surgeries were excluded. Tear locations were classified into five types, and the meniscus tear measurement variables included the presence of ramp, root, bucket-handle, and other types of tears. All injuries were confirmed by arthroscopy. Meanwhile, the presence and location of bone bruising were analysed and scored with the Whole-Organ Magnetic Resonance Imaging Score (WORMS) bone bruising subscale. RESULTS: A total of 291 patients were included. The prevalence rates of type I and type III injuries were 23/291 (7.9%) and 145/291 (49.8%) in the sagittal plane and 22/291 (7.6%) and 179/291 (61.5%) in the oblique coronal plane, respectively. The prevalence of medial meniscus tears with ACL tears was 126/291 (43.3%), while that of lateral meniscus tears with ACL tears was 77/291 (26.5%). The highest prevalence of medial meniscus injury with ACL tears was 15/22 (68.2%) for type I injuries. Bone bruises were located on the lateral femoral center in 125 patients (46%) and on the lateral tibia posterior in 132 patients (48%); the common areas of bone bruising were slightly correlated with type III ACL tears but not correlated with type I ACL tears. CONCLUSION: The plane in which an MRI scan is performed affects the classification of ACL tears. The tear type is associated with the prevalence of medial meniscus injuries, and medial meniscus tears are most prevalent in type I ACL tears. LEVEL OF EVIDENCE: IV.

Discoid lateral meniscus can be overlooked by magnetic resonance imaging in patients with meniscal tears.

PURPOSE: MRI evaluation of torn lateral meniscus was compared with arthroscopy. This study calculates the sensitivity, specificity, and accuracy of MRI in determining the presence or absence of discoid lateral meniscus (DLM) for different tear types. METHODS: MR imaging of 156 knees with arthroscopically confirmed lateral meniscus tears was analysed. There were 78 knees (70 patients) in non-DLM group and 78 knees (74 patients) in DLM group on arthroscopy as the reference standard. The presence of DLM on MRI was determined by an orthopaedic surgeon and a radiologist, who were blinded to the arthroscopic findings. The presence of discoid meniscus on MRI was determined by coronal and sagittal measurements, considering the tear pattern of lateral meniscus. The tear pattern was categorized into six types based on arthroscopic findings: horizontal, longitudinal, radial, combined radial, degenerative, and complex tear. The sensitivity, specificity, and accuracy of MRI were calculated for each type of lateral meniscus tear. In addition, we analysed the reason for non-detection of discoid meniscus on preoperative MRI. RESULT: The sensitivity for determining the presence of discoid meniscus was 58% for radial tear, 57% for combined radial tear, and 65% for longitudinal tear, whereas the specificity was 100% for all tear groups. In the presence of radial or longitudinal tear, the accuracy of MRI was significantly lower than having no radial and longitudinal tear (p < 0.001). The presence of discoid meniscus was not recognized on MRI because of large radial tear (12 knees), deformed bucket-handle tear (6 knees), and inverted flap tear (3 knees). CONCLUSIONS: MRI was not successful in determining the presence or absence of DLM in radial tear, combined radial tear, and longitudinal tear. When there are large radial tear, deformed bucket-handle tear, and inverted flap tear in lateral meniscus, it is recommended to consider the possibility of DLM. This information can help to make accurate diagnosis of DLM, which allows appropriate surgical planning and facilitates patient's information on poor prognosis of DLM. LEVEL OF EVIDENCE: Level I.