Description
[Background]
The diagnosis of medial meniscus posterior root tear (MMPRT) is relatively difficult even when using several characteristic MRI findings. The purpose of this study was to investigate whether measuring the thickness of the medial meniscus (MM) could be a valuable screening tool for MMPRT.
[Materials and Methods]
To identify cases with isolated medial meniscus injuries, a consecutive group of 162 patients (166 knees) who underwent arthroscopic procedures, including meniscectomy, repair, or knee osteotomy, at our institution between January 2018 and June 2023 was included in this study. Patients with concomitant lateral meniscus injuries or knee ligament injuries were excluded. Medial meniscus injuries were further categorized based on the type of tear.
For cases without meniscal injuries, a consecutive group of 37 patients (37 knees) aged 30 years and older, who underwent arthroscopic ACL reconstruction during the same study period, and who exhibited no signs of meniscal injuries during intraoperative arthroscopic evaluation, was included.
Measurement of the maximum thickness of the medial meniscus (MTMM) was conducted preoperatively using coronal MRI images (Figure 1). A statistical investigation was conduct-ed to explore the relationship between meniscus thickness and meniscal injuries.
[Results]
The mean MTMM in the group without meniscus injury was 7.1 mm. In the group with isolated medial meniscus injury, the mean MTMM was 8.6 mm, with MMPRT observed in 32 knees exhibiting a mean MTMM of 10.7 mm. Notably, MTMM was found to be significantly larger in cases of MMPRT when compared to cases without identified medial meniscus injuries (P < 0.05, Table 1). Among the 32 cases of MMPRT, 27 cases (84.4%) exhibited MTMM greater than 1 cm. Additionally, out of the 34 cases with MTMM greater than 1 cm, MMPRT was present in 27 cases (79.4%).
[Discussion]
Based on the findings of this study, if the measurement of MTMM exceeds 1 cm, it strongly suggests the presence of MMPRT. Therefore, we propose defining this condition as a positive "Expansion sign."
