Comparison of the insertion of the posterior horn of the lateral meniscus: discoid versus non-discoid.

PURPOSE: The purpose of this study was to compare the insertion sites of the posterior horn between discoid and non-discoid lateral meniscus using magnetic resonance imaging (MRI).
METHODS: Two hundred and twenty-seven patients who had MRI scans before surgery and underwent arthroscopy were enroled in this study. A coronal view showing the narrowest width of the midbody of the lateral meniscus was chosen to measure the widths of the entire tibial plateau and the midbody of the lateral meniscus. Considering the ratio of the meniscal width to the tibial plateau width, the patients were divided into non-discoid, incomplete discoid, and complete discoid groups. On a coronal view accurately showing the insertion of the posterior horn of the lateral meniscus, a distance between the peak of the lateral tibial eminence and the centre of the insertion of the posterior horn, and a width of the lateral tibial plateau between the lateral edge of the tibial plateau and the peak of the lateral tibial eminence were measured.
RESULTS: The insertion centre of the posterior horn was located more medially in the incomplete and complete discoid groups than in the non-discoid group (p = 0.003, 0.010, respectively). When individual differences in the knee size were corrected, the insertion centre of the posterior horn in the incomplete discoid and complete discoid groups was located more medially than in the non-discoid group (p = 0.009, 0.003, respectively).
CONCLUSION: The insertion centre of the posterior horn of the lateral meniscus is located more medially to the apex of the lateral tibial eminence in the discoid group than in the non-discoid group. This finding needs to be considered for an accurate position of the posterior horn of lateral meniscus during the lateral meniscal allograft transplantation. LEVEL OF EVIDENCE: IV.