Medial Meniscus Extrusion Volume in the Knee Flexion Position Does Not Worsen after Transtibial Pullout Repair for Medial Meniscus Posterior Root Tears: A 3-year Follow-up

This study aimed to evaluate the progression of medial meniscus (MM) extrusion (MME) volume (MMEV) at knee joint extension/flexion up to 3 years after pullout repair of MM posterior root tears (MMPRT) and to assess its relationship with clinical outcomes. A retrospective analysis was conducted in 15 patients who underwent pullout repair of unilateral MMPRT and open magnetic resonance imaging (MRI) examination preoperatively and at 1 and 3 years postoperatively. An open MRI was performed at knee joint extension and flexion. MME and MMEV at knee joint extension, MM posterior extrusion (MMPE), and MMEV at knee joint flexion were evaluated. Clinical scores were recorded preoperatively and at 1 and 3 years postoperatively. The correlations between changes in MME, MMPE, and MMEV from the preoperative period to 3 years postoperatively (ΔMMEV) and clinical scores from the preoperative period to 3 years postoperatively were evaluated. MME and MMEV at knee joint extension increased significantly from preoperatively to 1 year (<i>p</i> = 0.001 and <i>p</i> = 0.016) and to 3 years (<i>p</i> < 0.001 and <i>p</i> = 0.010), with no significant change from 1 to 3 years (<i>p</i> = 0.319 and <i>p</i> = 0.840). MMPE at knee joint flexion decreased significantly from preoperatively to 1 year (<i>p</i> = 0.007) and to 3 years (<i>p</i> = 0.002), whereas no difference was observed from 1 to 3 years (<i>p</i> = 0.672). MMEV at knee joint flexion showed no significant longitudinal changes (all <i>p</i> > 0.644). After false discovery rate (FDR) adjustment, all clinical outcomes, except the pain visual analog scale, demonstrated significant time effects. No significant correlation was observed between ΔMME, ΔMMPE, and ΔMMEV at knee joint extension and clinical outcomes before/after FDR adjustment. Although moderate correlations between ΔMMEV at knee joint flexion and clinical outcomes were observed before adjustment, none remained significant after FDR correction. Three years after transtibial pullout repair for MMPRT, MMPE at knee joint flexion significantly improved, maintaining MMEV at knee joint flexion without deterioration. ΔMMEV at knee joint flexion may correlate with clinical score improvement; however, further research is required.