Medial Meniscal Extrusion of Greater Than 3 Millimeters on Ultrasound Suggests Combined Medial Meniscotibial Ligament and Posterior Medial Meniscal Root Tears: A Cadaveric Analysis

Purpose: To evaluate how the meniscotibial ligament (MTL) affects meniscal extrusion (ME) with or without concomitant posterior medial meniscal root (PMMR) tears and to describe how ME varied along the length of meniscus. Methods: ME was measured using ultrasonography in 10 human cadaveric knees in conditions: (1) control, either (2a) isolated MTL sectioning, or (2b) isolated PMMR tear, (3) combined PMMR+MTL sectioning, and (4) PMMR repair. Measurements were obtained 1 cm anterior to the MCL (anterior), over the MCL (middle), and 1 cm posterior to the MCL (posterior) with or without 1,000 N axial loads in 0 degrees and 30 degrees flexion. Results: At 0 degrees, MTL sectioning demonstrated greater middle than anterior (P <.001) and posterior (P <.001) ME, whereas PMMR (P =.0042) and PMMR+MTL (P <.001) sectioning demonstrated greater posterior than anterior ME. At 30 degrees, PMMR (P <.001) and PMMR+MTL (P <.001) sectioning demonstrated greater posterior than anterior ME, and PMMR (P =.0012) and PMMR+MTL (P =.0058) sectioning demonstrated greater posterior than anterior ME. PMMRthornMTL sectioning demonstrated greater posterior ME at 30 degrees compared with 0 degrees (P =.0320). MTL sectioning always resulted in greater middle ME (P <.001), in contrast with no middle ME changes following PMMR sectioning. At 0 degrees, PMMR sectioning resulted in greater posterior ME (P <.001), but at 30 degrees, both PMMR and MTL sectioning resulted in greater posterior ME (P <.001). Total ME surpassed 3 mm only when both the MTL and PMMR were sectioned. Conclusions: The MTL and PMMR contribute most to ME when measured posterior to the MCL at 30 degrees of flexion. ME greater than 3 mm is suggestive of combined PMMR thorn MTL lesions. Clinical Relevance: Overlooked MTL pathology may contribute to persistent ME following PMMR repair. We found isolated MTL tears able to cause 2 to 2.99 mm of ME, but the clinical significance of these magnitudes of extrusion is unclear. The use of ME measurement guidelines with ultrasound may allow for practical MTL and PMMR pathology screening and preoperative planning.