Isolated Posterior Lateral Meniscofemoral Ligament Tears Show Greater Meniscal Extrusion in Knee Extension, and Isolated Posterior Lateral Meniscal Root Tears Show Greater Meniscal Extrusion at 30° Using Ultrasound: A Cadaveric Study

Purpose: To quantify the effects that posterior meniscofemoral ligament (pMFL) lesions have on lateral meniscal extrusion (ME) both with and without concomitant posterior lateral meniscal root (PLMR) tears and describe how lateral ME varied along the length of the lateral meniscus. Methods: Ultrasonography was used to measure ME of human cadaveric knees (n = 10) under the following conditions: control, isolated pMFL sectioning, isolated PLMR sectioning, pMFL+PLMR sectioning, and PLMR repair. ME was measured anterior to the fibular collateral ligament (FCL), at the FCL, and posterior to the FCL in both unloaded and axially loaded states at 0 degrees and 30 degrees of flexion. Results: Isolated and combined pMFL and PLMR sectioning consistently demonstrated significantly greater ME when measured posterior to the FCL compared with other image locations. Isolated pMFL tears demonstrated greater ME at 0 degrees compared with 30 degrees of flexion (P < .05), whereas isolated PLMR tears demonstrated greater ME at 30 degrees compared with 0 degrees of flexion (P < .001). All specimens with isolated PLMR deficiencies demonstrated greater than 2 mm of ME at 30 degrees flexion, whereas only 20% of specimens did so at 0 degrees. When the pMFL was sectioned following an isolated PLMR tear, there was a significant increase in ME at 0 degrees (P < .001). PLMR repair after combined sectioning restored ME to levels similar to that of controls in all specimens when measured at and posterior to the FCL (P < .001). Conclusions: The pMFL protects against ME primarily in full extension, whereas the presence of ME in the setting of PLMR injuries may be better appreciated in knee flexion. With combined tears, isolated repair of the PLMR can restore near-native meniscus position. Clinical Relevance: The stabilizing properties of intact pMFL may mask the presentation of PLMR tears and delay appropriate management. Additionally, the MFL is not routinely assessed during arthroscopy due to difficult visualization and access. Understanding the ME pattern of these pathologies in isolation and combination may improve detection rates so that the source of patients' symptoms can be addressed to satisfaction.