Investigating the Chronology of Meniscus Root Tears: Do Medial Meniscus Posterior Root Tears Cause Extrusion or the Other Way Around?

Abstract

Background: Meniscus root tears are increasingly being recognized. Meniscal extrusion has previously been associated with medial root tears; however, the relationship between secondary meniscal restraints, such as the meniscotibial (MT) ligament, extrusion, and root tears has yet to be formally evaluated.

Purpose: To better understand the association between MT ligament competence, medial meniscal extrusion, and medial meniscus posterior root tears (MMPRTs) as well as to determine the progression of meniscal extrusion over time.

Study design: Case series; Level of evidence, 4.

Methods: Serial magnetic resonance imaging (MRI) scans were reviewed for patients who showed evidence of medial meniscal extrusion and MMPRTs on at least 1 of ≥2 available MRI scans. All patients were symptomatic at the time of diagnosis. All MRI scans were analyzed independently by 2 board-certified musculoskeletal radiologists. MT ligament disruption, medial meniscal extrusion, and MMPRTs were recorded for each MRI scan. The time between MRI scans, presence of insufficiency fractures, and Outerbridge classification for the medial femur and tibia were also evaluated.

Results: Overall, 27 knees in 26 patients were included in this study, with a total of 63 MRI scans analyzed (21 knees with 2 MRI scans, 3 with 3 MRI scans, and 3 with 4 MRI scans). All patients demonstrated clear medial meniscal extrusion and MT ligament disruption before the subsequent development of MMPRTs (P < .001). Mean extrusion at the time of initial MRI was 3.3 ± 1.1 mm and increased significantly to 5.5 ± 1.8 mm at the time of first imaging with an identified MMPRT (P < .001). The mean time between initial MRI and the first identification of an MMPRT on later MRI was 1.7 ± 1.6 years.

Conclusion: In a sample of 27 symptomatic knees with serial MRI scans both before and after an MMPRT diagnosis, all patients demonstrated MT ligament disruption and associated meniscal extrusion before the development of subsequent medial meniscus root tears. These findings suggest that MT ligament disruption and medial meniscal extrusion represent early and predisposing events contributing to MMPRTs. Therefore, this provides a possible explanation of why meniscal extrusion is not corrected with medial meniscus root repair.

Keywords: MMPRT; extrusion; medial meniscal extrusion; medial meniscus posterior root tear; meniscotibial ligament.

Figure 1.

Illustration of the proposed progression of meniscal extrusion to a medial meniscus posterior root tear (MMPRT). (A) Meniscotibial (MT) ligament stress and attenuation. (B) Progressive loss of MT ligament function, increased root stress, and early meniscal extrusion. (C) MMPRT and associated increasing extrusion. (D) Rapid articular degeneration in the setting of an incompetent extruded meniscus.

Figure 2.

Serial magnetic resonance imaging showing the progression of a meniscotibial (MT) ligament tear, medial meniscal extrusion, and eventual medial meniscus posterior root tear. (A) Initial T2-weighted coronal imaging demonstrates bright MT ligament edema (arrow) while the root remains intact (arrowhead). There is a degenerative signal in the meniscus with irregularity and trace extrusion. (B1) Repeat imaging at 4 months demonstrates a further increase in the signal and MT ligament attenuation (arrow), increased extrusion, and (B2) new partial tearing and an increased signal in the meniscus root (arrowhead). (C1) Imaging at 6 months from baseline demonstrates marked attenuation of the MT ligament (arrow), substantial extrusion, the progression of femoral chondromalacia, and (C2) a concurrent full-thickness radial root tear (arrowhead). (D) At 8 months, there is radiographic loss of the MT ligament (arrow) and clearly visible complete tearing and displacement of the meniscus root (arrowhead).