Review of Meniscus Root Tears
The meniscus plays a role in the distribution of tibiofemoral forces, joint congruency, and shock absorption (6, 7). The medial and lateral menisci are suspended to the tibia via ligament-like structures known collectively as the meniscal roots (1). The meniscus roots will anchor the anterior and posterior horn of the medial and lateral menisci to the tibia (3). There are other ligamentous supports of the meniscus that go beyond the scope of this review including the menisotibial ligaments, popliteomeniscal fascicles, meniscofibular ligaments, and meniscofemoral ligaments (3).
The main goal of the meniscus root is to prevent meniscus extrusion so that the meniscus can continue to decrease load to the articular cartilage (1). When an axial load acts upon the joint, it directs forces towards the outside of the joint and then there is a counter tensile stress (AKA hoop stress) by the meniscus to resist this force and distribute forces evenly across the joint surface (8). The loss of hoop stress of the meniscus can lead to the development of osteoarthritis (1).
Injuries to the meniscus root can be acute or chronic. Root tears have been identified in 4.3% of all arthroscopic knee surgeries and over half have been of the posterior meniscus root (6). Acute medial meniscus root tears are seen in young athletes with a hyperextension mechanism (4). Acute on chronic medial meniscus root tears are found in moderate osteoarthritis (4).
The anterior horn of the medial meniscus root inserts on the intercondylar crest and has a larger area of insertion than the anterior horn of the lateral meniscus (6). As a result of the larger area of insertion and thicker root, the anterior roots can withstand greater forces than the posterior roots (6).
One of the most common roots injured is the posterior medial meniscus root ligament (PMMRL) (1). The insertion of the PMMRL is between the posterior cruciate ligament and the posterior root of the lateral meniscus (1). Injures to the PMMRL are associated with higher rates of total knee arthroplasty (4).
There is no physical exam test that accurately identified meniscus root tears (6). The typical mechanism suggestive of a meniscus root injury is pain with deep knee flexion or pain after an acute twisting episode (6). A 3T MRI has a 100% positive predictive value for a medial root tear (6). On MRI, signs of a root tear are 3mm of meniscus extrusion, subchondral marrow edema, and a “ghost” sign (6). The ghost sign is the sudden absence of the meniscus between sagittal plane images (6). More than 3mm of meniscus extrusion seen on an MRI is commonly found in patients with moderate to severe medial compartment articular cartilage loss (7).
There is emerging evidence regarding the surgical repair of meniscal root tears. Early evidence shows a slowing of the progression of OA with meniscus root repair (6). Further evidence is needed into different techniques for meniscus root repairs.
The meniscus roots play an important role in maintaining joint congruency and proper distribution of forces across the meniscus. Tears of the meniscus roots can lead to increased articular cartilage degeneration and early knee OA. As a result, prompt diagnosis with MRI may lead to surgical treatment in select patients.
By Gregory Rubin, DO
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