At Issue

Medial meniscal root tears: Fix it or leave it alone

Question: In your opinion, when do you fix medial meniscal root tears? When do you leave them alone?

Proper diagnosis yields higher patient satisfaction after medial meniscal root repair

Medial and lateral menisci are crescent-shaped fibrocartilage structures that provide joint congruity, stabilization and lubrication and act as “shock absorbers” for joint preservation. During weight-bearing activities, the menisci dissipate axial loads and contain hoop stresses. The medial meniscus transmits approximately 50% of the total joint load of the knee medial compartment, thus protecting the articular cartilage from excessive force.

Matthew H. Blake

Matthew H. Blake

Darren L. Johnson

Darren L. Johnson

Tears to the medial meniscal root change the biomechanics and kinematics of the knee, which cause early degeneration of the joint. It has been shown the peak tibiofemoral contact pressure after a total meniscectomy is equal to a posterior medial meniscal root tear.

Recent kinematic/biomechanical studies have also shown the importance of the medial meniscus to anterior translation of the knee. Absence of the medial meniscus (entire medial meniscal root tear) places large stresses on the ACL, the primary ligament that prevents anterior translation of the knee.

Diagnosis

Coronal MRI of posterior medial meniscal root tear
Coronal MRI shows a posterior medial meniscal root tear.
Sagittal MRI shows the “ghost sign
This sagittal MRI shows the “ghost sign."
Axial MRI shows a posterior medial meniscal root tear
Axial MRI shows a posterior medial meniscal root tear.
Posterior medial meniscal root tear
A posterior medial meniscal root tear is shown.
Images: Johnson DL

Making a medial meniscal root tear diagnosis is difficult because the typical history of locking, catching or giving way is less likely to be present. More often, the patient will complain of joint line pain with a minor traumatic event, such as squatting. Likewise, physical exam findings of an effusion, a positive McMurray test and a positive Apley grind test are not usually present.

The most commonly encountered signs are posterior knee pain with deep flexion and joint line tenderness. Another exam finding is palpating the anteromedial joint line, while placing a varus stress on a fully extended knee and feeling for meniscal extrusion. This extrusion should disappear without stress.

Coronal MRI sequences are generally considered the best images for visualization of medial meniscal root tears (Figure 1). While visualization of the meniscal root may be difficult due to MRI slice size, type of MRI and strength of MRI, an extrusion larger than 3 mm highly correlates with a root tear. The “ghost sign” or absence of an identifiable meniscus anterior to the posterior cruciate ligament is also indicative of a root tear (Figure 2). Depending on the cut thickness, axial MRI images may display the root tear (Figure 3).

Treatment

Historically, medial meniscal root tears have been treated conservatively or by partial meniscectomy. With advances in surgical techniques and instrumentation, meniscal root repair is a viable option that can restore the biomechanics and kinematics of the knee (Figure 4). Although a successful outcome of a meniscal root repair is predicated upon appropriate indications for the repair, not all medial meniscal root tears should be repaired.