Are the Peripheral Stabilizers as Important as the Roots? – An RSA-Based Biomechanical Study of Meniscal Attachments

Abstract

Objectives:

The peripheral meniscal stabilizers (PS), composed of the meniscotibial ligament and meniscocapsular fibers, are of interest because their insufficiency can lead to extrusion. However, their exact function remains unclear. The aim of this study was to investigate the influence of the PS on meniscal kinematics. It was hypothesized that the PS act as important stabilizers of the medial meniscus (MM).

Methods:

Sixteen human knee joints were tested in a robotic setup (Kuka KR 60-3, operated via simVitro). The following motions were applied at 0°, 30°, 60°, and 90° of flexion under 200 N axial compression: 89 N anterior/posterior tibial translation, 8 Nm varus, and 5 Nm internal/external rotation. Three 1 mm tantalum markers were implanted in the anterior, intermediate, and posterior parts of the MM. A radiostereometric analysis (RSA) system with an accuracy of < 0.1 mm, consisting of two X-ray sources, a digital detector, a calibration box, and a custom MATLAB script, was used to determine the positions and movements of the respective meniscal regions.

After measuring the kinematics of the native meniscus (n = 16), either the PS or the posterior medial meniscus root (PMMR) was arthroscopically transected first, in a randomized order, in half of the specimens (n = 8 each). The kinematics of the MM were recorded in all three spatial planes and summarized as total movement (sum vector, in mm). After transection of each structure, the increase in meniscal mobility compared to the native state was calculated. Statistical analysis was performed using mixed linear models.

Results:

Under axial loading, transection of the PS alone, without cutting the PMMR, led to a significant increase in meniscal mobility at the intermediate portion (Fig. 1), anterior, and posterior portion. Regardless of which structure was transected second, meniscal instability increased significantly. Comparable findings were observed for translational, varus, and rotational movements. The largest increases in meniscal motion were seen in the posterior horn.

Figure 1:

Changes in the mobility of the pars intermedia after sequential transection of the peripheral stabilizers (PS; green) and the posterior medial meniscus root (PMMR; orange).

Conclusion:

Isolated insufficiency of the PS, and isolated PMMR injury, each resulted in comparable instability of the medial meniscus. Only the combined insufficiency of both structures led to a marked increase in meniscal instability. These findings suggest that the PS function as important stabilizers of meniscal kinematics and may be as relevant for meniscal stability as the roots. It can thus be concluded that the PS may partly compensate for the effects of a root tear.