DOI: 10.5061/dryad.1ns1rn8v9
title: Extrusion of medial and lateral meniscus before and after posterior root detachment

description: Despite contemporary surgical treatments of posterior meniscus root tears,
 there is a low rate of healing and an incidence of residual meniscus
 extrusion approaching 30%. Here, we characterized and compared the
 behavior of the medial and lateral meniscus in response to axial
 compression load and real-time dynamic motion using a cadaveric model.
 There were no differences in the amount of meniscus extrusion between the
 medial and lateral meniscus with a competent posterior root (0.338mm vs.
 0.235mm; p-value = 0.181). However, posterior root detachment resulted in
 a consistently increased amount of meniscus extrusion for the medial
 meniscus compared to the lateral meniscus (2.233mm vs. 0.4705mm; p-value
 &lt; 0.0001). Moreover, the medial and lateral menisci responded
 differently to the effects of knee flexion angle. Detachment of the
 posterior root of the medial meniscus resulted in an increase in extrusion
 at all angles of knee flexion, but was most pronounced (4.00mm ± 1.26mm)
 at 30-degrees of knee flexion. In contrast, the lateral meniscus only
 extruded (1.65mm ± 0.97mm) in full extension. Furthermore, only the medial
 meniscus extruded during dynamic flexion after posterior root detachment.
 These findings suggest that while meniscus extrusion occurs in both the
 medial and lateral meniscus, the functional consequences of extrusion are
 more significant for the medial meniscus than that of the lateral
 meniscus. Limiting the amount of meniscus extrusion after posterior root
 tear in response to static compressive forces and dynamic motion is
 necessary to recapitulate native meniscus function.
description: <strong>Equipment and set-up</strong>
 Custom fabricated grips were attached to an MTS 858 Bionics
 servo-hydraulic test system. The lower grip was fabricated using an axle
 system to release the knee rotational (medial/lateral) degree of freedom.
 The axle system was then mounted on two crossed roller slides (Deltron
 NBT-6160A) in an X-Y arrangement to allow degree of freedom release of the
 medial/lateral and anterior/posterior planes. Data acquisition included
 the specimen load, actuator displacement, and meniscus displacement, using
 a Lord Microstrain model M-DVRT-6 transducer (M-DVRT-6, 6.0mm stroke
 micro-miniature DVRT linear displacement Transducer, and DEMOD-DC,
 Miniature DC input, DC output signal conditioner, LORD Corporation, 459
 Hurricane Lane, Suite 102, Williston, Vermont 05495). Data were acquired
 using a Data Translation 16-bit digital to analog converter. The force
 generated during each testing protocol was recorded in real time. The
 upper grip was fabricated to allow positioning of the knee in the range of
 zero to one hundred degrees of flexion for mechanical testing during
 dynamic range of motion. <strong>Testing
 protocols</strong> Protocols simulated clinical
 knee activities during weight-bearing loading and passive
 non-weight-bearing dynamic range of motion. The amount of load delivered
 across the knee simulated that of a 75-kg person. Specimens were tested in
 the following sequence: posterior root intact and posterior root detached.
 <i>Axial compression load: </i>Testing was performed in load
 control in the axial direction. A ramp to a constant load to simulate a
 load from 25-N preload to full weight-bearing (1800-N) at 0.1-second ramp
 to set load, with manual return to preload performed in full knee
 extension (0-degrees of knee flexion). A sinusoidal cyclic load to
 simulate a walking gait at 20-cycle compressive ½ cycle sine wave, 25-N to
 set load with 1-sec cycle (0.3-second down, 0.3-second up, 0.4-second
 pause to stimulate swing phase of gait). This test was performed across
 0-, 30-, 45-, 60- and 90-degrees of knee flexion. <i>Dynamic
 non-weight-bearing range of motion: </i>Each knee was taken through
 a range of motion from 0- to 100-degrees of flexion. Meniscus extrusion
 was linked to range of motion data detected with a calibrated custom
 electronic goniometer in real-time.
 <strong>Statistical analysis</strong>
 Means and standard deviations or standard error of the means were
 calculated. Between group comparisons were performed using a Student’s
 t-test for two groups and analysis of variance (ANOVA) for more than two
 groups. Pairwise comparisons and post-hoc adjustments were performed if
 the ANOVA model was statistically significant. Linear regression was used
 to model the relationship between knee flexion and meniscus extrusion. A
 p-value &lt; 0.05 was considered statistically significant.
 Calculations were performed using GraphPad Prism 9.0.1 for Mac (San Diego,
 CA, USA).