Partial weight-bearing and range of motion limitation significantly reduce the loads at medial meniscus posterior root repair sutures in a cadaveric biomechanical model

Abstract

Purpose: The aim of this study was to investigate the influence of medial meniscus posterior root avulsion (MMPRA) before and after surgical treatment on the biomechanics of the knee joint, including suture repair forces during daily and crutch-assisted gait movements.

Methods: MMPRA were investigated in eight human cadaver knee joint specimens by a dynamic knee joint simulator with daily (normal gait, gait with additional rotational movement, standing up, sitting down) and rehabilitation-associated movements (crutch-assisted gait with limited flexion range of motion [30°] and 30% [toe-touch weight-bearing, TTWB] and 50% of body weight [partial weight-bearing, PWB]) with simulated physiologic muscle forces. Each specimen was tested in intact, torn and repaired (transtibial suture) state. The biomechanical parameters were: medial mean contact pressure and area, knee joint kinematics, medial displacement of the posterior meniscus horn and loading on the anchoring suture.

Results: Significant reduction of the contact area due to the avulsion was observed in all movements except for PWB and sitting down. MMPRA repair significantly increased the contact areas during all movements, bringing them to levels statistically indistinguishable from the initial state. MMPRA resulted in a medial displacement up to 12.8 mm (sitting down) and could be reattached with a residual displacement ranging from 0.7 mm (PWB) to 5.7 mm (standing up), all significantly (p < 0.001) reduced compared to the torn state. The mean peak anchoring suture load increased from TTWB (77 N), PWB (91 N) to normal gait (194 N), gait rotation (207 N), sitting (201 N; p < 0.01) and to standing up (232 N; p = 0.03).

Conclusion: Surgical treatment of MMPRA allows restoration of physiological knee joint biomechanics. Crutch-assisted movements reduce the loading of the repair suture, thus likewise the risk for failure. From a biomechanical point of view, crutch-assisted movements are recommended for the early rehabilitation phase after MMPRA repair.

Level of evidence: Level V.

Keywords: dynamic knee joint simulator; knee contact mechanics; medial meniscus posterior root avulsion; rehabilitation protocol; suture repair.

Figure 1

(a) Ring force transducer, fixed in a custom‐made holder to enable adequate suture pre‐tension. Illustration of a torn (b) and repaired (c) posterior horn with medially translated meniscus body and adapted ring force transducer (red rectangle) and (d) radiograph image with coordinate system and tantalum marker beads in the meniscus body (green rectangle).

Figure 2

(a) Dynamic knee simulator with embedded specimen, muscle simulation via steel cables, and (1) passive reflective rigid marker bodies (OptiTrack®, NaturalPoint, Inc.) at the femur and tibia, (2) Tekscan® pressure‐sensitive film (K‐scan sensor 4000, Tekscan, Inc.) and (3) ring force transducer (Wazau Mess‐Prüfsysteme GmbH). (b) Schematic drawing of the biomechanical test configuration.

Figure 3

Mean contact pressure (mean ± SD) measurements during six movements (four‐point crutch gait under 30% BW [TTWB] and 50% BW [PWB], Gait, gait with an associated 15° ankle rotation [GaitRotation], standing up [SitToStand] and sitting down [StandToSit]), for the intact (white bar), torn (hatched bar) and repaired (solid grey bar) meniscal state. One‐way analysis of variance and Tukey's multiple comparison test. BW, body weight; PWB, partial weight‐bearing; TTWB, toe‐touch weight‐bearing. *p ≤ 0.05; n = 8.

Figure 4

Mean contact area (mean ± SD) measurements during six movements (four‐point crutch gait under 30% BW [TTWB] and 50% BW [PWB], Gait, gait with an associated 15° ankle rotation [GaitRotation], standing up [SitToStand] and sitting down [StandToSit]), for the intact (white bar), torn (hatched bar) and repaired (solid grey bar) meniscal state. One‐way analysis of variance and Tukey's multiple comparison test. BW, body weight; PWB, partial weight‐bearing; TTWB, toe‐touch weight‐bearing. *p ≤ 0.05; n = 8.

Figure 5

Range of motion in internal (mean − SD) and external (mean + SD) tibial rotation measurements during six movements (four‐point crutch gait under 30% BW [TTWB] and 50% BW [PWB], Gait, gait with an associated 15° ankle rotation [GaitRotation], standing up [SitToStand] and sitting down [StandToSit]), for the intact (white bar), torn (hatched bar) and repaired (solid grey bar) meniscal state. Mixed model analysis and Tukey's multiple comparison test. BW, body weight; PWB, partial weight‐bearing; TTWB, toe‐touch weight‐bearing. *p ≤ 0.05; n = 8.

Figure 6

Medial displacement (mean ± SD) of the dissected posterior horn after MMPRA simulation and subsequent repair during six movements (four‐point crutch gait under 30% BW [TTWB] and 50% BW [PWB], Gait, gait with an associated 15° ankle rotation [GaitRotation], standing up [SitToStand] and sitting down [StandToSit]). Mixed model analysis and Bonferroni's multiple comparisons test. BW, body weight; MMPRA, medial meniscus posterior root avulsion; PWB, partial weight‐bearing; TTWB, toe‐touch weight‐bearing. *p ≤ 0.05; n = 5.

Figure 7

Peak repair suture force (min, median, max) in N during six movements (four‐point crutch gait under 30% BW [TTWB] and 50% BW [PWB], Gait, gait with an associated 15° ankle rotation [GaitRotation], standing up [SitToStand] and sitting down [StandToSi]). Friedmann test. BW, body weight; PWB, partial weight‐bearing; TTWB, toe‐touch weight‐bearing. *p ≤ 0.05, n = 7.