Elsevier

Journal of Biomechanics

Volume 44, Issue 16, 10 November 2011, Pages 2737-2740
Journal of Biomechanics

The shocking truth about meniscus

https://doi.org/10.1016/j.jbiomech.2011.08.026Get rights and content

Abstract

The menisci of the knee are structures integral to the long term health of the knee joint. The primary function of these tissues is to distribute load across the tibiofemoral joint by increasing the congruency of the joint, thereby decreasing the resultant stress experienced by the articular cartilages. The menisci also play a secondary role in stabilizing the joint, particularly in the anterior cruciate ligament deficient knee, and also have roles in joint lubrication and proprioception. Also, an oft-cited role of this tissue is that of a shock absorber. We will review the literature supporting this shock absorption paradigm and describe the limitations and errors in the conclusions made by these studies. Consequently, we will show that the literature is inconclusive with no support for the shock absorption paradigm, which should therefore not be stated as a function of the menisci. We will describe how one of the three articles in support of this paradigm actually could be interpreted to the contrary and support the idea that the menisci may play no significant role in shock absorption at the knee at all, with the two remaining papers being inconclusive.

Introduction

The menisci of the knee are complex structures, whose health is strongly correlated with the long term health of the knee, specifically the health of the articular cartilage (Roos et al., 2001, Roos et al., 1998, Mcdermott and Amis, 2006). The common description of the menisci is that they are semi-lunar fibrocartilagenous disks, whose main function is to increase the congruency of the tibiofemoral joint, thereby decreasing the stress in the joint through an increase in the contact area (Mcdermott et al., 2008). The role of the menisci in the joint is also commonly stated as being that of a shock absorber and secondary stabilizer with possible roles in aiding joint lubrication, proprioception and nutrition of articular cartilage (Mcdermott et al., 2008, Englund et al., 2009, Mow et al., 2005, Chevrier et al., 2009). While shock absorption is a role commonly stated in papers and textbooks describing the menisci, this function of the menisci is not intuitive. Moreover, upon further review of the literature, there is little evidence that shock absorption is indeed a significant function of the menisci. We will review the three most commonly cited studies, that support this shock absorption paradigm and attempt to refine the current knowledge of the role of the menisci in the joint.

Mechanically, a shock absorber is defined as a device that dissipates energy to modify the response of a mechanical system to applied shock (Piersol, 2010). One of the most common examples of shock absorbers would be those found in automobile suspension systems. In such systems, when vertical impulses are imparted to the vehicle, the resultant kinetic energy is dissipated via heat energy in a viscous fluid. In viscoelastic media such as soft tissues, energy dissipation can occur from fluid movement in the tissue, which generates heat, or through rearranging of the molecular structure of the solid components (Mak, 1986). Physiologically, shock absorption is necessary to reduce the magnitude of the forces transmitted and the energy imparted to the skeletal system during everyday activities such as heel strike during gait or landing from the flight phase of running. For example, during heel strike in gait, the head experiences only one-tenth of the accelerations experienced at the shank (Light et al., 1980). This attenuation of acceleration through the skeletal system provides a protective mechanism for the head and vestibular system (Cappozzo et al., 1978a). Significant energy is absorbed at the knee during gait: throughout load acceptance, 6.3 J of energy is absorbed (Winter, 1983). While the knee joint functions effectively to absorb this energy, the proposal here however, is that this is accomplished with minimal contribution from the menisci.

Section snippets

Critique of the existing literature

An early paper discussing the shock absorption capacity of the menisci was Mechanical changes in the knee after meniscectomy (Krause et al., 1976). In this study, canine and human knees were excised, and tested in an Instron universal testing machine. Load–deformation behavior was measured at varying flexion angles, strain rates and rotational alignments. The intact joints were then tested. Subsequently, a medial meniscectomy was performed and finally a lateral meniscectomy. Joint testing was

Conclusion

The menisci are important structures in the knee joint and their functions vary from their primary role as a load distributor to more secondary roles in stabilization, lubrication, nutrition and proprioception (Mcdermott et al., 2008). However, the oft-cited description of the menisci as a shock absorber is not supported by the literature. In the study by Krause et al., the assumption that the difference in force–deformation behavior of the joint between intact and meniscectomized specimens was

Conflict of interest statement

The authors have no conflict of interest.

Acknowledgments

This work was supported by Alberta Innovates Technology Futures, The Natural Sciences and Engineering Research Council of Canada and the Killam Foundation.

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