The presentation investigates the following characteristics of the meniscus; Role of the Meniscus Material Properties Structural Limitations / Failure Limits Mechanism & Treatment of Injuries

1. The Meniscus: Structure, Role &
Injuries
Chris Hattersley – MSc, BSc, ASCC, CSCS, CES

2. Overview
Investigate the following characteristics of the
meniscus;
• Role of the Meniscus
• Material Properties
• Structural Limitations / Failure Limits
• Mechanism & Treatment of Injuries

3. Gross Anatomy
• C shaped ends attached to tibia, which deepen it’s
articular surface and distribute impact forces
evenly.
• Also provides stability, lubrication and
proprioception through its insertional attachments.
• Attached by anterior and posterior horns as well as
MCL, MFL’s, anterior inter-meniscal ligament &
popliteus tendon.
• During flexion the menisci translate outwards and
posteriorly. The lateral meniscus is more mobile and
it’s anterior horn can displace up to 9.5mm
posteriorly.
• Medial meniscus is more frequently injured than
the lateral meniscus with a prevalence of 2:1
(Masouros et al, 2008)

4. Fibre Orientation
• The menisci are wedge shaped on cross section
and have different layers of fibres which run in
different angles.
• The superficial fibre layer are randomly
orientated mimicking hyaline cartilage, this
lowers friction between menisci, tibia & femur.
• Underneath this, one third of the fibres are
distributed in a radial pattern and two thirds are
in a circumferential pattern.
• The fibre orientation dictates how the meniscus
distributes forces and therefore how the fibres
can be compromised.
(Pereira et al, 2013)

5. Blood Supply
• Red – red zone is vascularized by the
perimeniscal capillary plexus, contains
fibroblast like cells and can heal.
• Red-white zone is at the border of the
vascular area, contains chondrocyte like
cells and has a limited capacity to heal.
• White zone is avascular, receives
nourishment from synovial fluid and
can’t heal.
• Not as adaptable as other tissues in the
body but, when healthy, still has the
capacity to remodel in response to
loading ‘Mechanotransduction’.
(Fox et al, 2014)

6. Cellular Structure
• The menisci is a stratified fibrocartilage tissue with
regional variation in its cellular structure, this
dictates it’s material properties.
• Chondrocytes construct the extracellular matrix
consisting of type l, ll & lll collagen and
glycosaminoglycans (GAG).
• Collagen provides structure & elasticity, GAG provides
structure but also attracts water.
• The inner two thirds are more deformable than the
outer third.
• Chondroitin & glucosamine sulphate are involved in
the formation of GAG, so people with cartilage
damage sometimes supplement with that.
(Pereira et al, 2013)

7. Material Properties
• Elastic properties of materials are measured by
the Young’s modulus.
• Young’s modulus = stress x strain
• The compressive elastic modulus of the
meniscus is very low meaning it is the most likely
structure in the knee to deform under axial load.
• It’s high water content coupled with its collagen
& GAG structure means the meniscus
compresses under load, but has the elasticity to
return to it’s originally shape.
• Under load it is squeezed out of the joint
creating a hoop, shear & radial tensile stress.
Highly deformable under compression = Effective Shock Absorber
(Masouros et al, 2008)

8. Shock Absorption
• The main role of the meniscus is to evenly
distribute impact forces through the knee &
to maintain joint stability.
• As the femoral condyles roll over the
menisci it compresses and increases it’s
circumference.
• Absorbs 70-99% of the joints load.
• If the meniscus is damaged it increases the
load per unit area and accelerates the
degeneration of cartilage and subchondral
bone usually leading to OA.
(McDermott et al, 2008)

9. Mechanism of Injury
• As the knee is placed between 2 large
levers it experiences very high forces
which can cause injury to the
meniscus through repetitive chronic
loading or an acute traumatic event.
• A meniscus tear is usually caused by
twisting or turning quickly. These tears
can occur when you lift something
heavy or play sports.
• Can occur alongside a ligament injury,
ACL, MCL etc.
• As you get older the meniscus gets
worn and it’s water content is
reduced, this is natural with aging but
can make it tear more easily.
(Fox et al, 2014)

10. Meniscus Tears

11. Meniscus Sources of Stress
Tension
Fluid Pressure
Compression
Fluid Flow
Hydrostatic
Pressure
Strain / shear
(McNulty & Guilak, 2015)
Chronic Loading:
Time / Age
Acute Loading:
Traumatic Injury

12. Force Distribution
- It is apparent that meniscus tears happen in consistent patterns and this is
associated with the inherent way this structure dissipates force.
Tissue Loading > Tissue Tolerance = Tissue Failure
Hoop Stress Radial Tensile Stress Shear Stress
https://www.abdn.ac.uk/ims/research/musculoskeletal/meniscus-1206.php

13. How can the tissue fail?
Menisci sitting on the
tibia, showing how
loading forces them
outwards to produce a
hoop stress around the
curve.
- The way the meniscus dissipates force corresponds strikingly with the most
common tears highlighting weaknesses in its structure.
Radial tensile
stress from the
centre outwards
can cause a radial
tear.
Sheer stress
between the inner
and outer layer can
also cause a tear.
https://www.abdn.ac.uk/ims/research/musculoskeletal/meniscus-1206.php

14. • History of traumatic injury to the knee
• Knee pain on weight bearing activities,
walking, sit to stand etc.
• Delayed swelling of the knee
• Popping , clicking or locking of the
knee joint
• Stiffness of the knee
• Loss of full range of motion
• Tenderness on the knee joint line
• Pain with squatting
(Brukner, 2012)
Signs & Symptoms

15. Meniscus Injury Assessment - Old
McMurray’s Test Apley's Test

16. Meniscus Injury Assessment - Current
Thessaly's Test
• McMurrays & Apley’s tests can cause
unnecessary pain and risk further
injury to the meniscus.
• It is therefore preferred to make a
diagnosis using a patients subjective
history & identifying any of the
previously mentioned signs &
symptoms.
• If necessary Thessaly’s test can be
used which is less invasive than
McMurray’s / Apley’s.
(Alexanders et al, 2016)

17. Imaging
• MRI is the modality of choice when a meniscal
tear is suspected.
• Grade 0 – Normal intact meniscus
• Grade I – Intra-substance globular appearing
signal, not extending to the articular surface
• Grade II – Linear increased signal patterns, not
extending to the articular surface
• Grade III – Abnormal signal intersects the superior
and/or inferior articular surface
(Fox et al, 2014)

18. Treatment Options
Non surgical Meniscal repair
Meniscectomy Graft / Implant

19. Rehabilitation
- Reduce pain and inflammation.
- Improve joint range of motion.
- Strengthen leg muscles,.
- Improve alignment , biomechanics and
proprioception.
- Rehabilitation normally around 6-8 weeks.
Non-Surgical Treatment:
- Preferred option
- Aims to heal or reduce
symptoms
Surgical Treatment:
- May be required for large
tears or if a fragment breaks
away
- Short term relief but long
term problems i.e. OA.
(Brukner, 2012)

20. References
• Aspden., R. (1985). ‘A model for the function and failure of the
meniscus’. Proc.Instn.Mech.Engrs.[H], J.Eng.Med. 14:119-122.
• Brindle,. et al. (2001). ‘The Meniscus: Review of Basic Principles With Application to Surgery and
Rehabilitation’. Journal of Athletic Training, v.36(2), pp.160-169
• Brukner, P.,( 2012). Brukner & Khan's clinical sports medicine. North Ryde: McGraw-Hill.
• Fox, A., Wanivenhaus, F., Burge, A., & Rodeo, S. (2014), ‘The human meniscus: A review of anatomy,
function, injury, and advances in treatment: The Meniscus: Anatomy, Function, Injury and
Treatment’ ,Clinical Anatomy, 28, pp 1-19.
• Masouros, S., Mcdermott, I., Amis, A., & Bull, A (2008), ‘Biomechanics of the meniscus-meniscal
ligament construct of the knee’ , Knee Surgery, Sports Traumatology, Arthroscopy, 12, 1121-1132.
• McDermott, I.D., Masouros, S.D. and Amis, A.A., (2008). ‘Biomechanics of the menisci of the
knee’. Current Orthopaedics, 22(3), pp.193-201.
• Mcnulty, A., & Guilak, F. (2015), ‘Mechanobiology of the meniscus’, Journal of Biomechanics, 48, pp
1469-1478.
• Periera, H., Silva-Correia., J., Oliveira, J., & Reis., L. (2013), ‘ The Meniscus: Basic Science’, Meniscal
Transplantation. Springer, Berlin, Heidelberg.
• Sanchez-Adams, J., & Athanasiou, K. (2012) ‘Biomechanics of meniscus cells: regional variation and
comparison to articular chondrocytes and ligament cells’ Biomechanics and Modelling in
Mechanobiology, 11, pp 1047–1056.