Meniscus: The “Gasket” of the Knee

Everything you ever wanted to know but were afraid to ask…

When it comes down to it, the knees are truly an amazing feat of engineering (at least from a biomechanical point of view).  What other joint in body can not only bend and straighten (over 140 degrees of movement!), allow you to boogie (think pivoting), as well as handle up to 10 times your body weight (when downhill skiing)? (1)

Part of the reason behind the knee’s incredible mobility AND loading properties is due to the meniscus – which I like to think of as the “gasket” of the knee.  It is made of 2 wedge-shaped cartilage rings (1 “C”-shaped & 1 “O”-shaped) that sit between the tibia (main shin bone) and femur (thigh bone).  They’re made of approximately 72% water, 21% collagen, and 7% other cells which is a similar composition to that of the Achilles tendon on the back of your heel. (2,3)

Back in 1897, Bland-Sutton described the menisci as “functionless”(4).  This could not be further from the truth.  Like a gasket, the menisci improve the connection between 2 hard surfaces and help with shock absorption. (4)

The knee joint is like a tennis ball on a dessert plate – the bottom surface of the femur is rounded and the top of the tibia has a relatively flat surface (in fact, it’s called a tibial plateau!).  The wedge-shape of the menisci increase the surface area between the 2 bones and thereby also reduce the stress over the joint surfaces(4). Surgical removal of the meniscus has been shown to increase contact forces between the 2 surfaces by more than 350%! (2)

Unfortunately, these structures too can get damaged – either in one big traumatic plant and twist (usually resulting in damage to some of the surrounding ligaments) or “degenerative” damage (slowly, over time) (4).

These “gaskets” do have 1 design flaw – poor blood flow.  There are no arteries or veins within the knee joint capsule itself.  All oxygen and nutrients have to diffuse in from the outside and get pumped around with the physical movement of the knee itself.  Approximately 10-30% (ie. the outer edges) of the meniscus has a half-decent blood supply and therefore is able to heal/repair (2,4) over time.  The inner 70-90% either heals more slowly or may not heal at all (2).

That DOESN’T mean that you are stuck with painful knees. Up to 36% of asymptomatic or pain-free knees can have meniscal damage (as seen in MRIs) (5,6,7).  At least some of these meniscal tears can be considered similar to getting wrinkles in our skin as we get older – nothing to be concerned about.

So, how do I know if my menisci are contributing to my knee pain?

• You have pain along the inner and outer edges of your knee joint
• And/or Pain during pivoting on the knee
• Your knee locks in a bent or straight position

 

Note however that arthritis and knee ligament sprains can also cause similar symptoms.  These should be assessed by a physiotherapist.

What can I do about my knee?

Through physiotherapy we want to:

• Support healing of the outer (and inner) meniscus as best as we can with a gentle movement program (thereby helping the “healing” oxygen and nutrients circulate within the knee itself and diffuse to the inner layers of the meniscus)
• Strengthen the muscles of the knee to help improve support around your knee
• Decrease pain and any local sensitivity
• Improve control (or proprioception – more about that in the next blog article!) of your knee, thereby increasing your confidence on your leg

Your physiotherapist can help create an individualized program to help you achieve all of these goals and get you back to THRIVING!

 

Written By:

 

Susan Herdman

Registered Physiotherapist

 

 

 

 

References:

1. VCH: Exercise Guide for Knee Replacement Surgery (2005) & Westby MD. Arthritis Care & Research 2001: 45: 501 Accessed Apr 9/2021: http://www.grpt.ca/handouts/Patient-Exercise-Guide-Knee-Replacement-Surgery.pdf
2. Makris EA, Hadidi P, & Athanasiou KA (2011). The knee meniscus: Structure function, pathophysiology, current repair techniques, and prospects for regeneration. Biomaterials 32 p.7411-7431. Accessed Apr 9/2021: https://athanasioulab.bme.ucdavis.edu/files/2014/04/Makris-2011-The-knee-meniscus_-s.pdf
3. Sharma P & Maffulli N. (2005 Jan). Current concepts review – Tendon injury and tendinopathy: Healing and repair. Jof Bone & Joint Surgery 87-A(1). Accessed Apr 9/2021: http://www.scottsevinsky.com/pt/reference/physiology/jbjs_tendonopathy_tendinosis_healing_repair.pdf
4. Mayman DJ & Gill TJ (in Magee DJ, Zachazewski JE, & Quillen WS). (2009) Chapter 17: Injuries to the Meniscus and Articular Cartilage (in Pathology and Intervention in Musculoskeletal Rehabilitation). Elsevier Saunders – Missouri, St. Louis.
5. Zanetti M, Pfirrmann CWA, Schmid MR, Romero J, Seifert B, & Hodler J. (2003 Sept) Patients with suspected meniscal tears: Prevalence of abnormalities seen on MRI of 100 symptomatic and 100 contralateral asymptomatic knees.AJR: 181, p.635-641. Accessed Apr 9/2021: https://www.ajronline.org/doi/pdf/10.2214/ajr.181.3.1810635
6. LaPrade RF, Burnett QM, Veenstra MA, & Hodgman CG. (1994) The prevalence of abnormal magnetic resonance imaging findings in asymptomatic knees with correlation of magnetic resonance imaging to arthroscopic findings in symptomatic knees. Am J of Sports Medicine Vol 22(6) p 739-745. Accessed Apr 9/2021: https://drrobertlaprademd.com/wp-content/uploads/2015/07/prevalence-of-abnormal-mri-findings-in-asymptomatic-knees-1994.pdf
7. Kornick J, Trefelner E, McCarthy S, Lange R, Lynch K, & Jokl P. (1990) Meniscal abnormalities in the asymptomatic population at MR Imaging. Radiology Vol 177(2).  Accessed Apr 9/2021: https://pubs.rsna.org/doi/10.1148/radiology.177.2.2217786