- Medial Meniscus
- Lateral Meniscus
- Crescent-shaped wedges of fibrocartilage oriented circumferentially
- Positioned between the tibial plateaus and the femoral condyles in the medial and lateral compartments
- Menisci possess collagen fibers oriented circumferentially
- These circumferential fibers are bound by radially oriented fibers
- Made primarily of type I collagen bundles
- Circumferential and radially oriented to help prevent tearing
- Contain types I and II neuroreceptors
- Possible proprioceptive and mechanoreceptive capacities
- Larger of the two menisci
- C-shaped and covers about 50% of the medial tibial plateau
- Posterior horn is larger than anterior horn
- Bony attachments to the anterior and posterior horns at the meniscal root
- Peripherally, attaches to the joint capsule, deep fibers of the MCL
- Providers anteroposterior stability to the knee
- Stronger attachment to joint capsule, less mobile, more susceptible to separation and tears
- More circular than the medial meniscus
- Covers about 70% of the lateral tibial plateau
- Posterior and anterior horns are similar in size
- Anterior attachment next to the ACL
- Posterior attachment behind intercondylar eminence, anterior to the attachment of the medial meniscus
- It also has attachment to the PCL via meniscofemoral ligaments, popliteomeniscal fasculi and the ligament of Wrisberg
- Congenital variant with abnormal morphology, can create innate instability of the lateral meniscus
- Thicker, poor tissue quality, less vascularity than a normal meniscus
- Prone to tears which can be symptomatic or asymptomatic
Watanabe Classification for Discoid Meniscus
- Type I/ Wrisberg
- Least common, meniscotibial attachment of lateral meniscus is absent
- Most unstable variation of discoid meniscus
- Type II/ complete
- Most common type, meniscus covers the entire tibial plateau
- Typically thickened and hypertrophic
- Type III/ incomplete
- More common than Type I, less common than Type II
- partially covers tibial plateau, also thickened
- Normal tibial attachment
- Menisci transmits 50% of joint compressive forces in full extension
- Approximately 85% of the load in 90° of flexion
- Protect articular cartilage
- Shock absorption
- Augment lubrication
- Rotation of the opposing articular surfaces
- Joint nutrition
- Tibiofemoral joint stability
- Joint congruency
- The blood supply to the meniscus begins in the periphery which allows these regions to have the best healing
- The outer third is considered red due to the good blood supply
- The inner two thirds is considered white and is avascular, relies on synovial fluid for nutrition
- Vascular classification
- Based on the side of the tear they can be classified as white-white, red-red, or white-red.
- Those tears in the white-white are avascular and typically do not heal.
- Originates from geniculate arteries: superior, inferior, medial and lateral
- Perimeniscal capillary plexus originating in the knee’s capsular and synovial tissues
- Needs to be updated
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- Hirschmann, M. T., and N. F. Friederich. "Classification: discoid meniscus, traumatic lesions." The Meniscus (2010): 241-246.
- Chambers, Henry G., and Reid C. Chambers. "The natural history of meniscus tears." Journal of Pediatric Orthopaedics 39 (2019): S53-S55.
- Lee SJ, Aadalen KJ, Malaviya P, et al. Tibiofemoral contact mechanics after serial medial meniscectomies in the human cadavcadaveric knee. Am J Sports Med 2006;34(8):1334-1344.
- Zimny ML, Albright DJ, Dabezies E. Mechanoreceptors in the human medial meniscus. Acta Anat Basel 1988;133(1):35-40.
- van Schie, Peter, et al. "Intra-operative assessment of the vascularisation of a cross section of the meniscus using near-infrared fluorescence imaging." Knee Surgery, Sports Traumatology, Arthroscopy (2021): 1-10.