Meniscus

Description

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  (A) Basic anatomy of the knee. (B) Cross-sectional diagram of the meniscus.
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  (A) Anatomy of the meniscus viewed from above (B) Axial view of a right tibial plateau showing sections of the meniscus and their relationship to the cruciate ligaments. AL, anterior horn lateral meniscus; AM, anterior horn medial meniscus; PCL, posterior cruciate ligament; PL, posterior horn lateral meniscus; PM, posterior horn medial meniscus.
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  Axial image (C) shows the normal appearance of the menisci, location of sagittal slices (lines 1. and 2.) in B, C and D. Sagittal images show the typical bow-tie configuration of the meniscal body corresponding to line 1 (B) and the opposing triangles of the horns corresponding to line 2 (C and D). Moreover, the horns of the LM are similar in size and shape (C), whereas the posterior horn of the MM is larger than the anterior horn (D)
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  Anatomy of the menisci (right knee). Anatomy of the meniscofemoral ligaments. ACL: anterior cruziate ligament. PCL: posterior cruziate ligament.
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  A variety of meniscal tears are illustrated.]]

Meniscal anatomy and relationship to important structures of the knee joint

Schematic diagram of meniscus anatomy

Anatomical variation in vascularization and cell population of the meniscus.

Other Names

• Medial Meniscus
• Lateral Meniscus
• Menisci
• Knee meniscus
• Meniscal cartilage
• Semilunar cartilage
• Fibrocartilage of the knee
• Tibiofemoral meniscus

General

• 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

Structure

• 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

Medial Meniscus

• 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

Lateral Meniscus

• 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

Illustration of the Watanabe classification of discoid meniscus. 1 (complete type), 2 (incomplete type), 3 (Wrisberg type)

Components of meniscus

Discoid Meniscus

• 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

Primary function

• Menisci transmits 50% of joint compressive forces in full extension
• Approximately 85% of the load in 90° of flexion

Contributes To

• Protect articular cartilage
• Shock absorption
• Augment lubrication
• Rotation of the opposing articular surfaces
• Joint nutrition
• Tibiofemoral joint stability
• Joint congruency
• Proprioception

Vascular Supply

Schematic drawing of the blood supply of the meniscus demonstrating the different vascular zones (RR is red, RW is red-white, WW is white)

Medial and lateral meniscus zones and relevant anatomical relations. ACL, anterior cruciate ligament; PCL, posterior cruciate ligament

• Distribution
  • 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

Innervation

• Medial Meniscus innervated by articular branches of:
  • Saphenous Nerve
  • Nerve to Vastus Medialis
  • Obturator Nerve (posterior articular branch)
  • Tibial Nerve
• Lateral Meniscus innervated by articular branches of:
  • Common Fibular Nerve
  • Tibial Nerve (posterior articular branches)
  • Nerve to Vastus Lateralis

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Clinical Significance

• Meniscus Tear
• Multiligament Knee Injury
• Knee Dislocation
• Parameniscal Cyst

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See Also

• Knee Anatomy (Main)
• Knee Pain (Main)
• Physical Exam Knee

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