Meniscal Lesions: Diagnosis and Treatment

Robert S. P. Fan, MD, Richard K. N. Ryu, MD

Disclosures
In This Article

Anatomy

The menisci of the knee joint are fibrocartilaginous C-shaped disks that occupy the joint space between the femur and the tibia.

Embryologically, the menisci form from mesenchymal tissue and appear as distinct structures by the eighth to tenth week of gestational development. Initially highly cellular, the perinatal meniscus also has an abundance of blood vessels. Progressive and gradual changes occur from birth to mid-adolescence, consisting of decreasing cellularity, decreasing vascularity, and increasing collagen content. As the developing child becomes progressively more ambulatory, the collagen fibers become oriented in order to adapt to the weight-bearing stresses.[1]

The meniscus represents fibrocartilaginous tissue composed of collagen and cells of either fibroblast or chondrocyte origin. The meniscus is approximately 75% water. The organic matrix is composed of approximately three quarters collagen, with type I collagen predominating.[2] The collagen fibers are oriented in a characteristic fashion. The most superficial fibers are oriented radially. Most of the collagen fibers, however, are found in the deep layer and are arranged in a circumferential orientation, which follow the periphery. The radial fibers are woven between the circumferential fibers, which help to provide structural integrity. The arrangement of fibers enables them to resist the hoop stresses that are produced at the meniscus during weight bearing.[3]

In cross section, the menisci are triangular, being thicker at the periphery and tapering to a thin free edge centrally. The superior surfaces are concave to accommodate the convexity of the femoral condyles. The medial meniscus is semilunar in shape and is thinner and narrower anteriorly. The posterior horn is thicker and wider, averaging approximately 10.6 mm.[4] The anterior and posterior horns are attached to the intercondylar eminence with an additional slip from the posterior horn attaching to the posterior cruciate ligament. The peripheral circumference is firmly attached to the capsule by the coronary ligaments. The medial meniscus is also firmly attached to the posterior oblique ligament. The medial meniscus covers approximately 64% of the medial tibial plateau. The lateral meniscus covers approximately 84% of the lateral tibial plateau. It is more circular than the medial meniscus and is also more uniform in width (average, 12 to 13 mm).[4]

The anterior and posterior horns of the lateral meniscus also attach to the intercondylar eminence, but in closer proximity to the anterior cruciate ligament than the medial meniscus. The peripheral attachment of the lateral meniscus to the capsule is thinner and looser than on the medial side. In addition, there is no attachment in the region of the popliteal hiatus, and there is no attachment of the lateral meniscus to the lateral collateral ligament (Figure 1).

Figure 1.

Schematic axial view of the tibial plateau, demonstrating the medial and lateral menisci. (Reprinted with permission.)

Warren R, Arnoczky SP, Wickiewicz TL. Anatomy of the Knee. In: Nicholas JA, Hershman EB, eds. The Lower Extremity and Spine in Sports Medicine. St. Louis, Mo: Mosby; 1986:657-694.

 

Meniscofemoral ligaments can be found in 70% of knees.[5] These represent accessory knee ligaments that attach to the medial femoral condyle from the posterior horn of the lateral meniscus. The posterior meniscofemoral ligament of Wrisberg can be found coursing posterior to the posterior cruciate ligament. The anterior meniscofemoral ligament of Humphrey passes anterior to the posterior cruciate ligament. These vary considerably in size, but average 20% of the size of the posterior cruciate ligament.[6]

The meniscus is typically an avascular structure with the primary blood supply limited to the periphery. Studies by Arnoczky and Warren have demonstrated that only the peripheral 10% to 30% of the meniscus is vascularized.[7] These vessels are derived from the middle, medial, and lateral geniculate arteries. The inner free margin of the meniscus is avascular and is nourished by the synovial fluid through diffusion (Figure 2).

Figure 2.

Frontal section of the medial compartment demonstrates the microvasculature of the medial meniscus. The perimeniscal capillary plexus (PCP) permeates through the peripheral border of the meniscus. F: Femur; T: Tibia. (Reprinted with permission.)

Arnoczky SP, Warren RF. Microvasculature of the human meniscus. Am J Sports Med. 1982;10:90-95.

 

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