Assistant
Definition
By Gregory R. Waryasz, MD
The medial meniscus of the musculoskeletal system is characterized by being located in the medial joint compartment and is wider than the lateral meniscus.
It is part of the knee joint. It consists of fibrocartilage and is approximately 70% water.
Its unique structural feature is that it is cresent-shaped or C-shaped. On cross-section it appears triangular. The fibers run circumferentially. The medial meniscus covers about 64% of the condyle surface. The medial meniscus is 10mm wider and ranges from 3 to 5 mm thick.
The anterior horn of the meniscus is attached to the anterior intercondylar area of the tibia, anterior to the anterior cruciate ligament.
The posterior horn is attached to the posterior intercondylar area, anterior to the posterior cruciate ligament.
Medially it is attached to the deep surface of the medial collateral ligament.
The transverse ligament connects the anterior portions of the menisci.
The coronary ligament of the knee/meniscotibial ligament connects the inferior portion of the menisci to the tibial plateau.
The blood supply to the medial meniscus is from the superior medial, inferior medial, and middle genicular arteries with venous drainage from the accompanying veins.
There are three different zones of vascularity including a red-red, red-white, and white-white zone. The red-red zone is on the peripheral third of the meniscus and is vascularized. The red-white zone is in the middle third of the meniscus and is avascular, but borders the red-red zone. The white-white zone is the central third of the meniscus. The white-white zone is avascular.
The medial meniscus as well as all other bones, muscles, and ligaments of the body are derived of mesodermal origin in the embryo.
The function of the medial meniscus is to absorb force. After a meniscectomy or meniscal removal, contact stresses increase up to three times. As the knee is further flexed, more force is transferred to the posterior horn. The peripheral attachments are stronger with the medial meniscus making it less mobile.
Common diseases include meniscal tears, meniscal cysts, and discoid meniscus.
Meniscal tears can occur with trauma or by degenerative changes.
A meniscal cyst is a cystic lesion located on the peripheral part of the meniscus associated with a meniscal tear.
A discoid meniscus is a larger than normal meniscus. It more commonly affects is the lateral meniscus.
Commonly used diagnostic procedures include clinical history, physical exam, and MRI.
It is usually treated with physical therapy and NSAIDs. Surgery can be performed either with a large open incision or performed with arthroscopy for meniscal tears and cysts.
References
Elstrom J, Virkus W, Pankovich (eds), Handbook of Fractures (3rd edition), McGraw Hill, New York, NY, 2006.
Koval K, Zuckerman J (eds), Handbook of Fractures (3rd edition), Lippincott Williams & Wilkins, Philadelphia, PA, 2006.
Lieberman J (ed), AAOS Comprehensive Orthopaedic Review, American Academy of Orthopaedic Surgeons, 2008.
Moore K, Dalley A (eds), Clinically Oriented Anatomy (5th edition), Lippincott Williams & Wilkins, Philadelphia, PA, 2006.
Wheeless?s Textbook of Orthopaedics: Medial Meniscus (http://www.wheelessonline.com/ortho/medial_meniscus)