A meniscus is a crescent-shaped

fibrocartilaginous Fibrocartilage consists of a mixture of white fibrous tissue and cartilaginous tissue in various proportions. It owes its inflexibility and toughness to the former of these constituents, and its elasticity to the latter. It is the only type of ...

anatomical structure that, in contrast to an

articular disc The articular disk (or disc) is a thin, oval plate of fibrocartilage present in several joints which separates synovial cavities. This separation of the cavity space allows for separate movements to occur in each space. The presence of an articula ...

, only partly divides a joint cavity.Platzer (2004), p 208 In

human Humans (''Homo sapiens'') are the most abundant and widespread species of primate, characterized by bipedalism and exceptional cognitive skills due to a large and complex brain. This has enabled the development of advanced tools, cultu ...

s they are present in the knee,

wrist In human anatomy, the wrist is variously defined as (1) the carpus or carpal bones, the complex of eight bones forming the proximal skeletal segment of the hand; "The wrist contains eight bones, roughly aligned in two rows, known as the carp ...

, acromioclavicular, sternoclavicular, and

temporomandibular joint In anatomy, the temporomandibular joints (TMJ) are the two joints connecting the jawbone to the skull. It is a bilateral synovial articulation between the temporal bone of the skull above and the mandible below; it is from these bones that it ...

s; in other animals they may be present in other joints. Generally, the term "meniscus" is used to refer to the cartilage of the knee, either to the

lateral Lateral is a geometric term of location which may refer to: Healthcare *Lateral (anatomy), an anatomical direction * Lateral cricoarytenoid muscle * Lateral release (surgery), a surgical procedure on the side of a kneecap Phonetics *Lateral co ...

or medial meniscus. Both are

cartilaginous Cartilage is a resilient and smooth type of connective tissue. In tetrapods, it covers and protects the ends of long bones at the joints as articular cartilage, and is a structural component of many body parts including the rib cage, the neck a ...

tissues that provide structural integrity to the knee when it undergoes

tension Tension may refer to: Science * Psychological stress * Tension (physics), a force related to the stretching of an object (the opposite of compression) * Tension (geology), a stress which stretches rocks in two opposite directions * Voltage or el ...

and

torsion Torsion may refer to: Science * Torsion (mechanics), the twisting of an object due to an applied torque * Torsion of spacetime, the field used in Einstein–Cartan theory and ** Alternatives to general relativity * Torsion angle, in chemistry Bi ...

. The menisci are also known as "semi-lunar" cartilages, referring to their half-moon, crescent shape. The term "meniscus" is from the Ancient Greek word (), meaning "crescent".

Structure

The menisci of the knee are two pads of

tissue which serve to disperse friction in the knee joint between the lower leg ( tibia) and the thigh (

femur The femur (; ), or thigh bone, is the proximal bone of the hindlimb in tetrapod vertebrates. The head of the femur articulates with the acetabulum in the pelvic bone forming the hip joint, while the distal part of the femur articulates wit ...

). They are

concave Concave or concavity may refer to: Science and technology * Concave lens * Concave mirror Mathematics * Concave function, the negative of a convex function * Concave polygon, a polygon which is not convex * Concave set * The concavity of a ...

on the top and flat on the bottom, articulating with the tibia. They are attached to the small depressions ( fossae) between the condyles of the tibia (intercondyloid fossa), and towards the center they are unattached and their shape narrows to a thin shelf.Gray's (1918), 7b The blood flow of the meniscus is from the periphery (outside) to the central meniscus. Blood flow decreases with age and the central meniscus is avascular by adulthood, which slows healing. Menisci show low-intensity on MRI images.

Function

The menisci act to disperse the weight of the body and reduce friction during movement. Since the condyles of the femur and tibia meet at one point (which changes during

flexion Motion, the process of movement, is described using specific anatomical terms. Motion includes movement of organs, joints, limbs, and specific sections of the body. The terminology used describes this motion according to its direction relativ ...

and extension), the menisci spread the load of the body's weight. This differs from sesamoid bones, which are made of

osseous tissue A bone is a rigid organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red and white blood cells, store minerals, provide structure and support for the body, ...

and whose function primarily is to protect the nearby tendon and to increase its mechanical effect.

Clinical significance

Injury

sport Sport pertains to any form of competitive physical activity or game that aims to use, maintain, or improve physical ability and skills while providing enjoyment to participants and, in some cases, entertainment to spectators. Sports can, ...

s and

orthopedics Orthopedic surgery or orthopedics ( alternatively spelt orthopaedics), is the branch of surgery concerned with conditions involving the musculoskeletal system. Orthopedic surgeons use both surgical and nonsurgical means to treat musculoskeletal ...

, people sometimes speak of "torn cartilage" and will actually be referring to an injury to one of the menisci. There are two general types of meniscus injuries: acute tears that are often the result of trauma or a sports injury and chronic or wear-and-tear type tears. Acute tears have many different shapes (vertical, horizontal, radial, oblique, complex) and sizes. They are often treated with surgical repair depending upon the patient's age as they rarely heal on their own. Chronic tears are treated symptomatically: physical therapy with or without the addition of injections and anti-inflammatory medications. If the tear causes continued pain, swelling, or knee dysfunction, then the tear can be removed or repaired surgically. The

unhappy triad The unhappy triad, also known as a blown knee among other names, is an injury to the anterior cruciate ligament, medial collateral ligament, and meniscus. Analysis during the 1990s indicated that this 'classic' O'Donoghue triad is actually an un ...

is a set of commonly co-occurring knee injuries which includes injury to the medial meniscus.

Conservative management

Conservative management is often considered first for a smaller or chronic tear that does not appear to require surgical repair. It consists of activity modification or physical therapy to strengthen and increase the range of motion.

Surgical treatment

Two surgeries of the meniscus are most common. Depending on the type and location of the tear, the patient's age, and physician's preference, injured menisci are usually either repaired or removed, in part or completely (meniscectomy). Each has its advantages and disadvantages. Many studies show the meniscus serves a purpose and therefore doctors will attempt to repair when possible. However, the meniscus has poor blood supply, and, therefore, healing can be difficult. Traditionally it was thought that if there is no chance of healing, then it is best to remove the damaged and non-functional meniscus, although at least one study has shown that there is little significance if a meniscectomy is done. However, resuming high intensity activities may be impossible without surgery as the tear may flap around, causing the knee to lock. A 2017

clinical practice guideline Clinical may refer to: Healthcare * Of or about a clinic, a healthcare facility * Of or about the practice of medicine Other uses * ''Clinical'' (film), a 2017 American horror thriller See also * * * Clinical chemistry, the analysis of bodily flu ...

strongly recommends against surgery in nearly all patients with degenerative knee disease.

Etymology

The term meniscus derives from

Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...

, meaning "crescent". The word was used for curved things in general, such as a necklace or a line of battle.''Lexicon of Orthopaedic Etymology'', p. 199

Additional images

Image:Braus 1921 284.png Image:Braus 1921 285.png

References

;Sources * * * * * {{DEFAULTSORT:Meniscus (Anatomy) Joints