Meniscus (anatomy)

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Structure of the knee joint
Menisci of the knee joint of man

As meniscus (plural: menisci , latinisiert meniscus / menisci . From Greek μηνίσκος mēnískos, moon-shaped body ', half-moon', diminutive of mene, Moon ') is referred to in the anatomy of a disc-shaped (in the knee crescent-shaped) cartilage in a joint . In contrast to a disc , a meniscus does not divide the joint cavity completely. In mammals there are two large menisci in the knee joint and numerous smaller menisci in other joints (e.g. interphalangeal joint ), which often derive from the capsule and protrude into the joint. Menisci occur in the knee joint and in other joints in birds too ( spoke-ulnar joint , wrist, spine).

function

In the knee joint there is an inner meniscus ( meniscus medialis) and an outer meniscus (meniscus lateralis) , which are located between the joint surfaces of the thighbone ( femur ) and the shinbone ( tibia ). Both calculations ( FEM ) and laboratory measurements underline the importance of the knee joint menisci in the (pressure) force transmission between the two articular surfaces (of the femur and the shin bone ) of the knee joint. The knee joint menisci consist mainly of collagen fibers (around 90%), which absorb the tensile forces. Tensile forces arise mainly in the vicinity of the anterior and posterior horns, which are anchored to the tibial plateau by short ligaments anterior (front) and posterior (rear). Additional tensile stress arises from the deformation of the menisci z. B. in squats . In addition to these basic types of stress, due to the shape of the menisci, it is very likely that they also ensure better distribution of the synovial fluid on the articular cartilage for friction reduction and nutrition.

It has been known since 1948 and is now generally recognized that people with a surgically removed meniscus significantly increase the risk of early osteoarthritis . Due to the mobility of the menisci (especially the outer meniscus), they also enlarge the joint surface on the tibia plateau or the contact surface for the head of the femur. Due to the shape of the joint ( bicondylar joint ) of the knee, in addition to pure flexion and extension movements, rotations by a few degrees, which are forced as a so-called final rotation when fully extended in the intact knee joint , as well as displacements (translations) forwards and backwards are possible. The articular surfaces of the tibial plateau would be unsuitable for this without the menisci.

Damage to the meniscus apparatus

Tear in the posterior horn of the medial meniscus (see arrow, view from the side). The anterior horn is intact

Injuries to the menisci mostly affect athletes or people whose activities overstrain their knees, such as tilers . Sports that are particularly at risk for meniscus injuries include football , fencing , tennis , handball , skiing , snowboarding , wakeboarding , wakeskate , water skiing , squash , badminton , basketball , discus throwing , javelin throwing , skateboarding , rugby , karate , gymnastics , trampoline and cycling (due to accidents). A meniscus injury usually occurs with rapid rotation (~ rotation of the shin and thighbone around the longitudinal axis) of the knee joint as well as with rapid bending or stretching (~ movement around the transverse axis). During these movements, the free edge of the meniscus gets between the joint bodies and tears in part (e.g. as a tear in the basket handle) or completely.

Disc meniscus

The disc meniscus is a congenital malformation of the knee joint meniscus . It can lead to a snap phenomenon and pain, which typically begins between the ages of six and eight.

Meniscus contusion

The harmless variant of a meniscus lesion (injury) is called a meniscus squeeze . Here, conservative treatment and a break in sports of around three weeks are sufficient. In some cases , a relief incision can support the healing process.

Meniscal rupture

It looks different with a meniscus tear (meniscus rupture). Inner meniscus injuries ( i.e. the meniscus medialis ) are much more common than those of the outer meniscus. The cracks are divided into longitudinal, radial or oblique cracks (lobes) according to their direction. With regard to the spatial level, a distinction is made between vertical cracks and horizontal cracks. Special forms are complex cracks, the basket handle crack and a "flipped meniscus". The diagnosis is made through clinical examination, magnetic resonance imaging and arthroscopy (joint endoscopy).

A basket handle tear is the name given to a meniscus tear that runs parallel to the main direction of the fibers. The meniscus is split lengthways along its course, the front and rear ends of the fragment continue to be connected to the rest of the meniscus. The free edge moves into the joint space, causing acute pain and can unexpectedly block joint movement.

Basket handle tear, view from the front; large parts of the outer meniscus (red) are shifted inwards into the joint, inner meniscus (green) are still intact

Degenerative changes

Just as the cartilage surface of a joint changes degeneratively over time, so do the menisci. The meniscus tissue is rolled out under load and becomes thinner and thinner until it finally tears. These changes are collectively referred to as meniscopathy and are part of what happens in the development of osteoarthritis . In the case of accidental injuries that are to be classified as occupational accidents, the histological examination of the meniscus tissue is of decisive importance for the recognition of an accident context. Other degenerative changes can also be caused by an eversion angle other than zero degrees.

The current standard procedure for treating degenerative changes in the meniscus - arthroscopic partial meniscectomy - was tested for effectiveness in a 2013 study. The study showed that after one year the operation had no advantages over a sham operation. This is in line with some existing similar studies.

literature

  • Becker R., Schaller C. (2015): Image atlas meniscus surgery: Fundamentals, technology. Application . KVM Verlag, ISBN 3-940698-99-7
  • P. Fehrmann and J. Mockenhaupt (1991): Theoretical and experimental analyzes on the importance of the intact and the damaged meniscus for the static stress on the knee joint . In: Trauma Surgery 17 (4), pp. 187–193. PMID 1949353
  • TJ Fairbank (1948): Knee joint changes after meniscectomy . In: J Bone Joint Surg Am . 30 (4), pp. 664-670. PMID 18894618 , (0nline)
  • M. Englund et al. (2008): Incidental meniscal findings on knee MRI in middle-aged and elderly persons. In: N Engl J Med 359 (11), pp. 1108-1115. PMID 18784100
  • M. Lengsfeld et al. (1990): On the importance of shape differences between the medial and lateral knee joint meniscus for functional changes in position . In: Trauma Surgery 17 (1991), pp. 309–315 (No. 6)

Individual evidence

  1. ↑ P. Fehrmann and J. Mockenhaupt: Theoretical and experimental analyzes on the importance of the intact and the damaged meniscus for the static stress on the knee joint. European Journal of Trauma. ISSN  1439-0590
  2. ^ TJ Fairbank: Knee joint changes after meniscence . J Bone Joint Surg Br, London, England, 1948
  3. ^ Meniscus update. S. Waldt in Radiologie up2date 4/2013 p. 285
  4. ↑ Raine Sihvonen, Mika Paavola, Antti Malmivaara, Ari It 1, Antti Joukainen, Heikki Nurmi, Juha Kalske, Teppo LN J rvinen: Arthroscopic Partial Meniscectomy versus Sham Surgery for a Degenerative Meniscal Tear. In: New England Journal of Medicine. 369, 2013, pp. 2515-2524, doi : 10.1056 / NEJMoa1305189
  5. ↑ J. Bruce Moseley, Kimberly O Malley, Nancy J. Petersen, Terri J. Menke, Baruch A. Brody, David H. Kuykendall, John C. Hollingsworth, Carol M. Ashton, Nelda P. Wray: A Controlled Trial of Arthroscopic Surgery for Osteoarthritis of the Knee. In: New England Journal of Medicine. 347, 2002, pp. 81-88, doi : 10.1056 / NEJMoa013259
  6. ↑ Alexandra Kirkley, Trevor B. Birmingham, Robert B. Litchfield, J. Robert Giffin, Kevin R. Willits, Cindy J. Wong, Brian G. Feagan, Allan Donner, Sharon H. Griffin, Linda M. D Ascanio, Janet E. Pope, Peter J. Fowler: A Randomized Trial of Arthroscopic Surgery for Osteoarthritis of the Knee. In: New England Journal of Medicine. 359, 2008, pp. 1097-1107, doi : 10.1056 / NEJMoa0708333
  7. ↑ Jeffrey N. Katz, Robert H. Brophy, Christine E. Chaisson, Leigh de Chaves, Brian J. Cole, Diane L. Dahm, Laurel A. Donnell-Fink, Ali Guermazi, Amanda K. Haas, Morgan H. Jones, Bruce A. Levy, Lisa A. Mandl, Scott D. Martin, Robert G. Marx, Anthony Miniaci, Matthew J. Matava, Joseph Palmisano, Emily K. Reinke, Brian E. Richardson, Benjamin N. Rome, Clare E. Safran -Norton, Debra J. Skoniecki, Daniel H. Solomon, Matthew V. Smith, Kurt P. Spindler, Michael J. Stuart, John Wright, Rick W. Wright, Elena Losina: Surgery versus Physical Therapy for a Meniscal Tear and Osteoarthritis. In: New England Journal of Medicine. 368, 2013, pp. 1675–1684, doi : 10.1056 / NEJMoa1301408