Log in Sign up. Articles Cases Courses Quiz. About Recent Edits Go ad-free. Edit article. View revision history Report problem with Article. Citation, DOI and article data. Knipe, H. Knee menisci. Reference article, Radiopaedia. URL of Article. On this page:.
Quiz questions. Niitsu M. Magnetic Resonance Imaging of the Knee. Springer Berlin Heidelberg. The two menisci of the knee are crescent-shaped wedges that fill the gap between the tibia and femur. The menisci provide joint stability by creating a cup for the femur to sit in.
The outer edges are fairly thick while the inner surfaces are thin. If the menisci were missing, the curved femur would move on the flat tibia. The medial meniscus , located on the inside of the knee, is more of an elongated "C"- shape, as the tibial surface is larger on that side.
The medial meniscus is more commonly injured because it is firmly attached to the medial collateral ligament and joint capsule. The lateral meniscus , on the outside of the knee, is more circular in shape. Most patients are asymptomatic, but injury to the meniscus can occur with minor trauma. The Wrisberg variant may present with a snapping knee due to hypermobility. Radiographs are usually not diagnostic, but they may show a high fibula head and a widened lateral joint space.
In the Wrisberg variant, the morphology of the meniscus may be normal, but the posterior fascicles and meniscotibial ligament are absent and a high signal fluid cleft interposed between the posterior horn and the capsule may simulate a peripheral tear Figure 6. The meniscus may also become hypertrophic. Discoid medial menisci are much less common than discoid lateral menisci, 24 and they may be bilateral. When bilateral, they are usually symmetric.
The reported prevalence is 0. Radiographs may show cupping of the medial tibial plateau, proximal medial tibial physis collapse and widening of the medial joint space Figure 7. There are no specific MR criteria for classifying discoid medial menisci, and the MR criteria for discoid lateral menisci are used for discoid medial menisci Figure 8. A Wrisberg type variant has not been documented in the medial meniscus.
Associated anomalies in a discoid medial meniscus are not uncommon; they include an anomalous insertion of the anterior horn of the medial meniscus into the anterior cruciate ligament as previously described , meniscal cyst, 26 discoid lateral meniscus in the same knee Figure 9 , 25 and pathologic medial patella plica.
Normal variants of the meniscus are relatively uncommon and are frequently asymptomatic, although there is a greater propensity for discoid menisci to tear. However, recognizing these variants is important, as they can be misinterpreted for more significant pathology on MRI. The most common of these meniscal variants is the discoid lateral meniscus, and the least common is complete congenital absence of the menisci.
Normal variants of the meniscus. Appl Radiol. Clinical Departments Normal variants of the meniscus. Milo Sewards, MD. The main functions of the menisci can be summarized as providing: Stability. The ligaments are the most important stabilizers, with the menisci assuming a secondary function. This secondary function is enhanced with intact ligaments. Lubrication and nutrition. The knee menisci act as spacers between the femur and the tibia. By doing so, they prevent friction and contact between the distal femur and tibia and allow for the diffusion of the normal joint fluid and its nutrients into the articular cartilage.
Maintenance of the integrity of the articular cartilage is critical to preventing the development of post-traumatic or degenerative arthritis. Shock absorption The menisci lower the stress applied to the articular cartilage; thereby, they have a role in preventing the development of degenerative arthritis.
Congenital meniscal hypoplasia There are reported cases of complete absence of the medial meniscus as described in thrombocytopenia absent radius syndrome TAR syndrome. Anomalous insertion of the meniscus Anomalous insertion of the medial meniscus AIMM has been described, and it is typically into the anterior cruciate ligament.
Meniscal cartilage contains a range of matrix glycoproteins, the identities and functions of which have yet to be determined. Electrophoresis and subsequent staining of the polyacrylamide gels reveals bands with molecular weights varying from a few kilodaltons to more than kDa. The adhesive glycoproteins constitute a subgroup of the matrix glycoproteins. Such intermolecular adhesion molecules are therefore important components in the supramolecular organization of the extracellular molecules of the meniscus.
The meniscus is a relatively avascular structure with a limited peripheral blood supply. The medial, lateral, and middle geniculate arteries which branch off the popliteal artery provide the major vascularization to the inferior and superior aspects of each meniscus Figure 5.
A premeniscal capillary network arising from the branches of these arteries originates within the synovial and capsular tissues of the knee along the periphery of the menisci.
Perimeniscal capillary plexus PCP can be seen penetrating the peripheral border of the medial meniscus. F, femur; T, tibia. Reprinted with permission from Arnoczky and Warren. Bird and Sweet examined the menisci of animals and humans using scanning electron and light microscopy. These canals may play a role in the transport of fluid within the meniscus and may carry nutrients from the synovial fluid and blood vessels to the avascular sections of the meniscus.
The knee joint is innervated by the posterior articular branch of the posterior tibial nerve and the terminal branches of the obturator and femoral nerves. The lateral portion of the capsule is innervated by the recurrent peroneal branch of the common peroneal nerve. These nerve fibers penetrate the capsule and follow the vascular supply to the peripheral portion of the menisci and the anterior and posterior horns, where most of the nerve fibers are concentrated.
The mechanoreceptors within the menisci function as transducers, converting the physical stimulus of tension and compression into a specific electrical nerve impulse. Studies of human menisci have identified 3 morphologically distinct mechanoreceptors: Ruffini endings, Pacinian corpuscles, and Golgi tendon organs.
Type II Pacinian mechanoreceptors are low threshold and fast adapting to tension changes. These neural elements were found in greater concentration in the meniscal horns, particularly the posterior horn.
The asymmetrical components of the knee act in concert as a type of biological transmission that accepts, transfers, and dissipates loads along the femur, tibia, patella, and femur.
Several studies have reported that various intra-articular components of the knee are sensate, capable of generating neurosensory signals that reach spinal, cerebellar, and higher central nervous system levels. The biomechanical function of the meniscus is a reflection of the gross and ultrastructural anatomy and of its relationship to the surrounding intra-articular and extra-articular structures. The menisci serve many important biomechanical functions.
In a study on ligamentous function, Brantigan and Voshell reported the medial meniscus to move an average 2 mm, while the lateral meniscus was markedly more mobile with approximately 10 mm of anterior-posterior displacement during flexion. The anterior and posterior horn lateral meniscus ratio is smaller and indicates that the meniscus moves more as a single unit.
Thompson et al found that the area of least meniscal motion is the posterior medial corner, where the meniscus is constrained by its attachment to the tibial plateau by the meniscotibial portion of the posterior oblique ligament, which has been reported to be more prone to injury. The greater differential between anterior and posterior horn excursion may place the medial meniscus at a greater risk of injury. Diagrams showing the mean movement mm in each meniscus during flexion shaded and extension hashed.
Reproduced with permission from Thomspon et al. The differential of anterior horn to posterior horn motion allows the menisci to assume a decreasing radius with flexion, which correlates to the decreased radius of curvature of the posterior femoral condyles. The function of the menisci has been clinically inferred by the degenerative changes that accompany its removal. Fairbank described the increased incidence and predictable degenerative changes of the articular surfaces in completely meniscectomized knees.
Firm attachments by the anterior and posterior insertional ligaments prevent the meniscus from extruding peripherally during load bearing. Free body diagram of forces acting on the meniscus during loading.
As the femur presses down on the meniscus during normal loading, the meniscus deforms radially but is anchored by its anterior and posterior horns F ant and F post. During loading, tensile, compressive, and shear forces are generated. A tensile hoop stress F cir results from the radial deformation, while vertical and horizontal forces F v and F h result from the femur pressing on the curved superior surface of the tissue.
A radial reaction force F rad balances the femoral horizontal force F h. Reprinted with permission from Athanasiou and Sanchez-Adams. The menisci play a vital role in attenuating the intermittent shock waves generated by impulse loading of the knee with normal gait.
The geometric structure of the menisci provides an important role in maintaining joint congruity and stability. The superior surface of each meniscus is concave, enabling effective articulation between the convex femoral condyles and flat tibial plateau. When the meniscus is intact, axial loading of the knee has a multidirectional stabilizing function, limiting excess motion in all directions.
Markolf and colleagues have addressed the effect of meniscectomy on anterior-posterior and rotational knee laxity. Recently, Musahl et al reported that the lateral meniscus plays a role in anterior tibial translation during the pivot-shift maneuver. The menisci may also play a role in the nutrition and lubrication of the knee joint. The mechanics of this lubrication remains unknown; the menisci may compress synovial fluid into the articular cartilage, which reduces frictional forces during weightbearing.
There is a system of microcanals within the meniscus located close to the blood vessels, which communicates with the synovial cavity; these may provide fluid transport for nutrition and joint lubrication. The perception of joint motion and position proprioception is mediated by mechanoreceptors that transduce mechanical deformation into electric neural signals.
Mechanoreceptors have been identified in the anterior and posterior horns of the menisci. The microanatomy of the meniscus is complex and certainly demonstrates senescent changes.
With advancing age, the meniscus becomes stiffer, loses elasticity, and becomes yellow. Shear between these layers may cause pain. The torn meniscus may directly injure the overlying articular cartilage.
Ghosh and Taylor found that collagen concentration increased from birth to 30 years and remained constant until 80 years of age, after which a decline occurred. Peters and Smillie observed an increase in hexosamine and uronic acid with age.
McNicol and Roughley studied the variation of meniscal proteoglycans in aging ; small differences in extractability and hydrodynamic size were observed. The proportions of keratin sulfate relative to chondroitinsulfate increased with aging. Petersen and Tillmann immunohistochemically investigated human menisci ranging from 22 weeks of gestation to 80 years , observing the differentiation of blood vessels and lymphatics in 20 human cadavers.
At the time of birth, nearly the entire meniscus was vascularized. In the second year of life, an avascular area developed in the inner circumference.
In the second decade, blood vessels were present in the peripheral third. After 50 years of age, only the peripheral quarter of the meniscal base was vascularized. The dense connective tissue of the insertion was vascularized but not the fibrocartilage of the insertion. Blood vessels were accompanied by lymphatics in all areas. Arnoczky suggested that body weight and knee joint motion may eliminate blood vessels in the inner and middle aspects of the menisci.
A requirement for nutrition via diffusion is the intermittent loading and release on the articular surfaces, stressed by body weight and muscle forces. Magnetic resonance imaging MRI is a noninvasive diagnostic tool used in the evaluation, diagnosis, and monitoring of the menisci.
MRI is widely accepted as the optimal imaging modality because of superior soft tissue contrast. On cross-sectional MRI, the normal meniscus appears as a uniform low-signal dark triangular structure Figure 9.
A meniscal tear is identified by the presence of an increased intrameniscal signal that extends to the surface of this structure. A sagittal magnetic resonance proton-density image of a healthy knee depicting the medial menisci arrows.
The concave superior meniscal surface improves contact with the femoral epicondyles, and a flat undersurface improves contact with the tibial plateau. The periphery is thicker than the central portion, allowing for firm attachment to the joint capsule.
Several studies have evaluated the clinical utility of MRI for meniscal tears. In general, MRI is highly sensitive and specific for tears of the meniscus. There have been discrepancies between MRI diagnoses and the pathology identified during arthroscopic examination. Increased signal intensity in the anterior horn does not necessarily indicate a clinically significant lesion. The menisci of the knee joint are crescent-shaped wedges of fibrocartilage that provide increased stability to the femorotibial articulation, distribute axial load, absorb shock, and provide lubrication to the knee joint.
Preservation of the menisci is highly dependent on maintaining its distinctive composition and organization. We wish to thank Tom Cichonski for his assistance in the formatting of this manuscript. References 7 , 25 , 51 , , , , , National Center for Biotechnology Information , U. Journal List Sports Health v. Sports Health. Alice J.
Scott A. Author information Copyright and License information Disclaimer. This article has been cited by other articles in PMC. Abstract Context: Information regarding the structure, composition, and function of the knee menisci has been scattered across multiple sources and fields. Results: This study highlights the structural, compositional, and functional characteristics of the menisci, which may be relevant to clinical presentations, diagnosis, and surgical repairs.
Conclusions: An understanding of the normal anatomy and biomechanics of the menisci is a necessary prerequisite to understanding the pathogenesis of disorders involving the knee. Keywords: knee, meniscus, anatomy, function. Meniscal Phylogeny and Comparative Anatomy Hominids exhibit similar anatomic and functional characteristics, including a bicondylar distal femur, intra-articular cruciate ligaments, menisci, and asymmetrical collateral.
Embryology and Development The characteristic shape of the lateral and medial menisci is attained between the 8th and 10th week of gestation. Gross Anatomy Gross examination of the knee menisci reveals a smooth, lubricated tissue Figure 1. Open in a separate window. Figure 1. Figure 2. Medial meniscus The semicircular medial meniscus measures approximately 35 mm in diameter anterior to posterior and is significantly broader posteriorly than it is anteriorly.
Meniscofemoral ligaments The literature reports significant inconsistencies in the presence and size of meniscofemoral ligaments of the lateral meniscus.
Figure 3. Figure 4. Figure 5. Matrix Glycoproteins Meniscal cartilage contains a range of matrix glycoproteins, the identities and functions of which have yet to be determined. Vascular Anatomy The meniscus is a relatively avascular structure with a limited peripheral blood supply.
Figure 6. Neuroanatomy The knee joint is innervated by the posterior articular branch of the posterior tibial nerve and the terminal branches of the obturator and femoral nerves.
Biomechanical Function The biomechanical function of the meniscus is a reflection of the gross and ultrastructural anatomy and of its relationship to the surrounding intra-articular and extra-articular structures. Figure 7. Load Transmission The function of the menisci has been clinically inferred by the degenerative changes that accompany its removal. Figure 8. Shock Absorption The menisci play a vital role in attenuating the intermittent shock waves generated by impulse loading of the knee with normal gait.
Joint Stability The geometric structure of the menisci provides an important role in maintaining joint congruity and stability. Joint Nutrition and Lubrication The menisci may also play a role in the nutrition and lubrication of the knee joint.
Proprioception The perception of joint motion and position proprioception is mediated by mechanoreceptors that transduce mechanical deformation into electric neural signals.
Maturation and Aging of The Meniscus The microanatomy of the meniscus is complex and certainly demonstrates senescent changes. Magnetic Resonance Imaging of The Meniscus Magnetic resonance imaging MRI is a noninvasive diagnostic tool used in the evaluation, diagnosis, and monitoring of the menisci. Figure 9.
Conclusions The menisci of the knee joint are crescent-shaped wedges of fibrocartilage that provide increased stability to the femorotibial articulation, distribute axial load, absorb shock, and provide lubrication to the knee joint. Acknowledgments We wish to thank Tom Cichonski for his assistance in the formatting of this manuscript.
References 1. The extracellular matrix of the meniscus. Knee Meniscus: Basic and Clinical Foundations. Isolation and characterization of high-buoyant-density proteoglycans from semilunar menisci.
J Bone Joint Surg Am. Adams ME, Muir H.
0コメント