Discoid meniscus in human fetuses: A systematic review.

BACKGROUND: Discoid meniscus (DM) is a rare variant of regular knee anatomy. Compared to standard meniscus it is thicker and abnormal in shape; these characteristics make it more prone to tear. It is a congenital defect whose correct etiology is still debated and far from being clarified. The purpose of this systematic review is to evaluate evidences of DM in human fetuses in order to assess whether embryological development may have a role. METHODS: A systematic review was performed on PubMed, Scopus, and Embase with different combinations of the keywords "discoid meniscus", "embryology", "fetus", "neonatal". Search yielded 1013 studies, on which we performed a primary evaluation. RESULTS: Seven studies were considered including a total of 1378 fetal menisci specimens, from 396 different fetuses. Discoid shape was not found represented as a normal stage of prenatal development. From 782 lateral menisci analyzed, only 86 (10.86%) were discoid (13 complete, 73 incomplete type). None of medial menisci was found to be discoid. Lateral meniscus was observed to cover a larger surface of tibial plateau than medial one until 28th gestational week. CONCLUSION: Lateral meniscus seems to be more prone to discoid shape for its natural tendency of covering a larger surface of the tibial plateau during fetal stages. However the fact that a discoid shape was not found in the majority of fetuses suggests that it is not a normal stage of fetal development. To support a single etiological factor it will be appropriate to have further morphological and morphometric studies.

Structure, function, and defect tolerance with maturation of the radial tie fiber network in the knee meniscus.

The knee menisci are comprised of two orthogonal collagenous networks-circumferential and radial-that combine to enable efficient load bearing by the tissue in adults. Here, we assessed how the structural and functional characteristics of these networks developed over the course of skeletal maturation and determined the role of these fiber networks in defect tolerance with tissue injury. Imaging of the radial tie fiber (RTF) collagen structure in medial bovine menisci from fetal, juvenile, and adult specimens showed increasing heterogeneity, anisotropy, thickness, and density with skeletal development. The mechanical analysis showed that the tensile modulus in the radial direction did not change with skeletal development, though the resilience (in the radial direction) increased and the tolerance to defects in the circumferential direction decreased, in adult compared to fetal tissues. This loss of defect tolerance correlated with increased order in the RTF network in adult tissue. These data provide new insights into the role of the radial fiber network in meniscus function, will lead to improved clinical decision-making in the presence of a tear and may improve engineering efforts to reproduce this critical load-bearing structure in the knee.

Morphological structure and variations of fetal lateral meniscus: the significance in convenient diagnosis and treatment.

PURPOSE: The aim of this study is to evaluate of morphometry of the lateral meniscus (LM) and determine incidence of the LM shapes. METHODS: This study was performed on fetal cadaver collection of Anatomy Department of Necmettin Erbakan University. Fifty human fetal cadavers (25 female, 25 male human fetal cadavers) were used in this study. Microdissection was performed. Morphometric measurements were performed. LM were classified into four types and five subtypes. RESULTS: In this study, it was identified that all parameters which were measured were found to be increased with gestational ages. Four morphological types and five morphological subtypes were determined. It was found that 12% of the LM were crescent-shaped, 66% of the LM were C-shaped, 14% of the LM were incomplete-disc-shaped, 2% of the LM were disc-shaped, 6% of the LM were variant C-shaped. CONCLUSIONS: A few studies on fetal meniscal anatomy and its development were performed. Each new study is important for having detailed anatomy and development of the fetal menisci which will have both clinical and anatomical impacts during childhood and adulthood for orthopedic surgeons and anatomists, respectively. The most important results of this study were the detailed objective analysis of the macroscopic fetal growth of LM. It was significantly observed that four morphological types and five morphological subtypes of LM. The results of the present study related with both the observation of morphological development of the fetal meniscal anatomy, and its morphological variants, are important in terms of improving our knowledge, and clinical approach on the description, and the management of the symptomatic lateral discoid meniscus tears in children, adolescents, and adults. The clinical relevance of this study was that this classification of fetal menisci could ameliorate our current understanding of the morphology of lateral meniscus in adult, further.

Formation and maturation of the murine meniscus.

Meniscal injuries are commonplace, but current surgical repair procedures do not prevent degenerative joint changes that occur after meniscal injury and often lead to osteoarthritis. Successful tissue regeneration in adults often recapitulates events that occur during embryogenesis, suggesting that understanding the regulatory pathways controlling these early processes may provide clues for developing strategies for tissue repair. While the mouse is now widely used to study joint diseases, detailed knowledge of the basic biology of murine meniscus is not readily available. Here, we examine meniscal morphogenesis in mice from embryonic day 13.5 (E13.5) to 6 months of age using histology, in situ hybridization, and immunohistochemistry. We find that the meniscus is a morphologically distinct structure at E16 when it begins to regionalize. At birth, the meniscus has a distinguishable inner, avascular, round chondrocyte cell region, an outer, vascularized, fibroblast cell region, and a surface superficial zone. Maturation begins at 2 weeks of age when the meniscus expresses type I collagen, type II collagen, type X collagen, and MMP-13 in specific patterns. By 4 weeks of age, small areas of ossification are detected in the anterior meniscal horn, a common feature seen in rodents. Maturation appears complete at 8 weeks of age, when the meniscus resembles the adult structure complete with ossifying tissue that contains bone marrow like areas. Our results provide, the first systematic study of mouse meniscal development and will be a valuable tool for analyzing murine models of knee joint formation and disease. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1683-1689, 2017.

Gene signature of the embryonic meniscus.

The meniscus is a fibrocartilagenous disc in the knee that protects the joint from damage. Meniscal injuries are common, however repair efforts are largely unsuccessful and are not able to prevent the degenerative changes that result in development of osteoarthritis. Tissue regeneration in adults often recapitulates events of embryonic development, suggesting the regulatory pathways controlling morphogenesis are candidate repair signals. Here we use laser capture microdissection to collect mouse embryonic day 16 (E16) meniscus, articular cartilage, and cruciate ligaments. RNA isolated from these tissues was then used to perform genome-wide microarray analysis. We found 38 genes were differentially expressed between E16 meniscus and articular cartilage and 43 genes were differentially expressed between E16 meniscus and cruciate ligaments. Included in our data set were extracellular matrix proteins, transcription factors, and growth factors, including TGF-ß modulators (Lox, Dpt) and IGF-1 pathway members (Igf-1, Igfbp2, Igfbp3, Igfbp5). Ingenuity Pathway Analysis revealed that IGF-1 signaling was enriched in the meniscus compared to the other joint structures, while qPCR showed that Igf-1, Igfbp2, and Igfbp3 expression declined with age. We also found that several meniscus-enriched genes were expressed either in the inner or outer meniscus, establishing that regionalization of the meniscus occurs early in development.

An approach to comparative anatomy of the acetabulum from amphibians to primates.

The objective of this study was to investigate the anatomy, both macroscopic and microscopic, of the soft tissue internal structures of the hip joint in animal species and in three human hips (an adult and two fetuses). We dissected the hip joints of 16 species and compared the anatomical features of the soft tissue from the respective acetabula. In addition, a histological study was made of the specimens studied. In amphibians, we found a meniscus in the acetabulum, which was not observed in any of the other species studied. The isolated round ligament is observed from birds onwards. In the group of mammals analysed, including the human specimens, we found a meniscoid structure in the acetabular hip joint. Furthermore, we found that the meniscoid structure forms an anatomo-functional unit with the round ligament and the transverse ligament of the coxofemoral joint. These discoveries suggest the participation of the soft tissue anatomy in adaptative changes of species.

Morphological variants of lateral meniscus of the knee: a cadaveric study in South Indian human fetuses.

In the present study, the objectives were to study the morphology of the lateral menisci (LMs) in human fetuses from a South Indian population and to verify the developmental etiology of the discoid lateral meniscus (DLM). The study included 106 fetal knee joints which were fixed in 10% formalin. After dissecting the joints, the morphological variants of the shapes of the LMs were macroscopically noted and classified as discoid and nondiscoid. The nondiscoids were subdivided into C-shaped and crescentic. The discoid lateral menisci (DLMs) were divided into complete and incomplete discoid. From our observations, 82.1% of the LMs were found to be nondiscoid. Among them, 62.3% were C-shaped and 19.8% were crescentic. The remaining 17.9% of the LMs had a discoid shape, and among these, 14.1% were incomplete discoid and 3.8% were completely discoid. Bilaterality of the discoid shape was observed in 26.6% of the cases. There was a female preponderance (11:8) among LMs with discoid morphology. In conclusion, the prevalence of DLM according to the present study was estimated as 17.9%. Our findings favor Kaplan's theory, as the majority of the fetuses of various gestational ages had nondiscoid LMs. Even the youngest fetus (CRL 88 mm, 14 weeks of gestation) exhibited a lateral tibial plateau that was incompletely covered by the meniscus, which did not exhibit a discoid shape. We believe that the DLM is anomalous and arises through variant morphogenesis.

Morphology of the medial meniscus of the knee in human fetuses.

OBJECTIVES: The objectives were to study the morphology of the medial menisci in human fetal knee joints and to verify the developmental etiology of the discoid meniscus. MATERIAL AND METHODS: The study was carried out on 106 fetal knee joints and the morphological variants of the shapes of the medial menisci were macroscopically noted and classified. RESULTS: From our observations, 46.2% of the medial menisci were crescentic shaped, 23.6% were sided V-shaped, 13.2% had sided U-shape, 9.4% of them were sickle shaped, and 7.5% were C-shaped. In 54.71% of the cases, the medial meniscus shape was different on either side knees of the fetuses. No discoid medial menisci were seen. CONCLUSIONS: The majority of the knees were having crescentic or semi lunar shaped medial menisci and the shape of the medial meniscus was different on right and left side knee joint of the fetuses in more than fifty percent of the cases. The observations favor Kaplan's theory, as there were no discoid medial menisci observed from the fetuses of various gestational ages. Even the youngest fetus (CRL 88 mm, 14 weeks of gestation) exhibited the medial tibial plateau incompletely covered by the menisci, which did not exhibit the discoid shape. The discoid meniscus must be an abnormal finding and is due to abnormal morphogenesis.

Immunolocalization of lymphatic vessels in human fetal knee joint tissues.

We immunolocalized lymphatic and vascular blood vessels in 12- and 14-week-old human fetal knee joint tissues using a polyclonal antibody to a lymphatic vascular endothelium specific hyaluronan receptor (LYVE-1) and a monoclonal antibody to podoplanin (mAb D2-40). A number of lymphatic vessels were identified in the stratified connective tissues surrounding the cartilaginous knee joint femoral and tibial rudiments. These tissues also contained small vascular vessels with entrapped red blood cells which were imaged using Nomarsky DIC microscopy. Neither vascular nor lymphatic vessels were present in the knee joint cartilaginous rudiments. The menisci in 12-week-old fetal knees were incompletely demarcated from the adjacent tibial and femoral cartilaginous rudiments which was consistent with the ongoing joint cavitation process at the femoral-tibial junction. At 14 weeks of age the menisci were independent structural entities; they contained a major central blood vessel containing red blood cells and numerous communicating vessels at the base of the menisci but no lymphatic vessels. In contrast to the 12-week-old menisci, the 14-week meniscal rudiments contained abundant CD-31 and CD-34 positive but no lymphatic vessels. Isolated 14-week-old meniscal cells also were stained with the CD-31 and CD 34 antibodies; CD-68 +ve cells, also abundant in the 14-week-old menisci, were detectable to a far lesser degree in the 12-week menisci and were totally absent from the femoral and tibial rudiments. The distribution of lymphatic vessels and tissue macrophages in the fetal joint tissues was consistent with their roles in the clearance of metabolic waste and extracellular matrix breakdown products arising from the rapidly remodelling knee joint tissues.

Development of the meniscus of the knee joint in human fetuses.

Discoid meniscus of the knee joint occurs at a higher incidence in the lateral than in the medial menisci. Although its developmental origin has been suggested, it remains unclear. To verify the developmental etiology, we examined the meniscus of the knee joint in 41 human fetuses (from 14 to 30 weeks of gestation) and 14 adults (from 56 to 91 years of age) comparatively. The articular surfaces of the tibia and meniscus of the left knees in 40 fetuses and 14 adults were photographed and each area was measured by Scion Image (Scion; http://www.scioncorp.com). Morphometric analyses revealed that the proportion of the area of meniscus to that of the plateau was continuously higher in the lateral side than in the medial side. The right knee joints of seven fetuses were histologically observed, and the layered structure of fibers developed earlier in the lateral meniscus than in the medial in fetuses. The observed differential development of lateral and medial sides of the meniscus may be involved in the etiology of discoid meniscus.

Arthroscopic study of the knee joint in fetuses.

PURPOSE: The purpose of this study was to macroscopically examine the fetal knee joint via arthroscopy. We have attempted to identify and describe the specific characteristics of the fetal knee joint, how it evolves during the last few weeks of intrauterine development, and any possible variations with regard to the adult knee. TYPE OF STUDY: Observational anatomic case series. METHODS: We used 20 frozen fetuses with a gestational age of 24 to 40 +/- 2 weeks, obtained from spontaneous abortions. Examination was performed with standard arthroscopic surgical equipment, using a 2.7-mm optical lens. Whenever possible, we tried to use standard arthroscopic portals. Images were obtained for comparison with the adult knee. RESULTS: Suprapatellar and infrapatellar septa were an almost consistent finding. The suprapatellar septum always opened laterally and was intact in the developmentally younger specimens. We found 2 mediopatellar septa. The femoral attachment of the anterior cruciate ligament (ACL) differed in appearance from that of the adult in that it was more ribbon-like. The lateral meniscus had a more spread-out appearance than its adult counterpart, especially in the specimens of a younger gestational age. We were surprised at the easy accessibility of the popliteal hiatus and the clear arthroscopic vision we were able to obtain of the involved structures. CONCLUSIONS: To our knowledge, this is the first arthroscopic study to target the fetal knee. The results indicate minimal differences when compared with the adult knee, and for some structures, such as the popliteal hiatus, the anatomy seen was easier to discern than in adult knee arthroscopy.

Meniscal and articular cartilage injury in the skeletally immature knee.

Meniscal and articular cartilage injuries in skeletally immature patients appear to be occurring with increased frequency, particularly in athletically active children. The orthopaedic surgeon should understand the principles of diagnosis and management, as well as be aware of current surgical treatment options available.

Development of the popliteomeniscal fasciculi in the fetal human knee joint.

PURPOSE: The purpose of this study is to better understand the function of the popliteomeniscal fasciculi and their relationship to the popliteus tendon and the lateral meniscus by describing these structures during embryonic development. TYPE OF STUDY: Anatomic dissection and histologic evaluation. METHODS: Twelve fresh-frozen lower extremity specimens (6 paired limbs) from second and third trimester human fetuses were obtained from spontaneous abortions. Each specimen was fixed in formalin and decalcified in 9.0% nitric oxide. The specimens were prepared by removal of all skin and most of the soft tissues before dissection of the lateral meniscus, parts of the posterolateral joint capsule, and the popliteus tendon and muscle. The right-side specimens were sectioned in the transverse plane, and the left-side specimens in the coronal plane. Histologic sections were prepared with H&E and Masson's trichrome stains. Light microscopy was used to evaluate the lateral meniscal attachment, with detailed attention to the popliteomeniscal fasciculi. RESULTS: The close interrelationship of lateral meniscus and popliteus tendon, especially during embryologic development, does give a better understanding how the fasciculi stabilize the lateral meniscus and allow the popliteus tendon to function as a retractor of the lateral meniscus. The fasciculi consist of 3 layers including a dense collagen layer, a vascular layer, and a synovial or capsular layer. CONCLUSIONS: During embryologic development, the fasciculi appeared to provide a vascular supply to the lateral meniscus adjacent to the popliteal hiatus where the meniscus is devoid of capsular attachments.

Differential effects of embryonic immobilization on the development of fibrocartilaginous skeletal elements.

The importance of mechanical influences during skeletal development has been well established in both experimental studies and computer models. Under conditions of embryonic immobilization, it has been observed that the early stages of joint formation proceed normally (up to and including interzone formation), but the later stages of joint cavitation and maintenance are impaired, resulting in fusion of the cartilaginous elements across the presumptive joint line. Two structures in particular are noticeably absent from late-stage synovial joints in immobilized chick embryos: the menisci of the tibiofemoral joint and the plantar tarsal sesamoid of the tibiotarsal joint. Both of these fibrocartilaginous structures are known to serve mechanical functions in postnatal animals, helping to distribute loads within the joint and, in the case of sesamoid structures, to provide a mechanical advantage to muscles acting across the joint. We demonstrate in this study that embryonic immobilization differentially affects the developmental fate of these two distinct fibrocartilages. The absence of the plantar tarsal sesamoid in late-stage immobilized embryos is due to a failure in the initial formation of this structure. In contrast, the early stages of meniscus formation proceed normally. Without the normal mechanical stimuli of skeletal muscle contractions, however, the meniscus fails to mature and ultimately degenerates.

Development of the human knee joint.

BACKGROUND: Many studies have been published on the development of the human knee joint, but different investigators disagree on its morphogenetic time table. Most discrepancies center on the cavitation of the knee joint and the participation of the superior tibiofibular joint in the joint knee system. METHODS: We summarize our observations of the development of the knee joint in 50 serially sectioned human embryonic and fetal lower limbs (26 embryos and 24 fetuses). RESULTS: The epiphysis of the femur and tibia become condryfied from O'Rahilly stage 18, and ossification begins during the 13th week of development. The patella appears as a dense blastema during O'Rahilly stage 19, becomes condryfied during O'Rahilly stage 22, and begins its ossification during the 14th week of development. The knee joint cavity appears during O'Rahilly stage 22, initially as the femoropatellar joint. This process begins at the periphery of the articular interzone. The superior tibiofibular joint communicates with the lateral meniscotibial joint between 10 and 11 weeks of development and becomes separated from the 13 week on. The menisci arise from the eccentric portions of the articular interzone during O'Rahilly stage 22; however, until week 9 of development, they are not easily distinguishable. CONCLUSIONS: We establish the morphogenetic time table of the human knee joint.

[External discoid menisci. Apropos of a familial series of 6 cases]. / Ménisques externes discoïdes. A propos d'une série familiale de six cas.

Discoid meniscus is a well-known meniscal dysmorphia affecting more often the lateral meniscus of the knee. Familial series are exceptional with only two reported instances. A new series of three bilateral symptomatic cases of lateral discoid menisci was reported in a family of three brothers and sisters, whom parents had never suffered from their knees. During operative procedure four complete and two incomplete types were found. Two complete and four partial meniscectomies have been performed followed by four good results in the five with sufficient follow-up. The origin of this malformation is unknown. The phylogenetic and ontogenetic studies give no explanation and genetic factors seem to have a minor role.

Congenital rudimentary medial meniscus--report of a case of development arrest of medial meniscus.

We present an unusual case, where the medial meniscus does not coincide with the embryological development of the formation of a discoid cartilage. A fairly, careful perusal of English literature since 1945 to date makes us feel that the following case merits recording. The meniscus had a normal anterior horn attached to the intercondylar area, in front of the anterior cruciate ligament. Medially, it was attached to the capsule and the condylar surface of the medial tibial plateau. The posterior horn was rounded, smooth, and floating free of any attachments. It was approximately 2 cms in length, semilunar in shape, and extended posteriorly up to the anterior margin of the medial collateral ligament. The rest of the medial tibial plateau had no other protective covering.

On the etiology of congenital malformation of the meniscus.

In order to explain the occurrence of malformed meniscus in man, dissections were carried out in various vertebrates; they revealed that menisci shaped like a plate, disc, or ring are physiological components of the knee joint in several vertebrates. Microscopic examinations of tissue sections through the knee joint of human embryos revealed that the meniscus develops from an intermediate mesodermal blastema, which has the shape of a thick plate in the early embryonic period. The occurrence of a malformed meniscus in man may be explained by persistence of a very early embryonic stage and also possibly by reversal to a phylogenetic shape.

[Study of the development of the human knee joint]. / Beitrag zum Studium der Entwicklung des Kniegelenks des Menschen.

By studying a complete series of sections of the human knee joint during the period in which the joint gap develops we have found out that the knee joint contains a high broad septum (the mediastinum genus), in which there are many broad vessels. These vessels feed the cruciate ligament anlages, the meniscus anlages and the cartilagenous models of the adjacent bone anlages. In the human embryo the mediastinum genus splits the knee joint into a lateral and a medial half. Communication between these 2 halves is between the small contact surfaces of the patella and femur anlages.