Microscopic anatomy of the visceral fasciae

The term ‘visceral fascia’ is a general term used to describe the fascia lying immediately beneath the mesothelium of the serosa, together with that immediately surrounding the viscera, but there are many types of visceral fasciae. The aim of this paper was to identify the features they have in common and their specialisations. The visceral fascia of the abdomen (corresponding to the connective tissue lying immediately beneath the mesothelium of the parietal peritoneum), thorax (corresponding to the connective tissue lying immediately beneath the mesothelium of the parietal pleura), lung (corresponding to the connective tissue under the mesothelium of the visceral pleura), liver (corresponding to the connective tissue under the mesothelium of the visceral peritoneum), kidney (corresponding to the Gerota fascia), the oesophagus (corresponding to its adventitia) and heart (corresponding to the fibrous layer of the pericardial sac) from eight fresh cadavers were sampled and analysed with histological and immunohistochemical stains to evaluate collagen and elastic components and innervation. Although the visceral fasciae make up a well‐defined layer of connective tissue, the thickness, percentage of elastic fibres and innervation vary among the different viscera. In particular, the fascia of the lung has a mean thickness of 134 μm (± 21), that of heart 792 μm (± 132), oesophagus 105 μm (± 10), liver 131 μm (± 18), Gerota fascia 1009 μm (± 105) and the visceral fascia of the abdomen 987 μm (± 90). The greatest number of elastic fibres (9.79%) was found in the adventitia of the oesophagus. The connective layers lying immediately outside the mesothelium of the pleura and peritoneum also have many elastic fibres (4.98% and 4.52%, respectively), whereas the pericardium and Gerota fascia have few (0.27% and 1.38%). In the pleura, peritoneum and adventitia of the oesophagus, elastic fibres form a well‐defined layer, corresponding to the elastic lamina, while in the other cases they are thinner and scattered in the connective tissue. Collagen fibres also show precise spatial organisation, being arranged in several layers. In each layer, all the fibrous bundles are parallel with each other, but change direction among layers. Loose connective tissue rich in elastic fibres is found between contiguous fibrous layers. Unmyelinated nerve fibres were found in all samples, but myelinated fibres were only found in some fasciae, such as those of the liver and heart, and the visceral fascia of the abdomen. According to these findings, we propose distinguishing the visceral fasciae into two large groups. The first group includes all the fasciae closely related to the individual organ and giving shape to it, supporting the parenchyma; these are thin, elastic and very well innervated. The second group comprises all the fibrous sheets forming the compartments for the organs and also connecting the internal organs to the musculoskeletal system. These fasciae are thick, less elastic and less innervated, but they contain larger and myelinated nerves. We propose to call the first type of fasciae ‘investing fasciae’, and the second type ‘insertional fasciae’.     

A comparative multi‐site and whole‐body assessment of fascia in the horse and dog: a detailed histological investigation

Fascia in the veterinary sciences is drawing attention, such that physiotherapists and animal practitioners are now applying techniques based on the concept of fascia studies in humans. A comprehensive study of fascia is therefore needed in animals to understand the arrangement of the fascial layers in an unguligrade horse and a digitigrade dog. This study has examined the difference between the horse and the dog fascia at specific regions, in terms of histology, and has compared it with the human model. Histological examinations show that in general the fascia tissue of the horse exhibits a tight and dense composition, while in the dog it is looser and has non‐dense structure. Indeed, equine fascia appears to be different from both canine fascia and the human fascia model, whilst canine fascia is very comparable to the human model. Although regional variations were observed, the superficial fascia (fascia superficialis) in the horse was found to be trilaminar in the trunk, yet multilayered in the dog. Moreover, crimping of collagen fibers was more visible in the horse than the dog. Blood vessels and nerves were present in the loose areolar tissue of the superficial and the profound compartment of hypodermis. The deep fascia (fascia profunda) in the horse was thick and tightly attached to the underlying muscle, while in the dog the deep fascia was thin and loosely attached to underlying structures. Superficial and deep fascia fused in the extremities. In conclusion, gross dissection and histology have revealed species variations that are related to the absence or presence of the superficial adipose tissue, the retinacula cutis superficialis, the localization and amount of elastic fibers, as well as the ability to slide and glide between the different layers. Further research is now needed to understand in more detail whether these differences have an influence on the biomechanics, movements and proprioception of these animals.     

The fascia of the limbs and back – a review

Although fasciae have long interested clinicians in a multitude of different clinical and paramedical disciplines, there have been few attempts to unite the ensuing diverse literature into a single review. The current article gives an anatomical perspective that extends from the gross to the molecular level. For expediency, it deals only with fascia in the limbs and back. Particular focus is directed towards deep fascia and thus consideration is given to structures such as the fascia lata, thoracolumbar fascia, plantar and palmar fascia, along with regional specializations of deep fascia such as retinacula and fibrous pulleys. However, equal emphasis is placed on general aspects of fascial structure and function, including its innervation and cellular composition. Among the many functions of fascia considered in detail are its ectoskeletal role (as a soft tissue skeleton for muscle attachments), its importance for creating osteofascial compartments for muscles, encouraging venous return in the lower limb, dissipating stress concentration at entheses and acting as a protective sheet for underlying structures. Emphasis is placed on recognizing the continuity of fascia between regions and appreciating its key role in coordinating muscular activity and acting as a body-wide proprioceptive organ. Such considerations far outweigh the significance of viewing fascia in a regional context alone.     

Hyaluronan within fascia in the etiology of myofascial pain

The layers of loose connective tissue within deep fasciae were studied with particular emphasis on the histochemical distribution of hyaluronan (HA). Samples of deep fascia together with the underlying muscles were taken from neck, abdomen and thigh from three fresh non-embalmed cadavers. Samples were stained with hematoxylin–eosin, Azan-Mallory, Alcian blue and a biotinylated HA-binding protein specific for HA. An ultrasound study was also performed on 22 voluntary subjects to analyze the thickness of these deep fasciae and their sublayers. The deep fascia presented a layer of HA between fascia and the muscle and within the loose connective tissue that divided different fibrous sublayers of the deep fascia. A layer of fibroblast-like cells that stained prominently with Alcian blue stain was observed. It was postulated that these are cells specialized for the biosynthesis of the HA-rich matrix. These cells we have termed “fasciacytes”, and may represent a new class of cells not previously recognized. The ultrasound study highlighted a mean thickness of 1.88 mm of the fascia lata, 1.68 mm of the rectus sheath, and 1.73 mm of the sternocleidomastoid fascia. The HA within the deep fascia facilitates the free sliding of two adjacent fibrous fascial layers, thus promoting the normal function associated with the deep fascia. If the HA assumes a more packed conformation, or more generally, if the loose connective tissue inside the fascia alters its density, the behavior of the entire deep fascia and the underlying muscle would be compromised. This, we predict, may be the basis of the common phenomenon known as “myofascial pain.”     

Fascial bundles of the infraspinatus fascia: anatomy,function, and clinical considerations

The infraspinatus fascia is a tough sheet of connective tissue that covers the infraspinatus fossa of the scapula and the muscle within. Muscle fibers originate from the fossa and fascia and then travel laterally to insert on the greater tubercle of the humerus. Frequently the infraspinatus fascia is quickly removed to appreciate the underlying muscle, but the fascia is an interesting and complex structure in its own right. Despite having a characteristic set of fascial bundles, no contemporary anatomy texts or atlases describe the fascia in detail. The infraspinatus fascia was dissected in detail in 11 shoulders, to characterize the fascial bundles and connections that contribute to it. Thereafter, 70 shoulders were dissected to tabulate the variability of the fascial bundles and connections. Six characteristic features of the infraspinatus fascia were noted: a medial band, an inferior‐lateral band, and superior‐lateral band of fascia, insertion of the posterior deltoid into the infraspinatus fascia, a transverse connection from the posterior deltoid muscle to the infraspinatus fascia, and a retinacular sheet deep to the deltoid and superficial to the infraspinatus and teres minor muscles. Although other structures of the shoulder are more frequently injured, the infraspinatus fascia is involved in compartment syndromes and the fascial bundles of this structure are certain to impact the biomechanical function of the muscles of the posterior shoulder.     

Fascial structures and autonomic nerves in the female pelvis: A study using macroscopic slices and their corresponding histology

We investigated the topographical anatomy of the pelvic fasciae and autonomic nerves using macroscopic slices of five decalcified female pelves. The lateral aspect of the supravaginal cervix uteri and superior-most vagina issued abundant thick fiber bundles. These visceral fibrous tissues extended dorsolaterally, joined another fibrous tissue from the rectum (the actual lateral ligament of the rectum) and attached to the parietal fibrous tissues at and around the sciatic foramina (i.e. the sacrospinous ligament, thick fasciae of the coccygeus and piriformis and dorsal end of the covering fascia of the levator ani). The inferior or ventral vagina also issued thick fiber bundles communicating with the levator ani fascia. This connection between the vagina and levator fascia, when stretched, seemed to provide a macroscopic morphology called the arcus tendineus fasciae pelvis. The overall morphology of the visceroparietal fascial bridge exhibited a bilateral wing-like shape. The fascial bridge complex was adjacent but dorso-inferior to the internal iliac vascular sheath and located slightly ventral to the pelvic splanchnic nerve. However, the pelvic plexus and its peripheral branches were embedded in the fascial complex. The hypogastric nerve ran along and beneath the uterosacral peritoneal fold, which did not contain thick fibrous tissue. During surgery, in combination with the superficially located vascular sheath, the morphology of the visceroparietal fascial bridge and associated nerves seemed to be artificially changed and developed into the so-called cardinal, uterosacral, uterovesical and/or rectal lateral ligaments. The classical and original concepts of these pelvic fascial structures may need to be altered to adjust to these surgical observations.     

Fascia redefined: anatomical features and technical relevance in fascial flap surgery

Fascia has traditionally been thought of as a passive structure that envelops muscles, and the term “fascia” was misused and confusing. However, it is now evident that fascia is a dynamic tissue with complex vasculature and innervation. A definition of fascia as an integral tissue has been provided here, highlighting the main features of the superficial and deep fasciae. Wide anatomic variations and site-specific differences in fascial structure are described, coupled with results of our extensive investigations of fascial anatomy. This will enable surgeons to make better decisions on selecting the appropriate fascia in the construction of fascial flaps. The use of the superficial or deep fasciae in the creation of a fascial flap cannot be selected at random, but must be guided by the anatomical features of the different types of fasciae. In particular, we suggest the use of the superficial fascia, such as the parascapular fascio-cutaneous free flap or any cutaneous flap, when a well-vascularized elastic flap, with the capacity to adhere to underlying tissues, is required, and a fascio-cutaneous flap formed by aponeurotic fascia to resurface any tendon or joints exposures. Moreover, the aponeurotic fascia, such as the fascia lata, can be used as a surgical patch if the plastic surgeon requires strong resistance to stress and/or the capacity to glide freely. Finally, the epimysial fascia, such as in the latissimus dorsi flap, can be used with success when used together with the underlying muscles. Clearly, extensive clinical experience and judgment are necessary for assessment of their potential use.     

Skin ligaments: regional distribution and variation in morphology

Skin ligaments (SL) (L. retinacula cutis) are present extensively in the face, hands, feet, and in breast tissue, but have seldom been reported elsewhere in the body. The traditional histological view of the subcutaneous region is that it comprises a matrix of loose connective tissue devoid of fibrous specializations. The purpose of this study was to determine the structure and distribution of skin ligaments. Eight embalmed cadavers (3 males, 5 females, 69-90 years of age) were used in this study. Tissue was prepared using the E12 plastination technique. Macroscopic and microscopic examination demonstrated the widespread presence in the limbs and most of the rest of the body of fibrous strands linking the base of the dermis and the superficial fibers of the underlying deep fascia. The morphology and distribution of these skin ligaments were similar in the individuals examined. Variations in the structure of the skin ligaments depended on the presence of underlying muscle, neurovascular bundles, intermuscular septa and adipose tissue. We conclude that skin ligaments are complex fibrous structures that are present over most of the body. They form an extensive peripheral network in the subcutaneous fat. These 'ligaments' seem to provide an anchorage of skin to deep fascia that is flexible and yet resistant to mechanical loading from multi-directional forces. The use of the E12 plastination technique coupled with fluorescent confocal microscopy has been of benefit in visualizing and delineating SLs from other soft tissue structures in three planes.     

The connective tissue and glial framework in the optic nerve head of the normal human eye: light and scanning electron microscopic studies

The arrangement of connective tissue components (i.e., collagen, reticular, and elastic fibers) and glial elements in the optic nerve head of the human eye was investigated by the combined use of light microscopy and scanning electron microscopy (SEM). Light-microscopically, the optic nerve head could be subdivided into four parts from the different arrangements of the connective tissue framework: a surface nerve fiber layer, and prelaminar, laminar, and postlaminar regions. The surface nerve fiber layer only possessed connective tissue elements around blood vessels. In the prelaminar region, collagen fibrils, together with delicate elastic fibers, formed thin interrupted sheaths for accommodating small nerve bundles. Immunohistochemistry for the glial fibrillary acidic protein (GFAP) showed that GFAP-positive cells formed columnar structures (i.e., glial columns), with round cell bodies piled up into layers. These glial columns were located in the fibrous sheaths of collagen fibrils and elastic fibers. In the laminar region, collagen fibrils and elastic fibers ran transversely to the optic nerve axis to form a thick membranous layer - the lamina cribrosa - which had numerous round openings for accommodating optic nerve fiber bundles. GFAP-positive cellular processes also ran transversely in association with collagen and elastin components. The postlaminar region had connective tissues which linked the lamina cribrosa with fibrous sheaths for accommodating nerve bundles in the extraocular optic nerve, where GFAP-positive cells acquired characteristics typical of fibrous astrocytes. These findings indicate that collagen fibrils, as a whole, form a continuous network which serves as a skeletal framework of the optic nerve head for protecting optic nerve fibers from mechanical stress as well as for sustaining blood vessels in the optic nerve. The lamina cribrosa containing elastic fibers are considered to be plastic against the mechanical force affected by elevation of the intraocular pressure. The present study has also indicated that glial cells with an astrocytic character play an important role in constructing the connective tissue framework characteristic of the optic nerve head.     

The fasciacytes: A new cell devoted to fascial gliding regulation

Hyaluronan occurs between deep fascia and muscle, facilitating gliding between these two structures, and also within the loose connective tissue of the fascia, guaranteeing the smooth sliding of adjacent fibrous fascial layers. It also promotes the functions of the deep fascia. In this study a new class of cells in fasciae is identified, which we have termed fasciacytes, devoted to producing the hyaluronan‐rich extracellular matrix. Synthesis of the hyaluronan‐rich matrix by these new cells was demonstrated by Alcian Blue staining, anti‐HABP (hyaluronic acid binding protein) immunohistochemistry, and transmission electron microscopy. Expression of HAS2 (hyaluronan synthase 2) mRNA by these cells was detected and quantified using real time RT‐PCR. This new cell type has some features similar to fibroblasts: they are positive for the fibroblast marker vimentin and negative for CD68, a marker for the monocyte‐macrophage lineage. However, they have morphological features distinct from classical fibroblasts and they express the marker for chondroid metaplasia, S‐100A4. The authors suggest that these cells represent a new cell type devoted to the production of hyaluronan. Since hyaluronan is essential for fascial gliding, regulation of these cells could affect the functions of fasciae so they could be implicated in myofascial pain. Clin. Anat. 31:667–676, 2018. © 2018 Wiley Periodicals, Inc.     

The connective tissue of the adductor canal – a morphological study in fetal and adult specimens

The adductor canal is a conical or pyramid-shaped pathway that contains the femoral vessels, saphenous nerve and a varying amount of fibrous tissue. It is involved in adductor canal syndrome, a claudication syndrome involving young individuals. Our objective was to study modifications induced by aging on the connective tissue and to correlate them to the proposed pathophysiological mechanism. The bilateral adductor canals and femoral vessels of four adult and five fetal specimens were removed en bloc and analyzed. Sections 12 µm thick were obtained and the connective tissue studied with Sirius Red, Verhoeff, Weigert and Azo stains. Scanning electron microscopy (SEM) photomicrographs of the surfaces of each adductor canal were also analyzed. Findings were homogeneous inside each group. The connective tissue of the canal was continuous with the outer layer of the vessels in both groups. The pattern of concentric, thick collagen type I bundles in fetal specimens was replaced by a diffuse network of compact collagen bundles with several transversal fibers and an impressive content of collagen III fibers. Elastic fibers in adults were not concentrated in the thick bundles but dispersed in line with the transversal fiber system. A dynamic compression mechanism with or without an evident constricting fibrous band has been proposed previously for adductor canal syndrome, possibly involving the connective tissue inside the canal. The vessels may not slide freely during movement. These age-related modifications in normal individuals may represent necessary conditions for this syndrome to develop.     

Quantification of hyaluronan in human fasciae: variations with function and anatomical site

Recently, alterations in fascial gliding‐like movement have been invoked as critical in the etiology of myofascial pain. Various methods have been attempted for the relief of this major and debilitating clinical problem. Paramount have been attempts to restore correct gliding between fascial layers and the movement over bone, joint, and muscular structures. One of the key elements that underlies such fascial movement is hyaluronan. However, until now, the precise content of hyaluronan within fasciae has been unknown. This study quantifies for the first time the hyaluronan content of human fascial samples obtained from a variety of anatomic sites. Here, we demonstrate that the average amount varies according to anatomic site, and according to the different kinds of sliding properties of the particular fascia. For example, the fascia lata has 35 μg of hyaluronan per gram of tissue, similar to that of the rectus sheath (29 μg g^?1). However, the types of fascia adherent to muscle contain far less hyaluronan: 6 μg g^?1 in the fascia overlying the trapezius and deltoid muscles. In the fascia that surrounds joints, the hyaluronan increases to 90 μg g^?1, such as in the retinacula of the ankle, where greater degrees of movement occur. Surprisingly, no significant differences were detected at any site as a function of age or sex (P ‐value > 0.05, t ‐test) with the sole exception of the plantar fascia. This work can provide a better understanding of the role of hyaluronan in fascia. It will facilitate a better comprehension of the modulation of the hyaluronan‐rich layer that occurs in relation to the various conditions that affect fascia, and the diverse factors that underlie the attendant pathologies.     

Slick,Stretchy Fascia Underlies the Sliding Tongue of Rorquals

The tongue of rorqual (balaenopterid) whales slides far down the throat into the expanded oral pouch as an enormous mouthful of water is engulfed during gulp feeding. As the tongue and adjacent oral floor expands and slides caudoventrally, it glides along a more superficial (outer) layer of ventral body wall musculature, just deep to the accordion-like ventral throat pleats. We hypothesize that this sliding movement of adjacent musculature is facilitated by a slick, stretchy layer of loose areolar connective tissue that binds the muscle fibers and reduces friction: fascia. Gross anatomical examination of the gular region of adult minke, fin, and humpback whales confirms the presence of a discrete, three-layered sublingual fascia interposed between adhering fasciae of the tongue and body wall. Histological analysis of this sublingual fascia reveals collagen and elastin fibers loosely organized in a random feltwork along with numerous fibroblasts in a watery extracellular matrix. Biomechanical testing of tissue samples in the field and laboratory, via machine-controlled or manual stretching, demonstrates expansion of the sublingual fascia and its three layers up to 250% beyond resting dimensions, with slightly more extension observed in anteroposterior (rather than mediolateral or oblique) stretching, and with the most superficial of the fascia's three layers. Anat Rec, 2018. © 2018 Wiley Periodicals, Inc. Anat Rec, 302:735–744, 2019. © 2018 Wiley Periodicals, Inc.     

A hypothetical explanation for the aging of skin. Chronologic alteration of the three-dimensional arrangement of collagen and elastic fibers in connective tissue.

To provide a morphologic basis for a better understanding of the "aging" of human skin, the authors studied the three-dimensional arrangement and chronological alterations of the fibrous components of the connective tissue using rats aged 2 weeks to 24 months with a new technique for scanning electron microscopy. These studies showed that with postnatal growth there was a dynamic rearrangement of the collagen and elastic fibers: an ordered arrangement of mature collagen bundles was attained by producing a distortion of the elastic fiber meshwork of relatively straight fibers. During adulthood, there was a subsequent tortuosity of the distorted elastic fibers coupled with an incomplete rebuilding of the elastic fiber network, laid down in a form to interlock with the collagen bundles. These changes provide a model for explaining manifestations of aged skin, such as laxity, sagging, and wrinkling. The tortuously fixed elastic fibers imply that they have been stretched and have lost their original elasticity and ability to restitute short and straight. Interlocking of both collagen and elastic fibers should disturb the two independent fibrous systems, as would normally be the case, and thus decrease tissue compliance.     

The anococcygeal ligaments: Cadaveric study with application to our understanding of incontinence in the elderly

The term “anococcygeal ligament (ACL)” has been used to refer to two distinct structures: a superficial fibrous band originating from the myosepta of the external anal sphincter (EAS) and running upwards to the coccyx (the superficial ACL); and a deep fibrous band originating from the periosteum of the coccyx, merging with the thick presacral fascia and attaching to the superior end of the EAS (the deep ACL). In the present work, elastic fiber histology and muscle immunohistochemistry of sagittal sections obtained from 15 donated elderly male cadavers showed that superficial ACL, corresponding to a superficial fascia or skin ligament, was composed of very tortuous elastic fibers, with a fine elastic fiber mesh at their coccygeal attachment; whereas the deep ACL was composed of almost straight collagen and elastic fibers, intermingled with the coccygeal periosteum. Due to the weak insertion into the coccyx and the wavy course, the superficial ACL is unlikely to provide, even in association with contraction of the longitudinal anal muscle, a stable mechanical support to maintain the configuration of the EAS. Being similar to the suspensory ligament of breast, tissue repair of the skin ligament would not have a mechanical role. In contrast, the deep ACL, in association with the thick presacral fascia, likely plays a role in maintaining a suitable positioning of the anorectum to the coccyx. However, their relative lack of smooth muscles compared with rich elastic fibers indicates that both ACLs may become permanently overextended under conditions of long‐term mechanical stress. Clin. Anat. 28:1039–1047, 2015. © 2015 Wiley Periodicals, Inc.     

Fibrous structure of connective tissue in the vocal fold of the Japanese monkey (Macaca fuscata).

Fibrous structures in the vocal fold were studied in 8 adult Japanese monkeys. Their vocal folds were fixed with formalin and longitudinal and cross-sections were prepared. Some of the samples were treated with 10% NaOH to digest cellular components and elastic fibers, and some of them were treated with 90% formic acid to digest cellular components and collagen fibers. Each sample was then fixed with OsO4, dehydrated, dried at the critical point, ion-coated, and studied under a scanning electron microscope. The lamina propria mucosae in Japanese monkeys was thinner than that in humans and consisted of a superficial layer rich in connective tissue and a deep layer poor in this tissue. Both collagen fibers and elastic fibers mostly ran straight, and the fiber distribution and morphology slightly differed according to the depth of the layer. Their density was higher in upper layers. In the muscle layer, connective tissue surrounding muscle fibers was scarce. The fibrous structure of the monkey vocal fold is simpler than that of human vocal fold, and these findings reflect the short and monotonous phonation of monkeys.     

The three-dimensional ultrastructure of the collagen fibers, reticular fibers and elastic fibers: a review]

Fibrous components of the connective tissue are light-microscopically classified into three types: collagen fibers, reticular fibers and elastic fibers. The present paper reviews the three-dimensional ultrastructure of these fibrous components, mainly based on our studies by scanning electron microscopy. The collagen fibers are shaped like tapes or cords about 1 to 20 microns in diameter. Each fiber is a bundle of fibrils running roughly parallel to each other. These collagen fibrils vary in diameter from 30 to 300 nm depending on their locating area of the body, and show a repeating pattern of depressed and protruding segments on the surface. The reticular fibers consist of collagen fibrils about 20-40 nm in diameter, which run singly or in small bundles. They are usually interwoven elaborately to form thin lace-like sheets or sheaths attaching to basal laminae of such cells as epithelial, endothelial and muscular cells. These fibers are considered to play an important role not only in adhering the cells to the collagen fibers, but also in constituting the skeletal framework suitable for individual cells and tissues. The elastic fibers consist of two different components: elastin and fibrillin. Elastin forms unit fibrils of 0.1-0.2 micron thickness which are arranged in bundles or laminae specific to individual organs and tissues. Fibrillin, on the other hand, forms microfibrils about 10 nm in diameter running in or along elastin bundles. These microfibrils also form delicate networks separate from elastin components. For a comprehensive understanding of the fibrous components in the connective tissue, the author proposed categorizing them into two systems: the collagen fibrillar system as a supporting framework of tissues and cells, and the fibrillin-elastin fibrillar system for distributing stressing forces uniformly in tissues.     

Fetal Development of Fasciae around the Arm and Thigh Muscles: A Study Using Late Stage Fetuses

To obtain a better understanding of multi‐laminar deep fascia covering skeletal muscles, we examined nondecalcified histological sections of the arm and thigh of 20 human fetuses aged 25–33 weeks. Morphologies of the fasciae varied between sites and specimens, but the initial morphology was most likely to be a thin and loose sheet on the external surface of the muscles (fascia‐1 or F1). When the F1 became wavy, thick and tight, it was detached from the muscle surface. Beneath the F1, the second lamina of fascia (F2) appeared on the muscle surface and it was also detached. In this manner at 25–33 weeks' gestation, fasciae covering the triceps and vastus lateralis muscles had a three‐layered configuration (F1, F2, and F3). Due to significant individual variations, this process was not correlated to the ages and sizes of specimens. Muscle contractions might facilitate the detachment. In these muscles, the intramuscular tendon joined the F2 or F3 and the latter became thick and aponeurotic. Along the finally developed lamina, muscle fibers carried a desmin‐positive spot for insertion. Increased laminae were accompanied by a reduced number of CD68‐positive macrophages and, nerves were absent, near the developing fascia. In contrast to skin ligaments or superficial fasciae showing de novo development in loose tissue, a deep or muscle‐covering fascia seemed to originate from the skeletal muscle itself at the surface, and this process was repeated to produce multi‐layered fascia. Depending on sites, collagen fibers were added by the intramuscular tendon. Anat Rec, 301:1235–1243, 2018. © 2018 Wiley Periodicals, Inc.     

Pes anserinus: layered supportive structure on the medial side of the knee

The pes anserinus is composed of a combination of tendinous insertions of the sartorius, gracilis and semitendinosus muscles. Precise knowledge of the structures on the medial side of the knee and the relationships between fascia and tendons is critical for diagnosis, surgery, and the development of improved operative procedures of the knee. To obtain precise data on the layered structures associated with the fascia cruris on the medial side of the knee and the fibrous bundles attached to them, we dissected nine legs of five adult cadavers. We observed a superficial longitudinal fibrous bundle on the superficial surface of the sartorius and a deep longitudinal fibrous bundle on the aponeurotic membrane covering the tendon of the gracilis muscle. The distal parts of the tendons of the gracilis and semitendinosus were found to have aponeurotic membranes, and these membranes were fused with the fascia cruris. These two longitudinal fibrous bundles and the aponeurotic membranes from the gracilis and semitendinosus tendons fused with the fascia cruris, and a small tendinous expansion from the semimembranosus muscle fused with the aponeurotic membrane from the semitendinosus tendon and tibial collateral ligament as well as the fascia covering the medial head of the gastrocnemius and fascia cruris. Based on the considerable tension from the sartorius, gracilis, semitendinosus, semimembranosus and gastrocnemius muscles, these bundles, membranes, and muscles may act as a complex tensor fasciae cruris muscle and play a significant role as stabilizers of the medial side of the knee joint in the upright posture.     

Pectoral and femoral fasciae: common aspects and regional specializations

The aim of this study was to analyse the organization of the deep fascia of the pectoral region and of the thigh. Six unembalmed cadavers (four men, two women, age range 48–93 years old) were studied by dissection and by histological (HE, van Gieson and azan-Mallory) and immunohistochemical (anti S-100) stains; morphometric studies were also performed in order to evaluate the thickness of the deep fascia in the different regions. The pectoral fascia is a thin lamina (mean thickness ± SD: 297 ± 37 μm), adherent to the pectoralis major muscle via numerous intramuscular fibrous septa that detach from its inner surface. Many muscular fibres are inserted into both sides of the septa and into the fascia. The histological study demonstrates that the pectoral fascia is formed by a single layer of undulated collagen fibres, intermixed with many elastic fibres. In the thigh, the deep fascia (fascia lata) is independent from the underlying muscle, separated by the epimysium and a layer of loose connective tissue. The fascia lata presents a mean thickness of 944 μm (±102 μm) and it is formed by bundles of collagen fibres, arranged in two to three layers. In each layer, the fibres are parallel to each other, whereas the orientation of the fibres varies from one layer to the adjacent one. The van Gieson elastic fibres stain highlights the presence of elastic fibres only in the more external layer of the fascia lata. In the thigh the epimysium is easily recognizable under the deep fascia and presents a mean thickness of 48 μm. Both the fascia lata and pectoral fascia result innerved, no specific differences in density or type of innervations is highlighted. The deep fascia of the pectoral region is morphologically and functionally different from that of the thigh: the fascia lata is a relatively autonomous structure with respect to the underlying muscular plane, while the pectoralis fascia acts as an additional insertion for the pectoralis major muscle. Different portions of the pectoralis major muscle are activated according to the glenohumeral joint movements and, consequently, selective portions of the pectoral fascia are stretched, activating specific patterns of proprioceptors. So, the pectoralis muscle has to be considered together with its fascia, and so as a myofascial unit, acting as an integrated control motor system.