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0008-3194/2012/179–191/$2.00/©JCCA 2012

Fascia: a morphological description and classification system based on a literature review Myroslava Kumka, MD, PhD* Jason Bonar, BScKin, DC

Fascia is virtually inseparable from all structures in Le fascia est pratiquement inséparable de toutes les the body and acts to create continuity amongst tissues structures du corps, et il sert à créer une continuité to enhance function and support. In the past fascia entre les tissus afin d’en améliorer la fonction et le has been difficult to study leading to ambiguities in soutien. Il a déjà été difficile d’étudier le fascia, ce qui nomenclature, which have only recently been addressed. a donné lieu à des ambiguïtés dans la nomenclature, Through review of the available literature, advances qui n’ont été abordées que récemment. Grâce à un in fascia research were compiled, and issues related examen de la documentation disponible, les avancées to terminology, descriptions, and clinical relevance of dans la recherche sur le fascia ont été compilées, fascia were addressed. Our multimodal search strategy et les problèmes relevant de la terminologie, des was conducted in Medline and PubMed databases, with descriptions et de la pertinence clinique du fascia ont été other targeted searches in Google Scholar and by , traités. Nous avons adopté une stratégie de recherche utilizing reference lists and conference proceedings. multimodale pour nos recherches dans les bases de In an effort to organize nomenclature for fascial données Medline et PubMed, avec des recherches ciblées structures provided by the Federative International dans Google Scholar et manuelles, au moyen de listes de Committee on (FICAT), we références et de comptes rendus de congrès. developed a functional classification system which Dans le but d’organiser la nomenclature des includes four categories of fascia: i) linking, ii) structures du fascia fournie par le Federative fascicular, iii) compression, and iv) separating fasciae. International Committee on Anatomical Terminology Each category was developed from descriptions (FICAT, traduction libre : comité fédératif international in the literature on gross , , and de terminologie anatomique), nous avons mis au point ; the category names reflect the function of un système de classification fonctionnel qui comprend the fascia. quatre catégories de fascia : les i) de liaison, An up-to-date definition of fascia is provided, as well ii) fasciculaire, iii) de compression et iv) de séparation. as descriptions of its function and clinical features. Our Chaque catégorie a été élaborée à partir de descriptions se trouvant dans la littérature portant sur l’anatomie macroscopique, l’histologie et la biomécanique. Le nom de chaque catégorie se rapporte à la fonction du fascia. Une définition à jour du fascia est fournie, ainsi que des descriptions de ses fonctions et caractéristiques cliniques. Notre classification emploie la terminologie

*Canadian Memorial Chiropractic College, Department of Anatomy Correspondence should be addressed to: Myroslava Kumka, 6100 Leslie Street, Toronto ON M2H 3J1, Canada Tel: 416-482-240 ext: 175 Email: [email protected] ©JCCA 2012

J Can Chiropr Assoc 2012; 56(3) 179 Fascia: a morphological description and classification system based on a literature review

classification demonstrates the use of internationally acceptée à l’échelle internationale dans le cadre d’une accepted terminology in an ontology which can improve ontologie qui peut améliorer la compréhension des understanding of major terms in each category of fascia. termes importants dans chaque catégorie de fascia. (JCCA 2012;56(3):179-191) (JCCA 2012;56(3):179-191) key words: fascia, connective , classification, mots clés : fascia, tissu conjonctif, classification, anatomy, histology, terminology, innervations, manual anatomie, histologie, terminologie, innervations, therapy thérapeutique manuelle

Introduction tice. Indeed, a number of experts have called for further Fascia is an uninterrupted viscoelastic tissue which forms development on the description and nomenclature of all a functional 3-dimensional .1-3 It sur- fasciae and have made significant contributions of their rounds and penetrates all structures of the body extending own.5-7 from head to toe, thus making it difficult to isolate and Recent advances in research within the fields of bio- develop its nomenclature.1 The Federative International mechanics, gross anatomy, and histology, provide the Committee on Anatomical Terminology (FICAT), in international research community with an opportunity to the 1998 edition of , points out improve the terminology associated with fascia, thereby significant flaws in the nomenclature system for fascia, improving intra- and inter-professional communications.5, largely stemming from the anglocentric of the 8-10 However, discrepancies still exist concerning the of- terms used, and lack of formal international applicability.4 ficial definition, terminology, classification and clinical The usage of the terms superficial fascia and significance of fascia.5-6 is considered incorrect by the FICAT because histological For example, the FICAT broadly defines fascia as terminology referring to layers of the sheaths, sheets or other dissectible connective tissue ag- varies too much internationally to be generalized by these gregations. The First International Fascia Research Con- two terms.4 Common names of certain fascia are also gress (2007) formulated a comprehensive definition of fa- considered to be inaccurate, e.g., Scarpa’s, Camper’s, and scia as the component of the connective tissue Colles’. It is suggested that they be replaced with sub- system, emphasizing its uninterrupted, three-dimensional cutaneous tissue of , sub- web-like extensions and highlighting its functional at- cutaneous tissue of abdomen fatty layer and membranous tributes.1,4 The Congress went on to include and layer of , respectively.4 Terminologia Anatom- capsules, muscular septa, , retinacula, ica gives a long list of terms related to their definition of aponeuroses, , myofascia, neurofascia and other fascia, and attempts to offer a system for grouping vari- fibrous collagenous tissues as forms of fascia, inseparable ous fasciae based on embryological origins and modes from surrounding connective tissues.1 The broad nature of development. However, clear details on the groupings of these two definitions is controversial, and not all of the and justification for this strategy are not given, and it re- tissues have been widely accepted into common usage. mains difficult to organize and properly use the multiple Thus, a consistent terminology to classify and categor- fascial terms. Furthermore, the application of these terms ize fascia has not been formally established and accepted for communication in research, education, and clinical internationally.5-6 Gray’s textbook approach to naming fa- practice remains difficult and impractical. In light of the scia regionally based on the adjacent or overlaying struc- contribution made by the FICAT on fascial terminology, tures is a practical approach, however, this suggests fascia it is important to utilize their on terminology and has a beginning and an end, which is not true to its form.11- suggest how it may be further arranged and used in prac- 12 Thus, the topographical approach is important when

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identifying regional fascia, but it is not used consistently al characteristics identified in the literature, and utilizing in practice internationally, nor does it help to describe the internationally accepted terminology from the FICAT.4,24 functional role of the regional fascia. A more recent ontology highlights the importance of Methods: two functional forms of fascia, connecting and discon- A review of the literature on fascia was conducted with necting, for which orientation and descriptions of fa- electronic searches of EBSCO databases, PubMed, and scia’s role in are key justifications for each Google Scholar, along with hand searches of proceedings category.7 In support of this principle, there is an exten- from the past two International Fascia Research Con- sive body of work demonstrating that significant amounts gresses (2007, 2009). Search strategies in EBSCO and of are transmitted amongst multiple antagonist and PubMed consisted of individual and combined MeSH synergistic muscle groups across joint capsules through term searches for “Fascia” and “Connective Tissue” various sections of extra- and intramuscular fascia.7-8,13-15 using specific limiters for our topic to emphasize anat- Although the recent ontologies grounded in fascial omy. These search terms were also paired separately with function represent an advance in classification, the com- various keywords – “terminology”, “extracellular ma- plexities of fascia make it necessary to expand on these trix”, “collagen”, and “function”. Results were limited to two categories (connecting and disconnecting) to further English, full text peer reviewed journal articles, confer- sort and describe all groups of fascia according to their ence proceedings, and textbooks. was limited attributes reported recently in the literature.7 These addi- to articles with abstracts related to morphology, termin- tional attributes include: collagen type ratio, extracellular ology, and/or clinical aspects of fascia. Information was matrix , fiber types, myofascial force trans- then used to help organize fascia terminology, utilizing mitting potential, details on fiber orientation, and influ- terms from two texts: Terminologia Anatomica and Ter- ence on the .8,16-21 minologia Histologica.4,24 Lack of consistent terminology has a negative effect on communication within health professions, and im- Results pedes collaborations in research.22 Since fascia represents In section A below, we present the results of our literature a topic of growing interest worldwide, it should be a pri- review, discussing the anatomical, histological, and bio- ority to reduce ambiguity in fundamental terms so that mechanical features of fascia, and its innervation. Then this field of research can properly advance. For example, in section B, we outline our resulting proposal for a new the lack of common definitions and nomenclature hinders classification system (Table 1) incorporating these fea- communication between those involved in the process of tures of fascia. It is important to first understand the key diagnosis and treatment of pelvic pathologies in every- characteristics and the divergent classifications of fascia day practice.23 One study revealed this by comparing the at gross anatomical, histological, and biomechanical per- unofficial/common terms being used in the field and the spectives before outlining the details of these four cat- terms provided by the Terminologia Anatomica, demon- egories. strating how this text can be used to improve consistency in the nomenclature. While we do accept the validity of a A. Literature Review topographical approach in naming fascia, it does not take into account the fact that fascia doesn’t have a beginning I. Overview and end like muscle, nor does a topographical approach The range of research advances revealed in the literature account for fascia’s microscopic features, or diversity of includes observations on imaging, advanced its functional characteristics.5-7,12 and techniques, as well as modeling of tissue de- formation, and in vitro cellular processes.10,12,25-30 Areas Purpose of interest at the past two (2009, 2010) Fascia Research The aim of the present study is to develop a classifica- Congresses have included: biomechanics, innervation, tion system for fascial structures, based primarily on their vascularisation, molecular structure, clinical relevance, functional properties, but also incorporating morphologic- and terminology.31 Upon review of the advances in fascia

J Can Chiropr Assoc 2012; 56(3) 181 Fascia: a morphological description and classification system based on a literature review

research, we see that fascia is not a passive structure, but a behavior in a living, hydrated body, has been conducted functional organ of stability and , virtually insepar- with recent fluoroscopic imaging under the of the able from all surrounding tissue. dorsal , shedding new light on how this sliding collagenous system works.32-33 These observations dem- II. Gross Anatomy onstrate that fascia incorporates a water dense vacuolar Gross anatomical studies of fascia demonstrate an ar- system able to slide independent of the rate of contraction ray of characteristics based on location, density, fiber in muscle around it and able to conduct structures like ca- direction, and fascia’s relationship to surrounding struc- pillaries throughout sections of myofascia.32-33 The visco- tures.19,26-27 Based on location, the FICAT describes the elastic nature of fascia can only be observed in hydrated following fasciae: i) in relation to the body regions: fascia tissue, and in embalmed tissue we are only observing an of head and , fascia of trunk, and fascia of limbs, ii) artifact of the living tissue. A better appreciation for the in relation to the surrounding structures: subcutaneous true gross appearance of fascia can be gained through fascia, fascia of muscles, visceral fascia, parietal fascia, fresh body , and in vivo via direct imaging and fascia extraserosalis which represents any other fa- techniques.34 scia which lies inside the parietal fascia and outside the Pathological changes in fascia have been observed visceral fascia.4 with special imaging techniques, such as ultrasonic elas- Fascia’s key characteristic, continuity, helps explain tography that displays deformation and the elasticity of concepts such as myofascial force transmission.3 Hunjing soft tissues.34 This technology allows a non-invasive esti- describes biomechanical features of extramuscular and mation of tissues stiffness based on the fact that soft tis- intramuscular force transmission in specimens where sue has greater tissue displacement than when surrounding connective tissues are seen to influence force externally compressed.10 By further quantifying the prop- potential and connect muscle groups.13-15 Dissectional ob- erties of the soft tissues, as with recent 3-D mathematical servations of the intramuscular connective tissue (IMCT) models of fascial deformation, insight will be gained into show this fascia to influence length of to im- the effects of manual treatments beneath the skin and how prove force production.15 Other morphological descrip- the body responds to various .30,35-36 tions of fascia characterize it as being optimally designed to take up tensional forces in the musculoskeletal system. III. Histology In the past, classical dissection techniques have essen- Fascia has specific cells, , and fiber tially ignored fascia , simply removing it to get to muscle types that make it a form of connective tissue proper.16,37-38 and deeper structures.5 Subsequently, it was revealed A better understanding of fascia at the cellular level gives through careful dissection that fascia commonly occurs insight into its functional properties.39 Clear changes to as an undulating layered system of different connective the (ECM) in the form of adhesive tissue types.19,28-29 Three-dimensional models of the cru- sites between microscopic filaments have been studied in ral and thoracolumbar fasciae demonstrate that the “deep “scarred” fascia.40-41 Collagen types have also been shown fasciae” are formed of three sub-layers of connective tis- to vary with mechanical forces and strains.39 We hypoth- sue with different densities and orientations.19,29 It was esize that the functional properties of fascia are reliant on discovered that in each sub-layer the collagen are the composition of the ECM, specific cells, and filaments, parallel to each other, whereas the orientation between including but not limited to the ratio of collagen types. the fibers of adjacent layers changes, forming an angle of Collagen, a triple , is the key struc- approximately 70-80 degrees with each other.29 This al- tural fiber that gives connective tissue its ability to resist lows denser fascial sheets to slide freely over underlying tension.17,37-38 There are twenty five distinct collagen types layers, without significant friction, and enhances fascia’s recognized in the Ross histology textbook and , and ability to take up in virtually all directions.29 twenty eight collagen types recognized in the latest re- It is difficult to gain an appreciation for the true appear- view by Gordon.16,37 Although, is the main ance of fascia, aside from basic structure, in embalmed type accounting for 90% of the ’s collagen, cadavers. Direct observation of fascia’s appearance and fascia contains an array of collagen type combinations in-

182 J Can Chiropr Assoc 2012; 56(3) M Kumka, J Bonar

cluding, but not limited to, types I, III, IV, V, VI, XI, XII, ition.46,47 These adaptations have been demonstrated in XIV, XXI.16-17,37-38 Collagen provides resistance to tension the supraspinatus , transverse acetabular , and stretch, which commonly occur in fascial tissues, transverse ligament of atlas, as well as various other liga- such as ligaments, tendons, sheaths, muscular fascia and ments and tendons throughout the body.47,48 deeper fascial sub-layers.37 within fascia demonstrate contractile Collagen type III, also known as , is in- properties and contain - filaments typically volved in forming the scaffolding for the cells of the loose seen in .49-51 The significance of these con- connective tissues related to the , vascular tractile properties remains unclear, however in-vitro ob- walls, and smooth muscle.1-2,17A collagen needs the servations of autonomous contraction of myofibroblasts support of not only fibrillar collagen types, but also a mix harvested from porcine and rat fascia when stimulated of non-fibrillar forms known as fibril-associated with various pharmacological agents (i.e., mepyramine, with interrupted triple helices (FACITs).16 The functions of angiotensine, glyceryltrinitrate) have been repeated in FACITs include: i) anchoring to the , different labratories.52-53 An estimation of tension created ii) regulating the diameter of , iii) forming lattice by contraction of myofibroblasts when extrapolated to a networks, and iv) acting as transmembrane structures.16 large fascial sheet (i.e., ) may pro- These fibrils are important to the integrity and function of duce tension within the musculoskeletal system between fascia within the ECM. Elastic fibers within the ground 30-40N.51 The significance of this contractile property re- substance give fascia its characteristic stretch.29,37-38,42 mains hypothetical and reproduction of these contractile A combination of multiple types of collagen within the forces in-vivo in response to efferent neural stimulus is extracellular matrix forms a unique structure, like a blue- yet to be done. print that reflects the function and compliance of fascia in Increased concentration of myofibroblasts in patho- various regions.16-17 Without a characteristic fiber arrange- logical fascia has been observed, suspected to create tis- ment and composition for each fascial region, it is likely sue in clinical conditions like palmar fascial that fascia would not withstand stresses or have the same (Dupuytren’s ), plantar fascial fibro- function. matosis (Ledderhose’s disease), and adhesive capsulitis The cells within fascia include (, (frozen ).49,54-56 Fascia is also susceptible to the myofibroblasts), , and various migrating white actions of typical cells of influencing com- cells.27,41-42 Fibroblasts are highly adaptable to their munication, growth, and function.37,38 environment, and show a capacity to remodel in response Fiber orientation in fascia is important to its overall to the direction of various mechanical stimuli, produ- structure and function, and can be viewed with the un- cing biochemical responses.29,41,43-45 If function changes, aided , polarized light, or various microscopic tech- as with increased mechanical stress, or prolonged im- niques.18,27,57 It is a consistent observation that the fibers mobilization, deoxyribonucleic acid (DNA) transcription are oriented parallel to predicted force vectors, and are of pro-collagen in the fibroblasts will change types (e.g., likely to resist tension.18,27,57 Based on certain common collagen type I into collagen type III), or undifferentiated characteristics, including the fiber arrangement, connect- types may adapt towards a more functionally appro- ive tissue proper is classified by the Terminologia Histo- priate lineage (e.g., ).42,45-48 logica as and dense connective Benjamin et al, studied the morphological changes ob- tissue.24 The dense connective tissue is sub-categorized servable in various tendons and ligaments in response to as: i) unidirectional parallel ordered dense connective tis- biomechanical stresses.46 It was established that the tis- sue, ii) multidirectional parallel ordered dense connective sue structure and the molecular composition of ECM are tissue, iii) woven connective tissue, iv) irregular fuso- directly correlated with the local mechanical forces.46,47 cellular connective tissue.24 Under significant states of compression, tissue once populated with fibroblasts, becomes invested predomin- IV. ately with and forms specialized connect- Mechanotransduction entails significant cellular change ive tissue, , with further solid mineral depos- that occurs in response to biomechanical tension and

J Can Chiropr Assoc 2012; 56(3) 183 Fascia: a morphological description and classification system based on a literature review

compression. These stimuli exert their effects within the the , and encapsulated endings with distinctive ar- cells through filaments of the ECM, and so mechanical rangements of non-neuronal cells that completely enclose stimulation leads to a cascade of events which eventu- the terminal parts of the axons.73 Some of these recep- ally influences the activity in the nucleus.48,58,59 Mechano- tors function as both a and a transduction is produced as cells convert a diversity of (types III and IV receptors).73 that arises in muscles, mechanical stimuli, transmitted throughout the ECM, into tendons, ligaments, and is detected by these recep- chemical activity to regulate morphology and function of tors. There have been conflicting results in the research, tissues.60-61 The cellular responses include the release of but most recent evidence has revealed small diameter free interleukins, kinases and other biochemicals.61-62 nerve endings in the thoracolumbar fascia of and hu- Local injury in a tissue can have widespread conse- mans.69 One investigation has revealed the presence of quences via mechanotransduction’s role in stimulating these fibers on electronmicroscopy18, meanwhile another quiescent cells to form active fibroblasts.62 This mechan- group has demonstrated calcitonin gene-related ism of cellular activation via mechanical force has been (CGRP) and substance P (SP) within the same fibers, sug- hypothesized to play a role in embryological develop- gesting afferent function, including nociception.69 Further ment as part of the induction process of mesenchymal work must be done on human specimens as currently the cells throughout the .63 Clinically, the effects of best evidence is heavily reliant on models. mechanotransduction have been observed with the inter- Langevin et al, developed a pathophysiological model vention of .64 There is evidence to suggest of low based on connective tissue nociception, that the insertion of acupuncture needles into the fascia after demonstrating on the structural altera- stimulates the activity of fibroblasts, presumably through tions of the low back connective tissues.34,70 Fascial con- physical strain exerted on the transmembranous micro- nections within different motor units, and different func- filaments in the ECM.65-66 Needles will also cause dis- tional synergists, can provide an alternative explanation placement of that tissue, and twisting of the needle once for distributions, which often do not fol- it is inserted can cause further displacement of the fascia low either nerve pathways or the morphology of a single as measured with ultrasonic elastomyography.35 Simple muscle.74 manual pressure has also been demonstrated, through Many encapsulated endings found in fascia are mech- deformation, to cause alterations in the viscoelasticity of anoreceptors that respond to mechanical pressure or tissue.30,36 These cellular and filamentous responses may deformation, and include Golgi receptors, Pacinian cor- provide a theoretical framework for the therapeutic mech- puscles, and Ruffini’s corpuscles.18,26,75-76 Different tech- anisms of soft tissue therapies.36,67-68 An understanding of niques of tissue manipulation may stimulate the above re- mechanotransduction reveals that for and injury ceptors: the high-velocity thrust manipulations and vibra- it is not only the gross observable reaction of tissues that tory techniques likely stimulate Pacinian receptors, while is of interest, but also the biomechanical response of the slow, deep soft tissue techniques likely target Ruffini’s ECM within fascia. bodies.75-76 Knowing what receptors are more signifi- cantly concentrated in a particular target tissue can help V. Innervation a manual practitioner choose the method of stimulus and Electron and special staining procedures technique (e.g., deep pressure, light , stretch, ten- demonstrate that fascia is populated by sensory neural fib- sion, or vibration).75-76 Understanding that certain types of ers, suggesting that fascia contributes to proprioception fascia are more densely populated with certain particular and nociception, and may be responsive to manual pres- receptors can aid in the overall understanding of the body sure, temperature, and vibration.18,26,69,70 Some receptors and creating more effective approaches to manual treat- found within fascia may be responsive to, and influence ments. some autonomic responses, such as lowering blood pres- sure.71-72 B. Classification System On a structural basis, two classes of sensory receptors In an effort to organize nomenclature for fascia provided are recognized: free nerve endings as terminal branches of by the FICAT, we developed a functional classification

184 J Can Chiropr Assoc 2012; 56(3) M Kumka, J Bonar

system which includes four categories of fascia: i) link- as joint linkages and tendinous arches ultimately provid- ing, ii) fascicular, iii) compression, and iv) separating ing proprioceptive information when tension is exerted.7 fasciae. The passive linking fasciae can only transmit force when All fascia-related terminology provided in the Ter- they are stretched and loaded, while dynamic fasciae can minologia Anatomica can be subsumed within these four theoretically contract more autonomously like smooth categories (Table 1).4 This system is not meant to be a muscle, thereby affecting tension in the musculoskeletal reductionist approach to the fascial system, but a mode system, but not significant enough to be the primary mov- of exploring and better understanding the complex inter- er of limbs.51 action of functions that exist within the system. Each re- gion of the body contains multiple categories, suggesting II. Fascicular Fascia that every region of the body has a complex mixture of Fascicular fascia forms adaptable tunnels which bundle different fascial types. To illustrate this concept, the vessels as well as fascicles within muscle, tendon, is an example of a body region which contains all four and . Fascicular fascia plays an important role in fascial categories: Illiotibial band (Linking), organization, transport, strength and locomotion.39 This of the quadriceps femoris muscle (Fascicular), category is organized as a mixture of both loose and dense (Compression), and (Separating). regular multidirectional connective tissues.24 Types I and III collagen are the major components of these tissues I. Linking Fascia with lesser amounts of Types V, VI, XII, and XIV.16,39,79 The linking category is predominantly dense regular par- Fascicular fascia of the muscle comprises three dis- allel ordered unidirectional connective tissue proper with tinct layers of IMCT: surrounding whole a significant amount of collagen type I.16,24 This includes muscles, perimysium separating fascicles or bundles of fasciae of muscles, fasciae of regions (head & neck, trunk, muscle fibers within the muscle, and cov- limbs), aponeuroses, tendinous arches and neurovascular ering the individual muscle fibers.39 Forming the muscle sheaths.4 architecture, this network of collagen fibers can be seen This category is subdivided into dynamic and passive as an extensive matrix of tunnels that connects and dis- divisions. The dynamic division includes major fascial sipates force within muscle, provides intramuscular path- groups more significantly related to movement and joint ways and mechanical support for large and small nerves, stability, and characterized by higher concentrations of blood vessels and lymphatics.32,39,79 The fascicular fascia contractile and proprioceptive fibers. The dynamic div- of the muscle converges into a dense regular connect- ision is composed of fasciae of muscles (investing layer, ive tissue link at the myotendinous junction to become fascia of individual muscle), and fasciae of the trunk.4 The fascicular fascia of the tendon, comprising endotendon, innervation of dynamic linking fascia functionally differ- peritendon and epitendon.5,7,79 At this junction, fascicular entiates it from other categories, permitting it to contrib- fascia is richly innervated by Golgi tendon organs which ute to nociception and proprioception. For example, the are stimulated by .37,38 Tension in the thoracolumbar fascia (TLF) contributes to spinal stabil- tendon results in a decrease in tonus in contiguous ity and makes firm connections between the trunk and striated muscle fibers.70 limbs.77 It is also densely innervated by free nerve end- IMCT is essential for myofascial force transmission ings and Paciniform corpuscles which respond to rapid (as outlined in Results section A I), enhancing the forces pressure and vibration.2,18,73,78 produced by muscles.8 Fascicular fasciae allow forces to The passive division is acted on by other extramuscu- be transferred from within muscle to synergistic muscles, lar tissues to maintain continuity throughout the body or and also, via the extramuscular pathway, through the link- form tunnels and sheaths.7 The passive division incorpor- ing fascia, to antagonistic muscles.8,13-14 The fascicular ates fasciae of muscles (muscle sheaths), fasciae of the fascia forms the connective tissue envelope for nerve head and neck, fasciae of limbs, aponeuroses, tendinous fascicles and whole peripheral nerves: and arches, and retinaculae.4 This group can act as muscular , respectively.37,38 The perineurium serves as a insertion points, such as the epicranial , and metabolically active diffusion barrier that contributes to

J Can Chiropr Assoc 2012; 56(3) 185 Fascia: a morphological description and classification system based on a literature review

Table 1 Fascial categories: function, terms, and histological features Fascial Function (Examples) Terminologia Histological category Terminologia Anatomica4 Histologica24 features16,37 L Dynamic Fasciae of muscles (investing layer) Dense regular Collagen types: i – role in movement and & fasciae of individual muscles: parallel ordered I, XII, XIV n stability unidirectional k Supraspinatus fascia connective tissue i – critical to Deltoid fascia proper n myofascial force Actin-myosin g transmission Fasciae of trunk: filaments Thoracolumbar fascia – creates significant Diaphragmatic fascia pretension in fascia Pacinian musculature corpsules, Fasciae of limbs/membrorum Free nerve endings Axillary fascia Passive Fasciae of muscles (muscle sheath) Dense regular Collagen types: – maintains continuity, woven I, III, XII, XIV passive force connective tissue transmission Head & Neck Multidirectional – proprioceptive parallel ordered communication connective tissue throughout the body Ligamentum nuchae Ligamentum flavum Golgi tendon organs, Pacinian Fasciae of limbs/membrorum & Ruffini’s Intermuscular septae corpuscles Anterior talofibular ligament Aponeuroses Erector spinae aponeurosis Plantar aponeurosis Tendinous arches Muscular & vascular spaces/lacunae Iliopectineal arch Tendinous arch of soleus Fascicular – provides myofascial Intramuscular & extramuscular Loose Collagen types: force transmission & fasciae. Neurovascular sheaths connective tissue I, III, IV, V, proprioceptive feedback XII, XIV for movement control Endomysium Dense regular Perimysium multidirectional – maintains protection for Epimysium parallel ordered Golgi tendon nerves and vessels Endotendon connective tissue organs Peritendon – allows vascular sheaths Paratendon Dense irregular to be in continuity with connective tissue Endoneurium Perineurium Epineurium

186 J Can Chiropr Assoc 2012; 56(3) M Kumka, J Bonar

Table 1 (Continued) Fascial Function (Examples) Terminologia Histological category Terminologia Anatomica4 Histologica24 features16,37 Compression Fasciae of limbs/membrorum Dense regular Collagen type I – provides stocking, Brachial fascia woven compression and tension connective tissue compartmental effects Dorsal fascia of hand Elastin Fascia lata Multidirectional – influences venous return Crural fascia parallel ordered Dorsal fascia of connective tissue Ruffini’s – enhances proprioception, corpuscles muscular efficiency and coordination

Separating Parietal Fascia Loose Collagen types: – compartmentalizes Parietal pleura connective tissue III, V, VII organs and body regions Fibrous to maintain structural Dense irregular Extracellular functions Parietal fusocellular matrix: reticular Endoabdominal fascia connective tissue and elastic fibers – promotes sliding and Endopelvic fascia reduces friction during Reticular motion Visceral fascia fibers provide a cellular – responds to stretch and Visceral pleura framework distention Serous pericardium Visceral peritoneum Elastin – provides physical Visceral support and Visceral pelvic fascia Pacinian and absorption Ruffini’s corpuscles – limits the spread of Extraserosal fascia infection Sternopericardial ligaments Bronchopericardial membrane Pulmonary ligaments Extraperitoneal fascia Investing fascia Subcutaneous tissue of abdomen Membranous layer of perineum

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the formation of a blood-nerve barrier.80 The blood ves- of tissues over one another, it may still form adhesions sels that supply the nerves travel in the epineurium.80 from faulty movement patterns or injury.54 These two layers of the fascicular fascia are innervated by FICAT’s terms for separating fascia include: parietal the nervi nervorum, which can evoke nociception through fascia, visceral fascia, extraserosal fascia, investing/sub- the release of CGRP and may create neurogenic inflam- cutaneous fascia, formerly known as fascia superficialis.4 mation.81 An inflammation of the nervi nervorum causes This category also includes synovial sheaths and fasciae the inflammatory reaction of the nerve’s fascial envelopes of limbs.4 Parietal fascia lies outside the parietal layer of to induce the mechanical sensitivity, which can manifest serosa such as pericardium, pleura and peritoneum, and as local, radicular, or neuropathic pain.75,82,83 lines the wall of a .4 Visceral fascia lies im- mediately outside the visceral layer of the serosa and sur- III. Compression Fascia rounds the viscera.4,85 Extraserosal fascia lies within the Compression fascia is a mixture of dense regular woven space between the visceral and parietal fasciae.4 and multidirectional parallel ordered connective tissue This fascia class is a complex connective tissue matrix, layers that ensheath whole limbs to create a stocking ef- ensheathing everything from body cavities to individual fect.24,84 This fascial category plays an important role in organs. It separates, supports, and compartmentalizes­ or- locomotion and venous return due to its influence on com- gans and regions in order to maintain proper structural partmental pressure, muscle contraction and force distri- and functional relationships throughout the body. This bution.20,29,84 For example, the crural fascia is composed group of fascia has a unique appearance and texture upon of two or three layers of parallel ordered collagenous observation, ranging from transparent woven sheets to a fiber bundles, each layer being separated by a thin layer fuzzy cotton-like consistency.28 of loose connective tissue.19,29 The spatial orientation of The innervation of separating fascia serves primarily the collagen fibers changes from layer to layer within the to distension and compression of tissues. More de- compression fascia.29 The presence of loose connective tailed histological analyses are necessary to reveal with tissue interposed between adjacent layers permits local certainty the fascial innervations of these deep layers. sliding, allowing the single layers to respond more effect- However, concentrations of Pacinian corpuscles (de- ively.29 tecting deep pressure) and Ruffini’s corpuscles, which Examples of this type of fascia are observed in the responding slowly to sustained pressure and tangential limbs and are observed as fascia lata, crural fascia, bra- forces, are thought to be present in much of separating chial fascia, and antebrachial fascia. While there are pro- fascia, for example, in subcutaneous tissue.28,70,86 Deep prioceptors embedded in this fascia, its role as a sensory sustained pressure may be necessary for manual practi- organ is less significant than that of the linking, or fascicu- tioners to affect this fascial tissue. lar categories. Conclusion IV. Separating Fascia Through this article, we have reviewed advances in fa- Separating fascia is generally loose connective tissue scia research and addressed issues related to terminology and dense irregular fusocellular connective tissue.24 The and classification of fascia. The literature supports defin- reticular Type III collagen fibers and elastic fibers are ing fascia as an innervated, continuous, functional organ the major components of the ECM of separating fascia, of stability and motion that is formed by 3-dimensional with small amounts of collagen Types V, VII.16-17 While collagen matrices. In an effort to organize the nomencla- the reticular fibers provide a supporting framework for ture of fascia, we devised a functional classification sys- the cellular constituents, the elastic fibers form a three- tem which includes four categories of fascia: i) linking, ii) dimensional network to allow separating fascia to re- fascicular, iii) compression, and iv) separating fasciae. spond to stretch and distention.­ 28,37 Separating fascia div- These categories were developed based primarily on ides the body in visible sheets and layers of varying fibers the functional properties of fasciae, with further observa- allowing it to take up forces and friction in all directions. tions from the literature on gross anatomical, histological While its major function is to allow more efficient sliding and biomechanical features, and terms unique to each cat-

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