Myofascial junction: Emerging insights into the connection between deep/muscular fascia and muscle.

Muscles and fasciae are mutually connected and are influenced by force transmission. However, the anatomical connectivity and histological features of these structures remain unclear. The aim of this study was to assess the evidence for connection between muscles and deep/muscular fasciae. We assessed this relationship in different topographical regions of human cadavers and in mice. The results showed that myofascial junctions (MFJ) were made up of collagen I immune-positive structures occupying an average area of 5.11 ± 0.81 µm2, distributed in discrete regions at the interface between muscle and fascia with an average density of 9.7 ± 2.51 MFJ/mm and an average inclination angle of 35.25 ± 1.52°. These specialized structures also showed collagen III and HA immunopositivity and the presence of elastic fibers. The human myofascial junction can be visualized, opening emerging insights into the connection between deep/muscular fascia and muscle.

Dissociation of N2 on a Si(111)-7x7 Surface at Room Temperature.

We demonstrate that the strong N2 bond can be efficiently dissociated at low pressure and ambient temperature on a Si(111)-7x7 surface. The reaction was experimentally investigated by scanning tunnelling microscopy and X-ray photoemission spectroscopy. Experimental and density functional theory results suggest that relatively low thermal energy collision of N2 with the surface can facilitate electron transfer from the Si(111)-7x7 surface to the π*-antibonding orbitals of N2 that significantly weaken the N2 bond. This activated N2 triple bond dissociation on the surface leads to the formation of a Si3 N interface.

Hearing and Seeing Nerve/Tendon Snapping: A Systematic Review on Dynamic Ultrasound Examination.

Nerve/tendon snapping can occur due to their sudden displacement during the movement of an adjacent joint, and the clinical condition can really be painful. It can actually be challenging to determine the specific anatomic structure causing the snapping in various body regions. In this sense, ultrasound examination, with all its advantages (especially providing dynamic imaging), appears to be quite promising. To date, there are no comprehensive reviews reporting on the use of dynamic ultrasound examination in the diagnosis of nerve/tendon snapping. Accordingly, this article aims to provide a substantial discussion as to how US examination would contribute to 'seeing' and 'hearing' these pathologies' different maneuvers/movements.

What's old is new again: The anatomical studies of Franklin P. Mall and the fascial-interstitial spaces.

Franklin Mall was one of the foremost scientists of the turn of the 19th century, an exemplary mentor as well as researcher, and his revolutionary contributions are still relevant today. Mall's early training in Leipzig with Wilhelm His and Carl Ludwig provided him with an unusual perspective on the integration of anatomy and physiology, and his interest in the links between structure and function guided the work he carried out after joining the faculty of the new Johns Hopkins University School of Medicine. Mall carried out innovative studies on the one hand using dye injection to trace blood and lymphatic supplies to different organs and on the other hand using "putrefaction" to digest tissues and study the organization of the reticular space, demonstrating that it was the underlying source of support for all the organs. These two studies of Mall's, carried out independently, provide the basis for modern studies integrating the understanding of fascia and interstitial spaces.

Blood supply to the superficial fascia of the abdomen: An anatomical study.

The aim of this study was to examine data demonstrating that Scarpa's fascia, a superficial fascia of the anterior abdominal wall, is a vascularized tissue. Specimens of the fascia of seven volunteers undergoing abdominoplasty surgical procedures at the Plastic Surgery Unit of the University of Padova Medical Center were collected. Fractal analysis and quantitative assessment of the vascular network of the fascia was carried out, exploiting the presence of blood in the vessels. Each sample was divided and processed for histological/immunohistochemical analysis (into 5 micron-paraffin embedded sections and cryo-sectioned free-floating samples) as well as for electron microscopy study. A rich vascular pattern forming a fine, dense meshwork with an area percentage of 6.20% ± 2.10% von Willebrand factor stained vessels was noted in all the specimens of the fascia examined; the area percentage of the αSMA-stained vessels was 2.93% ± 1.80%. The diameters of the vessels fell between the 13 and 65 µm range; the network was composed of arteries, veins, capillaries and lymphatic segments. Topological results showed that the vascular network within Scarpa's fascia is well branched (segments: 6615 ± 3070 and 8.40 ± 3.40 per mm2 ; crossing points: 3092 ± 1490 and 3.40 ± 1.90 per mm2 ). Fractal analysis (fractal dimension = 1.063 ± 0.10; lacunarity = 0.60 ± 0.10) revealed that this particular vascular network has an optimal spatial distribution and homogeneity occupying the entire space of the superficial fascia. These findings could undoubtedly be useful to plastic surgeons as well as to pain management specialists.

From Muscle to the Myofascial Unit: Current Evidence and Future Perspectives.

The "motor unit" or the "muscle" has long been considered the quantal element in the control of movement. However, in recent years new research has proved the strong interaction between muscle fibers and intramuscular connective tissue, and between muscles and fasciae, suggesting that the muscles can no longer be considered the only elements that organize movement. In addition, innervation and vascularization of muscle is strongly connected with intramuscular connective tissue. This awareness induced Luigi Stecco, in 2002, to create a new term, the "myofascial unit", to describe the bilateral dependent relationship, both anatomical and functional, that occurs between fascia, muscle and accessory elements. The aim of this narrative review is to understand the scientific support for this new term, and whether it is actually correct to consider the myofascial unit the physiological basic element for peripheral motor control.

Detection of Mast Cells in Human Superficial Fascia.

The recent findings showed that the superficial fascia is a fibrous layer in the middle of hypodermis, richly innervated and vascularized, and more complex than so far demonstrated. This study showed the presence of mast cells in the superficial fascia of the human abdomen wall of three adult volunteer patients (mean age 42 ± 4 years; 2 females, 1 male), by Toluidine Blue and Safranin-O stains and Transmission Electron Microscopy. Mast cells are distributed among the collagen bundles and the elastic fibers, near the vessels and close to the nerves supplying the tissue, with an average density of 20.4 ± 9.4/mm2. The demonstration of the presence of mast cells in the human superficial fascia highlights the possible involvement of the tissue in the inflammatory process, and in tissue healing and regeneration processes. A clear knowledge of this anatomical structure of the hypodermis is fundamental for a good comprehension of some fascial dysfunctions and for a better-targeted clinical practice.

A New Player in the Mechanobiology of Deep Fascia: Yes-Associated Protein (YAP).

Recent studies have demonstrated that fascial fibroblasts are susceptible to mechanical stimuli, leading to the remodeling of the extracellular matrix (ECM). Moreover, the extensive literature on Yes-associated protein (YAP) has shown its role in cell mechanics, linking cell properties, such as shape, adhesion, and size, to the expression of specific genes. The aim of this study was to investigate the presence of YAP in deep fascia and its activation after a mechanical stimulus was induced via a focal extracorporeal shockwave (fESW) treatment. Thoracolumbar fascia (TLF) samples were collected from eight patients (age: 30-70 years; four males and four females) who had undergone spine elective surgical procedures at the Orthopedic Clinic of University of Padova. YAP was measured in both tissue and TLF-derived fibroblasts through immunoblotting. COL1A1 and HABP2 gene expression were also evaluated in fibroblasts 2, 24, and 48 h after the fESW treatment. YAP was expressed in all the examined tissues. The ratio between the active/inactive forms (YAP/p-YAP) of the protein significantly increased in fascial fibroblasts after mechanical stimulation compared to untreated cells (p = 0.0022). Furthermore, COL1A1 and HABP2 gene expression levels were increased upon treatment. These findings demonstrate that YAP is expressed in the deep fascia of the thoracolumbar region, suggesting its involvement in fascial mechanotransduction processes, remodeling, regeneration, and fibrogenesis. This study indicates, for the first time, that YAP is a "new player" in the mechanobiology of deep fascia.

Elastic Fibres in the subcutaneous tissue: Is there a difference between superficial and muscular fascia? A cadaver study.

BACKGROUND: In last years the role of fascia in proprioception and pain has been confirmed in numerous papers, but the real structure of fasciae is not still entirely known. To date, many studies have evaluated the elastic fibres in arteries, ligaments, lungs, epidermis and dermis, but only two studies exist about the elastic fibres in the fasciae, and they did not distinguish between superficial (in the subcutaneous tissue) and deep/muscular fasciae. The aim of the study was to assess the percentage of elastic fibres between superficial and deep fascia. MATERIALS AND METHODS: Three full thickness specimens (proximal, middle and distal respectively) were taken from each of four regions of the thigh of three non-embalmed cadavers: the anterior (Ant), the lateral (Lat), the posterior (Post) and the medial (Med) aspect. Thus, a total of 12 specimens were collected from each analysed thigh and histological Weigert Van Gieson stains was performed. Three sections per specimen were considered for the morphometric analysis. RESULTS: In all the specimens the superficial and deep fasciae were clearly recognizable. The difference in percentage of elastic fibres between superficial and deep fasciae in same region for all four was highly significant (p < 0.001). They are abundant in the superficial fascia than deep fascia. CONCLUSIONS: In the light of these findings is evident that the superficial (in the subcutaneous tissue) and deep fasciae have different elasticity. This difference may improve grading of fascial dysfunction in dermatological diseases as burns, scars and lymphedema to better plan treatments.

Fascial Innervation: A Systematic Review of the Literature.

Currently, myofascial pain has become one of the main problems in healthcare systems. Research into its causes and the structures related to it may help to improve its management. Until some years ago, all the studies were focused on muscle alterations, as trigger points, but recently, fasciae are starting to be considered a new, possible source of pain. This systematic review has been conducted for the purpose of analyze the current evidence of the muscular/deep fasciae innervation from a histological and/or immunohistochemical point of view. A literature search published between 2000 and 2021 was made in PubMed and Google Scholar. Search terms included a combination of fascia, innervation, immunohistochemical, and different immunohistochemical markers. Of the 23 total studies included in the review, five studies were performed in rats, four in mice, two in horses, ten in humans, and two in both humans and rats. There were a great variety of immunohistochemical markers used to detect the innervation of the fasciae; the most used were Protein Gene Marker 9.5 (used in twelve studies), Calcitonin Gene-Related Peptide (ten studies), S100 (ten studies), substance P (seven studies), and tyrosine hydroxylase (six studies). Various areas have been studied, with the thoracolumbar fascia being the most observed. Besides, the papers highlighted diversity in the density and type of innervation in the various fasciae, going from free nerve endings to Pacini and Ruffini corpuscles. Finally, it has been observed that the innervation is increased in the pathological fasciae. From this review, it is evident that fasciae are well innerved, their innervation have a particular distribution and precise localization and is composed especially by proprioceptors and nociceptors, the latter being more numerous in pathological situations. This could contribute to a better comprehension and management of pain.

The Effects of Aging on the Intramuscular Connective Tissue.

The intramuscular connective tissue plays a critical role in maintaining the structural integrity of the muscle and in providing mechanical support. The current study investigates age-related changes that may contribute to passive stiffness and functional impairment of skeletal muscles. Variations in the extracellular matrix in human quadriceps femoris muscles in 10 young men, 12 elderly males and 16 elderly females, and in the hindlimb muscles of 6 week old, 8 month old and 2 year old C57BL/6J male mice, were evaluated. Picrosirius red, Alcian blue and Weigert Van Gieson stainings were performed to evaluate collagen, glycosamynoglycans and elastic fibers. Immunohistochemistry analyses were carried out to assess collagen I, collagen III and hyaluronan. The percentage area of collagen was significantly higher with aging (p < 0.01 in humans, p < 0.001 in mice), mainly due to an increase in collagen I, with no differences in collagen III (p > 0.05). The percentage area of elastic fibers in the perimysium was significantly lower (p < 0.01) in elderly men, together with a significant decrease in hyaluronan content both in humans and in mice. No significant differences were detected according to gender. The accumulation of collagen I and the lower levels of hyaluronan and elastic fibers with aging could cause a stiffening of the muscles and a reduction of their adaptability.

An anatomical comparison of the fasciae of the thigh: A macroscopic, microscopic and ultrasound imaging study.

Although the number of Ultrasound (US) imaging studies investigating the fascial layers are becoming more numerous, the majority tend to use different reference points and terminology to describe their findings. The current work set out to compare macroscopic and microscopic data of specimens of the fascial layers of the thigh with US imaging findings. Specimens of the different fascial layers of various regions of the thigh were collected for macroscopic and histological analyses from three fresh cadavers and compared with in vivo US images of the thighs of 20 healthy volunteers. The specimens showed that the subcutaneous tissue of the thigh is made up of three layers: a superficial adipose layer, a membranous layer/superficial fascia, and a deep adipose layer. The deep fascia is composed of an aponeurotic fascia, which envelops all the thigh muscles and is laterally reinforced by the iliotibial tract and an epimysial fascia, which is specific for each muscle. The morphometric measurements of the thickness of the superficial fascia were different (anterior: 153.2 ± 39.3 µm; medial: 128.4 ± 24.7 µm; lateral: 154 ± 28.9 µm; and posterior: 148.8 ± 33.2 µm) as were those of the deep fascia (anterior: 556.8 ± 176.2 µm; medial: 820.4 ± 201 µm; lateral: 1112 ± 237.9 µm; and posterior: 730.4 ± 186.5 µm). The US scans showed a clear picture of the superficial adipose tissue, the superficial fascia, and the deep adipose tissue, as well as the deep fasciae. The epimysial and aponeurotic fasciae of only some topographic areas could be independently identified. The US imaging findings confirmed that the superficial and deep fascia have different thicknesses, and they showed that the US measurements were always larger with respect to those produced by histological analysis (p < 0.001) probably due to shrinkage during the processing. The posterior region (level 1) of the superficial fascia had, for example, a mean thickness of 0.56 ± 0.12 mm at US, while the histological analysis showed that it was 148.8 ± 33.2 µm. Showing a similar pattern, the thickness of the deep fascia was as follows: 1.64 ± 0.85 mm versus 730.4 ± 186.5 µm. Study results have confirmed that US can be considered a valid, non-invasive instrument to evaluate the fascial layers. In any event, there is a clear need for a set of standardised protocols since the thickness of the fascial layers of different parts of the human body varies and the data obtained using inaccurate reference points are not reproducible or comparable. Given the inconsistent terminology used to describe the fascial system, it would also be important to standardise the terminology used to define its parts. The difficulty in distinguishing between the epimysial and aponeurotic/deep fascia can also impede data interpretation.

Improving Outcomes in Carotid Body Tumors Treatment: The Impact of a Multidisciplinary Team Approach.

BACKGROUND: The purpose of this study was to evaluate how a multidisciplinary approach, including patients and familiar genetic counseling, preoperative succinate-dehydrogenase (SDH) gene mutation analysis, preoperative adjunctive endovascular procedures (PAEPs) and postoperative rehabilitative team may affect the outcomes in patients who underwent surgery for carotid body tumors (CBTs). METHODS: Fifty-seven consecutive CBT resections were performed from January 1995 to December 2019 in a single center institution. Two groups of patients were compared: group A (1995-2003; n = 10) and group B (2004-2019; n = 47), treated before and after the establishment of a multidisciplinary approach to CBTs. Group A and group B were evaluated retrospectively and prospectively for SDH mutations, respectively. PAEPs (external carotid artery stenting, percutaneous transfemoral embolization or direct percutaneous puncture of the tumor with simultaneous embolization) were performed only in patients of group B, when the size of the tumor exceeded the 45 mm. Primary endpoints were blood loss (BL) and cranial nerve injuries. Secondary endpoint was the number of new silent masses (NSMs) discovered after genetic evaluation. RESULTS: SDH mutations were found in 2 patients of group A and in 11 patients of group B. There were no significant differences in mass diameter between the groups. A significant difference regarding the surgical procedure time was observed in the 2 groups, with a higher time in the group A (Group A: 180 ± 77.3; Group B: 138 ± 54.5, P= 0.04). BL was significantly lower in group B (203 ± 69.5 mL vs. 356 ± 102 mL; P = 0.0001), as well as for patients underwent PAEPs vs. those underwent direct surgery (n = 15, 149 ± 53 mL vs. n = 42, 273 ± 88 mL; P = 0.0001). No differences between transient and persistent cranial nerve injuries were observed between the 2 groups. Carotid reconstruction was necessary for 2 patients of group A (n = 2 vs. n = 0; P = 0.02). Unilateral tumor recurrence was detected in 7 patients, with a significantly higher rate (P ≤ 0.002) in patients carrying SDH mutations compared to those without SDH mutation (wild-type). SDH mutations detected in the groups lead to discover 7 NSMs (group A n = 1 vs. group B n = 6; P = 1.00). CONCLUSION: The impact of the multidisciplinary team suggests that surgical resection still remains the gold standard for the treatment of CBTs, but the use of PAEPs in selected cases may reduce surgical procedure time, BL and the need for reconstructive carotid surgery. Genetic counseling and SDH gene analysis allow to diagnose NSMs in asymptomatic patients. Larger studies should be considered to evaluate the effectiveness of postoperative rehabilitative program.

A Closer Look at the Cellular and Molecular Components of the Deep/Muscular Fasciae.

The fascia can be defined as a dynamic highly complex connective tissue network composed of different types of cells embedded in the extracellular matrix and nervous fibers: each component plays a specific role in the fascial system changing and responding to stimuli in different ways. This review intends to discuss the various components of the fascia and their specific roles; this will be carried out in the effort to shed light on the mechanisms by which they affect the entire network and all body systems. A clear understanding of fascial anatomy from a microscopic viewpoint can further elucidate its physiological and pathological characteristics and facilitate the identification of appropriate treatment strategies.

Pilot Study of Sacroiliac Joint Dysfunction Treated with a Single Session of Fascial Manipulation® Method: Clinical Implications for Effective Pain Reduction.

Background and Objectives: Sacroiliac joint dysfunction (SIJD) generally refers to pain in the lower back due to abnormal sacroiliac joint movement, either from hypomobility or hypermobility. It is considered to be the principal cause in up to 40% of low back pain cases. In literature, it emerges that the "fascia", by its anatomical continuity, if altered or densified in different regions of the body with respect to the sacroiliac joint and its surroundings, may have a fundamental role in the genesis of SIJD and low back pain. The purpose of the present study is to evaluate the effectiveness of incorporating a single session of Fascial Manipulation®-Stecco method®, treating the muscular fasciae at distance from the painful region. Materials and Methods: Twenty patients with acute and chronic sacroiliac joint dysfunction (SIJD) were recruited (16 males and 4 females, mean age of 46.6 ± 12.98 years). Patients underwent a predefined assessment protocol, followed by an evaluation of myofascial pain and subsequent manipulation of the fascia at points at least 20 cm away from the posterior inferior iliac spines (PIIS). Each patient underwent three pain evaluations: pre-treatment (t0), post-treatment (t1), and at a 1-month follow-up (t2). For the evaluation in t0, t1 the numerical rating scale (NRS) for the intensity of pain and the algometer for the pain threshold at the PIIS were used; in t2 only the NRS scale. Results: The results obtained by comparing the algometer measurements with the NRS values between t0 and t1 were in both cases statistically significant (p < 0.0001), whereas the comparison between the NRS values at t1 and at t2 was not statistically significant (p > 0.05). Conclusions: A single Fascial Manipulation treatment, even when applied at least 20 cm from the PIIS, can potentially decrease pain around the SIJ. The inclusion of this type of approach in SIJD can allow for improved patient management, better tolerance for other treatments and a more rapid application of pain-free exercise programs.

Role of fasciae around the median nerve in pathogenesis of carpal tunnel syndrome: microscopic and ultrasound study.

This study investigated the connections between the median nerve paraneural sheath and myofascial structures near it, from both macroscopic and microscopic points of view. Four samples of median nerve and surrounding tissues were excised from nine non-embalmed upper limbs for microscopic analysis. Ultrasound images were analysed in 21 healthy subjects and 16 carpal tunnel syndrome patients to evaluate median nerve transversal displacement during finger motion at carpal tunnel and forearm levels. An anatomical continuity between epimysium and paraneural sheath and a reduction of paraneural fat tissue from proximal to distal was found in all samples. Median nerve displacements at both levels were significantly reduced in carpal tunnel syndrome subjects (P < 0.001). It was observed that the median nerve is not an isolated structure but is entirely connected to myofascial structures. Therefore, unbalanced tension of epimysial fasciae can affect the paraneural sheath, limiting nerve displacement, and consequently this must be included in carpal tunnel syndrome pathogenesis.

Sensitivity of the Fasciae to the Endocannabinoid System: Production of Hyaluronan-Rich Vesicles and Potential Peripheral Effects of Cannabinoids in Fascial Tissue.

The demonstrated expression of endocannabinoid receptors in myofascial tissue suggested the role of fascia as a source and modulator of pain. Fibroblasts can modulate the production of the various components of the extracellular matrix, according to type of stimuli: physical, mechanical, hormonal, and pharmacological. In this work, fascial fibroblasts were isolated from small samples of human fascia lata of the thigh, collected from three volunteer patients (two men, one woman) during orthopedic surgery. This text demonstrates for the first time that the agonist of cannabinoid receptor 2, HU-308, can lead to in vitro production of hyaluronan-rich vesicles only 3-4 h after treatment, being rapidly released into the extracellular environment. We demonstrated that these vesicles are rich in hyaluronan after Alcian blue and Toluidine blue stainings, immunocytochemistry, and transmission electron microscopy. In addition, incubation with the antagonist AM630 blocked vesicles production by cells, confirming that release of hyaluronan is a cannabinoid-mediated effect. These results may show how fascial cells respond to the endocannabinoid system by regulating and remodeling the formation of the extracellular matrix. This is a first step in our understanding of how therapeutic applications of cannabinoids to treat pain may also have a peripheral effect, altering the biosynthesis of the extracellular matrix in fasciae and, consequently, remodeling the tissue and its properties.

Effects of Cesarean Section and Vaginal Delivery on Abdominal Muscles and Fasciae.

Background and objectives: Possible disorders after delivery may interfere with the quality of life. The aim of this study was to ascertain whether abdominal muscles and fasciae differ in women depending on whether they experienced transverse cesarean section (CS) or vaginal delivery (VA) in comparison with healthy nulliparous (NU). Materials and methods: The thicknesses of abdominal muscles and fasciae were evaluated by ultrasound in 13 CS, 10 VA, and 13 NU women (we examined rectus abdominis (RA); external oblique (EO); internal oblique (IO); transversus abdominis (TrA); total abdominal muscles (TAM = EO + IO + TrA); inter-rectus distance (IRD); thickness of linea alba (TLA); rectus sheath (RS), which includes anterior fascia of RS and posterior fascia of RS (P-RS); loose connective tissue between sublayers of P-RS (LCT); abdominal perimuscular fasciae (APF), which includes anterior fascia of EO, fasciae between EO, IO, and TrA, and posterior fascia of TrA). Data on pain intensity, duration, and location were collected. Results: Compared with NU women, CS women had wider IRD (p = 0.004), thinner left RA (p = 0.020), thicker right RS (p = 0.035) and APF (left: p = 0.001; right: p = 0.001), and IO dissymmetry (p = 0.009). VA women had thinner RA (left: p = 0.008, right: p = 0.043) and left TAM (p = 0.024), mainly due to left IO (p = 0.027) and RA dissymmetry (p = 0.035). However, CS women had thicker LCT (left: p = 0.036, right: p < 0.001), APF (left: p = 0.014; right: p = 0.007), and right IO (p = 0.028) than VA women. There were significant correlations between pain duration and the affected fasciae/muscles in CS women. Conclusions: CS women showed significant alterations in both abdominal fasciae and muscle thicknesses, whereas VA women showed alterations mainly in muscles. Thinner RA and/or dissymmetric IO, wider IRD, and thicker LCT and APF after CS may cause muscle deficits and alteration of fascial gliding, which may induce scar, abdominal, low back, and/or pelvic pain.

Fascial entrapment neuropathy.

Entrapment neuropathies are debilitating clinical conditions, creating significant morbidity in the upper and lower extremities in terms of pain, sensory abnormalities, and motor weakness, becoming a challenge to diagnose and treat. Because entrapments can have multiple origins, a misinterpretation of anatomy during examination can lead to incorrect diagnosis and treatment. This review addresses understanding of the anatomy of fascia that can play an important role in this syndrome. There is a specific microenvironment around the nerve composed of connective tissues that include deep fascia, intermuscular septa, epineurium, and perineurium. The microenvironmental modifications can be translated into change in mobility with consequence decreasing of the independency of the nerve from the surrounding structures lading to entrapments and "internal stretch lesion." The entrapments reported in this article reinforce the importance of fascia tissue in generating common symptoms that pose more difficult diagnostic challenges and may often be confused with more common clinical conditions. Clin. Anat. 32:883-890, 2019. © 2019 Wiley Periodicals, Inc.

Inter-rater reliability and variability of ultrasound measurements of abdominal muscles and fasciae thickness.

Ultrasound (US) imaging is being increasingly used by Physical and Rehabilitation Medicine (PRM) specialists to measure the thickness of abdominal muscles. The current study set out to assess the inter-rater reliability of US measurements of the thickness of the abdominal muscles/fasciae. Three raters (1 = orthopedic specialist, expert on fasciae; 2 = PRM resident; 3 = PRM specialist) with different levels of US training examined the abdominal muscles and fasciae of a healthy volunteer under supine resting and dynamic conditions following a standard US protocol. The probe was positioned along the right lateral abdominal wall at the height of the 12th rib: (1) above the umbilicus at the linea alba, (2) to the side of and approximately 2 cm from the umbilicus, (3) along the mammillary line, and (4) along the anterior axillary line. Each rater measured 17 anatomical structures six times during two sessions. The relative error of the measurements (intra-rater variability) was slightly higher for the fasciae than for the muscles, and during the dynamic condition than the resting condition. Inter-rater reliability was good under both conditions for the fasciae (Intraclass Correlation Coefficient = ICC = 0.83) and excellent for the muscles (ICC = 0.99). Knowledge of the fascial anatomy of the abdominal wall is essential for accurate ultrasound examinations and for improving reliability. These findings confirm that US imaging is a reliable, non-invasive, cost-effective instrument for evaluating the abdominal muscles/fasciae. Clin. Anat. 32:948-960, 2019. © 2019 Wiley Periodicals, Inc.