Re: 근막 조직학 탐구를 통한 '통증치료' 2025

[문형철]

세포 / 구조물모양 (그림 기준)발견 시기주요 기능 및 특징

Fasciacytes	파란색 원형 세포	2018년 (Carla Stecco)	- 히알루론산(HA)을 주로 생산 - 근막 각 섬유성 층 표면에 군집으로 존재 - 층 사이 미끄러운 환경 유지 (“미끄러짐 조절 전문 세포”)
Fibroblasts	검은색 다이아몬드 모양	오래전 (기본 결합조직 세포)	- 결합조직의 가장 흔한 세포 - 콜라겐, 엘라스틴 등 세포외 기질(ECM) 생산·유지·분해 - 기계적 자극(압력, stretch)에 반응해 조직 강도 조절
Myofibroblasts	돌기가 있는 검은색 다이아몬드	-	- 섬유아세포에서 유래 - 평활근처럼 수축 능력 보유 - 근막 긴장(tension) 조절, 상처 치유, 섬유화(fibrosis)에 중요 - 과활성화 시 근막 두꺼워짐·경직 유발
Telocytes	녹색, 길고 가느다란 세포 돌기	2010년경 (fascia 연구 활발 2015~)	- 매우 긴 돌기(telopodes)로 세포 간 네트워크 형성 - 기계수용(mechanosensitive) 능력 - 세포 간 신호 전달, 조직 재생, 간질(interstitial) 커뮤니케이션 관여
Free nerve endings	노란색 물결선	-	- 유리 신경 종말 (캡슐 없음) - 통각(nociception) 주로 감지 - 기계적(압력, stretch), 화학적 자극에 민감 - 후두 신경통에서 말초 감작(peripheral sensitization)의 핵심 요소
Loose connective tissue rich in HA	파란색 얇은 층	-	- 히알루론산(HA)이 풍부한 느슨한 결합조직 - 층간 미끄러짐(gliding) 촉진 - 충격 흡수 및 영양 공급 역할

근막은
단순한 “막”이 아니라
여러 층으로 이루어진 복잡한 결합조직.

그림은
깊은 근막(deep fascia)의 전형적인 층상 구조를 보여주며,
주로 다음과 같은 층으로 구성:

• 섬유성 층(Fibrous layer): 두꺼운 갈색 부분으로, 주로 콜라겐 섬유(collagen fibers)가 빽빽하게 배열되어 강도와 지지력을 제공합니다. 이 층이 여러 개 평행하게 쌓여 있으며, 그 사이에 얇은 느슨한 결합조직(loose connective tissue)이 끼어 있습니다.
• 느슨한 결합조직 층 (파란색으로 표시): 히알루론산(HA, hyaluronic acid)이 풍부하여 조직이 미끄럽게 미끄러짐(gliding)을 가능하게 합니다. 근육 움직임 시 층간 마찰을 줄여주는 윤활제 같은 역할입니다.

주요 세포와 구조물 (범례에 따른 설명)

1. Fasciacytes (파란색 원형 세포)
   • 비교적 최근(2018년경) 발견된 특화된 세포입니다.
   • 히알루론산(HA)을 주로 생산합니다.
   • 근막의 각 섬유성 층 표면에 작은 군집으로 존재하며, 층 사이의 미끄러운 환경을 유지하는 데 핵심적입니다.
   • “미끄러짐 조절 전문 세포”라고 볼 수 있습니다.
2. Fibroblasts (검은색 다이아몬드 모양)
   • 결합조직의 가장 흔한 세포입니다.
   • 콜라겐, 엘라스틴 등 세포외 기질(ECM)을 생산·유지·분해합니다.
   • 기계적 자극(압력, Stretch)에 반응하여 조직의 강도를 조절합니다.
3. Myofibroblasts (돌기가 있는 검은색 다이아몬드)
   • 섬유아세포(fibroblast)에서 유래하지만, 평활근처럼 수축 능력을 가진 세포입니다.
   • 근막의 긴장(tension)을 조절하고, 상처 치유나 섬유화(fibrosis) 과정에서 중요합니다.
   • 과도하게 활성화되면 근막이 두꺼워지거나 경직될 수 있습니다.
4. Telocytes (녹색, 길고 가느다란 세포 돌기)
   • 2016년경 fascia에서 발견된 비교적 새로운 세포입니다.
   • 매우 긴 돌기(telopodes)를 가지고 있어 세포 간 네트워크를 형성합니다.
   • 기계수용(mechanosensitive) 능력이 있으며, 세포 간 신호 전달, 조직 재생, 간질(interstitial) 커뮤니케이션에 관여합니다.
5. Free nerve endings (노란색 물결선)
   • 유리 신경 종말로, 캡슐에 싸여 있지 않은 가장 단순한 신경 말단입니다.
   • 통각(nociception), 즉 통증을 주로 감지합니다.
   • 기계적 자극(압력, stretch), 화학적 자극 등에 민감하며, 후두 신경통에서 중요한 말초 감작(peripheral sensitization)의 주요 요소입니다.
6. Loose connective tissue rich in HA (파란색 얇은 층)
   • 히알루론산이 풍부한 느슨한 결합조직입니다.
   • 층간 미끄러짐을 돕고, 충격 흡수와 영양 공급 역할을 합니다.

https://pmc.ncbi.nlm.nih.gov/articles/PMC12797365/

1. 논문 개요 

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2. 방법론: 어떤 논문들을 모았나?

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3. 주요 결과

①: 각 근막의 두께·구조·HA·신경

3.1 핵심 근막들의 미세 구조 요약 그림

(아래는 논문 Table 2 내용을 기반으로 한 개념도입니다.)

[그림 1. 주요 fascial plane의 두께·구조·신경·임상 block의 관계 개념도]

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4. 주요 개념 그림으로 정리

4.1 PRISMA 흐름과 연구 설계

[그림 2. PRISMA 흐름도 개념 설명]

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이 그림은 이 논문이 현재까지 인체 근막 histology에 대해 가장 종합적인 systematic review임을 보여줍니다.

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4.2 “다층 근막 + loose CT → block 확산” 개념도

[그림 3. Deep fascia의 다층 구조와 국소마취제 확산 모델]

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5. 임상·연구적 의미 (Regional Anesthesia 관점)

5.1 왜 마취과·통증의학에서 이 histology가 중요한가?

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6. 몇 가지 정리

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Summary

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J Anesth Analg Crit Care

. 2025 Dec 5;6:5. doi: 10.1186/s44158-025-00322-2

Histology of the fascial planes: a systematic review of the microstructural foundations of regional anesthesia

Alessandro De Cassai 1,2,✉, Francesco Marrone 3, Yunfeng Sun 4,5, Annalisa Boscolo 1,2,6, Tommaso Pettenuzzo 1,2, Paolo Navalesi 1,2, Carla Stecco 7

• Author information
• Article notes
• Copyright and License information

PMCID: PMC12797365  PMID: 41345736

Abstract

Background

Fascia, once viewed as a passive structural tissue, is now recognized as a biologically active interface integral to musculoskeletal stability, force transmission, proprioception, and nociception. Despite the increasing clinical use of fascial plane blocks, the microanatomy of fasciae relevant to regional anesthesia remains poorly characterized. Understanding their histological features—including innervation, vascularization, and microstructure—is critical to optimizing anesthetic efficacy and elucidating mechanisms of pain and tissue response.

Methods

This systematic review was prospectively registered on the Open Science Framework (reference: yk4ua, 19 September 2025) and reported according to PRISMA guidelines. MEDLINE, Embase, and Cochrane CENTRAL were searched from inception to September 2025 without language or date restrictions. Eligible studies included histological or microanatomical investigations of human fascial planes relevant to regional anesthesia (e.g., pectoral, thoracolumbar, abdominal, and fascia lata). Data were extracted independently by multiple reviewers, and study quality was assessed using the Anatomical Quality Assessment (AQUA) tool. Findings were synthesized qualitatively by anatomical region.

Results

Seventeen studies met inclusion criteria, encompassing fasciae from the thoracic, abdominal, lumbar, and lower limb regions. Fasciae exhibited considerable structural heterogeneity but shared a multi-layered organization of dense and loose connective tissue laminae rich in type I collagen. The fascia lata and thoracolumbar fascia demonstrated highly ordered collagen fiber orientation, multilaminar organization, and dense innervation, whereas thinner fasciae (e.g., pectoral fascia) showed simpler single-layer structures with fewer neural and vascular elements. Hyaluronic acid content ranged from 29 to 35 µg/g, with fasciacytes identified as the principal secretory cells. Nerve fibers—often associated with vessels and collagen bundles—were consistently present across all deep fasciae, with regional variations in density and mechanoreceptor type. Pathological changes, such as thickening, increased vascularization, and inflammatory infiltration, were reported in chronic pain states.

Conclusions

The fascia should be viewed as a dynamic, active tissue network rather than a passive sheath. Methodological limitations—including small sample sizes, regional heterogeneity, and histological artifacts—restrict current understanding. Future multimodal studies integrating histology, imaging, and biomechanics are warranted to clarify how fascial microstructure affects anesthetic diffusion, pain modulation, and postoperative recovery.

Supplementary Information

The online version contains supplementary material available at 10.1186/s44158-025-00322-2.

Keywords: Fascia, Histology, Regional anesthesia, Interfascial plane block, Innervation, Thoracolumbar fascia, Fascia lata, Pain

Introduction

Fascia, long considered a passive, inert supporting structure, has emerged in recent decades as a dynamic, biologically active connective tissue interface central to musculoskeletal integrity, force transmission, sensorimotor integration, and nociception [1]. Its ubiquitous presence throughout the body—from the subcutaneous layers to the deep musculoskeletal compartments and visceral sheaths [2]—and its functional coupling with nerves, vasculature, and extracellular matrix render fascia a tissue of increasing interest in perioperative and pain medicine [3, 4].

Despite this growing interest and the widespread clinical application of fascial plane techniques in recent years—both as anatomical targets for various interfascial blocks and as potential sources of myofascial or postoperative pain—our understanding of their histological structure remains surprisingly limited. Most traditional descriptions are based on macroscopic dissection [5, 6], whereas histological and ultrastructural studies are few, heterogeneous, and often restricted to specific anatomical regions [7, 8].

However, understanding fascia at the histological level is especially relevant in anesthesiology and regional analgesia. All the interfascial blockade techniques aim to deposit local anesthetic into fascial planes. Nevertheless, several key characteristics, such as the efficacy, spread, and duration of analgesia, may depend on the microstructure, permeability, and nerve density of those fasciae. Moreover, surgical manipulation, scarring, or inflammation of fascial tissues may incite remodelling or sensitization, with implications for post-operative pain or chronic pain states. The histologic diversity of different fasciae underscores the need for region-specific studies correlating microscale structure to anesthetic diffusion and nerve block outcomes. In this systematic review, we aim to synthesize current histologic knowledge of fasciae relevant to regional anesthesia practice and highlight gaps relevant to anesthesiology practice.

Methods

This systematic review was prospectively registered on Open Science Framework (reference: yk4ua, first registered on 19 September 2025). The PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines were followed in the preparation of this manuscript [9, 10].

Search strategy

We conducted a systematic search of the medical literature for the identification, screening, and inclusion of relevant studies. The databases MEDLINE, Embase, and Cochrane CENTRAL, all accessed through Ovid, were searched from inception to 19 September 2025, with no restrictions on language or publication year. The search string used to query the Ovid database is shown in Supplementary material 1.

Inclusion/exclusion criteria

Studies were included and excluded according to the following PIOS criteria: (P) human subjects or human cadaveric specimens (I) studies were included if they involved micro-anatomical investigations using dissection and/or histological examination of the following fascial planes–pectoralis fascia, serratus anterior investing fascia, thoracolumbar fascia, abdominal fasciae (transversalis fascia, fascia of the internal oblique muscle, fascia of the transversus abdominis muscle, rectus sheath), fascia iliaca/fascia lata, (O) innervation patterns, microvascular architecture, and histological characteristics encompassing fascial composition, collagen fibers’ orientation, and layer thickness (S) eligible study designs included original anatomical research based on cadaveric dissection and/or histological analysis.

Study selection

All retrieved records were exported and uploaded into the web-based software Rayyan (https://www.rayyan.ai/), a web-based tool for systematic review management. Two reviewers (FM and YS) independently screened titles and abstracts, classifying each study as included, excluded, or undecided. Any discrepancies between reviewers were resolved by consultation with a third investigator (ADC).

Data extraction and retrieval‎

Following identification of eligible studies, three reviewers (FM, YS, and ADC) independently extracted data from each included article using a standardized form. Disagreements were resolved through discussion and reassessment of the original publication. For continuous variables, means and standard deviations (or medians and interquartile ranges when appropriate) were extracted. For categorical variables, absolute counts and percentages were recorded.

Risk of bias assessment

The risk of bias of included anatomical studies was appraised using the Anatomical Quality Assessment (AQUA) tool, adapted where appropriate [11]. The AQUA tool is a structured instrument designed to eval‎uate the methodological quality and risk of bias in anatomical research. It assesses key domains such as study objectives, methodology, reporting transparency, and reproducibility.

Two independent reviewers (YS and FM) assessed the risk of bias, and any disagreements were resolved by consulting a third reviewer (ADC).

Data synthesis

A qualitative synthesis was performed summarizing findings for innervation, vascularization, and histological structure of each fascial plane. When comparable quantitative data were available (e.g., fascial thickness), descriptive statistics were reported. Results were presented in structured tables and summarized narratively according to anatomical region.

Results

Flow of the study with research articles’ retrieval‎ is depicted as PRISMA flowchart in Fig. 1.

Fig. 1.

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PRISMA flowchart

Initial screening identified 1997 studies, and 14 additional studies were checked by reviewing the references of included articles and eval‎uating the articles citing the included articles. Of these, 1152 search results were excluded during the preliminary screening as they were unrelated or duplicates. Of the remaining 58 articles, 41 articles were further excluded according to our inclusion/exclusion criteria, leaving a total of 17 articles included for qualitative synthesis. The list of articles excluded at the full-text review stage, along with the corresponding reasons for exclusion, is provided in the Supplementary material 1 (SDC1).

Study characteristics

The characteristics of the included studies are presented in Table 1, while a summary of the main features of the fasciae investigated is provided in Table 2. In summary, we included 17 research articles from 10 different countries [12–28]. Tissues were harvested from surgical patients in five articles, from cadavers in nine, from both in one study, while in two studies it was not explicitly stated. Most of the studies were at low risk of bias; two had an unclear risk, and four were at high risk of bias (Table 3).

Table 1.

Characteristics of the included studies

AuthorCountryCOIFasciaNAge (year)Gender (M)Sample

Bednar (1995) [12]	Canada	None	TLF	24	NS	NS	Surgical
Fede (2018) [13]	Italy	NS	FL,RS	15	27 to 98	6 (40%)	Surgical
Hirsch (1963) [14]	United States	NS	TLF	NS	NS	NS	NS
Marpalli (2021) [15]	India	None	TLF	20	NS	NS	Embalmed C
Pans (2000) [16]	Belgium	NS	TF	40	56.6 ± 14.5	35 (87.5%)	Surgical, Fresh C
Pirri (2020) [17]	Italy	None	FL	3	60 ± 5	2 (66.7%)	Fresh C
Przybycień (2024) [18]	Poland	None	TLF	4	47 to 96	4 (100%)	Fixed C
Rodrigues (1990) [19]	Brazil	None	TF	20	13 to 81	20 (100%)	Surgical
Stecco (2007) [20]	Italy	NS	P	13	79.9	10 (76.9%)	Fresh C
Stecco (2008) [21]	Italy	None	FL	6	69	4 (66.7%)	Fresh C
Stecco (2009) [22]	Italy	NS	P	6	69	4 (66.7%)	Fresh C
Stecco#2 (2009) [23]	Italy	None	PF, FL	6	48 to 93	4 (66.7%)	Fresh C
Szczesny (2013) [24]	Poland	NS	RS	49	44.8	22(56.4%)	Surgical
Tesarz (2011) [25]	Germany	NS	TLF	3	NS	2 (66.6%)	Surgical
Tesh (1987) [26]	United Kingdom	NS	TLF	NS	NS	NS	NS
Ugwoke (2025) [27]	Slovenia	None	FL, TLF	4	65 to 74	4 (100%)	Fresh C
Yahia (1992) [28]	Canada	NS	TLF	7	30 to 46	6 (85.7%)	Surgical

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C cadaver, FL fascia lata, NS not stated, P pectoralis fascia, RS rectus sheath, TLF thoraco lumbar fascia. Numerical data are presented as reported in the primary sources, either as mean with or without standard deviation, or as a range

Table 2.

Micro-anatomical characteristics of key fascial planes and their potential relevance to regional anesthesia

FasciaRA technique of interestMean thickness and structureMean HA content (µg)Nerve fibers

Fascia lata	Fascia iliaca block	805 to 944 µm with anterior to posterior thickness gradient	35.4 ± 3	+
Pectoral fascia	Interpectoral plane block Pectoserratus plane block	297 µm with cranio-caudal thickness gradient	NI	+
Rectus sheath	Rectus sheath block	densely packed fibrous bundles interspersed with small amounts of adipose tissue	29.1 ± 0.2	NI
Fascia transversalis	Transversalis fascia plane block Quadratus lumborum plane block	thin layer composed by an elastic system comprising three distinct fiber types—oxytalan, elaunin, and elastic fibers	NI	NI
Thoracolumbar fascia	Erector spinae plane block Retrolaminar plane block Quadratus lumborum plane block	Up to 1500 µm. Two-layers with a trilaminar structure with each lamina separated by thin, loose connective tissue rich in type I collagen	NI	±

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RA regional anesthesia, NI no information

+ confirmed in histological studies

± not confirmed in all histological studies

Table 3.

Risk of bias

Author (year)D1D2D3D4D5Overall

Bednar (1995) [12]	Low	Low	Low	Low	Low	Low
Fede (2018) [13]	Low	Low	Low	Low	Low	Low
Hirsch (1963) [14]	High	High	High	High	High	High
Marpalli (2021) [15]	High	Low	Low	Low	Low	High
Pans (2000) [16]	Low	Low	Low	Low	Low	Low
Pirri (2020) [17]	Low	Low	Low	Low	Low	Low
Przybycień (2024) [18]	Unclear	Low	Low	Low	Low	Unclear
Rodrigues (1990) [19]	Low	Low	Low	Low	Low	Low
Stecco (2007) [20]	Low	Low	Low	Low	Low	Low
Stecco (2008) [21]	Low	Low	Low	Low	Low	Low
Stecco (2009) [22]	Low	Low	Low	Low	Low	Low
Stecco#2 (2009) [23]	Low	Low	Low	Low	Low	Low
Szczesny (2013) [24]	Low	Low	Low	Low	Low	Low
Tesarz (2011) [25]	High	Low	Low	Low	Low	High
Tesh (1987) [26]	High	High	High	Low	Low	High
Ugwoke (2025) [27]	Low	Low	Low	Low	Low	Low
Yahia (1992) [28]	Low	Unclear	Low	Low	Low	Unclear

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D1 objectives and subject characteristics, D2 study design, D3 methodology characterization; D4 descriptive anatomy, D5 reporting of results

Fascia lata (FL)

The mean thickness of FL ranges approximately from 805 [27] to 944 µm [23], showing regional variation along the limb. An anterior-to-posterior thickness gradient has been demonstrated, with FL tending to be thinner on the medial surface of the thigh. Measured thicknesses across regions were 556.8 ± 176.2 µm anteriorly, 820.4 ± 201 µm medially, 1112 ± 237.9 µm laterally, and 730.4 ± 186.5 µm posteriorly [27]. The mean hyaluronic acid (HA) content is 35.4 ± 3 μg per gram of tissue [13]. The HA is produced by small clusters of fibroblast-like cells that are positive for the fibroblast marker vimentin, but not for anti-CD68, the fasciacytes [29].

The micro-architecture of the FL exhibits a multi-layered structure, with each layer separated by thin, loose connective tissue rich in type I collagen [17, 27]. In each layer, the fibers are parallel to each other, whereas the orientation of the fibers varies from one layer to the adjacent one [23]. The outer layers (superficial and deep) show characteristics similar to those of the epimysial fascia, while the median layer shows an aponeurotic aspect [21]. The outer layers form a thin lamina characterized by a high density of nerve fibers. The superficial layer comprises fibroblasts, adipocytes, nerve fibers, and blood vessels [27] with a particularly rich presence of neurovascular and elastic components [23]. The deep layer shares a similar composition, consisting of loosely arranged collagen and numerous fibroblasts, but exhibits a lower density of neurovascular and elastic elements [27]. The intermediate layer is composed of several different layers of densely packed collagen fibers regularly aligned but varying from layer to layer [21] with a characteristic crimped pattern and sparse elongated fibroblasts aligned parallel to the fibers; elastic fibers are nearly absent [27]. Numerous vessels, averaging 102 ± 35 μm in diameter, coursed tortuously through the collagen layers of the muscular fascia. Nerve fibers were present in all deep fascia specimens—abundant around vessels and evenly distributed within the fibrous matrix [21]. Larger nerves were encased in loose connective tissue, while smaller fibers attached to collagen bundles, often running perpendicularly and likely responsive to collagen stretch [21, 23].

Pectoral fascia

The pectoral fascia appears as a thin collagen layer (mean thickness of 297 μm) with a thickness that increases in a cranio-caudal direction, demonstrating a mean thickness of 131 μm (± 19 μm) in the subclavicular region, 182 μm (± 84 μm) in the mammary region, and 578 μm (± 42 μm) in the inferior thorax region.

The micro-architecture of the pectoral fascia is composed of a single layer of undulated collagen fibers interspersed with numerous elastic fibers, within which small nerves can be identified. Multiple septa extend from its inner surface, establishing close connections between the fascia and the pectoralis major muscle. The proportion of elastic fibers relative to collagen fibers is estimated to be approximately 15%. S100 staining revealed nerve endings distributed homogeneously throughout the entire pectoral fascia [22, 23]. These correspond to mechanoreceptors—such as Ruffini and Pacinian corpuscles—as well as free nerve endings, the latter predominantly located in proximity to blood vessels [20].

Rectus sheath and fascia transversalis

The rectus sheath is composed of densely packed fibrous bundles interspersed with small amounts of adipose tissue, with a mean HA content of 29.1 ± 0.2 µg per gram of tissue [13].

The fascia transversalis is a thin layer of deep fascia that lies deep to the rectus sheath and runs throughout the abdominal wall. It is composed of an elastic system comprising three distinct fiber types—oxytalan, elaunin, and elastic fibers—arranged in a precise hierarchical sequence among fibrils, fibers, and collagen fiber bundles, respectively [19]. With aging, the proportion of oxytalan fibers decreases, while the amorphous component of the elastic fibers increases [19]. In morbidly obese individuals, fiber density is reduced, the normal architecture is disrupted, and the bundles appear thinner, less regularly arranged, and contain approximately five times less elastin [24].

The hydration percentage is comparable between the fascia transversalis and the rectus sheath; however, the collagen concentration per milligram of dry weight is significantly higher in the rectus sheath. Conversely, the percentages of extractable collagen obtained using NaCl, acetic acid, and pepsin are significantly greater in the fasciae. Qualitatively, fasciae show a decrease in the proportion of β-chains and a trend toward a lower type I/III collagen ratio compared with the rectus sheath [16].

Thoracolumbar fascia (TLF)

The thoracolumbar fascia has been described as a tri-layer or two-layer structure. In the three-layer model, the thoracolumbar fascia has posterior, middle, and anterior layers that enclose the erector spinae and quadratus lumborum muscles, with the anterior layer covering the psoas major. In the two-layer model, the fascia is simplified into superficial and deep parts, excluding the psoas fascia, which is considered a separate structure. In this manuscript, we will refer to the two-layer model.

The posterior layer presents a progressive thickness from thoracic to sacral regions varying from 190 to 450 μm [15], while some studies reported even greater thicknesses, up to 1500 μm [30].

The micro-architecture of the TLF is complex, with specific characteristics for each of the layers. However, each of the two layers has a trilaminar structure, with each lamina separated by thin, loose connective tissue rich in type I collagen [27].

In the superficial layer, the superficial lamina contains fibroblasts, adipocytes, and neurovascular elements, while the deep lamina consists of loosely arranged collagen fibers and abundant fibroblasts, but fewer elastic and vascular components [27].

The intermediate lamina, which has the greatest volume fraction, comprises dense collagen sublayers with different spatial orientations—each separated by a thin layer of loose connective tissue. Fibroblasts and elastic fibers are sparse throughout this region [27]. The number of intermediate laminae varies with spinal level, showing a gradual increase from the cranial to the sacral regions [26].

Nerve endings in the TLF were first identified 50 years ago [14], but a more detailed characterization has been accomplished only recently. Anti-S100 immuno-stain revealed the presence of small nerves in both the borderline between the muscle and the inner surface of the TLF superficial layer, as well as on the medial side of the TLF superficial layer [18]. However, the innervation is not evenly distributed among the two layers of the TLF; the outer lamina of the superficial layer is the most densely innervated, whereas the deep layer, corresponding to the tendon of the latissimus dorsi muscle, is largely devoid of nerve endings [25]. Moreover, the sacral region is more highly innervated than the thoracic regions [15]. Some authors identified two types of mechanoreceptors—Ruffini corpuscles (Type I) and Vater–Pacini corpuscles (Type II)—along with nerve bundles [28]. However, these findings should be interpreted with caution, as several studies have been unable to replicate them [31].

Alterations of the TLF have been reported in patients with chronic back pain and no history of surgery or interventional pain treatments (such as epidural injections). In these patients, the TLF exhibits thickening, microcalcification, infiltration by lymphocytes and plasmacells, together with increased vascularization [12].

Discussion

This systematic review synthesizes current histological evidence on human fasciae relevant to regional anesthesia, highlighting substantial anatomical diversity among fascial planes. Across regions, fascia exhibits a multi-layered architecture, with alternating dense and loose connective tissue laminae containing variable concentrations of collagen, elastic fibers, vessels, and nerve endings. Such heterogeneity likely underpins the differing patterns of anesthetic spread and efficacy observed in interfascial plane blocks (Fig. 2). The fascia lata and thoracolumbar fascia, for instance, display highly organized collagen networks and abundant innervation—features that may influence both mechanical tension and nociceptive sensitivity—whereas thinner fasciae such as the pectoral fascia show simpler collagen organization and fewer layers. All these considerations are crucial for fully understanding the potential effects of fascial blocks in regional anesthesia [32].

Fig. 2.

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Schematic representation of an aponeurotic fascia

The structural complexity of fascia suggests that its role extends far beyond a passive supporting framework. Contemporary fascial research [31] proposes that fascia is a dynamic, continuous tissue network that evolves hierarchically from embryonic development and continuously adapts to mechanical stress. This conceptual shift reframes fascia as an active participant in force transmission, proprioception, and tissue homeostasis—an understanding increasingly relevant to perioperative medicine, where fascial integrity and remodelling may affect postoperative pain and functional recovery [33].

Clinical implications

A growing body of literature supports the notion that the structural characteristics of fascial planes actively influence the effectiveness of regional anesthesia techniques. However, quantitative data directly linking measured fascial thickness or nerve density to predictable changes in block duration remains limited. Consequently, most of the discussion points addressed in this paragraph are based on pragmatic and physiological reasoning rather than evidence from large cohort studies or randomized controlled trials.

Fascial microstructure and the anatomical variability of different fascial layers may exert a substantial influence on the clinical performance of fascial plane blocks. Among the most important features to consider is fascial innervation. The presence of abundant free nerve endings in some fascial layers—but not in others—suggests that certain fasciae may themselves serve as primary targets of local anesthetic, rather than functioning solely as conduits to larger peripheral nerves. This concept is particularly relevant in the context of myofascial pain, where the fascia has been proposed as a true “pain generator” [34] and where direct modulation of fascial nociceptors may contribute substantially to the analgesic effect of fascial plane blocks [35], while variability in fascial innervation and microstructure may partly explain the inconsistent clinical block patterns and dermatomal coverage frequently observed with these techniques [36].

Indeed, emerging evidence suggests that even microanatomical variations in fascial layers—including layer thickness and extracellular-matrix composition—play a critical role in modulating the spread, onset, and duration of local anesthetic in fascial plane blocks [37]. Denser or thicker fascial layers may act as partial barriers to bulk flow, thereby limiting immediate transverse distribution of the injected solution and slowing onset, whereas looser layers facilitate more widespread dispersion [36, 37], while a richness in HA may promote local anesthetic spread. Finally, the pharmacokinetics of FPBs appear to reflect both local diffusion and systemic absorption, with unpredictable contributions from each pathway, further modulated by fascial vascular microstructure; this underlies not only the variable block durations reported in clinical practice but also explains the rapid adsorption and the increased risk of local anesthetic toxicity when compared with peripheral nerve blocks [38–40]. However, despite these mechanistic hypotheses, there remains a lack of quantitative, patient-level data correlating measured fascial thickness or nerve density with clinical outcomes, underlining the need for future imaging–anatomy–pharmacokinetic studies.

Risk of bias

Assessment of the included studies using the AQUA tool highlighted important sources of potential bias. Several studies were rated as high risk due to incomplete reporting of subject characteristics, lack of prospective study registration, or partial description of results, which limits confidence that our review captures all relevant data. Consequently, some observed features may reflect particular subsets of patients rather than generalizable findings. Given the small sample sizes across studies, further stratification or subgroup analysis was not feasible. To mitigate the impact of these biases, we deliberately avoided quantitative synthesis and instead performed a qualitative, narrative synthesis of the retrieved results. This approach allows integration of the available histological evidence while minimizing the risk of overinterpretation of findings derived from methodologically limited studies.

Limitations

Interpretation of histological findings must be tempered by methodological limitations. Classical anatomical dissection traditionally removes fascial layers to reveal muscle, thereby emphasizing myocentric over fascial structures and underestimating fascia’s continuity and mechanical significance. Furthermore, conventional histological processing—particularly fixation, dehydration, and staining—may introduce artifacts such as shrinkage, distortion, and disruption of the delicate collagen-elastin-hyaluronan matrix, potentially obscuring the true in vivo architecture of the deep fascia [41–43]. These technical constraints underscore the need for more advanced imaging and preservation methods, such as confocal microscopy, multiphoton imaging, or cryo-histology, to better capture the living dynamics of fascial tissue. A further limitation of our review is that, while we identified relevant micro-anatomical data for several fascial planes, we were unable to locate histological studies in humans for others. Although some animal studies were available, these were excluded in accordance with our PICOS criteria, as their findings could not be reliably translated to human anatomy. Similarly, given our PICOS, we excluded studies not specifically focusing on histological examination, which means we may have missed relevant information that could have been retrieved from macroscopic dissection or imaging studies. The absence of human histological evidence for certain fasciae may reflect a true lack of distinct anatomical structures; however, it is also possible that relevant studies were missed due to the search strategy employed, including the choice of keywords, databases, and search filters. We also acknowledge that our investigation was not exhaustive for all fasciae of potential relevance to anesthesiologists. While many key fascial planes were examined, others remain uninvestigated and warrant future systematic exploration. Finally, while several studies report associations between fascial thickening, increased vascularization, and inflammatory infiltration in chronic pain states, these findings derive largely from small, heterogeneous samples. The evidence base remains limited by regional variability, small sample sizes, and inconsistent methodological rigor.

Conclusions

The fascia should be viewed as a dynamic, active tissue network rather than a passive sheath. Methodological limitations—including small sample sizes, regional heterogeneity, and histological artifacts—restrict current understanding. Future multimodal studies integrating histology, imaging, and biomechanics are warranted to clarify how fascial microstructure affects anesthetic diffusion, pain modulation, and postoperative recovery.

Supplementary Information

44158_2025_322_MOESM1_ESM.docx (15.2KB, docx)

Supplementary Material 1: The list of articles excluded at the full-text review stage, along with the corresponding reasons for exclusion.

Acknowledgements

None.

Authors’ contributions

ADC conceived the study, coordinated the review process, and drafted the main manuscript text. FM and YS performed the literature search, data extraction, and contributed to manuscript revision. AB and TP contributed to data interpretation and manuscript editing. PN supervised the project and provided critical revisions. CS contributed anatomical expertise and assisted in data interpretation and manuscript review. All authors read and approved the final manuscript.

Funding

None.

Data availability

All the data used to prepare this manuscript are presented in the manuscript and in the supplementary material.

DeclarationsCompeting interests

Alessandro De Cassai serves as an Associate Editor for the Journal of Anesthesia, Analgesia and Critical Care and was invited to submit this manuscript. This role had no influence on the editorial or peer review process. The other authors declare no conflicts of interest

Footnotes

Publisher’s Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

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