Surgical anatomy of the anterior musculocapsular complex of the hip: a macroscopic and microscopic anatomical reappraisal

Abstract

This study aimed to delineate the macroscopic and microscopic topography of muscles surrounding the anterior aspect of the hip joint and the underlaying joint capsule. Seven fresh-frozen cadavers were bilaterally dissected as per study protocol. Eleven hip joints were evaluated macroscopically, while three hip joints underwent histological analysis. Additionally, twenty hip bones and femurs were examined for the osseous morphology near the anterior portion of the articulating surfaces. Macroscopically, the rectus femoris muscle contributed to the articular capsule exclusively through its reflected head. The iliocapsularis and iliopsoas muscles were in direct contact with the articular capsule. Although the iliocapsularis muscle was adherent to the capsule throughout its whole course, the iliopsoas muscle was connected to the capsule through the iliopectineal bursa. Microscopically, different spatial thickness of the capsule was observed, with the thicker regions corresponding to the capsular ligaments. Osseous landmarks, relevant to the course of the iliopsoas muscle, included the iliopsoas notch and a groove for the psoas major muscle. Furthermore, split of the anterior inferior iliac spine and the “subspine” were constant findings corresponding to the origin of the direct head of the rectus femoris and the iliocapsularis muscles, and attachment of the medial band of the iliofemoral ligament, respectively. On the head of the femur, the Poirier’s facet (35.0%), the Allen’s fossa (60.0%), and the so-called plaque (50.0%) were observed. Conclusively, we introduce the concept of a four-layered anterior musculocapsular complex of the hip, aiming to aid the orthopaedic surgeon in both hip replacement and preservation procedures.

Introduction

The anterior hip capsule is frequently exposed due to an increased popularity of anterior-based approaches to the hip joint and advancements in hip arthroscopy. Such interests contributed to an expand in the anatomical knowledge of the intra- and pericapsular structures of the hip, facilitating accurate surgical procedures, and explaining both physiological and pathophysiological processes [1-8]. Improved understanding of the functional anatomy showed that the anatomical interactions between the articular capsule of the hip joint, including ligamentous apparatus, and adjacent muscles assure both static and dynamic stability to the hip joint [8, 9]. Therefore, surgical disruption of its natural morphology or its inherent abnormal morphological characteristics, thus, may lead to many pathological scenarios, such as hip instability, femoroacetabular impingement, iliopsoas impingement and tendinitis, or labral tears [5, 10-14].

Individually, the functional mechanisms have been revealed upon gross anatomical dissections, and eventually in biomechanical testings [2, 6, 9, 15]. Nevertheless, many of the existing publications lack complex interpretations as they are focused only on individual structures with little attention to their topographical relationships to surrounding structures and their attachment sites. Furthermore, the bony landmarks of the adjoining soft tissues are often overlooked in the literature, despite their clinical relevance for radiological imaging and intraoperative orientation, as they are easily palpable.

Despite the fair description of the gross anatomy of the anterior portion of the articular capsule of the hip joint and surrounding structures, several gaps and inconsistencies remain, necessitating detailed structural assessment. In particular, the topography of ligaments and above-coursing muscles, as well as their osseous footprints, has been evaluated either separately, has not been described at all, or has not been described in a broad clinical context. Therefore, the purpose of this study is to describe in detail the topographical relationship between the muscles around the anterior aspect of the hip joint and the underlaying joint capsule both macroscopically and microscopically. Furthermore, this study seeks to outline the less-known osseous structures, including soft-tissue origins, insertions or passage footprints, relevant to the articular anatomy to enhance preoperative planning and intraoperative orientation. It was hypothesized that the intimate relationship of these structures would represent surgically relevant landmarks and would further contribute to explanation of both pathological and physiological changes concerning the hip joint.

Materials and Methods

The study was approved by the Ethics Committee for Multi-Centric Clinical Trials of the University Hospital Motol and Second Faculty of Medicine, Charles University in Prague (No. EK-1107/22).

Specimens and dissection technique

A total of fourteen hip joints from seven fresh-frozen cadavers (four females and three males; mean age 68.3±12.9 years) of Central-European origin were utilized in this study. The cadavers were stored at –4°C and were allowed to thaw overnight prior to dissection. All specimens were free of any deformities or surgical incisions around the hip.

The cadavers were placed supine and the hip joints were dissected in accordance with the following standardized protocol. The dissection started with a 15×15 cm square incision, with the superolateral edge over the anterior superior iliac spine, and subsequent removal of the skin. The subcutaneous adipose tissue was removed and the fascia lata was reached. The fascia was longitudinally incised above the interval between the sartorius and tensor fasciae latae muscles, and was bluntly separated from the underlaying muscles. Then, the sartorius muscle was transected close to its origin at the anterior superior iliac spine. Once the rectus femoris muscle was visualized it was observed for any capsular contributions. Subsequently, its conjoint belly was proximally cut, so that the origins on the ilium were preserved. In eleven specimens, the muscles overlaying the hip capsule were individually exposed and further observed, and the joint capsule was evaluated for any connections with the nearby coursing muscles.

Histological analysis

Three specimens out of the fourteen hip joints were used for histological evaluation. In these cases, the anterior portion of the articular capsule was resected en bloc with the surrounding muscles. The collected specimens were stored in 4% formaldehyde and underwent embedding according to routine laboratory protocols. Transverse sections of the samples with a thickness of 4 μm were obtained and stained with H&E. The transverse sections were performed (1) right above the level of the acetabular labrum, (2) at the level of the labrum, and (3) 5 mm below the level of the labrum. Light microscope BX51 (Olympus) with a digital camera DP72 (Olympus) was used for image recording. We utilized the ImageJ v. 2.0.0 software (National Institutes of Health) for processing and analysis of the acquired images which allowed us to compute spatial thickness in histological specimens by calibrating the built-in measuring tools from a known distance in the images.

Analysis of dry bones

Twenty hip bones (twelve right and eight left) and twenty femurs (ten right and ten left) of unknown sex were obtained from the collection of the Department of Anatomy, Second Faculty of Medicine, Charles University, Prague, Czech Republic, to explore the osseous morphology around the anterior aspect of the hip joint. The location of prominences and grooves was examined in respect to the findings in fresh-frozen cadaveric hips.

Results

Soft-tissue anatomy

The rectus femoris muscle did not directly communicate with the anterior aspect of the hip capsule as it was separated by a solid fatty layer. An exception was its reflected head which originated above the superior acetabular margin, from the supraacetabular sulcus, and was slightly blended with the proximal capsular attachment just below the supraacetabular sulcus. The second head of the rectus femoris muscle, the direct head, originated from the superior portion of the anterior inferior iliac spine. Both heads merged at the level of the center of the head of the femur and formed a common belly.

The most laterally located muscle on the anterior aspect of the articular capsule was the constant iliocapsularis muscle (Fig. 1A). It originated from the anterior inferior iliac spine, just below the origin of the direct head of the rectus femoris muscle, with a superomedial extension. The iliocapsularis muscle inserted onto the lesser trochanter of the femur. The most lateral portion of the muscle belly was clearly visible, but the medial two-thirds were hidden under the fibers of the iliacus muscle. After detachment of its insertion, the iliocapsularis muscle was adherent to the capsule through its whole length and after its release it left a visible footprint on the capsule (Fig. 1B).

Fig. 1.

Anterior aspect of the left hip of a 75 year-old male specimen. (A) The iliopsoas and ilicapsularis muscles and underlaying articular capsule are shown. (B) The iliocapsularis muscle is removed and the iliopsoas muscle is transected close to its insertion to reveal the connection of the psoas major muscle with the articular capsule through the iliopectineal bursa (asterisk). The iliacus muscle is retracted medially with no connection with the capsule. (C) The anterior portion of the articular capsule and iliacus muscle are resected to reveal the course of the psoas major muscle. (D) The psoas major muscle is reflected proximally to expose the iliopsoas notch at the acetabular margin. The anterior and medial femoral retinacula of Weitbrecht are shown coursing on the neck of the femur. M, medial; D, distal; L, lateral; P, proximal; IPM, iliopsoas muscle; ICM, iliocapsularis muscle; RFM, rectus femoris muscle; PMM, psoas major muscle; ILM, iliacus muscle; fICM, footprint of the iliocapsularis muscle; ARW, anterior retinaculum of Weitbrecht; IN, iliopsoas notch; MRW, medial retinaculum of Weitbrecht.

The anteromedial portion of the articular capsule occupied the iliopsoas muscle (Fig. 1A). In all cases it was composed of the muscular fibers of the iliacus and the psoas major muscles, which became tendinous approximately in the middle of the head of the femur (Fig. 1C). The iliacus muscle overlaid the superior pubic ramus and a small portion of the acetabular margin. On the other hand, the course of the psoas major muscle was limited to a depression on the acetabular margin, the so-called iliopsoas notch (Fig. 1C, D). None of the observed specimens featured any accessory insertional tendons of the iliopsoas muscle as it solely inserted onto the lesser trochanter of the femur as a common tendon. The iliacus muscle was easily elevated but the psoas major muscle was firmly connected with the capsule. The psoas major muscle was adherent through the iliopectineal bursa proximally but distally it fused directly with the capsule (Fig. 1B).

After excision of the anterior portion of the hip joint capsule, the anterior (present in six limbs; 54.5%) and medial (present constantly; 100%) femoral retinacula (of Weitbrecht) were found coursing in continuity with the neck of the femur (Fig. 1D). While the medial retinaculum neighbored only with the relatively muscle-free capsule, the anterior one laid under a portion of the capsule in a tight contact with the iliopsoas muscle proximally and the iliocapsularis muscle distally (Fig. 1C).

Microscopic anatomy

Microscopically, the iliocapsularis and iliopsoas muscles were isolated from each other by a septum formed of connective tissue, confirming the existence of two separate muscles (Fig. 2A, B). The septum was continuous with the fasciae of both muscles. Between the iliopsoas muscle and the articular capsule was the iliopectineal bursa. The iliopectineal bursa extended throughout the whole portion of the psoas major muscle, and did not laterally exceed the extent of the septum between the iliopsoas and iliocapsularis muscles. Approximately in the middle of the length of the iliopectineal bursa there was a tendinous component of the iliopsoas tendon, surrounded by the muscular fibers, forming the transitional zone of the insertional tendon (Fig. 2C).

Fig. 2.

Transverse H&E-stained histological sections of the articular capsule with surrounding muscles. (A) The iliopectinal bursa is shown posterior to the iliopsoas muscle. The lateral extent of the bursa reaches the level of the septum between the iliopsoas and iliocapsularis muscles. (B) Detailed appearance of the septum between the iliopsoas and iliocapsularis muscles which is continuous with fascia. (C) Transitional zone of the centrally located iliopsoas tendon and muscular belly adjacent to the iliopectineal bursa. P, posterior; M, medial; A, anterior; L, lateral; C, capsule; S, septum; ICM, iliocapsularis muscle; IPB, iliopectineal bursa; IPM, iliopsoas muscle; IPT, iliopsoas tendon; mIPM, muscular fibers of the iliopsoas muscle.

Computational analysis of the articular capsule revealed variable spatial thickness. The thinnest zone of the capsule was located beneath the psoas major muscle (Fig. 3A), while the remaining portion of the capsule was consistently thicker throughout the studied region (Fig. 3B). The thin zone represents a “weak” area which has a triangular shape and is bordered by the medial band of the iliofemoral ligament laterally and pubofemoral ligament medially. Based on the macroscopic and microscopic appearance, the iliofemoral and pubofemoral ligaments are not distinct and well-defined structures, but rather thickenings of the capsule, represented by thickened regions of the articular capsule described above.

Fig. 3.

Transverse H&E-stained histological sections of the articular capsule 5 mm below the acetabular labrum showing regions with different capsular thickness. (A) The thinnest region corresponding to the weak area. (B) Thick region corresponding to the iliofemoral ligament.

Periacetabular osseous anatomy

On the hip bones, several structures that were to some extent present in all cases (100%) are described inherent to the soft-tissue anatomy. The anterior inferior iliac spine was divided by a transverse crest into superior and inferior facets (Fig. 4A). The superior facet corresponds to the origin of the direct head of the rectus femoris muscle. Conversely, the inferior facet represents a partial origin of the iliocapsularis muscle. From the most distal tip of the inferior facet there is a groove extending superomedially, which marks the extension of the origin of the iliocapsularis muscle medial to the direct head of the rectus femoris muscle (Fig. 4B). Just below the anterior inferior iliac spine, a small impression for attachment of a thickened portion of the articular capsule, corresponding to the iliofemoral ligament, was present (Fig. 4A). Posterior to this impression there was the supraacetabular sulcus for the origin of the reflected head of the rectus femoris muscle (Fig. 4C).

Fig. 4.

Constant osseous structures around the anterosuperior aspect of the acetabulum. (A) The anterior inferior iliac spine consists of two facets (superior delineated by black dotted line and inferior by white dotted line) divided by a bony crest. The impression for the iliofemoral ligament is located just below the anterior inferior iliac spine (grey arrow). (B) The groove extending superomedially from the most distal tip of the inferior facet of the anterior inferior iliac spine for the origin of the iliocapsularis muscle (white arrowheads). (C) The supraacetabular sulcus for the origin of the indirect head of the rectus femoris muscle (black arrowheads). I, inferior; L, lateral; M, medial; S, superior; P, posterior; A, anterior.

An osseous groove for the psoas major muscle was located on the anterior portion of the acetabulum (Fig. 5B, C). It was bordered laterally by the anterior inferior iliac spine and the groove for the iliocapsularis muscle, while the medial border represents the iliopubic eminence. This groove terminates in the iliopsoas notch, once the psoas major muscle reaches the acetabular margin (Fig. 5A).

Fig. 5.

Constant osseous structures around the anterosuperior aspect of the acetabulum. (A) The iliopsoas notch at the acetabular margin (black arrowheads). (B, C) The osseous groove for the psoas major muscle, bordered laterally by the anterior inferior iliac spine and the groove for the iliocapsularis muscle, and medially by the iliopubic eminence (white arrowheads). I, inferior; L, lateral; M, medial; S, superior; P, posterior; A, anterior.

Osseous anatomy of the proximal femur

Three variable structures related to the anterior aspect of the head and neck of the femur were identified. In seven cases (35.0%), a lateral extension of the articular surface of the head of the femur, known as the Poirier’s facet, was found (Fig. 6A). In twelve cases (60.0%), there was an area of exposed trabeculae just below the edge the of articular surface of the femoral head (Fig. 6B). This finding represents the Allen’s fossa. Lastly, a rough area bordered by a low bony rim was present in ten cases (50.0%) (Fig. 6C). This structure represents the so-called femoral plaque. In two of the observed cases (10.0%) all three aforementioned structures appeared concomitantly (Fig. 6C).

Fig. 6.

Variable osseous structures on the proximal femur. (A) The Poirier’s facet (dotted line). (B) The Allen’s fossa (arrowhead). (C) Concomitant appearance of the Poirier’s facet (dotted line), femoral plaque (black arrowheads) and Allen’s fossa (white arrowhead). D, distal; L, lateral; M, medial; P, proximal.

Discussion

This study combines anatomical and histological observations of fresh-frozen hips with analysis of the articulating bones of the hip joint. Our findings reveal the close relationship of the rectus femoris, iliopsoas and iliocapsularis muscles with the anterior portion of the articular capsule and intraarticular structures. Such knowledge allows to draw conclusions facilitating the understanding of the functional anatomy of the hip. Due to the intricate relations presented herein we refer to the anterior pericapsular interactions as the “anterior musculocapsular complex (AMCC)” of the hip. The AMCC can be defined in four consecutive layers which are individually discussed below (Fig. 7).

Fig. 7.

Schematic illustration of the anterior musculocapsular complex with distinction of its four layers. RH, reflected head of rectus femoris muscle; DH, direct head of rectus femoris muscle; RFM, rectus femoris muscle; ICM, iliocapsularis muscle; IM, iliacus muscle; IPM, iliopsoas muscle; PMM, psoas major muscle; IPB, iliopectineal bursa; latIFL, lateral band of iliofemoral ligamet; medIFL, medial band of iliofemoral ligament; PFL, pubofemoral ligament; MRW, medial retinaculum of Weitbrecht; ARW, anterior retinaculum of Weitbrecht.

First muscular layer

When approaching the anterior aspect of the hip joint, the rectus femoris muscle covers the AMCC, and, thus, forms an imaginary roof over this topographical site. The rectus femoris muscle contributes partially to the articular capsule via its reflected head, which originates from the supraacetabular sulcus and slightly overlaps with the proximal attachment of the articular capsule. According to previous publications, the rectus femoris muscle may feature a third femoral head that connects with the capsule [16, 17]. The third head was reported to be spanning between the anterior aspect of the greater trochanter of the femur and the distal portion of the reflected head, just proximal to its fusion with the direct head. However, in our observations, we did not encounter such a capsular contribution in any of our cases.

Right underneath the rectus femoris muscle there is a well-developed fat pad that separates the conjoint muscle belly from the anterior aspect of the articular capsule. The extent of the fat pad reaches distally the vastus lateralis and gluteus maximus muscles [18]. It is believed that fibrosis of this fat pad, as a consequence of repetitive traumatization, may cause pain around the hip due to formation of adhesions between the capsule and pericapsular muscles that are in contact with the aforementioned adipose layer [18].

Second muscular layer

The second layer of the AMCC is characterized by two muscles: the iliopsoas and the iliocapsularis muscles. Both muscles were found in a tight contact with the articular capsule. The iliopcapsularis was firmly adherent to the capsule throughout its entire course from the anterior inferior iliac spine and adjacent groove to the lesser trochanter of the femur. The latter one, the iliopsoas muscle was composed of the psoas major and the iliacus muscles. The iliacus muscle laid on the anterior aspect of the capsule but was not connected to it, and could be easily elevated to visualize the underlaying iliocapsularis muscle. On the other hand, the psoas major muscle was adherent to the anterior capsular portion. In contrast to Tsutsumi et al. [19], who reported in their cadaveric study of preserved specimens that the iliopsoas muscle is connected to the anterior capsule via its deep aponeurosis, we found that the psoas major muscle muscle is rather adherent to the anterosuperior part of the capsule through the iliopectineal bursa and becomes fused with capsule distally as it reaches the inferior portion of the capsule. The discrepancy between our findings and those of Tsutsumi et al. [19] might be theoretically caused by the poor visualization of bursae in formalin-fixed specimens. Nowadays, fresh-frozen specimens or cadavers prepared with advanced fixation methods are rather used to visualize bursae, eventually enhanced with injections of dye ink solutions to improve their visibility [20, 21].

The proximal periacetabular course of the psoas major muscle has its unique pathway bordered by osseous landmarks. The psoas major muscle runs within a groove between the anterior inferior iliac spine and the iliopubic eminence, which terminates at the iliopsoas notch. Although the iliopsoas notch is a well-known entity [22], we did not find any information on the groove for the psoas major muscle in the available literature. Furthermore, the term iliopsoas notch is not entirely correct because the notch contains only the psoas major muscle while the iliacus muscle courses more laterally. Therefore, to be strict, the notch should rather be called the psoas major notch.

Topographically, both the iliopsoas and iliocapsularis muscles cross the weak capsular area. This feature likely explains the dynamic stabilizing contribution of the iliopsoas and the iliocapsularis muscles for the head of the femur as both muscles restrain abnormal positioning and migration of the head of the femur during movement by providing a dynamic support. The iliocapsularis muscle was found hypertrophied in individuals with deficient bony coverage of the acetabulum, and hypotrophied with fatty infiltration in cases with sufficient bony anatomy of the acetabulum [23]. These observations confirm its important stabilizing effect on the femoral head in compromised hips. Additionally, Tsutsumi et al. [19] reported a continuity of the iliopsoas muscle and the iliofemoral ligament. Such a finding was interpreted that the iliofemoral ligament is able to transmit muscular power to the hip joint, and even when the ligament becomes loose the muscular contraction force allows maintenance of an adequate tension.

Third capsular layer

The articular capsule features regions with variable spatial thickness. This is explained by the fact that the iliofemoral, pubofemoral and ischiofemoral ligaments are not well-defined structures but are rather thickened parts of the articular capsule with specifically oriented fibers inherent to each ligament as shown in textbooks [1, 8, 19].

Imprecise illustrations of the articular capsule with the ligaments can be found in several literature sources. Many illustrations show the iliofemoral and pubofemoral ligaments as two neighboring structures at the anterior acetabular margin (Fig. 8A) [24]. However, this does not reflect the actual appearance of the ligaments because they are proximally separated by a weak area in the capsule underneath the iliopsoas muscle that contains the iliopectineal bursa. The weak area has a triangular shape with a base copying the contour of the acetabular margin, and distally the iliofemoral and pubofemoral ligaments come into contact to form the apex (Fig. 8B). We suspect that the presence of the weak area may be among the reasons leading to labral tears and iliopsoas impingement [11, 13]. In a combination with a well-developed iliopsoas notch the weak area of the articular capsule is not strong enough to restrain the contact pressure of the iliopsoas muscle. Presence of a pronounced iliopsoas notch decreases the bony support and reduces the size of the iliopubic eminence, which serves as a primary pulley of the iliopsoas muscle [11], and, thus, causes an increased pressure exerted on the acetabular labrum. A repetitive hip motion causes mechanical irritation of the acetabular labrum, transitioned through the weak area at the 3 o’clock position where the labral tears frequently occur [13]. Similarly, we suspect that the weak area may not provide a sufficient protective layer after total hip arthroplasty with capsular reconstruction. Again, in combination with a deep iliopsoas notch, the implanted acetabular cup overhangs the compromised anterior acetabular margin and the iliopsoas tendon is mechanically irritated by the sharp edge of the implant. Repeated hip movements then cause inflammation of the iliopsoas tendon and enlargement of the iliopectineal bursa. To support this theory, there were no significant differences in clinical outcomes between individuals undergoing hip replacement with capsulectomy and with capsular reconstruction, pointing toward the insufficient coverage of the acetabular cup by the weak area [25, 26].

Fig. 8.

Schematic illustrations showing (A) the imprecise appearance and (B) the actual anatomical appearance of the hip capsular ligaments. IFL, iliofemoral ligament; PFL, pubofemoral ligament; WA, weak area.

The iliofemoral ligament attaches proximally to a small depression below the anterior inferior iliac spine. According to Tsutsumi et al. [9] this structure should be called the “subspine”. Unlike other capsular attachments on the anterior aspect of the acetabulum, the part of the capsule with the iliofemoral ligament is loaded with a high mechanical stress due to the stabilizing ligamentous function. In line with the Wolff’s law, mechanical stress stimulates remodeling of the bone to make it resistant to an increased loading [9]. This is probably the underlaying cause of the impression below the anterior inferior iliac spine which can be used for identification of the proximal attachment of the iliofemoral ligament during imaging of bones, in particular during computed tomography examinations.

Fourth intraarticular layer

Within the intraarticular cavity, three synovial folds, referred to as the femoral retinacula of Weitbrecht (RW), can be found [27-29]. On the anteromedial aspect, relevant to the AMCC, there are the anterior and medial RW. The lateral retinaculum is topographically distant to be emphasized in the anterior pericapsular interactions dealt with herein. Their significance is attributed to the blood supply of the femoral head since they contain nutrient arteries [28]. Consistent with other studies, the medial retinaculum was constantly present but the anterior retinaculum was absent in nearly a half of the specimens. This absence might be explained by the hypovascularity and disappearance of the anterior retinaculum during postnatal period as a result of pressure forced by the iliopsoas tendon and iliofemoral ligament on the anterior aspect of the articular capsule [27, 28]. In addition, we suspect that the iliocapsularis muscle might be responsible for the hypovascularity or dissolution during maturity of the anterior retinaculum as well because, due to its course, it pressures against the neck of the femur distal to the iliopsoas muscle. Therefore, the involution of the anterior retinaculum is most likely a result of complex interactions between the second and third layers of the AMCC.

Several anatomical variations of the head and neck of the femur include the Poirier’s facet, the Allen’s fossa, and the femoral plaque, which may be easily mistaken. The Poirier’s facet refers to an extended articular surface of the head of the femur toward the anterior portion of the neck of the femur [29, 30]. Especially, the Poirier’s facet is discussed to be a cam type deformity, leading to a lack of sphericity of the head of the femur. Such cam type deformities may remain asymptomatic but are also known to cause the femoroacetabular impingement. Their development is most likely attributed to interactions between the neck and head of the femur and the capsular components [31]. Besides the above-mentioned capsular thickenings due to the passage of longitudinally oriented ligaments, the articular capsule also contains a circular thickening termed the zona orbicularis which surrounds the narrowest area of the articular cavity and forms a collar on the neck of the femur [32]. Grinding of this zona orbicularis and mechanical stress forced by the muscles from the second layer of the AMCC, together with individual susceptibility, are believed to cause the bony reaction and formation of the Allen’s fossa [31].

Limitations and strengths

We acknowledge some limitations to this study. The nature is a cadaveric study and provides only baselines for clinical implications, therefore, the theories must be verified in clinical or biomechanical studies. The sample size was relatively low to provide quantitative data, so the study is rather a descriptive morphological investigation. Also, the old age of the cadavers must be taken into account. Unlike most of the existing studies on the anatomy of the anterior pericapsular interactions, the present study was conducted on fresh-frozen cadavers which allows for better distinction of connective tissues and is not biased by tissue shrinkage due to the fixation process. Furthermore, this study explored the AMCC from an anatomical and histological point of view, and added the correlations with osseous structures.

In conclusion, this study presents surgical anatomy of the hip joint integrating both macroscopic and microscopic observations of cadaveric hips, and investigations of dry of hip bones and femurs. Due to the complexity of the anterior pericapsular hip anatomy we introduce the concept of a four-layered AMCC. A detailed understanding of the attachment sites and courses of distinct structures, such as the rectus femoris, iliocapsularis, and iliopsoas muscles, and capsular ligaments, likely explains functional anatomical patterns of the hip joint. Furthermore, identification of the osseous landmarks on the acetabulum and proximal femur, including the split anterior inferior iliac spine, subspine, iliopsoas notch, groove for the iliopsoas muscle, Poirier’s facet, Allen’s fossa, and plaque, should improve the interpretation of painful hip syndromes. This compendious investigation refines the contemporary knowledge, facilitates the understanding of the functional anatomy of the hip, and allows for reproducible landmarks to aid the orthopaedic surgeon in both hip replacement and hip preservation procedures.

Funding Statement

Funding This study was supported by the Charles University Grant Agency (GAUK, No. 174523).