Surgical and Radiologic Anatomy https://doi.org/10.1007/s00276-022-02954-3 ORIGINAL ARTICLE A newly discovered membrane at the origin of the proximal tendinous complex of the rectus femoris S. Mechó1,2 · I. Iriarte3 · R. Pruna4 · R. Pérez‑Andrés5 · A. Rodríguez‑Baeza6 Received: 27 March 2021 / Accepted: 21 April 2022 © The Author(s) 2022 Abstract Purpose The rectus femoris (RF) forms the anterior portion of the quadriceps muscle group. It has a proximal tendinous complex (PTC) which is constituted by a direct tendon (DT), an indirect tendon (IT), and a variable third head. Direct and indirect tendons finally converge into a common tendon (CT). All the PTC shows a medially sloping in its proximal insertion. We investigated several anatomical specimens and discovered a new component: a membrane connecting the CT with the anterior superior iliac spine. Such membrane constitutes a new origin of the PTC. The aim of this study was to clarify whether this membrane was an anatomical variation of the PTC or a constant structure and to describe its morphology and trajectory. Material and methods We dissected 42 cadaveric lower limbs and examined the architecture of the PTC. We paid special attention to the morphology and interaction patterns between the tendons and the membrane. Results We demonstrated that the membrane is a constant component of the PTC. It has a lateral to medial trajectory and is in relation to the common tendon, the DT, and IT, which present a medial slope. This suggests that the membrane has an stabilizer role for the PTC, acting as a corrector of the inclined vector of the complex. Conclusion The RF injuries are frequent in football. The newly discovered membrane is a constant component of the PTC and its integrity should be included in the algorithm to diagnose injuries. Keywords Rectus femoris · Proximal rectus femoris tendon · Thigh · Anterior superior iliac spine · Membrane Introduction The rectus femoris (RF) forms the most ventral layer of the quadriceps. It is the only one of the four muscles of the * S. Mechó quadriceps complex that crosses two joints. Besides being mechomeca@gmail.com part of the group of flexor muscles of the hip, it also extends 1 the knee joint, and stabilizes the pelvis in the standing posi- Department of Morphological Sciences (Human Anatomy and Embriology Unit), Faculty of Medicine, tion [6, 14–16, 21]. It is a bipennate muscle composed of Universitat Autònoma de Barcelona, Can Domènech Ave, fascicles that are pennated obliquely to the central tendon 08193 Bellaterra (Barcelona), Spain [14]. Its embryological development starts at the 17th stage 2 Department of Radiology, Medical Department (crown-rump length 11–14 mm, 41 days post fertilization) of Futbol Club Barcelona, Hospital of Barcelona-SCIAS, according to O’Rahilly et al. [17]. At this stage, we can iden- Bellaterra (Barcelona), Spain tify mesenchymal condensations of the femur, tibia, fibula, 3 Department of Physical Medicine and Rehabilitation, Ars and premuscle masses. The quadriceps femoris first develops Médica Clinics, Bilbao, Spain as a single mass overlying the anterior aspect of the middle 4 Department of Orthopedics and Sports Medicine, ICATME, of the femur’s shaft. Then, at the 20th stage (20 mm embryo) Barcelona, Spain according to O’Rahilly, all different heads of the quadriceps 5 Department of Radiology, Gemans Trias i Pujol Hospital, femoris are clearly demarcated and attached to the skeletal Badalona, Barcelona, Spain apparatus by distinct tendons [18]. 6 Department of Morphological Sciences (Human Anatomy Proximal origin of RF is made up of two components, and Embriology Unit), Faculty of Medicine, Universitat a direct tendon (DT) and an indirect tendon (IT) or reflex Autònoma de Barcelona, Barcelona, Spain 13 Vol.:(0123456789) Surgical and Radiologic Anatomy Fig. 1  a Anterior overview of a left thigh showing the membrane eral overview of a left thigh showing the proximal tendinous complex (m) that connects the common tendon (CT) to the anterior superior (PTC). The membrane is localized anterior to it iliac spine (ASIS). The membrane is opaque. b Illustration of a lat- (Fig. 1). The IT has been found to develop prior to the DT; with respect to the longitudinal axis of the muscle. It extends indeed, until the sixth fetal month, only the IT can be dis- along the anterior midline of the muscle, forming the central tinguished [22, 23, 26, 27]. A few centimeters from their septum. It later thins out and reach the lower third of the origins (approximately 2 cm from the origin of the DT and thigh, acquiring a linear shape with a long sagittal axis [6, 5.5 cm from the origin of the IT), both tendons converge in 9, 14, 15]. The myoconnective junction (MCJ) of the IT the common tendon (CT), and form the proximal tendinous has a greater craniocaudal extension than the one of the DT complex (PTC), a Y-shaped structure covered by a com- [14]. The IT performs its main function as a hip flexor once mon paratendon [1, 3, 5, 6, 8, 10, 14, 16, 19, 20, 22, 23, 26, flexion has begun. 27]. The DT originates from the anterior inferior iliac spine The RF is the component of the quadriceps that is more (AIIS) and the underlying rough surface, and it is formed of frequently injured in sports [4]. To better understand all the fibers with a longitudinal craniocaudal direction [1, 6–8, 14, structures that can be involved in myoconnective injuries, it 20, 22]. The IT originates from the supraacetabular sulcus is necessary to know in detail the anatomic characteristics and the lateral aspect of the capsule of the hip joint, and of the rectus femoris. In this study, we found a membrane- presents fibers in a transverse direction in the axial plane [1, localized anterior to the PTC (Fig. 1a), connecting it to the 6–8, 14, 20, 22]. anterior superior iliac spine (ASIS) that, to our knowledge, The DT is located more ventrally and presents an incli- has not been previously described. nation that is medial to the longitudinal axis of the muscle Hence, our objective is to introduce the newly-discovered (Fig. 1a). It has a short course with a very proximal myoten- membranous structure, determine if it is a fixed component dinous junction in the thigh. Moreover, its fascicular tendi- of the PTC, and describe its anatomy and relationship with nous structure is distributed along the anterior surface of the the PTC. muscle continuing with the myofascial junction (epimysium, perimysium, and muscle fiber fascicles) [2, 9, 15, 21]. It is mainly involved at the beginning of the hip flexion [3]. The IT has a triangular morphology, follows an anteropos- terior course (Fig. 1b), and usually has a medial inclination 13 Surgical and Radiologic Anatomy Materials and methods of the tensor fasciae latae muscle (TFL) in the quadriceps triangle was identified and the connective tissue anterior to We studied 42 hemipelvis that included the thigh from bod- the RF was dissected, between the S and TFL muscles. Then, ies donated to the Faculty of Medicine of the Universitat the S was distally sectioned and moved away respecting its Autònoma de Barcelona (UAB). The average age of the sub- iliac origin, and below, the membrane or fibrous lamina, jects was 79 years (range 54–98). 35.72% of the subjects which is the target of this study appears. were males and 64.28% females; 50% of the limbs were right We analyzed different morphological aspects of the mem- and 50% were left. brane: wideness, thickness, and distal insertion in the antero- Body donation at the UAB is regulated by an acceptance medial aspect of the CT. The wideness was assessed as the document approved by the Ethics Commission in Animal extension in the anteroposterior plane of the membrane with and Human Experimentation (file CEEAH 2904 of March respect to the anterior margin of the ASIS: we considered a 11, 2015). All hemipelvis were preserved by arterial per- membrane short when its anterior margin was deeper than fusion of modified Cambridge solution (phenol, ethanol, the anterior aspect of the ASIS; and medium or long, when glycerin, and formaldehyde) and maintained at 6–7°C until its anterior margin was at the same level or more anterior their use. than the ASIS (Fig. 2). The thickness was assessed accord- The hemipelvis were dissected and examined using a ing to the opacity of the membrane (opaque or transparent) standardized protocol, by planes from the anterior aspect (Figs. 1a, 2b). Finally, the distal insertion on the anterome- of the proximal thigh. The skin and subcutaneous cellular dial aspect of the CT was evaluated by dividing the CT into tissue were lifted to identify the sartorius muscle (S) and the proximal, middle, and distal thirds (Fig. 3). femoral (Scarpa’s) and quadriceps triangles. The superficial fascia of the S and the vascular and nerve contents of the Data analysis femoral triangle were also removed to expose the iliopsoas muscle (IP). Afterwards, the IP was dissected from the pel- The categorical variables were described as absolute fre- vic brim to its extra-pelvic portion in the proximal thigh, and quencies and percentages. The correlations between mor- the inguinal ligament (IL) was sectioned, keeping its inser- phological categories and demographic variables were tion in the anterosuperior iliac spine undamaged. The origin evaluated using pearson Chi-Square Test. The level of statis- tical significance was set at P < 0.05. The statistical software Fig. 2  a Lateral overview of the PTC of the right rectus femoris mus- margin of the ASIS. Medium and transparent membrane. c Anterior cle (RF). The membrane (arrowhead) shows a deeper anterior margin overview of the PTC of the right RF. The membrane (arrowhead) than the anterior margin of the ASIS. Short and opaque membrane. b shows its anterior margin in a more anterior position than the anterior Lateral overview of the PTC of the left RF. The membrane (arrow- margin of the ASIS. Long and transparent membrane head) shows its anterior margin at the same level than the anterior 13 Surgical and Radiologic Anatomy 13 Surgical and Radiologic Anatomy ◂Fig. 3   a Lateral overview of the PTC of the left RF. The distal mar- of the anterior surface of the CT of the RF to the lower part gin of the membrane (m) is marked by a dash line at the distal por- of the ASIS. It was located deep to the iliac origin of the S tion of the CT. In this case, we found an independent tendon attached to the IT. b Illustration of a lateral overview of the PTC. The distal and the iliac insertion of the IL. The DT had a medial slop- margin of the membrane (m) is marked by a dash line at the distal ing trajectory to reach its origin in the AIIS; therefore, it was portion of the CT. c Lateral overview of the PTC of the left RF. The positioned medially to the membrane. In many cases, the IT distal margin of the membrane (m) is marked by a dash line at the also had a medial sloping trajectory. Hence, the PTC usually middle portion of the CT. The anterior aspect of the direct tendon (DT) is behind the membrane. Indirect tendon (IT). d Illustration of a had a medial slope and the membrane a lateral slope (Fig. 5). lateral overview of the PTC. The distal margin of the membrane (m) The membrane was constantly present in all the samples is marked by a dash line at the middle portion of the CT studied. In 23/42 cases it was wide (medium and long mem- brane), and in 23/42 cases it was slightly thick (opaque). Finally, only in one case presented a canal containing the StatPlus: Mac Pro Version v7 (AnalySoft Inc) was used for muscular origin of the S (Fig. 6). data analysis. In Table 1, we show the distribution of the different mor- phological category according to gender and side. In gen- eral, there was a greater number of wide (medium and long) Results membranes and opaque membranes for both genders. How- ever, in the case of the left side, there were more transparent Underneath the S, a fibrous membrane was clearly identified, membranes (52.4%). In general, the majority of the mem- separating this muscle from the IP (Fig. 4a). The membrane branes show distal insertion in the CT. Finally, there were had an oblique course, from lateral to medial, and a medial no significant differences between gender and side (Table 2). concavity to accommodate the IP (Fig. 4b). It extended from the distal third (40/42 cases) or the middle third (2/42 cases) Fig. 4  a Anterior overview of a left thigh. We can identify the sec- muscle and a longitudinal thickening in the TFL’s fascia. The mem- tioned inguinal ligament (IL) with its insertion in the ASIS. The sar- brane (m) separates the iliopsoas and sartorius muscles. b Anterior torius muscle (S) was sectioned and removed, the lateral part of the overview of the PTC of the left RF. Note the lateral-to-medial-trajec- iliopsoas muscle (IP) was sectioned and reclined medially. There is tory of the membrane (m) and its medial concavity to accommodate an adipose tissue between the RF and the tensor fasciae latae (TFL) the IP removed 13 Surgical and Radiologic Anatomy Fig. 5  Illustration of an anteromedial overview of a left thigh show- ing the PTC. The red arrow represents the medial inclination of the PTC with respect to the longitudinal axis of the RF and the blue arrow represents the lateral trajectory of the membrane (colour figure Fig. 6  Anterior overview of a left thigh showing a splitting mem- online) brane (m) Table 1  Morphological Wideness Thickness Distal insertion characteristics of the membranes according to gender Short Medium Large Transparent Opaque Distal Middle and side. Number of cases in each category (absolute Female 12 (44.5%) 10 (37%) 5 (18.5%) 12 (44.5%) 15 (55.5%) 25 (92.6%) 2 (7.4%) frequencies and percentages) Male 7 (46.7%) 6 (40%) 2 (13.3%) 7 (46.7%) 8 (53.3%) 15 (100%) 0 Left 10 (47.6%) 9 2 (9.5%) 11 (52.4%) 10 (47.6%) 19 (90.5%) 2 (9.5%) (42.9%) Right 9 (42.9%) 7 5 (23.8%) 8 (38.1%) 13 (61.9%) 21 (100%) 0 (33.3%) Discussion lateral-to-medial trajectory, an inverted triangle shape from distal to proximal, and a variable antero-posterior extension. The new membrane that we describe is part of the PTC and In this study, we demonstrated that there are no significant is similar to a membrane that has been cited as an anatomi- differences in the morphological characteristics (thickness, cal variant of the RF by Macalister in 1875 [13, 25–27]. wideness, distal insertion level) of the membrane between However, we demonstrated that it is not a variant since it Table 2  Statistical results of Pearson Chi-Square test between the dif- was detected in all the hemipelvis that we studied. It con- ferent morphological categories, gender and side sists of connective tissue belonging to “the fascial system” according to the Fascia Nomenclature Committee [24]. This Wideness Thickness Distal insertion membrane connects the RF CT to the ASIS, representing Gender p value 0.9 p value 0.8 p value 0.3 an additional origin of the PTC. It is a thin band with a Side p value 0.4 p value 0.3 p value 0.1 13 Surgical and Radiologic Anatomy gender and side. The membrane thinness, its close relation with the intermuscular fatty planes, and its adjacent position to the epimysium of the IP make it difficult to visualize it by ultrasound. However, using high spatial resolution magnetic resonance imaging (MRI), in the axial and coronal views of the hemipelvis, we can visualize the membrane as a very thin hypointense band in all the sequences (anatomical and fluid sensitive sequences) (Fig. 7). Muscle lesions are the most common injuries in athletes and they represent more than 30% of the injuries in soccer players [4, 9]. In female professional players, the incidence of muscle injuries is similar to that in males, and the most affected muscle groups are the same (hamstrings, adductors, RF and soleus). However, one study identified in females a predominance of injuries in the quadriceps group (two times more frequent than in men) over the hamstrings [11]. The RF is the component of the quadriceps that is more frequently injured in sports that require repetitive kicking and sprinting, such as soccer and its different variants around the world [14, 15, 22, 28]. The MCJ of the central septum is the most common site of RF injured in soccer. This MCJ depends on the IT of the PTC [14, 15]. Different studies monitored these lesions in Australian footballers and showed that they are associated with a long time to rehabilitate (especially if proximal) and delayed return-to-play [15]. Therefore, from a clinical point of view, we are interested in studying all the elements of the RF and the relationships between them. We consider the newly discovered membrane as an addi- tional origin of the PTC. Considering the divergence of the DT and the IT, and their medial inclination with respect to the longitudinal axis of the RF, this membrane seems to act as a lateral stabilizer correcting this medial deviation; there- fore, it should be included in the radiological algorithm to monitor the PTC of the RF in the presence of a proximal ten- don injury. Finally, the assessment of the membrane integ- rity could help to decide the type of treatment to follow. In cases where both the direct and indirect tendons are injured, Lempainen demonstrated that athletes highly benefit from reattaching the proximal RF [12]. However, in cases of par- tial injuries, there are different options for the treatment, and it could be important to consider the integrity of the newly discovered membrane within the therapeutic algorithm. The present anatomical study describes a new component of the PTC of the RF. The PTC shows a medial slope and the Fig. 7  a Axial T1 weighted magnetic resonance (MR) image of the left pelvis. We can see the membrane (arrowhead) a thin hypointense membrane has a lateral trajectory to the ASIS; therefore, we band lateral to the iliac muscle (IL) and its relation with the proximal could suspect that it has a stabilizing function for the PTC. portion of the CT. IT; S; TFL; gluteus minimus (Gm); gluteus mag- Future studies could combine these anatomical findings with nus (GM). b Coronal T1 weighted MR image of the left pelvis. We advanced imaging techniques with two major aims: (1) con- can see a thicker hypointense membrane (arrow) lateral to the IL and its distal insertion to the distal portion of the CT. Its heterogeneous firm the possible stabilizing role of the newly discovered signal could be secondary to the presence of fat tissue within the con- PTC membrane; and (2) study the importance to assess the nective tissue. RF; S; TFL; Gm 13 Surgical and Radiologic Anatomy integrity of the membrane to finally choose the most appro- 6. Gyftopoulos S, Rosenberg ZS, Schweitzer ME, Bordalo-Rodri- priate treatment for proximal RF lesions. gues M (2008) Normal anatomy and strains of the deep musculo- tendinous junction of the proximal rectus femoris: mri features. Am J Radiol 190:W182–W186. https://​doi.​org/​10.​2214/​AJR.​07.​ Acknowledgements The authors sincerely thank those who donated 2947 their bodies to science so that anatomical research could be performed. 7. Hapa O, Bedi A, Gursan O, Akar MS, Güvencer M, Havitçioglu Results from such research can potentially increase mankind's overall H, Larson CM (2013) Anatomic Footprint of the Direct Head of knowledge that can then improve patient care. Therefore, these donors the Rectus Femoris Origin: cadaveric study and clinical series and their families deserve our highest gratitude. 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