The interaction between the vastus medialis and vastus intermedius and its influence on the extensor apparatus of the knee joint

Evacuation safety effects of a lightweight elevator-type evacuation device using carbon material: Focus on plantar pressure and muscle strength

BACKGROUND

Elevator-type evacuation devices have proven to be feasible in high-rise buildings through studies on safety performance and evacuation time. However, there is a lack of research on safety using biosignal analysis in the elderly population.

OBJECTIVE

A carbon material is used in this study to reduce the weight of an evacuation elevator. The impact on the human body is evaluated by conducting a satisfaction survey involving elderly and youth groups and quantitatively analyzing biological signals, including electromyography (EMG) and plantar pressure, during five repeated uses of the proposed device.

METHODS

The study involves 12 healthy adults in their 20s and 20 elderly individuals with no experience in using an evacuation elevator. The EMG and left and right plantar pressures are analyzed to evaluate the physical factors affected by repeated use.

RESULTS

The experiment results showed that the normalization of EMG to maximum voluntary contraction showed a significant decrease with repeated use, especially in the right tibialis anterior muscle. Moreover, plantar pressure shows a significant difference, which decreased with repetition, and the left and right balance gradually tilted to the left.

CONCLUSION

This suggests that with more repeated use, muscle tension decreases owing to adaptation, resulting in lower muscle activity and plantar pressure. Particularly, the tibialis anterior muscle experiences significant muscle activity, indicating increased load, but without any apparent danger. In the future, it will be necessary to evaluate elevators for disabled individuals.

Soft Tissue Lengthening for Flexion Dislocation of Patella

PURPOSE OF REVIEW

Obligatory dislocation of the patella (also known as habitual dislocation) is a rare subset of patellofemoral instability in which the patella dislocates every time the knee is flexed. The problem arises due to contracture of the quadriceps muscles. Soft tissue lengthening procedures such as quadriceps tendon lengthening are the mainstay of treatment, in contrast to medial patellofemoral reconstruction (MPFL-R) for the more common recurrent lateral patellar dislocation. The current review explores the existing literature surrounding the pathophysiology and treatment strategies for this unique cause of knee instability.

RECENT FINDINGS

Flexion dislocation of the knee often presents in children when they begin to walk. It is also termed obligatory or habitual because the patella dislocates laterally with each flexion and extension cycle of the knee. In contrast to other forms of patellar dislocation, the displacement is painless in obligatory dislocation. Likewise, the underlying biomechanical cause of this issue is related to contracture of tissues lateral to the patella rather than disruption of medial soft tissues as seen in recurrent/traumatic dislocation or subluxation of the patella. A number of procedures have been described for management of obligatory dislocation of the patella, with the general consensus that a combination of procedures including release/lengthening of the proximal lateral soft tissues as a critical component for a successful outcome. Soft tissue release/lengthening has been performed for over 50 years to treat obligatory dislocation of the patella. This procedure must be used in combination with other proximal and distal reconstructive with careful intraoperative assessment of knee flexion and patellar tracking for satisfactory outcomes. Further research using standardized outcome measures is needed to identify the optimal step-wise approach in treatment of obligatory patellar dislocation.

Neuromechanical Properties of the Vastus Medialis and Vastus Lateralis in Adolescents With Patellofemoral Pain

Background

An alteration in the force distribution among quadriceps heads is one possible underlying mechanism of patellofemoral pain. However, this hypothesis cannot be directly tested as there are currently no noninvasive experimental techniques to measure individual muscle force or torque in vivo in humans. In this study, the authors considered a combination of biomechanical and muscle activation measures, which enabled us to estimate the mechanical impact of the vastus medialis (VM) and vastus lateralis (VL) on the patella.

Purpose/Hypothesis

The purpose of this study was to determine whether the relative index of torque distribution for the VM and VL differs between adolescents with and without patellofemoral pain. It was hypothesized that, relative to the VL, the VM would contribute less to knee extension torque in adolescents with patellofemoral pain compared with controls.

Study Design

Cross-sectional study; Level of evidence, 3.

Methods

Twenty adolescents with patellofemoral pain and 20 matched control participants were included (38 female; age, 15.3 ± 1.8 years; weight, 58 ± 13 kg; height, 164 ± 8 cm). Muscle volumes and resting moment arms were quantified from magnetic resonance images, and fascicle lengths were obtained from panoramic B-mode ultrasonography. Muscle activation was estimated using surface electromyography during submaximal isometric tasks (wall-squat and seated tasks). Muscle torque was estimated as the product of muscle physiological cross-sectional area (ie, muscle volume/fascicle length), muscle activation (normalized to maximal activation), and moment arm.

Results

Across tasks and force levels, the relative contribution of the VM to the overall medial and lateral vastii torque was 31.0% ± 8.6% for controls and 31.5 ± 7.6% for adolescents with patellofemoral pain (group effect, P > .34).

Conclusion

For the tasks and positions investigated in this study, the authors found no evidence of lower VM torque generation (relative to the VL) in adolescents with patellofemoral pain compared with controls.

Distribution of the tensor of the vastus intermedius

The tensor of the vastus intermedius (TVI) was first described by Grob et al. in 2016. It originates from the anteroinferior greater trochanter and inserts into the upper patella and receives blood and nerves independently of other muscles. It has been overlooked, but since micro-surgery and detailed rehabilitation treatments are being developed, more research on it is warranted. Here we report on the TVI in a Korean cadaveric study. A total of 58 cadavers (41 males and 17 females) were included. Thighs were examined using a standardized dissection protocol. The quadriceps femoris muscle was identified and its components were defined by blunt dissection. A total of 116 lower limbs were dissected. In 40 of them, there was a separately innervated TVI muscle belly between the fasciae of the vastus lateralis (VL) and the vastus intermedius (VI) muscles. TVIs were classed as independent (ID), VI, and VL types according to the relative relationship between the TVI, VL, and VI, and subdivided into two parts: Part 1 was the proximal muscular portion of the TVI attached to the VL or VI, and part 2 was the distal aponeurotic area. TVIs were analyzed in detail via 58 Korean cadavers. We subdivided them on the basis of their location and association with related muscles. A larger study is needed to clarify the function and prevalence of the TVI.

Selective Repair of Motor Branches in the Femoral Nerve by Transferring the Motor Branches of Obturator Nerve: An Anatomical Feasibility Study

BACKGROUND

Anterior branch of the obturator nerve transfer has been proven as an effective method for femoral nerve injuries, but the patient still has difficulty in rising and squatting, up and downstairs. Here, we presented a novel neurotization procedure of selectively repairing 3 motor branches of the femoral nerve by transferring motor branches of the obturator nerve in the thigh level and assessing its anatomical feasibility.

METHODS

Eight adult cadavers (16 thighs) were dissected. The nerve overlap distance between the gracilis branch and the rectus femoris (RF) branch, the adductor longus (AL) branch and the vastus medialis (VM) branch, as well as the adductor magnus (AM) branch and the vastus intermedius (VI) branch were measured. Also, the axon counts of the donor and recipient nerve were evaluated by histological evaluation.

RESULTS

In all specimens, nerve overlap of at least 2.1 cm was observed in all 16 dissected thighs between the donor and recipient nerve branches, and the repair appeared to be without tension. There is no significant difference in the axon counts between gracilis branch (598 ± 83) and the RF branch (709 ± 151). The axon counts of the AL branch (601 ± 93) was about half of axon counts of the VM branch (1423 ± 189), and the axon counts of AM branch (761 ± 110) was also about half of the VI branch (1649 ± 281).

CONCLUSIONS

This novel technique of the combined nerve transfers below the inguinal ligament, specifically the gracilis branch to the RF branch, the AL branch to the VM branch, and the AM branch to the VI branch, is anatomically feasible. It provides a promising alternative in the repair of femoral nerve injuries and an anatomical basis for the clinical application of motor branches of the obturator nerve transfer to repair the motor portion of the injured femoral nerve.

Quadriceps Tendon Lengthening for Obligatory (Habitual) Patellar Dislocation in Flexion

Obligatory patella dislocation in flexion is an uncommon form of patellar instability, where the patella is located in extension and dislocates with every episode of knee flexion. This results in dramatically altered patellofemoral kinematics and can be extremely debilitating due to extensor strength deficits and lack of knee confidence in flexion. Concomitant pathology, which is often seen, includes a tight lateral retinaculum and a shortened extensor mechanism. Lengthening the extensor mechanism is a critical part of successful patellar stabilization, and has not been well-reported. Herein, we present a technique of quadriceps lengthening for the treatment of obligatory patellar dislocation.

Hip and Knee Joint Angles Determine Fatigue Onset during Quadriceps Neuromuscular Electrical Stimulation

Neuromuscular electrical stimulation (NMES) has been used to increase muscle strength and physical function. However, NMES induces rapid fatigue, limiting its application. To date, the effect of quadriceps femoris (QF) muscle length by knee and hip joint manipulation on NMES-induced contraction fatigability is not clear. We aimed to quantify the effects of different muscle lengths on NMES-induced contraction fatigability, fatigue index, and electromyographic (EMG) activity for QF muscle. QF maximum evoked contraction (QMEC) was applied in a 26 min protocol (10 s on; 120 s off; 12 contractions) in 20 healthy participants (24.0 ± 4.6 years old), over 4 sessions on different days to test different conditions. The tested conditions were as follows: supine with knee flexion of 60° (SUP60), seated with knee flexion of 60° (SIT60), supine with knee flexion of 20° (SUP20), and seated with knee flexion of 20° (SIT20). Contraction fatigability (torque decline assessed by maximal voluntary contraction [MVC] and during NMES), fatigue index (percentage reduction in MVC), and EMG activity (root mean square [RMS] and median frequency) of the superficial QF' constituents were assessed. After NMES, all positions except SUP20 had an absolute reduction in MVC (p < .001). Fatigue index was greater in SIT20 than in SIT60 (p < .001) and SUP20 (p = .01). There was significant torque reduction across the 12 QMEC in SUP60 and SIT60, up to 10.5% (p < .001–.005) and 9.49% (p < .001–.033), respectively. There was no torque reduction during NMES in SUP20 and SIT20. Fatigue was accompanied by an increase in RMS (p = .032) and a decrease in median frequency for SUP60 (p < .001). Median frequency increased only in the SUP20 condition (p = .021). We concluded that QF NMES-induced contraction fatigability is greater when the knee is flexed at 60° compared to 20°. In addition, a supine position promotes earlier fatigue for a 60° knee flexion, but it delays fatigue onset for a 20° knee flexion compared to the seated position. These results provide a rationale for lower limb positioning during NMES, which depends on training objectives, e.g., strengthening or task-specific functionality training.

Influence of Patellar Morphology Classified by Wiberg Classification on Knee Joint Function and Patellofemoral Tracking After Total Knee Arthroplasty Without Patellar Resurfacing

BACKGROUND

To evaluate the influence of patellar morphology on knee joint function and patellofemoral tracking in patients with primary osteoarthritis after total knee arthroplasty (TKA) without patellar resurfacing.

METHODS

We performed a retrospective study of 156 patients with primary osteoarthritis who underwent TKA without patellar resurfacing from April 2018 to July 2019. As per Wiberg classification, patients were divided into Wiberg type I (group A, n = 38), II (group B, n = 88), and III (group C, n = 30) groups. The clinical data, postoperative follow-up data, and radiological data between three groups were compared.

RESULTS

There was no statistically significant difference in the HSS score and Feller score between the three groups before surgery and at each follow-up point after surgery (P > .05). At the last follow-up, there were no significant differences in the height and relative thickness of the patella between the three groups (P > .05). However, the incidence of anterior knee pain was significantly higher in group C than in the group B (P < .05). The patellar tilt angle was significantly larger in group C than in the groups A and B (both P < .05). The patellar facet angle was significantly larger in group A than in group B and C, which was also significantly larger in group B than in group C (both P < .05).

CONCLUSION

Patients with three different morphologic types of the patella both exhibited improved knee joint function after TKA, however, patients with Wiberg type Ⅲ patella were more prone to have poor patellofemoral tracking and anterior knee pain after surgery.

Epimuscular myofascial force transmission from biarticular rectus femoris elongation increases shear modulus of monoarticular quadriceps muscles

This study aimed to examine the effect of rectus femoris (RF) elongation with passive hip angle change on the shear moduli of the vastus lateralis (VL) and medialis (VM) to verify whether Epimuscular myofascial force transmission (EMFT) occurs in the human quadriceps. Fourteen healthy men participated in this study. The shear moduli of the RF, VL, and VM were measured in four hip positions: flexion (Flex), extension and abduction (Ext-Abd), extension (Ext), and extension and adduction (Ext-Add). As the behavior of shear moduli may differ depending on the parts of the vasti muscles, we measured the medial and lateral parts of the VL (Medial-VL and Lateral-VL) and VM (Medial-VM and Lateral-VM). The shear moduli at the Ext and Ext-Add positions were higher than at the Flex position in the RF, VL, and VM. The shear moduli during Ext and Ext-Add were higher than at the Ext-Abd in the RF, VL, and Lateral-VM. Moreover, the shear modulus of the Lateral-VM was higher than of the Medial-VM (Flex: 8.5% higher; Ext-Abd: 15.6%; Ext: 30.2%; Ext-Add: 32.6%). The shear moduli of the VL and VM, which are monoarticular muscles of the knee, increased with passive hip extension or adduction with extension, even when the knee angle was kept constant. The results suggest that EMFT occurs in the quadriceps, and EMFT had a great impact in the Lateral-VM, which is anatomically adjacent to the RF, but it had little effect in the Medial-VM, which is further away from the RF.

Sex Differences and Patterns of Muscle Stiffness in the Knee Flexor and Extensor Musculature Through Analysis of Isolated Bellies

ABSTRACT

Martín-San Agustín, R, Benítez-Martínez, JC, Medina-Mirapeix, F, and Casaña-Granell, J. Sex differences and patterns of muscle stiffness in the knee flexor and extensor musculature through analysis of isolated bellies. J Strength Cond Res 35(4): 1044-1049, 2021-Muscle stiffness (MS) is one of the key factors in joint control. The purpose of this study was to determine sex differences in the MS of 5 isolated muscle bellies (biceps femoris [BF], semitendinosus [ST], rectus femoris [RF], vastus medialis [VM], and vastus lateralis [VL]) and in the pattern of differences among their respective MS. Twenty female and 20 male recreational athletes participated. Muscle stiffness was measured by tensiomyography using maximum radial deformation (Dm) as an indirect indicator of MS. Sex differences were observed only in the Dm of RF (mean difference = 2.07 mm, p < 0.05) when values were adjusted by body mass and stature. Males and females showed a similar pattern in the Dm between the muscle bellies: within the hamstrings, ST had a significantly higher Dm than BF in females (3.02 mm) and males (4.28 mm); within the quadriceps, RF also had a significantly higher value than VL and VM in females (6.50 and 7.38 mm, respectively) and males (4.87 and 4.82 mm, respectively). Sex differences in patterns were found between BF and the vastus muscles: the BF of females had a significantly higher Dm than VL (3.78 mm) and VM (4.51 mm), but this was not observed in males. Differences may imply different involvement of the bellies in countering the movements of the lower extremities. Our results can help to direct exercises to improve the MS in certain muscular bellies.

Morphometric analysis of vastus medialis oblique muscle and its influence on anterior knee pain

Healthy knees require full range squatting movements. Vastus medialis (VM) muscle regulates and adjusts the extensor apparatus that influences the patellofemoral function. This work was designed to investigate the anatomy and morphometry of vastus medialis oblique (VMO) muscle by widely used imaging techniques and investigate how VMO muscle participates in anterior knee pain. Ten dissected cadaveric specimens were examined, focusing on fiber orientations, origin, insertions and nerve supply of VMO muscle. Magnetic resonance imaging and ultrasound of VMO muscle were recorded. Anatomical cross-sectional areas of VMO muscle were determined in painless and painful knees and statistically analyzed. In cadaveric specimens, there was distinct separation between VM longus and VMO (change in fiber angle or fibro-fascial plane). VMO inserted directly into the medial proximal margin of the patella, capsule of the knee joint and continuous with the patellar tendon. Separate branch of femoral nerve run along the anteromedial border of the muscle. Anatomical cross-sectional area was significantly decreased in painful knee by -17.2%±11.0% at lower end of shaft of femur, -21.1%±6.0% at upper border of patella, -36.7%±11.0% at mid-patellar level. VMO is distinct muscle within quadriceps femoris group. VMO muscle would track the patella medially and participate in last phase of knee extension. Assessment of the VMO muscle anatomical cross-sectional area by ultrasonography may constitute promising and reliable tool to evaluate patellofemoral pain syndrome staging.

The Effect of Quadriceps Muscle Length on Maximum Neuromuscular Electrical Stimulation Evoked Contraction, Muscle Architecture, and Tendon-Aponeurosis Stiffness

Muscle-tendon unit length plays a crucial role in quadriceps femoris muscle (QF) physiological adaptation, but the influence of hip and knee angles during QF neuromuscular electrical stimulation (NMES) is poorly investigated. We investigated the effect of muscle length on maximum electrically induced contraction (MEIC) and current efficiency. We secondarily assessed the architecture of all QF constituents and their tendon-aponeurosis complex (TAC) displacement to calculate a stiffness index. This study was a randomized, repeated measure, blinded design with a sample of twenty healthy men aged 24.0 ± 4.6. The MEIC was assessed in four different positions: supine with knee flexion of 60° (SUP60); seated with knee flexion of 60° (SIT60); supine with knee flexion of 20° (SUP20), and seated with knee flexion of 20° (SIT20). The current efficiency (MEIC/maximum tolerated current amplitude) was calculated. Ultrasonography of the QF was performed at rest and during NMES to measure pennation angle (θ p ) and fascicle length (L f ), and the TAC stiffness index. MEIC and current efficiency were greater for SUP60 and SIT60 compared to SUP20 and SIT20. The vastus lateralis and medialis showed lower θ p and higher L f at SUP60 and SIT60, while for the rectus femoris, in SUP60 there were lower θ p and higher L f than in all positions. The vastus intermedius had a similar pattern to the other vastii, except for lack of difference in θ p between SIT60 compared to SUP20 and SIT20. The TAC stiffness index was greater for SUP60. We concluded that NMES generate greater torque and current efficiency at 60° of knee flexion, compared to 20°. For these knee angles, lengthening the QF at the hip did not promote significant change. Each QF constituent demonstrated muscle physiology patterns according to hip and/or knee angles, even though a greater L f and lower θ p were predominant in SUP60 and SIT60. QF TAC index stiffened in more elongated positions, which probably contributed to enhanced force transmission and slightly higher torque in SUP60. Our findings may help exercise physiologist better understand the impact of hip and knee angles on designing more rational NMES stimulation strategies.

CLINICAL TRIAL REGISTRATION

www.ClinicalTrials.gov, identifier NCT03822221.

Three-dimensional modelling of human quadriceps femoris forces

Quadriceps intramuscular anatomy is typically described in two dimensions. However, anatomical descriptions indicate fascicles in the quadriceps may have a three-dimensional orientation. The purpose of this investigation was to quantify the maximum force generating capacity of the individual quadriceps' muscles in three dimensions. Muscle architectural parameters were obtained from three cadaver specimens (two female) and input into a geometry-based multiple fascicle muscle force model. Vastus lateralis, vastus medialis, and rectus femoris had partitions which could be defined based on differences in the sense and direction of fascicles between partitions. Vastus lateralis and rectus femoris were bipennate due to partitions sharing an aponeurosis. Vastus lateralis deep and superficial partitions exerted posterior- (maximum: -29 ± 5 N) and anterior-directed (maximum: 58 ± 15 N) forces on their shared distal aponeurosis. Rectus femoris medial and lateral partitions exerted medial- (maximum: -38 ± 17 N) and lateral-directed (maximum: 19 ± 12 N) forces on their shared proximal aponeurosis. All vastus medialis fascicles ran along the proximal-distal axis. However, fascicles arising near the lesser trochanter also ran along the superficial-deep axis, while fascicles arising from the linea aspera ran along the medial-lateral axis. Thus, vastus medialis could be divided into longus and oblique partitions. Due to the large pennation angle, vastus medialis oblique could exert maximum medial-directed (-219 ± 93 N) and proximal-directed (279 ± 168 N) forces at approximately -40° and -70° knee flexion, respectively, indicating dual roles for vastus medialis oblique dependent on knee flexion angle.

Function of the Distal Part of the Vastus Medialis Muscle as a Generator of Knee Extension Twitch Torque

The distal part of the vastus medialis (VM) (VM obliquus: VMO) muscle acts as the medial stabilizer of the patella. However, it has been known to facilitate VMO contraction during training of the quadriceps femoris muscle in knee joint rehabilitation. This study aimed to examine the contribution degree of VMO as a knee joint extension torque generator. Sixteen healthy male volunteers participated in this study. Electrical muscle stimulation (EMS) was performed on VMO at 60° knee angle for 20 min to induce muscle fatigue. Knee extension twitch torques (TT) at 90° and 30° knee angle evoked by femoral nerve stimulation were measured before and after EMS. Although each TT at 90° and 30° knee angle significantly decreased after EMS, the decreased TT rate in both joint angles showed no significant difference. Our results show that VMO might contribute to the generation of the knee joint torque at the same level in the range from flexion to extension. Therefore, it was suggested that the facilitating the neural drive for VMO is important during the quadriceps femoris muscle strengthening exercise.

Triceps, quadriceps or pentaceps femoris? Need for proper muscle definition

INTRODUCTION

Over the last years, the definition of quadriceps femoris (QF) has evolved somewhat and some authors now define a fifth head: the tensor of vastus intermedius (TVI). Descriptions of the different components of QF in textbooks and recent findings remain confusing. Therefore, the aim of this study is to obtain more information on this possible fifth head.

MATERIALS AND METHODS

Twenty lower limbs of 10 embalmed cadavers, six females and four males, were investigated by macro-dissection. The dissection and separation of the different heads were performed with the fingers and a distinction between the different parts of the quadriceps was noted only if it was possible to separate the heads without scalpel to avoid artificial separation of muscle parts.

RESULTS

In 9 lower limbs we found a QF as classically described in textbook. TVI was found in only 7 limbs and in 4 cases we were not able to differentiate VI and VM or VI and VL (triceps femoris as described by Testut). These results, and the diversity of descriptions found in the literature have led us to review the definition of an isolated muscle.

CONCLUSION

In this study, the presence of TVI was not demonstrated in all limbs unlike previously published studies on the subject. Harmonisation of dissection techniques, but also a clear definition of a muscle is required in order to be able to compare studies and draw clear conclusions.

The Vastus Medialis Insertion Is More Proximal and Medial in Patients With Patellar Instability: A Magnetic Resonance Imaging Case-Control Study

Background:

The anatomy and function of the quadriceps muscle play a role in patellofemoral stability. Few studies have evaluated anatomic differences in the vastus medialis between patients with and without patellar instability.

Purpose:

To compare the anatomy of the vastus medialis using magnetic resonance imaging in patients with patellar instability to a control group.

Study Design:

Cross-sectional study; Level of evidence, 3.

Methods:

A group of patients with patellar instability were sex-matched with a control group with anterior cruciate ligament tears, meniscal injuries, or sprains; patients younger than 15 years were excluded. The anatomy of the vastus medialis was examined by the distance between the distal origin of the vastus medialis in the femur and the medial femoral condyle, the distance from the proximal pole of the patella to the most distal insertion of the muscle and its ratio to the length of the articular surface of the patella, and a qualitative description of the insertion position of the muscle fibers (directly in the patella or the medial retinaculum).

Results:

Both groups comprised 78 knees (48 female; 61.5%). The mean age in the control and patellar instability groups was 30.2 ± 7.8 years and 25.6 ± 7.5 years, respectively (P = .001). The distance from the vastus origin to the condyle was 27.52 ± 3.49 mm and 26.59 ± 3.43 mm, respectively (P = .041); the distance from the proximal pole of the patella to the most distal muscle insertion was 17.59 ± 5.54 mm and 15.02 ± 4.18 mm, respectively (P < .001); and the ratio of this distance to the joint surface was 0.586 ± 0.180 and 0.481 ± 0.130, respectively (P < .001). In 75.6% of knees in the patellar instability group, the insertion of the vastus was into the medial retinaculum and not into the patella compared with 52.6% in the control group (P = .003; odds ratio, 2.8).

Conclusion:

The distal insertion of the vastus medialis differed in knees with patellar instability, with a more proximal insertion and less patellar coverage relative to controls, and was more frequently found in the retinaculum instead of directly in the patella.

The Anatomy of the Articularis Genus Muscle and Its Relation to the Extensor Apparatus of the Knee

Background:

The anatomy of the articularis genus muscle has prompted speculation that it elevates the suprapatellar bursa during extension of the knee joint. However, its architectural parameters indicate that this muscle is not capable of generating enough force to fulfill this function. The purpose of the present study was to investigate the anatomy of the articularis genus, with special emphasis on its relationship with the adjacent vastus intermedius and vastus medialis muscles.

Methods:

The articularis genus muscle was investigated in 18 human cadaveric lower limbs with use of macrodissection techniques. All components of the quadriceps muscle group were traced from origin to insertion, and their affiliations were determined. Six limbs were cut transversely in the middle third of the thigh. The modes of origin and insertion of the articularis genus, its nerve supply, and its connections with the vastus intermedius and vastus medialis were studied.

Results:

The muscle bundles of the articularis genus were organized into 3 main layers: superficial, intermediate, and deep. The bundles of the superficial layer and, in 60% of the specimens, the bundles of the intermediate layer originated from both the vastus intermedius and the anterior and anterolateral surfaces of the femur. The bundles of the deep layer and, in 40% of the specimens, the bundles of the intermediate layer arose solely from the anterior surface of the femur. The distal insertion sites included different levels of the suprapatellar bursa and the joint capsule. A number of connections between the articularis genus and the vastus intermedius were found. While the vastus medialis inserted into the whole length of the vastus intermedius aponeurosis, it included muscle fibers of the articularis genus, building an intricate muscle system supplied by nerve branches of the same medial deep division of the femoral nerve.

Conclusions:

The articularis genus, vastus medialis, and vastus intermedius have a complex, interacting architecture, suggesting that the articularis genus most likely does not act as an independent muscle. With support of the vastus intermedius and vastus medialis, the articularis genus might be able to function as a retractor of the suprapatellar bursa. The finding of likely interplay between the articularis genus, vastus intermedius, and vastus medialis is supported by their concurrent innervation.

Clinical Relevance:

The association between the articularis genus, vastus medialis, and vastus intermedius may be more complex than previously believed, and this close anatomical connection could have functional implications for knee surgery. Dysfunction, scarring, or postoperative arthrofibrosis of the sophisticated interactive mechanism needs further investigation.