Quadriceps Muscle Anatomy

Overview
Rectus FemorisOrigin (Direct head): Anterior inferior iliac spine
Origin (Indirect head): Acetabular ridge
Insertion: Tibial tuberosity via patellar ligament & quadriceps tendon
Action: Extends the knee & flexes the hip
Innervation: Femoral nerve (L2, L3, L4)
Blood supply: Femoral artery
Vastus LateralisOrigin: Greater trochanter, intertrochanteric line, linea aspera, gluteal tuberosity, lateral intermuscular septum
Insertion: Lateral aspect of the patella & tibial tuberosity (via patellar ligament & quadriceps tendon)
Action: Knee extension
Innervation: Femoral nerve (L2, L3, L4)
Blood supply: Femoral artery
Vastus MedialisOrigin: Intertrochanteric line, spiral line (pectineal line), linea aspera, medial supracondylar line, adductor longus muscle, adductor magnus muscle, & medial intermuscular septum
Insertion: Medial border of patella, & tibial tuberosity (via patellar ligament & quadriceps tendon)
Action: Extends the knee
Innervation: Femoral nerve (L2, L3, L4)
Blood supply: Femoral artery
Vastus IntermediusOrigin: Anterior and lateral surface of the femur & lateral intermuscular septum
Insertion: Tibial tuberosity via patellar ligament & quadriceps tendon
Action: Extends the knee
Innervation: Femoral nerve (L2, L3, L4)
Blood supply: Femoral artery

Location & Overview

The quadriceps muscle group is commonly referred to casually as the ‘quads’. This muscle group is comprised of four large muscles located on the front of the thigh, within the thigh’s anterior compartment. A detailed diagram of the compartments of the thigh can be found in the ‘origin and insertions’ section below. The fibers of all four quadriceps muscles converge into a single quadriceps tendon, which attaches to the patella [1] [2]. The quadriceps perform an important role in knee extension and knee stabilisation, allowing for these muscles to play and important role activities such as walking, running, squatting, lunging, and jumping [3] [4]. The quadriceps muscle group is composed of the following four muscles:

quadriceps muscle group

Here we can see all of the quadriceps highlighted in red. The vastus intermedius is deep to the rectus femoris, so it is not visible in this picture.

Rectus Femoris

The rectus femoris muscle is unique within the quadriceps group, as it crosses both the hip and knee joints. It has a central location on the anterior thigh and is responsible for both flexing the hip and extending the knee, due to it being a biarticular muscle [5][6].

Vastus lateralis highlighted in red, seen from a superficial and anterior view

Pictured here is the rectus femoris highlighted in red, seen from an anterior view, amongst the other muscles of the leg.

Rectus femoris from an anterior view

Here we can see the rectus femoris in isolation from an anterior view.

Rectus femoris from a anterolateral view

Here we can see the rectus femoris in isolation from an anterolateral view.

Vastus Lateralis

The vastus lateralis is the largest and most powerful muscle of the quadriceps group, it is located on the lateral side of the thigh. It primarily extends the knee [7] [8]. The vastus lateralis is also a common site for intramuscular injections, due to its large size and accessibility [9] [10].

Vastus lateralis highlighted in red, seen from a superficial and anterior view

Pictured here is the vastus lateralis highlighted in red, seen from an anterior view amongst the other muscles.

Vastus lateralis from an anterior view

Here we can see the vastus lateralis in isolation from an anterior view.

Vastus lateralis from an anterolateral view

Here we can see the vastus lateralis in isolation from an anterolateral view.

Vastus lateralis from a lateral view

Here we can see the vastus lateralis in isolation from a lateral view.

Vastus Medialis

The vastus medialis is found on the medial side of the thigh, it extends the knee, and its oblique fibers contribute to stabilising the patella [11] [12]. The most distal muscle fibers of the vastus medialis are commonly referred to as the vastus medialis oblique (VMO) [13]. There has been some debate over the years amongst academics as to whether the VMO is a separate muscle, with its own innervation, as some anatomical studies had not found it to be distinct [14] [15] [16] [17]. However, the presence of the VMO is generally accepted by anatomists and surgeons [18] [19]. Research has also suggested that the VMO is innervated by a distinct branch of the femoral nerve compared to the rest of the muscle [20].

Vastus medialis muscle highlighted in red from a superficial view

Here we can see the vastus medialis muscle highlighted in red amongst the other muscles of the leg.

Vastus medialis muscle anterior view

Here we can see the vastus medialis muscle from an anterior view.

Vastus medialis muscle anterolateral view

Here we can see the vastus medialis muscle from an anterolateral view.

Vastus medialis muscle posterior view

Here we can see the vastus medialis muscle from a posterior view.

Vastus Intermedius

The vastus intermedius is located deep to the rectus femoris and it is another centrally positioned muscle within the quadriceps group. Its primary function is also knee extension [21] [22]. Some studies have reported individual variation where the vastus intermedius and vastus lateralis muscles are fused together, sometimes presenting as an almost complete fusion of the two muscles [23] [24].

vastus intermedius highlighted in red amongst the other muscles of the thigh

Here we can see the vastus intermedius highlighted in red amongst the other muscles of the thigh. Because the vastus intermedius is a deep muscle, the other quadriceps muscles have been removed from this image to reveal the vastus intermedius.

vastus intermedius anterior view

Here we can see the vastus intermedius from an anterior view.

vastus intermedius anterolateral view

Here we can see the vastus intermedius from an anterolateral view.

vastus intermedius medial view

Here we can see the vastus intermedius from a medial view.

Pathologies & Exercises

Some common pathologies which affect the quadriceps muscle group include: strains, tendinopathy and contusions. Quadriceps strains are usually caused by excessive force or overstretching, which can result in damage to the muscle and its tendons [25] [26]. Furthermore, muscle fatigue has also been suggested to increase risk of strains [27]. Contusions often occur from direct trauma to the muscle, which can cause: pain, bruising, swelling, and a reduction in range of motion [28] [29]. Quadriceps tendinopathy is generally an overuse injury involving inflammation or degeneration of the quadriceps tendon, which can result in pain and decreased muscular function [30] [31].

Exercises targeting the quadriceps muscle group can improve strength, hypertrophy, flexibility, and overall function of the lower limb. Some examples of exercises to strengthen and grow the quadriceps muscle group are: squats, lunges, Bulgarian split squats, leg presses, and leg extensions [32] [33] [34] [35] [36].

In the following sections, we will delve deeper into the origin and insertion, actions, innervation, and blood supply of the quadriceps muscle group.

Origins & Insertions

The four quadriceps muscles, namely the rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius, each have distinct origins and insertions which contribute to the overall function of the muscle group. Outlined below are the major landmarks of the femur followed by the origins and insertions for each of quadriceps muscle.

Image of the bony landmarks of the femur

Here we can see the landmarks of the femur. Seeing these landmarks will be useful for understanding the origins and insertions of the quadriceps.

Image of the compartments and muscles of the thigh and the medial, posterior, and anterior intermuscular septums.

This image shows the thigh muscles, compartments, and intermuscular septa. The image is a cross section view of the thigh at around mid-shaft level of the femur. This diagram will be useful in understanding the origins and insertions of the quadricep muscles listed below.

Image of the quadriceps tendon, patella, and patellar ligament

Here we can see the quadriceps tendon, patella, and patellar ligament. The fibers of all four quadriceps muscles converge into a single quadriceps tendon, which attaches to the patella and the patella ligament.

Rectus Femoris Attachments

The rectus femoris muscle has two muscular heads at its proximal end, resulting in two primary points of origin. The first head is the ‘direct head’ which originates from the anterior aspect of the inferior iliac spine. The inferior iliac spine is a bony prominence located on the lower portion of the iliac bone (part of the pelvic girdle) near the hip joint. The second head is the ‘indirect head’ which originates from the acetabular ridge. The acetabular ridge is an elevated margin found on the inner surface of the acetabulum, a socket that articulates with the head of the femur to form the hip joint. The rectus femoris inserts into the patellar tendon, which in turn connects onto the tibial tuberosity at the proximal end of the tibia (top of shinbone) [37] [38] [39].

Anatomical variations in the origins of the rectus femoris have been reported, though they are relatively rare. In some cases, the muscle may have additional heads or slips originating from the ilium or the capsule of the hip joint [40] [41].

Image of the two heads of origin of the rectus femoris muscle

Here we can see the two heads of origin of the rectus femoris. The direct head (originating at the anterior aspect of the inferior iliac spine) and the indirect head (originating at the acetabular ridge).

Image of the origins of the rectus femoris muscle

Here we can see the origins of the rectus femoris muscle marked in red. The direct head originates at the anterior aspect of the inferior iliac spine and the indirect head originates at the acetabular ridge.

Image of the insertion of the patellar ligament and rectus femoris

Here we can see the insertion of the patellar ligament on the tibial tuberosity marked in blue. The rectus femoris inserts into the patellar ligament via the quadriceps tendon.

Vastus Lateralis Attachments

The vastus lateralis muscle has multiple origin points. It starts from the greater trochanter, a large bony prominence at the proximal and lateral end of the femur. The next origin is the intertrochanteric line, a ridge connecting the greater and lesser trochanters—the two prominences on the proximal end of the femur. Another origin is the lateral aspect of the linea aspera, a ridge on the posterior side of the femur. The muscle also originates from the gluteal tuberosity, a roughened area on the femur’s posterior aspect, and the lateral intermuscular septum of the thigh—a deep fascia fold separating the anterior and posterior compartments of the thigh, dividing the vastus lateralis and biceps femoris muscles. The vastus lateralis inserts at the lateral aspect of the patella through the quadriceps tendon, which connects to the patellar tendon and ultimately inserts onto the tibial tuberosity of the tibia [42] [43] [44].

Image of the anterior origins of the vastus lateralis highlighted in red

Here we can see the anterior origins of the vastus lateralis, highlighted in red, on the anterior side of the femur (greater trochanter and intertrochanteric line).

Image of the posterior origins of the vastus lateralis highlighted in red

Here we can see the posterior origins of the vastus lateralis, highlighted in red, on the posterior side of the femur (lateral aspect of the linea aspera, gluteal tuberosity, and lateral intermuscular septum).

Image of the patella insertion of the vastus lateralis

Here we can see an insertion of the vastus lateralis, highlighted in blue, on lateral side of the patellar.

Image of the patellar tendon insertion

Here we can see the insertion of the patellar tendon at the tibial tuberosity. The vastus lateralis inserts into the quadriceps tendon which then connects to the patella and the patellar tendon.

Vastus Medialis Attachments

The vastus medialis muscle has several origin points. The first origin is the inferior part of the intertrochanteric line, which is the lower portion of a ridge connecting the greater and lesser trochanters on the femur. Another origin is the spiral line (pectineal line), a curved ridge on the medial side of the femur that wraps around from the intertrochanteric line. The next origin is the medial lip of the linea aspera, which is the inner edge of the ridge running along the posterior aspect of the femur. A further origin point is the proximal part of the medial supracondylar line, a ridge on the medial side of the femur located above the medial condyle. Additionally, the medial intermuscular septum serves as another point of origin for this muscle. The medial intermuscular septum is a deep fascia layer in the thigh that separates the medial and posterior muscle compartments, extending from the medial aspect of the linea aspera on the femur down to the medial aspect of the tibia. The final points of origin are on the adductor longus and adductor magnus muscles, both these muscles are part of the adductor group of muscles, located in the medial compartment of the thigh. The vastus medialis then inserts at the medial border of the patella through the quadriceps tendon. The quadriceps tendon also connects to the tibial tuberosity on the proximal tibia via the patellar ligament [45] [46] [47].

Image of the vastus medialis anterior origins

Highlighted in red we can see the vastus medialis’ anterior origin points (inferior part of the intertrochanteric line and also the spiral line, which is known as the pectineal line).

Image of the vastus medialis posterior origins

Highlighted in red we can see the vastus medialis’ posterior origin points (medial lip of the linea aspera and the proximal part of the medial supracondylar line).

Image of the vastus medialis insertion on the medial side of the patella

Highlighted in blue here we can see an insertion point of the vastus medialis, on the medial side of the patella.

Image of the insertion of the patellar tendon

Highlighted in blue, we can see the insertion of the patellar ligament. The vastus medialis inserts into the quadriceps tendon which then connects to the patella and the patellar ligament.

Vastus Intermedius Attachments

The vastus intermedius muscle originates from the anterior and lateral surfaces of the femur (the front and outer sides of the thigh bone). It it also originates from the lateral intermuscular septum, a deep fascia fold separating the anterior and posterior compartments of the thigh [48]. The vastus intermedius then inserts into the quadriceps tendon, alongside the other quadriceps muscles. The quadriceps tendon connects to the patellar ligament, which inserts onto the tibial tuberosity located on the proximal tibia [49] [50] [51].

Image of the origin of the vastus intermedius

Here we can see the origin of the vastus intermedius on the anterior and lateral surface of the femur.

Image of the insertion of the patellar tendon and vastus intermedius

Here we can see the insertion of the patellar tendon on the tibial tuberosity. The vastus intermedius fibres connect into the quadriceps tendon which then connects to the patella and the patellar ligament.

Actions

Collectively the quadriceps muscle group is responsible for actions at the hip and knee joints. Together, these muscles primarily function in knee extension and hip flexion. Each muscle within the quadriceps group contributes to these actions in a unique manner [52]. The quadriceps’ collective actions are essential for activities such as: walking, running, climbing stairs, and standing up from a seated position.

Collectively, the quadriceps muscle group function as an antagonist to the hamstring muscles at both the hip and knee joints. The hamstrings are primarily responsible for hip extension and knee flexion, so their actions oppose those of the quadriceps [53] [54].

Image of a person demonstrating the movement of knee extension.

In this image, you can see an example of knee extension, which is the action of straightening out your leg at the knee. The opposite movement of knee flexion is knee extension. The quadriceps are involved in knee extension.

Image of a person demonstrating the movement of hip flexion.

In this image, you can see an example of hip flexion, which is the action of raising your leg up in front of you and causing your hip to bend. If both legs are fixed, the torso will lean forward towards the legs. The opposite movement of hip flexion is hip extension. Only the rectus femoris is able to perform hip flexion.

Rectus Femoris Actions

As the only biarticular muscle in the quadriceps group, the rectus femoris is involved in both hip flexion and knee extension. Biarticular means that it crosses two joints. The rectus femoris is the only quadricep muscle involved in hip flexion because it is the only quadricep muscle that crosses the hip joint [55] [56] [57].

Vastus Lateralis Actions

The vastus lateralis primarily contributes to knee extension [58] [59]. It also plays an important role in stabilising the knee joint, working together with the vastus medialis to maintain proper tracking of the patella and prevent excessive sideways movement [60].

Vastus Medialis Actions

The vastus medialis primarily functions in knee extension [61] [62]. It is mainly active during the terminal range of extension (the end ranges of knee extension) [63]. However, “EMG studies have shown that all components of the quadriceps act in conjunction and that none of the components are predominantly responsible for fully extending the knee” [64]. The lower portion of this muscle, known as the vastus medialis oblique (VMO), helps stabilise the patella during knee extension and prevents patellar tracking issues [65] [66]. Although the vastus medialis does not cross the hip joint itself, it connects to the adductor longus and adductor magnus, which do cross the hip joint. However, the vastus medialis’ contribution to adduction is negligible compared to these direct hip adductors, and it is not a main action of the muscle. The vastus medialis likely plays more of a stabilising role during adduction, rather than directly contributing to the movement [67] [68].

Vastus Intermedius Actions

The vastus intermedius is located beneath the rectus femoris and contributes primarily to knee extension [69]. In addition to knee extension, the vastus intermedius is also involved with maintaining knee stability [70]. As one of the deeper quadricep muscles, the vastus intermedius provides support to the patella and helps distribute force across the knee joint. It has been suggested by Grob et al. (2018) that “substantial parts of the vastus intermedius directly contribute to the medial pull on the patella and help to maintain medial tracking of the patella during knee extension” [71].

Innervation

The quadriceps muscle group is innervated by the femoral nerve, which is a major branch of the lumbar plexus [72] [73]. The femoral nerve originates from the ventral rami of the spinal nerves L2, L3, and L4. The femoral nerve is one of the main nerves which supplies motor and sensory innervation to the muscles of the anterior compartment of the thigh, including the quadriceps muscles [74] [75]. Research has suggested that the VMO part of the vastus medialis is innervated by a distinct branch of the femoral nerve compared to the rest of the muscle [76].

Image of the quadriceps muscle innervation the femoral nerve

Here we can see the innervation of the quadriceps muscle group, the femoral nerve, which is a major branch of the lumbar plexus. The femoral nerve originates from the spinal nerve roots of L2, L3, and L4.

Femoral nerve highlighted in red

Here we can see the femoral nerve highlighted in red. The femoral nerve innervates the quadriceps muscle group. The femoral nerve originates from the spinal nerve roots of L2, L3, and L4.

Blood Supply

The quadriceps muscle group receives its blood supply from branches of the femoral artery, which is the main arterial supply to the thigh. The femoral artery is a continuation of the external iliac artery, and it enters the thigh deep to the inguinal ligament [77].

Rectus Femoris

The blood supply to the rectus femoris is provided by the lateral circumflex femoral artery, a branch of the femoral artery [78] [79].

Vastus Lateralis

The vastus lateralis is supplied by the lateral circumflex femoral artery and its branches, particularly the descending branch [80] [81].

Vastus Medialis

The blood supply to the vastus medialis is derived from the medial circumflex femoral artery and its branches, which is another branch of the femoral artery [82] [83].

Vastus Intermedius

The vastus intermedius receives its blood supply from perforating branches of the femoral artery, particularly the first and second perforating arteries [84] [85].

Image of the arteries of the lower limb

This image shows the arteries of the lower limb. You can see the femoral artery located in the thigh region, labelled on the right leg.

Want some flashcards to help you remember this information? Then click the link below:
Rectus Femoris Flashcards
Vastus Lateralis Flashcards
Vastus Medialis Flashcards
Vastus Intermedius Flashcards

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References

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