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The knee is a complex joint that allows the leg to bend and straighten, enabling us to walk, run, jump, and more. The knee joint is surrounded by several muscle groups, including the quadriceps, hamstrings, and gastrocs, which work together to provide stability and facilitate movement. The knee also contains important ligaments, cartilage, tendons, and nerves, all of which contribute to its function and help us perform daily activities.
| Characteristics | Values |
|---|---|
| Muscles surrounding the knee | Quadriceps, Hamstrings, Gastrocnemius, Soleus, Popliteus, Plantaris, Articularis Genu, Semitendinosus, Semimembranosus, Biceps Femoris, Vastus Lateralis, Vastus Intermedius, Vastus Medialis, Rectus Femoris, Adductor Magnus, Gracilis |
| Function | Move and stabilize the knee joint, control flexion or bending of the knee, provide leverage to the quadriceps muscle, decelerate the knee |
| Nerves | Femoral nerve, Sciatic nerve, Tibial nerve, Peroneal nerve |
| Bursae | Suprapatellar bursa, Prepatellar bursa, Infrapatellar bursa, Superficial prepatellar, Superficial and deep infrapatellar, Medial and lateral gastrocnemius |
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What You'll Learn
Quadriceps femoris
The quadriceps femoris muscle, commonly known as the quad muscle, is the strongest and most voluminous muscle in the human body. It gets its name from the Latin "quadriceps femoris", meaning "four-headed muscle", as it consists of four individual muscles: the rectus femoris, vastus medialis, vastus lateralis, and vastus intermedius.
The quadriceps femoris is located in the anterior compartment of the thigh, along with the sartorius muscle. It is innervated by the femoral nerve, which originates from L2, L3, and L4. All four parts of the quadriceps femoris are powerful extensors of the knee joint, allowing for movements such as walking, running, jumping, and squatting. The rectus femoris, in particular, can flex the hip, while the other three muscles extend the knee. The rectus femoris is also a flexor of the hip, swinging the leg forward during walking or running. Additionally, the vastus medialis plays a crucial role in stabilising the patella and the knee joint during gait.
The rectus femoris arises from the anterior inferior iliac spine and the superior edge of the acetabulum, making it a biarticular muscle. It consists of two heads that unite to form a common muscle belly, which runs down the thigh. The vastus medialis originates from several landmarks on the proximal femur, including the inferior part of the intertrochanteric line and the medial lip of the linea aspera. The vastus lateralis originates from the lateral face of the great trochanter, gluteal tuberosity, and lateral lip of the linea aspera. The vastus intermedius originates from the proximal three-fourths of the anterior and lateral faces of the femoral body and the lateral lip of the linea aspera.
The quadriceps femoris muscle is essential for daily activities such as climbing stairs or getting up from a chair. It is also an important muscle in sports, but this also makes it susceptible to trauma and repetitive strain injuries.
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Hamstrings
The hamstrings are skeletal muscles found at the back of the thigh, starting at the pelvis and extending to the knee. They are made up of thousands of long, elastic muscle fibres that help leg muscles contract and tighten. The three hamstring muscles are the biceps femoris, semitendinosus, and semimembranosus. These muscles are responsible for flexing or bending the knee, as well as extending the hip and rotating the lower leg. They also play a crucial role in stabilising the knee when it is extended and during activities such as jumping, running, and walking.
The hamstrings are particularly susceptible to injury, especially among athletes who run and sprint. A common hamstring injury is a "pulled hamstring" or strain, which can range from mild to severe. This can occur due to overstretched muscle fibres, excessive muscle strain during eccentric contraction, or extensive hip flexion while the knee is extended. To avoid hamstring injuries, it is important to stretch, warm up, and avoid pushing through pain in the hip, knee, and leg.
The biceps femoris is the most commonly injured hamstring muscle, followed by the semitendinosus. However, injuries to the semimembranosus are rare. When injured, imaging techniques such as ultrasound and MRI are used to determine the extent of the injury and plan for surgery if necessary.
The hamstrings work in conjunction with other muscle groups to facilitate movement. For example, during walking, the hamstrings decelerate the forward motion of the tibia, working as an antagonist to the quadriceps in the deceleration of knee extension. Additionally, the gastrocnemius and soleus muscles support the hamstrings in knee flexion and provide stability during activities such as jumping and running.
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Gastrocnemius
The gastrocnemius is a large muscle located in the posterior leg, forming the calf. The word comes from the Greek words γαστήρ (gaster), meaning stomach or belly, and κνήμη (kneme), meaning leg. The gastrocnemius is the bulk of the calf muscle, with its outline often visible beneath the skin. It has two heads that originate on the back of the femur and run down to the Achilles tendon. The medial head is higher and projects lower than the lateral head, and both can be felt joining the tendinous junction.
The gastrocnemius is one of the muscles that make up the calf, along with the soleus and plantaris. These three muscles are referred to as the triceps surae. The gastrocnemius and soleus are the two main muscles of the calf, and they come together above the heel to form the Achilles tendon. The gastrocnemius is a secondary knee flexor and supports the hamstrings in knee flexion, providing stability to the knee during activities such as jumping, running, and walking. It also helps to bend the knee and push the foot down (plantar flexion).
The gastrocnemius muscle has many fascial connections, transmitting tension to the foot, knee, hip, and lumbar area. The muscle fibres arise from the anterior aspect of the aponeurosis, which gradually narrows and fuses with the fibres of the deeper soleus muscle to form the calcaneal (Achilles) tendon. The small saphenous vein and the sural nerve run along the superficial surface of the muscle, and it is innervated by the anterior rami of S1 and S2 spinal nerves, carried by the tibial nerve into the posterior compartment of the leg.
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Popliteus
The popliteus muscle is a small but important muscle located in the posterior aspect of the knee joint. It is often referred to as the "key of the knee" or the "key to unlock the knee" because of its role in unlocking the knee joint when the leg is in an extended position. The popliteus muscle originates from the lateral condyle of the femur and the posterior horn of the lateral meniscus. It then inserts on the tibia just proximal to the soleal line and just below the tibial condyles. The popliteus tendon courses in the groove for the popliteus muscle on the lateral aspect of the lateral femoral condyle.
The popliteus muscle is the main stabilizer of the posterior knee region. It helps to stabilize the knee joint during weight-bearing activities. It also plays a crucial role in the gait cycle by controlling the internal and external rotation of the tibia during walking and running. The popliteus muscle is innervated by the tibial nerve and receives arterial blood supply mainly from branches of the popliteal artery, namely the inferior medial and lateral genicular arteries.
The popliteus muscle is accompanied by the tibialis posterior, flexor digitorum longus, and flexor hallucis longus, forming the deep posterior compartment of the leg. It forms the base of the popliteal fossa and is the only muscle in the deep posterior or superficial posterior fossa that acts solely on the knee joint as a posterolateral stabilizer. The popliteus is a capsular structure and separates the lateral meniscus from the lateral collateral ligament.
The popliteus muscle can be injured in conjunction with a rupture of the anterior cruciate ligament or injuries involving the lateral meniscus. These injuries typically occur in sports due to a direct blow to the anteromedial aspect of the knee in the flexed position. An isolated injury of the popliteus muscle is considered rare. Diagnosis of popliteus injuries can be challenging as these injuries may mimic other conditions. However, a clinical exam and imaging studies can help differentiate popliteus injuries from other knee joint conditions.
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Patella
The patella, also known as the kneecap, is the largest sesamoid bone in the human body. It is located at the front of the knee joint, within the patellofemoral groove of the femur. The patella is a crucial component of the knee joint, providing several essential functions.
The patella enhances the efficiency of the quadriceps muscle by increasing the moment arm during knee extension. It acts as a fulcrum, increasing the rotational effect of the force generated by the quadriceps. This additional leverage allows for greater torque during the final stages of knee extension.
The patella also protects the knee joint from physical trauma and friction. Its position within the quadriceps tendon shields the tendon from frictional forces by minimising contact with the femur. This protective function helps safeguard the deeper structures of the knee joint.
The patella has a triangular shape with anterior and posterior surfaces. The superior aspect of the patella is attached to the quadriceps tendon, while the inferior aspect is connected to the patellar ligament. The vastus intermedius muscle attaches to the base of the patella, and the vastus lateralis and vastus medialis muscles attach to its outer lateral and medial borders, respectively.
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Frequently asked questions
The two main muscle groups are the quadriceps on the front of the knee and femur, and the hamstrings on the posterior side.
The quadriceps are made up of four muscles: the vastus lateralis, vastus medialis, vastus intermedius, and rectus femoris.
The hamstrings are made up of three muscles: the biceps femoris, semitendinosus, and semimembranosus.
