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The knee is the body's largest joint, allowing for flexion and extension, and a small degree of medial and lateral rotation. The knee joint is formed by the femur, tibia, and patella, and is surrounded by an extensive network of ligaments and muscles. The medial compartment of the knee is where the rounded end of the femur bone (medial femoral condyle) sits on the flattened area of the tibia bone (medial tibial plateau). The muscles attaching near the medial compartment include the semimembranosus, semitendinosus, medial gastrocnemius, sartorius, and gracilis, which work to bend or flex the knee.
| Characteristics | Values |
|---|---|
| Muscles | Vastus medialis, Vastus medialis oblique (VMO), Articularis genus, Rectus femoris, Vastus lateralis, Vastus intermedius, Biceps femoris, Semitendinosus, Semimembranosus, Gastrocnemius, Sartorius, Gracilis, Popliteus, Quadriceps femoris, Hamstrings, Adductor magnus |
| Bones | Femur, Tibia, Patella, Fibula |
| Ligaments | Medial collateral ligament (MCL), Lateral collateral ligament (LCL), Anterior cruciate ligament (ACL), Posterior cruciate ligament (PCL), Tibial collateral ligament, Posterior oblique ligament, Oblique popliteal ligament, Medial patellofemoral ligament |
| Bursa | Suprapatellar, Prepatellar, Infrapatellar, Semimembranosus |
| Joints | Tibiofemoral, Patellofemoral |
| Cartilage | Articular cartilage, Meniscus |
| Nerves | Femoral nerve, Sciatic nerve, Tibial nerve, Peroneal nerve, Genicular branches of the femoral and popliteal arteries |
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What You'll Learn
Muscles that bend the knee
The knee joint is one of the largest and most complex joints in the body. It is a pivotal hinge joint that allows for straightening and bending in one direction, with some twisting. The knee joint is formed by the femur (thigh bone), the tibia (shin bone), and the patella (kneecap). The knee contains bones, cartilage, muscles, ligaments, tendons, bursae, and meniscus.
The hamstrings are the muscles that control flexion or bending of the knee. They also help to stabilize the knee when it's extended and assist in turning the knee inwards (internal rotation) and outwards (external rotation). The hamstrings attach at the base of the femur and the top of the tibia. The hamstring muscles include the biceps femoris, semitendinosus, and semimembranosus.
The popliteus muscle, located in the lower leg, is responsible for "unlocking" the knee joint after extension. The popliteus is located behind the knee joint and acts to "unlock" the knee by rotating the femur on the tibia, allowing for the lower leg to be flexed.
The knee joint permits four main movements: extension, flexion, lateral rotation, and medial rotation. Extension is produced by the quadriceps femoris, which inserts into the tibial tuberosity. Flexion is produced by the hamstrings, gracilis, sartorius, and popliteus. Lateral rotation is produced by the biceps femoris, while medial rotation is produced by the semimembranosus, semitendinosus, gracilis, sartorius, and popliteus.
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Muscles that straighten the knee
The knee joint is the largest joint in the human body. It is also one of the most complex and commonly injured joints. The knee connects the thigh bone (femur) to the shin bone (tibia) and helps us stand, move, and balance. The knee joint permits four main movements: extension, flexion, lateral rotation, and medial rotation.
The quadriceps femoris is responsible for knee extension or straightening the knee. The quadriceps is a group of four muscles found in the front of the thigh and over the knee. These four muscles are the vastus medialis, vastus intermedius, vastus lateralis, and rectus femoris. The vastus medialis is the innermost of the four quadriceps muscles, while the vastus lateralis is the outermost. The rectus femoris is the most superficial or closest to the surface, and the vastus intermedius lies deep underneath it.
The hamstrings, on the other hand, are responsible for knee flexion or bending the knee. The hamstrings include the semitendinosus, semimembranosus, and biceps femoris. The biceps femoris is one of three muscles that form the hamstring group at the back of the thigh. The semimembranosus is the most superficial of the hamstring muscles, found on the medial or inner side of the thigh. The semitendinosus is underneath the semimembranosus.
Other muscles that contribute to knee flexion include the gracilis, sartorius, and popliteus. The gracilis and sartorius are slender and long muscles that originate from the pelvis and attach to the medial tibia to help form the pes anserinus. The sartorius is particularly involved in multiple hip and knee motions.
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The adductor magnus muscle
The muscle bellies of the adductor and hamstring portions of the adductor magnus travel inferolaterally. The adductor portion inserts via a broad aponeurosis onto the gluteal tuberosity, linea aspera, and medial supracondylar line of the femur. The hamstring portion inserts via a rounded tendon onto the adductor tubercle and medial supracondylar line of the femur.
Along the insertion sites for the adductor magnus muscle, there are five gaps. The first to third gaps allow for the passage of the perforating arteries of the deep femoral artery, while the fourth gap allows for the passage of the distal end of this artery. The fifth gap, located between the insertion sites of the adductor and hamstring portions, is known as the adductor hiatus and allows for the passage of the femoral vessels. The adductor hiatus is an opening in the distal adductor magnus muscle, located approximately 12 cm proximal to the medial femoral condyle.
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The Vastus Medialis Oblique (VMO) muscle
The VMO muscle plays a crucial role in maintaining patellar stability. Weakness or alterations in its muscle activity can lead to patellar mal-tracking, resulting in instability and potential damage to surrounding structures. This can cause anterior knee pain and conditions such as Patellofemoral Pain Syndrome (PFPS). Strengthening exercises are often recommended for individuals with PFPS, as they tend to have a lower volume of VMO muscle.
The Vastus Medialis muscle as a whole, including the VMO portion, is essential for the final stages of knee extension. It aids in the locking mechanism of the knee joint and helps control the movement of the kneecap, providing stability. The VMO muscle fibres' positioning and direction counteract the natural tendency of the kneecap to glide towards the outer side of the knee during leg bending. By drawing the kneecap inwards, the VMO reduces friction and stabilises the joint.
Weakness in the Vastus Medialis Oblique muscle can impact both instantaneous strength and endurance, causing the muscle to tire prematurely. Misfiring is another issue, characterised by a delay in VMO activation or complete deactivation. Individuals with a weak VMO muscle are more susceptible to anterior knee pain and may benefit from targeted exercises. Clenching a squashy ball between the knees during vastus medialis exercises helps ensure proper activation of the VMO. Advanced exercises, such as lunges, step-ups, and step-downs, can be incorporated once individuals have achieved sufficient control and confidence in activating their VMO.
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The medial meniscus
The knee joint is the largest joint in the human body. It is a complex structure made up of bones, cartilage, muscles, ligaments, and nerves. The knee joint connects the thigh bone (femur) to the shin bone (tibia). The medial meniscus is a fibrocartilage semicircular band that spans the knee joint medially, located between the medial condyle of the femur and the medial condyle of the tibia. It is also referred to as the internal semilunar fibrocartilage. The medial meniscus has a crescent shape, while the lateral meniscus is more circular. The menisci are crescent-shaped bands of thick, rubbery cartilage attached to the tibia via coronary ligaments. They act as shock absorbers and stabilise the knee.
Healing of the medial meniscus is generally difficult unless the patient is very young, usually under 15 years old. The outer third of the meniscus has the best healing potential due to its blood supply, while the inner two-thirds have limited blood supply and thus limited healing ability. If the meniscus cannot heal or the damage is too severe, it may need to be removed (meniscectomy). However, this increases the risk of developing osteoarthritis in the knee later in life.
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Frequently asked questions
The medial knee refers to the medial compartment of the knee, which includes the medial femoral condyle, the medial tibial plateau, and the meniscus. The medial femoral condyle is the rounded end of the femur bone, which sits on the flattened area of the tibia bone called the medial tibial plateau. The meniscus is a C-shaped piece of cartilage that lies between these two bones and helps absorb forces, providing crucial protection to the knee.
Several muscles attach near the medial compartment of the knee and help with its movement. These include the semimembranosus, semitendinosus, medial gastrocnemius, sartorius, and gracilis, which work together to bend or flex the knee. The vastus medialis oblique (VMO), a quadriceps muscle, extends or straightens the joint.
The medial knee is susceptible to various injuries due to its complex anatomy. One common injury is a tear in the medial meniscus, which can occur during sports or other physical activities. Another is an injury to the medial collateral ligament (MCL), which can be assessed by observing pain during medial rotation of the leg. In a condition called the "unhappy triad," the ACL, MCL, and medial meniscus are all injured simultaneously.
