Logan Steele
The knee is a hinge joint that sits between the thigh and the shin, allowing the leg to bend and straighten. The knee is made up of many structures, including bones, tendons, ligaments, cartilage, and muscles. The main muscles that enable the knee to perform its functions are the quadriceps and hamstrings. The quadriceps is a group of four muscles at the front of the thigh, which allow the knee to straighten. The hamstrings are a group of three muscles at the back of the thigh, which allow the knee to bend. Another muscle that is closely associated with the knee is the popliteus muscle, which forms the floor of the popliteal fossa and is involved in knee flexion.
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What You'll Learn
Popliteus muscle
The popliteus muscle is a small, flat, triangular-shaped muscle in the lower leg. It is a deep muscle of the knee joint, forming the floor of the popliteus fossa. It is one of the main posterolateral stabilisers of the knee joint, causing both medial and lateral rotation of the knee. It is involved in both the closed chain phase and open-chain phase of the gait cycle.
The popliteus muscle is supplied by the tibial nerve, from spinal nerve roots L4 through S1, with approximately 2 to 3 parallel tibial nerve branches. The entry point of the nerve is the lateral distal margin of the muscle, which is found inferior to the fibular head, and then splits into anterior, medial, and lateral distributions throughout the muscle.
The muscle fibres originate from the lateral condyle of the femur and the posterior horn of the lateral meniscus, via a strong tendon called the popliteus tendon. From there it runs inferiorly and mediolaterally towards the tibia. It courses diagonally across the posterior upper tibia and a portion of the joint capsule, to lie as the deepest muscle of the posterior knee region.
The popliteus muscle assists in knee flexion and its function is decided according to the position of the lower extremity, i.e. weight-bearing or non-weight-bearing. In open chain kinematics, it rotates the tibia medially. In close chain kinematics, it laterally rotates the femur in the initial phase of knee flexion. With extension during weight-bearing, 'locking' of the knee occurs. In this state, the femur medially rotates on the tibia, allowing for full extension without muscular expenditure. To ''unlock' the knee, the popliteus muscle needs to contract, causing flexion and lateral rotation of the femur on the tibia.
The popliteus muscle is also associated with various injuries. Trauma, poor movement patterns, and posture can often impact the popliteus muscle, leading to weakness and injury. Iatrogenic injury to this muscle is common and can result in a poor functional prognosis. Anatomically smaller knees also require extra attention as they are more susceptible to popliteal injury.
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Knee anatomy
The knee is the body's largest joint, allowing movement through a hinge action. It is a synovial joint, meaning it has a wide range of motion. The knee joint is where the thigh bone (femur) meets the shin bone (tibia), with the patella (kneecap) sitting over the other bones at the front of the knee. The patella is a floating bone that acts as a fulcrum for the quadriceps muscle, allowing the knee to bend and straighten.
The knee joint is made up of two parts. The tibiofemoral joint is where the tibia meets the femur. The patellofemoral joint is where the patella meets the femur. The knee joint is surrounded by synovial fluid, which keeps it lubricated and protected. The bones are covered by articular cartilage, a slick, elastic material that absorbs shock and allows the bones to move smoothly with minimal friction. There are two crescent-shaped pads of cartilage between the tibia and femur bone, which reduce friction and disperse body weight across the joint. These are the lateral meniscus, on the outside of the knee, and the medial meniscus, on the inside.
The knee contains several ligaments, including the medial collateral ligament (MCL), which gives stability to the inner part of the knee, and the lateral collateral ligament (LCL), which stabilises the outer part. The anterior cruciate ligament (ACL) is located in the centre of the knee and prevents excessive forward movement of the tibia. The posterior cruciate ligament (PCL) is also in the centre and prevents the tibia from shifting backward. The MCL and LCL help to stabilise the knee if it is hit from the side. The ACL and PCL are responsible for stability from front to back.
The popliteus muscle is a small, thin, flat, triangular-shaped muscle in the lower leg. It is a deep muscle of the knee joint, forming the floor of the popliteus fossa. It is the only muscle in the posterior compartment of the lower leg that does not influence the ankle joint. It is a primary internal rotator of the tibia in a non-weight-bearing position. The popliteus muscle is prone to weakness and injury, especially following knee reconstruction surgery.
The main muscles that enable the knee to perform its functions are the quadriceps and hamstrings. Quadriceps are a group of four muscles that sit on the front of the thigh, allowing the knee to straighten. Hamstrings are a group of three muscles that sit on the back of the thigh and allow the knee to bend.
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Knee pain
The knee joint is formed by the intersection of bones, tendons, ligaments, cartilage, and muscles. The two main bones involved in the knee joint are the femur (thighbone) and the tibia (shin bone), with the patella (kneecap) sitting on top of the tibiofemoral joint. The patella is a floating bone that acts as a fulcrum for the quadriceps muscle, allowing the knee to bend and straighten. The quadriceps muscles at the front of the thighs enable the legs to straighten, while the hamstring muscles at the back of the thighs facilitate bending the leg at the knee.
Common causes of knee pain include sprained or strained ligaments and muscles, cartilage tears, tendonitis, and arthritis. A sprain or strain in the knee is often caused by a blow or sudden twist of the knee, resulting in pain, swelling, and difficulty walking. Cartilage tears can accompany sprains, and severe cases may require surgery. Tendonitis, or inflammation of the tendons, can occur due to overuse during activities like running, jumping, or cycling. Arthritis, particularly osteoarthritis, can cause knee pain and stiffness, typically affecting older individuals.
Diagnosing knee pain involves a medical examination and diagnostic procedures such as X-rays, MRIs, CT scans, or arthroscopy. Treatment options depend on the specific condition and its severity, ranging from non-operative methods like rest, ice, compression, and elevation (RICE protocol), to surgical interventions in more severe cases. Maintaining a healthy weight and engaging in low-impact exercises like cycling and swimming can also help manage and prevent knee pain.
The popliteus muscle is a small, thin, triangular-shaped muscle in the lower leg that forms the floor of the popliteus fossa. It is the deepest muscle in the posterior knee region and plays a crucial role in knee flexion and rotation. Trauma, poor movement patterns, and posture can impact the popliteus muscle, making it prone to weakness and injury.
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Knee injuries
The knee is a complex joint that allows the leg to bend and straighten, enabling movement such as walking, running, jumping, and going up and downstairs. It is the largest joint in the body and is particularly vulnerable to injuries due to its many components. The knee comprises four main structures: bones, cartilage, ligaments, and tendons. The bones that meet to form the knee joint are the femur (thighbone), tibia (shinbone), and patella (kneecap). The patella is a floating bone that acts as a fulcrum for the quadriceps muscle, allowing the knee to bend and straighten.
The knee's ligaments, tendons, and muscles are also integral to its function. The main muscles that enable the knee's movement are the quadriceps and hamstrings. The quadriceps, a group of four muscles at the front of the thigh, allow the knee to straighten. The hamstrings, a group of three muscles at the back of the thigh, allow the knee to bend. The patellar tendon, which attaches the quadriceps to the patella, can rupture or tear during sports. The hamstring muscles can also be strained or torn during sports activities.
The knee's ligaments provide stability to the joint. The medial collateral ligament (MCL) and lateral collateral ligament (LCL) are situated on the inside and outside of the knee, respectively, and help stabilise the knee against sideways impact. The anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL) are located inside the knee and cross each other as they run front to back and vice versa. The ACL is often injured during sports, particularly those involving cutting and pivoting movements, such as soccer, football, and basketball. The PCL is often injured by a blow to the front of the knee while it is bent.
The popliteus muscle is a small, thin, flat, triangular-shaped muscle in the lower leg. It is the deepest muscle of the posterior knee region and assists in knee flexion. It is one of the main posterolateral stabilisers of the knee joint and is prone to injury due to trauma, poor movement patterns, and posture. The meniscus, composed of two rubbery wedges of cartilage between the thighbone and shinbone, can tear during sports or slowly due to aging. This is referred to as a degenerative meniscus tear.
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Knee functions
The knee is a hinge joint that allows the leg to bend and straighten, enabling movement such as walking, running, cycling, swimming, going up and downstairs, sitting, and standing. It is the largest joint in the body and is constructed by four bones and an extensive network of ligaments and muscles. The knee is where the thigh bone (femur) meets the shin bone (tibia).
The knee's main movement is flexion-extension. The articular surfaces of the femur roll and glide over the tibial surface. The patella (kneecap) sits on top of the tibiofemoral joint in a groove in the front of the femur. The patella is a floating bone that acts as a fulcrum for the quadriceps muscle to function properly. The patellofemoral joint allows the patella to move up and down as the knee bends and straightens. The quadriceps muscle group is made up of four individual muscles that join together to form a single tendon, which inserts into the anterior tibial tuberosity. The patella is embedded in this tendon and increases the efficiency of quadriceps contractions. Contraction of the quadriceps pulls the patella upwards and extends the knee.
The hamstring muscle group is situated at the back of the thigh and is responsible for flexing or bending the knee, as well as providing stability on either side of the joint line. The knee also contains cartilage, like the meniscus, and ligaments, including the LCL, MCL, ACL, and PCL. The MCL and LCL sit on the sides of the knee and help stabilise the joint. The ACL and PCL are inside the knee and cross each other as they run front to back and vice versa. These two ligaments are responsible for giving the knee stability from front to back.
The popliteus muscle is a small, thin, flat, triangular-shaped muscle in the lower leg. It is a deep muscle of the knee joint, forming the floor of the popliteus fossa. It is one of the main posterolateral stabilisers of the knee joint, causing both medial and lateral rotation. The popliteus assists in knee flexion and its function is decided according to the position of the lower extremity, i.e. weight-bearing or non-weight-bearing.
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Frequently asked questions
The popliteus muscle is located behind the knee. It is also referred to as "The Key of the Knee" as it is responsible for "unlocking" the knee joint.
The primary function of the popliteus muscle is to unlock the knee joint by rotating the femur on the tibia when the foot is in contact with the ground. It also helps to stabilise the knee joint during weight-bearing activities.
The popliteus muscle is a small, thin, flat, triangular-shaped muscle in the lower leg. It is the deepest muscle in the posterior knee region.
