Knee + Legs

BONES

Knee: The articulation of 3 specific bones makes up the knee which are the femur, patella, and tibia. The fibula doesn't play a role in the knee joint, but it is a bone of the leg. The knee is a synovial hinge joint.

Leg: The leg is made up of 4 bones which are the femur, patella, tibia and fibula. 

Bones	Info about this bone	Picture
Femur	The longest and strongest bone in the body is known as the femur. The patella and femur articulate at an indentation which is called the patellar surface, which is located on the anterior side of the femur at its distal end. There are two condyles (medial and lateral) that are also located at the distal end, and are covered with a thick layer of articular cartilage.
Patella	The patella is also known as the kneecap and is a type of sesamoid bone. The patella covers, and is located at the front of the knee and it is a triangular bone. This bone is not attached to other bones via ligaments, it is actually suspended within a tendon. Helping reduce wear in the tendon which crosses over the knee, on the anterior side by reducing friction, is the role the patella plays.
Tibia	The tibia is also known as the shinbone and is a long bone. The femur articulates with this bone at its superior aspect forming the tibiofemoral joint. Long bones have a hard outer surface which is known as compact bone, and a perforated (more mesh-like) interior known as cancellous bone. This allows long bones to absorb significant amounts of pressure and long bones also contain the bone marrow that produces red blood cells.
Fibula	The fibula doesn't directly articulate with the femur or patella, and it is also the smaller bone of the two lower leg bones. Just like the tibia and femur, this bone is a long bone meaning it has a hard outer surface and a mesh-like interior. Another thing long bones consist of are growth plates, which are called epiphyseal plates that are located on either end. When compared with the tibia, the fibula plays a more supportive role and acts as a stabilizer for the knee.

LIGAMENTS

The ligaments which are present in and around the knee play a vital role in stabilizing the knee joint, since this joint is highly susceptible to injury. Although there are many ligaments present, we are going to focus on these 4 major ligaments:

• Medial Collateral Ligament (MCL) - This ligament runs from the medial epicondyle of the femur to the medial condyle of the tibia. The MCL helps with preventing side to side movement in the knee. 

• Lateral Collateral Ligament (LCL) - This ligament runs from the lateral epicondyle of the femur to the head of the fibula. The LCL also helps to prevent side to side movement in the knee, just like the MCL.

• Anterior Cruciate Ligament (ACL) - The ACL runs diagonally from the lateral femoral condyle to the anterior aspect of the tibia. This ligament helps to stabilize the femur so that it is prevented from slipping from its location on top of the tibia. Stress is placed on your ACL when you extend your knee.

• Posterior Cruciate Ligament (PCL) - The PCL runs from the lateral surface of the medial femur condyle to the posterior intercondylar area. This ligaments passes the ACL and creates a 'cross', hence the term 'cruciate'. Along with the ACL, this ligament helps to stabilize the femur so that it is prevented from slipping from its location on top of the tibia.

BONE MARKINGS

Around the knee joint, these are some of the significant bone markings:

• Condyles: The femur and tibia include both medial and lateral condyles, which serve as an attachment point for muscles. These condyles also act as the articulation point between the tibia and the femur.

• Epicondyles: Only the femur includes a medial and lateral epicondyle, which are bony protrusions that serve as attachment points.

• Menisci: The medial and lateral menisci are located between the tibia and femur and they are bands of thick cartilage which attach to the tibia. The menisci stabilize the knee and act as shock absorbers.  

• Greater Trochanter: The greater trochanter is located on the lateral side of the femur, and is slightly inferior to the head of the femur. It is a large protrusion which acts as an attachment site, for many hip and thigh muscles.

MUSCLES

Groups of muscles:

	Info about these muscles	Picture
Quadricep Muscles	Quadricep muscles are located on the anterior aspect of the thigh. Here, there are a number a muscles present. The quadriceps are composed of the vastus lateralis, vastus intermedius, vastus medius, the rectus femoris and also the gracilis muscle. The rectus femoris lies superficial to the vastus intermedius muscle. The quads are responsible for extension of the knee.
Hamstring Muscles	Hamstring muscles are located on the posterior aspect of the thigh. The hamstrings are composed of the semitendinosis, semimembranosus and the biceps femoris muscle. These muscles cross over the hip and knee joints, which is why they play a role in the movement of both joints. The hamstrings are responsible for flexion of the knee.

Anterior leg muscles:

	Info about this muscle	Picture
Vastus Lateralis	The Vastus Lateralis is one of four muscles which make up the quadriceps. This muscle is located on the lateral side of the anterior femur, and the action this muscle is in charge of is extension of the leg at the knee. It is also the largest and most powerful muscle of the quadriceps group.
Vastus Intermedius	The Vastus Intermedius is another one of the muscles which makes up the quadriceps. This muscle is located right beside the vastus lateralis, to the right. The Vastus Intermedius lies deep to the rectus femoris. The action that this muscle is in charge of is extension of the leg at the knee.
Vastus Medialis	The Vastus Medialis is the third muscle which makes up the quadriceps. This muscle is located on the lateral side of the anterior femur, and the action this muscle is in charge of is extension of the leg at the knee.
Rectus Femoris	The Rectus Femoris is the last muscle which makes up the quadriceps. This muscle is located in between the vastus lateralis and vastus medialis. It lies superficial to the vastus intermedius. The action that this muscle is in charge of is extension of the leg at the knee, as well as flexion of the hip.
Gracilis	The gracilis is located on the medial side of the thigh and is the most superficial muscle, on the medial side. It is a long and thin muscle that crosses from the lower end of the pelvis, to the top of the tibia. This muscle is in charge of the following actions: adduction of the hip, medial rotation of the thigh and it assists with flexion of the thigh at the knee.
Sartorius	This muscle is the longest muscle in the human body. It is a thin superficial muscle that runs down the length of the thigh. This muscle is in charge of the following actions: assists with hip flexion, knee flexion, medial rotation of the knee and lateral rotation of the hip.
Adductor Longus	The adductor longus is one of three adductor muscles that play a role in the anterior thigh. This muscles main function is adduction of the thigh at the hip. It also assists with medial rotation of the thigh at the hip.
Adductor Brevis	The adductor brevis is another one of the three adductor muscles, that play a role in the anterior thigh. This muscle is the smallest and shortest muscle, when compared with the other adductor muscles. Adduction of the hip is the movement that this muscle is in charge of.
Adductor Magnus	The Adductor Magnus is the last muscle which makes up the adductor muscles. This muscle is located on the medial side of the thigh and is a large triangular muscle. It is one of the biggest muscles of the human body and it lies deep to the adductor longus and adductor brevis. Medial rotation of the hip, adduction of the thigh at the hip and extension of the thigh at the hip are the three movements that this muscle is in charge of.

Posterior leg muscles:

	Info about this muscle	Picture
Semimembranosus	The Semimembranosus is one of three muscles which make up the hamstrings. It is located on the medial side of the posterior leg and it lies deep to the semitendinosus. T.
Semitendinosus	The Semitendinosus is another one of the muscles which make up the hamstings. This muscle lies superficial to the semimembranosus. The movements that this muscle is in charge of are also flexion and medial rotation of the knee.
Biceps Femoris	The Biceps Femoris is the last muscle which makes up the hamstrings and it is located on the lateral side of the Semimembranosus and Semitendinosus muscles. This muscle consists of two heads (long and short). The movements that this muscle is in charge of are flexion and lateral rotation of the knee.

TENDONS

Patellar (Quadricep) Tendon: The four muscles that make up the quadriceps all come together to form the patellar tendon. The four muscles are the vastus lateralis, vastus intermedius, vastus medialis, and rectus femoris. This tendon is located just below the patella (knee cap) and once this tendon crosses over the patella, it becomes the patellar ligament. 

Hamstring Tendon: The three muscles that make up the hamstrings all come together to form the hamstring tendon. The three muscles are the semimembranosus, semitendinosus and the biceps femoris. This tendon is located on the posterior side of the leg and inserts on the posterior tibia and fibula.

Iliotibial Band: This tendon is also called the IT band and it runs from the ilium of the hip, to the tibia of the lower leg. Many muscles, such as the gluteus maximus and tensor fascia lata insert on this tendon, and this tendon also helps to stabilize the knee and the hip. A common injury that often occurs in cyclists and long distance runners is known as iliotibial band syndrome. This injury manifests itself as knee pain, due to an inflammation in the bursa near the lateral epicondlye of the femur.

ORIGINS AND INSERTIONS

Anterior Compartment:

Posterior Compartment:

JOINTS

The knee is a synovial hinge joint. There are 3 main joints in the knee which are:

• Tibiofemoral Joint: This is a synovial hinge joint and it articulates between the condyles of the femur and the condyles of the tibia. Two movements that this joint may perform are flexion and extension. 

• Patellofemoral Joint: This joint is made up of the patella and tibia, and the patella is unique since it isn't connected to other bones via ligaments. Instead it is suspended in the tendon of the quadriceps. The patellofemoral joint does attach inferiorly, to the tibia via a ligament. Technically, this joint doesn't produce a unique movement, but it does help facilitate extension at the tibiofemoral joint. Lastly, it reduces friction during flexion and extension of the knee.

• Tibiofibular (Superior) Joint: This is a synovial plane joint and is the joint located between your tibia and fibula. A movement that this joint may perform is small gliding movements.

MOVMENTS

The different kinds of movements that occur at the knee and leg are flexion and extension, adduction and abduction, medial (internal) rotation and lateral (external) rotation. Since the knee is a synovial hinge joint, the knee moves like a hinge meaning it mainly allows for flexion and extension. The leg and knee have a limited range of motion and aren't able to move around as freely as other parts of the body, like your shoulder. That is why there is only a small amount of medial and lateral rotation that may occur.