Joints are a place in your body where two (or more) bones come together and movement is possible. That’s why they play an important roll in your yoga practice. Without joints no movement. Although movement is a big word, because some of your joints can’t move at all, but others can move a little and some can move a lot. The bigger the movement, the weaker the joint.
The important joints in yoga are:
- Shoulder joint: this joint has the most flexibility of all joints. It is formed by the union of the humerus, the scapula (shoulder blade), and the clavicle (collarbone). It is made up of two separate joints – the glenohumeral and acromio-clavicular joints. These two joints work together to allow the arm both to circumduct in a large circle and to rotate around its axis at the shoulder.
- The glenohumeral joint is a ball-and-socket joint formed between the articulation of the rounded head of the humerus (the upper arm bone) and the cup-like depression of the scapula, called the glenoid fossa The glenoid fossa forms a very shallow socket, so the muscles, ligaments and cartilage of the shoulder joint reinforce its structure and help to prevent dislocations. To further reinforce the shoulder, the four muscles of the rotator cuff extend from the scapula and surround the head of the humerus to both rotate the arm and prevent dislocation.It’s the joint that gets dislocated easiest. The ligaments are fairly loose giving this joint its flexibility.
- Elbow joint: there are two joints here: humerus and ulna (strongest of the two) and humerus and radius. The elbow joint is a complex joint formed between the distal end of the humerus in the upper arm and the proximal ends of the ulna and radius in the forearm. The elbow allows for the flexion and extension of the forearm relative to the upper arm, as well as rotation of the forearm and wrist.
- The rounded distal end of the humerus is divided into two joint processes – the trochlea on the medial side and the capitulum on the lateral side. The pulley-shaped trochlea forms a tight joint with the trochlear notch of the ulna surrounding it. On the lateral side, the concave end of the head of the radius meets the rounded, convex capitulum to complete the elbow joint. The loose union of the capitulum of the humerus and the head of the radius allows the radius to pivot as well as flex and extend. The pivoting of the radius allows for the supination and pronation of the hand at the wrist. Hyper flexibility in the elbow joint is common. It the joint is overstretched – what can happen in downward dog pose – the joint can get damaged. Building muscles in the arm, helps to prevent overstretching the joint.
- Hip joint; the hip joint is one of the most important joints in the human body. It allows us to walk, run and jump. It bears our body’s weight and the force of the strong muscles of the hip and leg. Yet the hip joint is also one of our most flexible joints and allows a greater range of motion than all other joints in the body except for the shoulder. The hip joint is a ball-and-socket joint formed between the os coxa (hip bone) and the femur. A round, cup-shaped structure on the os coax, known as the acetabulum, forms the socket for the hip joint. The rounded head of the femur forms the ball of the joint. If we bend forward, we are actually bending forward from the hips.
- Knee joint – brings the weight of the body over from the femur on the tibia. The knee joint is one of the strongest and most important joints in the human body. It allows the lower leg to move relative to the thigh, while supporting the body’s weight. Movements at the knee joint are essential to many everyday activities, including walking, running, sitting and standing.
- Ankle joint: the bones of the ankle and foot form the most distal region of the lower limb in the appendicular skeleton. These bones are responsible for the propulsion, balance, and support of the body’s weight through many diverse activities, such as standing, walking, running, and jumping. The ankle joint is formed by the union of the lower leg bones – the tibia and fibula – and the talus bone (one of a group of bones collectively known as the tarsus, located in the foot). Together, these three bones form a tight joint that permits the plantar flexion and dorsiflexion of the foot.
Let’s take a closer look at the knee joint to see how a joint works.
- The knee is a joint formed between three bones: the femur (above), tibia (below) and patella (in front; not shown in this picture). Two rounded, convex processes (known as condyles) on the distal end of the femur meet two rounded, concave condyles at the proximal end of the tibia. The patella lies in front of the femur on the anterior surface of the knee with its smooth joint-forming processes on its posterior surface facing the femur.
- Two internal ligaments – the anterior and posterior cruciate ligaments – help to maintain the proper alignment of the knee. The anterior cruciate ligament plays an important role in preventing hyperextension of the knee by limiting the anterior movement of the tibia. Directly behind the ACL is the posterior cruciate ligament which prevents the posterior movement of the tibia relative to the femur.
- On both sides of the knee joint are two more ligaments: the lateral collateral ligament and the medial collateral ligament. They prevent the knee from moving to far inwards or outwards. When we do poses where the knee is bend at a 90 degree angle we must take care we don’t let the knee ‘fall’ inwards or outwards, otherwise we put too much pressure on these ligaments.
Three types of joints
- Ligamentous / fibrous: thick tissue – little movement (bones of skull)
- Cartilaginous: semi movable; cartilage of ribs help move so we can breathe, between vertebras
- Synovial: most movable joints
Types of synovial joints
- Ball and socket: hip, shoulder
- Hinge: elbow, knee
- Gliding: acromion process and clavicle
- Saddle: base of thumb
- Pivot: first two vertebras: atlas (1) and axis (2)
- Condyloid: phalanges + metacarpals + wrist & wrist
In a synovial joint the two bones are separated by a little layer of synovial fluid. A thin membrane of connective tissue forms a capsule around the joint. This secretes the synovial fluid into the joint. The colorless fluid lubricates and nourishes the joint.
The four ligament (tough bands of fibrous tissue) link the bones together across the joint. They are inelastic, but flexible. They control the range of movement and protect the joint. The end of the bones are covered with articular cartilages. This is a dense layer of connective tissue, which covers the articulating surfaces of the bones within the capsule.
Major joints where compression can occur
In your yoga practice compression can limit your movement. Compression happens when two bones ‘hit’ each other. Not everybody has the some movement in their joints. We are all built differently. If one or both bones are longer than normal, they restrict our movement. This explains why some people are more flexible than others. Flexibility is not only created by muscles. Bones play an important part in our range of motion as well. The major joints where compression can happen are:
Source: Anatomie en fysiologie – Een inleiding – Frederic H. Martini & Edwin F. Bartholomew & www.innerbody.com