Movement Patterns at Joints
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- Flexion – bending. This occurs when the angle between the articulating bones is decreased. For example, by bending the knee and bringing the heel of the foot to the bottom. The angle between the tibia and the femur (at the back of the knee) has decreased, therefore, flexion has taken place at the knee joint. A muscle that causes flexion is known as a ‘flexor’. In the above example, the hamstrings were the flexor muscles.
- Extension – straightening. This occurs when the angle between the articulating bones is increased. For example, when straightening the leg, the angle between the femur and the tibia (at the back of the knee) increases, therefore, extension has taken place. Extreme extension can take place, and this usually occurs at an angle greater than 180°. This is known as hyper extension. A muscle that causes extension is known as an ‘extensor’. In the above example, the quadriceps group act as the extensor muscles.
- Abduction occurs when a body part is moved away from the midline of the body or other body part. Examples include placing the arms by the sides of the body and then raising them laterally (up to the side). In this case abduction at the shoulder joint has taken place. Spreading the fingers and lifting up a leg to the side are also examples of abduction. An easy way of remembering this is ‘abduct’ – to take away.
- Adduction is the opposite of abduction and occurs with movement towards the midline of the body or body part. For example, by lowering the arms back down to the sides of the body, movement towards the midline of the body has taken place, and therefore adduction has occurred. An easy way of remembering this is ‘add’ – for example, ‘adding’ the arm to the side of the body.
- Circumduction occurs when a circle is drawn by a body part, and the bone makes the shape of a cone as it moves around. It is a combination of flexion, extension, abduction and adduction. It can only truly occur at ball and socket joints at the hip and shoulder.
- Rotation occurs when the bone turns about its long axis within the joint. Rotation towards the body is known as internal or medial rotation, and rotation away from the body is called external or lateral rotation.
- Pronation occurs at the elbow and involves internal (medial) rotation between the radius and humerus, as well as the crossing of the radius and the ulna. It normally occurs when the palm of the hand is moved from facing upwards to facing downwards.
- Supination is the opposite of pronation and once again takes place at the elbow joint. This movement is external (lateral) rotation between the radius and the humerus, and occurs when the radius and ulna are parallel. When the palm of the hand is turned so that it faces upwards, supination has taken place.
- Plantarflexion takes place at the ankle joint, and occurs when the toes are pointed forward.
- Dorsiflexion also occurs at the ankle and occurs when the foot is raised upwards towards the tibia (shin).
- Inversion occurs when the sole of the foot is turned inward towards the midline of the body.
- Eversion occurs when the sole of the foot is turned outwards.
- Elevation occurs when a body part is moved upwards. For example, shrugging the shoulders.
- Depression occurs when a body part is moved downwards. An example would be lowering the shoulders back down.
- Horizontal flexion occurs when the arm is pulled across the chest when it is parallel to the floor.
- Horizontal extension occurs when the arm is returned from the above position out to the side.
- Lateral flexion occurs when the spine is flexed (i.e. angle is decreased) to the side. For example, during side bends or tilting the head to the side.
At all synovial joints, bones are secured to each other by ligaments. These are made out of strong and very tough fibrous tissue (collagen) that is slightly elastic, but does not allow much movement. Ligaments join bone to bone. They do not cause movement; that is caused by muscle action on the bones. Sometimes, as is the case with the knee joint, ligaments limit movement in certain directions, helping to maintain stability.
Tendons attach muscle to bone. These are strong flexible cords which transmit the pull of the muscle to the bone to create movement. They are also made from collagen. Tendons are strong but inelastic – they do not stretch.
Cartilage is a type of tissue which is present in all joints. There are two main types of cartilage:
- Hyaline (articular) cartilage – this is found at the end of the long bones inside the joints. It is smooth, tough and hard-wearing, protecting the ends of the bones from rubbing against each other when they move. Synovial fluid provides nutrients to this cartilage.
- White fibro-cartilage – this is found in the spine between the vertebrae, where it acts as a shock absorber. It is also found in more complex joints. In the knee, this cartilage forms crescent shaped pieces of cartilage, known as menisci, which are found between the two bones. They are very strong and act like shock absorbers between the bones.
Exercise and the joints
- Hyaline cartilage thickens protecting the bones from wear and tear.
- Tendons thicken and can withstand greater muscular force.
- Ligaments stretch slightly enabling a greater range of movement at the joint.