Irregular Bones
Irregular bones are so named due to their complex, individual shapes and the difficulty in classifying them. They have a variety of functions which include protection. Examples:
The Vertebra (protects the spinal cord and helps to absorb shock when running and jumping)
The bones of the face.
Sesamoid Bones
Sesamoid bones have a specialized function: they ease joint movements and resist friction and compression. They are usually developed in tendons and are covered with a layer of articular cartilage as they exist where bones articulate. Although generally small in appearance, Sesamoid bones do very in size, the largest and most obvious being the patella which is situated in the quadriceps femoris tendon and aids the smooth articulation and movement between the femur and the tibia. The patella also prevents the knee from hyperextension
Types of Joints
There are three types of joints; they are the fixed or fibrous joints, the cartilaginous or slightly moveable joints, and the synovial or freely movable joints.
Fixed or Fibrous Joints
These are very stable and allow no observable movement. Bones are often joined by strong fibres called sutures; e.g. the structures of the cranium.
Cartilaginous or slightly moveable joints
These are joined by tough, fibrous cartilage which provides stability and possesses shock absorption properties. However, a small amount of movement usually exists: for example, the articulations between the lumbar bones due to the intervertebral discs of cartilage.
Synovial or freely moveable joints
These are the most common type of joint in the body, and the most important in terms of physical activity, since they allow a wide range of movement.
Synovial joints can then be divided into six separate basic types;
Hinge joint
Pivot joint
Ellipsoid joint
Gliding joint
Saddle joint
Ball and socket joint.
Examples of the six different types of Synovial joints
The Hinge joint – this is a uniaxial joint which only allows movement in one plane. For example; the knee joint only allows movement back and forth. Strong ligaments exist in order to prevent any sideways movement.
The Pivot joint – this is also uniaxial, which allows rotation only. For example; the cervical vertebrae where the axis rotates on the atlas.
The Ellipsoid joint – this joint is biaxial, allowing movement in two planes. For example; the radio-carpal join of the wrist allows back and forth as well as side to side movement.
The Gliding join – this is formed where flat surfaces glide past one another; although mainly biaxial they may permit movement in all directions. For example; in the wrist, where the small carpal bones move against each other.
The Saddle joint – this is biaxial and generally occurs where concave and convex surfaces meet. For example: the carpo-metacarpal joint of the thumb.
The Ball and Socket joint – this allows the widest range of movement and occurs where a rounded head of a bone fits into a cup-shaped cavity. For example: in the hip and shoulder.
Movement patterns occurring in synovial joints
Flexion
Extension
Abduction
Adduction
Circumduction
Rotation
Pronation
Supination
Plantarflextion
Dorsiflextion
Inversion
Eversion
Definitions
Flexion – this occurs when the angle between the articulating bones is decreased, flexion occurs in the median plane about the horizontal axis. A muscle that causes flexion is known as a flexor. Example: by raising the lower arm up to touch the shoulder, the angle between the radius and the humerus at the elbow has decreased, flexion of the elbow has occurred.
Extension – this occurs when the angle of the articulating bones is increased, extension also occurs in the medium plane about the horizontal axis. A muscle causing extension is known as an extensor. Example: when standing up from a seated position, the angle between the femur and tibia increases, thus causing extension at the knee joint.
Abduction – this is movement of a body part away from the midline of the body or other body part. Abduction occurs in the frontal plane about the anterior-posterior axis, however horizontal abduction takes place in the horizontal transverse. Example: if arms are placed by the sides of the body and then raised laterally, abduction has occurred at the shoulder joint.
Adduction – this is the opposite of abduction and concerns movement towards the midline of the body or body part. Adduction occurs in the frontal plane about an anterior-posterior axis. However horizontal adduction takes place in the horizontal or transverse plane.
Circumduction – this occurs where a circle can be described by the body part and is simple a combination of flexion, extension, abduction and adduction. True Circumduction can only really occur at ball and socket joints of the shoulder and hip. Circumduction occurs in the median or frontal planes.
Rotation – rotation of a joint occurs where a bone turns about its axis within the joint, rotation towards the body is termed internal or medial rotation, rotation away from the body is called external or lateral rotation, rotation occurs in the horizontal plane about a longitudinal axis.
Pronation – Pronation occurs at the elbow and involves internal rotation between the radius and humerus, it typically occurs where the palm of the hand is moved facing upwards to facing downwards, it occurs in the horizontal plane about a longitudinal axis.
Supination – this is the opposite of Pronation and again takes place at the elbow. This time the movement is external rotation between the radius and humerus and generally occurs when the palm of the hand is turned so that it faces upwards, this takes place in the horizontal plane about a longitudinal axis.
Plantarflextion – this occurs at the ankle joint and is typified by the pointing of the toes, it occurs on the median plane about a horizontal axis.
Dorsiflextion – this also occurs at the ankle joint when the foot is raised upwards towards the tibia, this occurs in a median plane on a horizontal axis.
Inversion – this occurs when the sole of the foot is turned inwards and towards the midline of the body, this occurs on the frontal plane.
Eversion – eversion occurs when the sole of the foot is turned laterally outwards, this occurs in the frontal plane.
Examples Of joints and their Range of movements
Hinge Joint – Flexion and Extension
Pivot Joint – Rotation
Ellipsoid Joint – flexion, extension, adduction and abduction, giving Circumduction
Gliding Joint – a little movement in all directions.
Saddle Joint – flexion, extension, adduction and abduction, giving Circumduction
Ball and Socket Joint – Circumduction (adduction, abduction, flexion, extension)
Hinge Joint is found in the Elbow.
Pivot joint is found in the distal joints of the phalanges.
Ellipsoid joint is found in the metacarpophalangeal joint of the fingers.
Gliding joint is found between the clavicle and the sternum.
Saddle joint is found in the carpometacarpal joint of the thumb.
Ball and socket joint found in the hip.
In this picture the player is being lifted by two lifters in a rugby lineout, the rugby players are using many bones in this movement, and many movement types, they are using flexion and extension in the whole move of the life, as they go from a low crocheted flexed position, up into a tall extension, and so does the player being lifted, as they extend as high as possible to reach the ball in the air and gain and advantage over the opposite team.
In this photo the player has kicked a ball, he use’s many joints to do this, there is the gliding joint in the wrist, the pivot joint in the neck, the ball and socket joint in the hip, the saddle joint in the fingers, and the hinge joint in the knee.
The hip and the knee are allowing most of the movement in this kick, by using flexion and extension in the run up, and then full extension in the arms and the legs for the kick, which puts a lot of strain on the knee, but by its detailed joint type, it is able to take the strain of kicking without causing damage.