Joints and Movements
The Joints
Definition: A joint (articulation) is point of contact between bones or between bone and cartilage.
Joint Classifications
Joints are classified by: * The degree of movement they allow * The structure of the joint
The three types of joints that we will look at are: 1. Fibrous joints 2. Cartilaginous joints 3. Synovial joints
Fibrous Joints
These joints are also called "fixed" or "immoveable" joints, because they do not move. These joints have no joint cavity and are connected via fibrous connective tissue. The skull bones are connected by fibrous joints.

Cartilaginous Joints
These joints also have no joint cavity and the bones are connected tightly to each other with cartilage. These joints only allow a small amount of movement, so are also called "partly" or "slightly moveable" joints. The vertebrae are examples of cartilaginous joints.

Synovial Joints
Most of the joints in the body are synovial joints. These joints are "freely moveable" and are characterised by being surrounded by an articular capsule which contains the synovial fluid. Synovial fluid lubricates the joints, supplies nutrients to the cartilage and it contains cells that remove microbes and debris within the joint cavity. Because of the larger range of movements of these joints, there is an increased risk of injury eg dislocations. Synovial joints are located predominantly in limbs.
Many synovial joints also have ligaments either inside or outside the capsule.

The range of movement provided by these joints is determined by: * The closeness of the bones at the point of contact. Closer bones make stronger joints, but movements are more restricted. The looser the fit, the greater the range of movement. However, looser joints are more prone to dislocation. * The flexibility of the connective tissue and the position of the ligaments, muscles and tendons.
Different Types of Synovial Joints * Hinge - movement occurs primarily in a single plane eg elbow, knee , ankle, interphalangeal joints. * Ball and socket - allows movement around 3 axes - flexion / extension, abduction / adduction and rotation, eg shoulder, hip. * Pivot - a ring of bone and ligament surrounds the surface of the other bone - movement in one plane, primarily rotation eg between the atlas and axis (ie the cervical vertebrae numbers 1 and 2) and the radius and ulna. * Gliding - Flat bone surfaces allow side to side and backwards and forwards movements eg between carpals, tarsals, between the sternum and the clavicle (sterno-clavicular) and the scapula and the clavicle. * Condyloid - Not on syllabus * Saddle joints - eg thumb Notes:
Ligaments connect bone to bone - ligament - tough regularly arranged connective tissue, slightly elastic.
Tendons connect muscle to bone - tendon - non-elastic, flexible, connective tissue which allows the muscle to pull on the bone to create a movement. The tendon at the none moving end of a muscle is called the tendon of origin, at the moving end of a muscle it is called the tendon of insertion.
Exercise - long term effects on joints: 1. Stronger and denser bone 2. Denser cartilage 3. Ligaments stronger and will resist stretching 4. Tendons will become more flexible, and will form more attachments between the bone and the muscle 5. Increased supply of synovial fluid.
Joint Movements Anatomical PositionThe anatomical position is the universal starting position for describing movements, with the exception of horizontal flexion, which occurs when the arm moves forwards from an already abducted position (see later for explanation of these terms.)In the image on the right, the man is standing in the anatomical position, and the anatomical planes are shown.You do not need to know the planes in the syllabus, but they are used to describe movement. If the movement would not cross through the plane, it is said to occur within it. For example, if you turn your head to the right, the head moves in the horizontal plane (it is rotational moves that take place in the horizontal plane). If you lift your leg straight up, the movement occurs in the saggital plane. If you lift your leg to the side, the movement occurs in the frontal plane. Joint Movements (from anatomical position unless otherwise stated) Movement | Definition | Flexion | Narrowing joint angle in saggital plane (bending elbow) | Extension | Increasing joint angle in saggital plane (straightening elbows) | Hyperextension | Increasing angle more than in natural position, eg bending backwards | Abduction | Lifting a body part away from body midline (in frontal plane) | Adduction | Returning a body part to body midline (in frontal plane) | Rotation | Turning a body part on axis (horizontal plane) (not rotation all the way round - see circumduction). | Lateral flexion | Bending body sideways (frontal plane) | Lateral extension | Returning body to anatomical position | Elevation | Lifting a body part (shoulder shrugs) | Depression | Lowering a body part (dropping the jaw) | Protraction | Moving a body part outwards | Retraction | Bringing a body part back | Horizontal Flexion (starts from abducted position) | Moving arm forwards in horizontal plane | Horizontal Extension (starts from abducted position) | Returning arm to the abducted position | Dorsal Flexion | Bending ankle so that the toes are raised | Plantar Flexion | Hyperextending ankle joint so toes point downwards | Circumduction | Range of movements that create a complete circle (as opposed to a rotation of less than 360 degrees.) |
Notes:Flexion - joint angle decreases in size
Extension - joint angle increases in size
Hyperextension - increasing angle beyond natural position |