Types of joints

Bones and joints

Types of bones

The skeleton is composed of many bones which produce movement; each bone is connected to another by connective tissue.

The cranium is made up of fibrous connective tissue which is why it does not move. Fibro cartilage is used for areas such as in-between the vertebrae which provide semi-movable joints.

Synovial joints are the ones that allow free movement, and are held loosely together by ligaments which are a form of connective tissue. A sleeve-like ligament joins one bone loosely to another. This then forms a fibrous capsule, which allows free movement within a synovial joint.

The capsule is lined with a synovial membrane. This secretes fluid which is similar to the white of an egg. This fluid lubricates the joint; it also contains phagocytic cells, which, with the constant wear and tear at the joint, helps to remove the debris that is produced as well as nourishing the articular cartilage. This provides a smooth coating that covers the end of each bone, therefore protecting them from wear and tear which is brought about by friction.

Extra strength is produced by the ligaments that run outside the articular capsule or the inside of a joint. Discs of cartilage are contained in some joints which help to maintain stability.

Muscles are the main support for joints as they surround them:

The synovial joints in the body are:

• Hand

The type of joint is gliding.

The movement produced is clenching (flexion), stretching (extension).

• Foot

The type of joint is gliding.

The movement produced inversion and eversion.

• Toe

This is a hinge joint.

The movement produced is extension and flexion, the base of the toe joint allows abduction and adduction.

• Finger

This is a hinge joint and it produces the same movement as the toe.

• Wrist

The type of joint is a condyloid which is formed between the bones of the lower arm which are the radius and ulna and the wrist bones which are the carpals.

• Ankle

This is a hinge joint, which is formed between the bones of the lower leg tibia and fibula and also the talus of the foot. The action produced is dorsi flexion this is produced by the foot pulled up towards the knee and also plantar flexion, this is when the foot is being pointed.

• Forearm

The is a pivot joint which is formed between the ulna and head of the radius

The movement produced is supination when the palm of the hand turns up, and pronation when the hand is turned downwards.

• Elbow

This is a hinge joint, formed between the humerus and the ulna. The movement produced is flexion and extension of the arm.

• Knee

This is a hinge joint formed between the femur and tibia. The movement produced is flexion and extension of the leg.

• Shoulder

This is a ball and socket joint; the head of the humerus is ball shaped and this fits into the socket on the scapula. The movement produced is abduction, adduction, extension, flexion and rotation. Also arm circling which involves movement of this joint together with the shoulder.

• Hip

This is a ball and socket joint; the femur head is shaped like a ball and this fits into the pelvis socket. The movements produced are abduction, adduction, extension, flexion and rotation.

Fibrous joints

The type of examples of these joints is between the maxilla and mandible of the jaw, between the teeth where no movement occurs. Usually the bone’s edges are fused together into each other, as mentioned before in the sutures of the skull.

Fibro cartilage

Examples of these joints are the vertebrae spine and between the pubis bone. They have very slight movement. The joint is made up of a pad of fibro cartilage between the ends of the bones; this is the joint and this acts as a shock absorber.

Synovial joints

Synovial joints are by far the most common classification of joint within the human body. They are moveable and all have:

• A synovial capsule surrounding the entire joint.
• A synovial membrane, which lines the inner capsule and secretes synovial fluid – a lubricating liquid.
• Hyaline cartilage, which protects the ends of the articulating bones.

There are six types of synovial joints that are classified by the shape of the joint and the movement available.

Types of synovial joints