Articulations
Articulations, also known as joints, are the areas where bones come together to allow movement in the body. There are four structural classes of joints: bony fusion, fibrous, cartilaginous, and synovial, and three functional classes: synarthrosis, amphiarthrosis, and diarthrosis.
Functional Classes
· Synarthrosis are immovable joints that provide stability and support to the body. Examples include the sutures of the skull and the gomphoses of the teeth.
· Amphiarthrosis are slightly movable joints that allow for the joints to make incremental adjustments based on muscular stresses.
· Diarthrosis are movable joints that allow for a wide range of movement in the body. Examples include the synovial joints of the shoulder and knee.
Structural Classes
Figure 60: Sutures of the skull
Figure 61: Syndesmoses or Interosseous between radius and ulna
· Bony Fusion is also called synostosis. These joints are named so due to the fusing of multiple bones into a one during fetal development, examples include; the frontal bone and the coxal bones. These joint types are synarthrosis.
· Fibrous joints are characterized by the presence of fibrous connective tissue between the bones.
o Sutures are found in the skull and are immovable joints that fuse the bones together. The bones are held together by a thin layer of connective tissue called a sutural ligament. These joint types are synarthrosis.
o Syndesmoses are joints where the bones are held together by ligaments. Interosseous joints allow for limited movement and can be found between the radius and ulna. These joint types are amphiarthrosis.
o Gomphoses are specialized joints found in the teeth. They are held in place by the periodontal ligament, which attaches the tooth to the socket in the jawbone. These joint types are synarthrosis.
Figure 62: Synchondroses of costal cartilage
Figure 63: Symphyses highlighted in blue
· Cartilaginous joints are characterized by the presence of cartilage between the bones. There are two types of cartilaginous joints: synchondroses and symphyses.
o Synchondroses are joints where the bones are held together by hyaline cartilage. They are found in the growth plates of children and in the joints between the ribs and the sternum. These joint types are synarthrosis.
o Symphyses are joints where the bones are held together by fibrocartilage. They allow for limited movement and are found in the pubic symphysis and the intervertebral discs. These joint types are amphiarthrosis.
· Synovial joints are characterized by the presence of a joint cavity filled with synovial fluid surrounded by synovial membrane with articulation cartilage protecting the ends of the bones all encased in ligaments. They allow for a wide range of movement and are the most common type of joint in the body. There are six types of synovial joints: ball-and-socket, hinge, pivot, saddle, condyloid, and gliding. All synovial joints are diarthrosis.
o Ball-and-socket joints allow for a wide range of movement in all directions and are found in the shoulder and hip.
o Hinge joints allow for movement in only one plane, like a door hinge, and are found in the elbow and knee.
o Pivot joints allow for rotational movement and are found in the neck.
o Saddle joints allow for movement in two planes and are found in the thumb.
o Condyloid (Ellipsoid) joints allow for movement in two planes but not rotation and are found in the wrist.
o Planar joints allow for sliding or gliding movements and are found in the vertebrae and the bones of the wrist and ankle.
The structural and functional classes of joints is essential in the study of human anatomy and physiology. Different joints allow for different types of movement and provide stability and support to the body. The more movement a joint has, the more unstable it becomes.
Figure 64: Synovial Joint Anatomy
Joint Movements
Articulation movements are the different types of movements that occur at joints between bones in the human body. Understanding these movements is important for understanding how the body moves and functions. In this explanation, we will discuss the different types of articulation movements.
· Flexion is a movement that decreases the angle between two bones at a joint. For example, when you bend your elbow, you are flexing your arm at the elbow joint.
· Extension is the opposite of flexion and is a movement that increases the angle between two bones at a joint. For example, when you straighten your elbow, you are extending your arm at the elbow joint.
· Abduction is a movement that moves a body part away from the midline of the body. For example, when you raise your arm out to the side, you are abducting your arm at the shoulder joint.
· Adduction is the opposite of abduction and is a movement that brings a body part closer to the midline of the body. For example, when you lower your arm back down to your side, you are adducting your arm at the shoulder joint.
· Rotation is a movement that involves the turning of a bone around its own axis. For example, when you turn your head from side to side, you are rotating your neck at the cervical spine.
o Pronation is a rotation movement of the forearm that turns the palm of the hand down. For example, when you turn your forearm to place your palm facing down, you are pronating your forearm at the radioulnar joint.
o Supination is the opposite of pronation and is a rotation movement of the forearm that turns the palm of the hand up. For example, when you turn your forearm to place your palm facing up, you are supinating your forearm at the radioulnar joint.
o Lateral rotation refers to the movement of a body part away from the midline of the body. This movement occurs in joints that allow rotation, such as the hip or shoulder. During lateral rotation, the anterior surface of the body part rotates away from the midline, while the posterior surface rotates towards the midline. For example, in the hip joint, lateral rotation of the thigh would move the foot away from the midline of the body.
o Medial rotation refers to the movement of a limb or body part towards the midline of the body. This movement is produced by the contraction of muscles that attach to the bone being rotated. Medial rotation is important for various activities such as throwing a ball, reaching for an object, and walking. It is controlled by the nervous system and involves the coordination of multiple muscle groups working together.
· Circumduction is a combination of flexion, extension, abduction, and adduction movements. It is a circular movement that involves the movement of a body part in a cone shape. For example, when you move your arm in a circular motion, you are circumducting your arm at the shoulder joint.
· Dorsiflexion is a movement that brings the foot towards the shin. For example, when you lift your foot up towards your shin, you are dorsiflexing your foot at the ankle joint.
· Plantarflexion is the opposite of dorsiflexion and is a movement that extends the foot away from the shin. For example, when you point your toes down towards the ground, you are plantarflexing your foot at the ankle joint.
· Inversion is a movement that turns the sole of the foot towards the midline of the body. For example, when you turn your foot inwards, you are inverting your foot at the ankle joint.
· Eversion is the opposite of inversion and is a movement that turns the sole of the foot away from the midline of the body. For example, when you turn your foot outwards, you are everting your foot at the ankle joint.
Overview
Articulations, also known as joints, are the areas where bones come together to allow movement in the body. There are four structural classes of joints: bony fusion, fibrous, cartilaginous, and synovial, and three functional classes: synarthrosis, amphiarthrosis, and diarthrosis. Understanding the different types of joint movements and their functions is important for healthcare professionals in diagnosing and treating joint-related conditions and injuries.