Articulation and Joints ( Chapter 9)

Understand the association between mobility and stability in joints.

 

There is an inverse relationship between mobility and stability in joints:

  • The more mobile a joint is, the less stable it tends to be.

  • The more stable a joint is, the less mobility it usually has.

 

  Mobility = how much a joint can move.

  Stability = how strong and secure a joint is.

 

 

Know and understand the structural and functional classification of joints.

 

  • Fibrous Joints – Two bones are held together by dense regular connective tissue. These joints allow little or no movement.
    Examples: Sutures of the skull, teeth in sockets (gomphosis), distal tibiofibular joint.

  • Cartilaginous Joints – Bones are joined together by cartilage. These joints allow limited movement and provide support and shock absorption.
    Examples: Intervertebral discs, pubic symphysis, epiphyseal plates.

  • Synovial Joints – Have a fluid-filled synovial cavity where bones are enclosed within a capsule and joined together by various ligaments. These are the most freely movable joints.
    Examples: Shoulder, hip, elbow, knee, wrist.

Functional Classifications of Joints

  • Synarthrosis – Immovable joints.
    Examples: Sutures of the skull, teeth in sockets.

  • Amphiarthrosis – Slightly movable joints.
    Examples: Pubic symphysis, intervertebral discs.

  • Diarthrosis – Freely movable joints (all synovial joints).
    Examples: Shoulder, hip, knee, elbow.

 

 

Know, and understand in detail, the structural composition of synovial joints as well as the range of mobility that is seen amongst synovial joints.

 

Basic Features

  • Articular Capsule – Surrounds the 2 ends of the bones that articulate, forming a tight space filled with synovial fluid. The capsule has an outer fibrous layer for strength and an inner synovial membrane that produces synovial fluid.

  • Joint Cavity – Cavity within the capsule filled with synovial fluid. This space allows the bones to move freely with reduced friction.

  • Synovial Fluid – Thick, slippery fluid found inside the joint cavity. Functions to lubricate the joint, reduce friction, absorb shock, and nourish the articular cartilage.

  • Articular Cartilage – Found along the articulating ends of each bone and functions to reduce friction and protect the actual bone from wear and tear. Made of smooth hyaline cartilage.

  • Ligaments – Strong bands of connective tissue that connect bone to bone. They stabilize and strengthen the joint while limiting excessive movement.

  • Blood Vessels – Supply oxygen and nutrients to the surrounding tissues of the joint and help remove waste products.

Accessory Structures

  • Bursae – Fibrous, saclike structures that contain synovial fluid and are lined by a synovial membrane. They act like cushions or fat pads that fill spaces when bones move and the joint cavity changes shape. Often scattered around the periphery of a joint and function as packing material while providing protection and reducing friction between bones, tendons, and muscles.

  • Tendons – Attach muscles to bones and help stabilize joints. Tendons also assist with movement by transmitting the force of muscle contraction to the bone.

 

Synovial joints have the greatest range of motion of all joint types. The amount of movement depends on the shape of the joint surfaces and supporting ligaments/muscles.

 

 

 

 

 

Know and understand the types of synovial joints.

  Planar (Gliding) Joints – Uniaxial/nonaxial joints that allow small sliding or gliding movements.
Example: Wrist joints (intercarpal joints).

  Hinge Joints – Uniaxial joints that allow movement in one direction (flexion and extension).
Example: Elbow.

  Pivot Joints – Uniaxial joints that allow rotational movement.
Example: Atlas and dens (C1–C2 vertebrae).

  Condyloid (Ellipsoid) Joints – Biaxial joints that allow movement in two planes.
Example: Fingers/knuckles (metacarpophalangeal joints).

  Saddle Joints – Biaxial joints with greater flexibility and movement in two planes.
Example: Thumb joint.

  Ball-and-Socket Joints – Multiaxial joints that allow movement in all directions, including rotation.
Example: Hips and shoulders.

 

 

 

Be able to identify and distinguish amongst uniaxial, biaxial and multiaxial joints.

 

 Uniaxial Joints – Bones move in one plane/axis.
Examples: Hinge joints (elbow) and pivot joints (atlas-axis).

  Biaxial Joints – Bones move in two planes/axes.
Examples: Condyloid joints (fingers/knuckles) and saddle joints (thumb).

  Multiaxial Joints – Bones move in multiple planes/axes and allow the greatest range of motion.
Example: Ball-and-socket joints (hips and shoulders).

 

 

Know and be able to demonstrate the terms for movement at synovial joints.

Flexion: Decreasing the angle of the joint, bending the joint

Extension: Increasing the angle of the joint, straightening the joint

Dorsiflexion: Decreasing the angle of the ankle joint

Plantarflexion: Increasing the angle of the ankle joint

Elevation: Moving a body part in a superior position

Depression: Moving a body part in an inferior position

Eversion: Rotating the ankle so that the sole of the foot points away from the other

Inversion: Rotating the ankle joint so that the sole of the foot points toward the other

Abduction: Moving a limb away from the medial line of the body

Adduction: Moving a limb towards the medial line of the body

Lateral Rotation: Rotating a limb away from the center line of the body

Medial Rotation: Rotating a limb away towards the center line of the body

Pronation: Rotating the forearm so that the palm faces down

Supination: Rotating the forearm so that the palm faces up

Retraction: Posterior movement bringing the shoulders back

Protraction: Anterior Movement bringing the shoulders forward

Lateral Flexion: Bending the spine to the side away from the medial line of the body.