Anatomy of Joints

Joints

• Joints are where two or more bones meet. Movement may or may not occur between them.
• Joints are classified according to the tissue between the articulating bones.
• Synovial joints have a fluid-filled space (synovial cavity) separating the bones.

Types of Joints by Structure

• Synovial Joints
  • Characterized by a fluid-filled space between the bones, allowing for free movement.
  • Include subcategories like hinge, ball and socket, ellipsoid, saddle, gliding.
• Fibrous Joints
  • Immovable or slightly movable joints, held together by fibrous connective tissue.
  • Sutures in the skull are an example.
• Cartilaginous Joints
  • Slightly movable joints, connected by cartilage.
  • Examples include synchondroses (growth plates) and symphyses (pubic symphysis, intervertebral discs).

Synovial Joint Features

• Articular Cartilage: Smooth cartilage covering the bone surfaces to reduce friction.
• Articular Capsule: A fibrous capsule surrounding the joint to provide support, with inner synovial membrane.
• Synovial Fluid: Fluid within the cavity that reduces friction and provides nutrients for cartilage.
• Accessory Ligaments: (Extracapsular and intracapsular) ligaments that provide additional support and stability around or inside the joint.

Fibrous Joints

• Sutures: Found only in the skull, these are immovable joints connected by a thin layer of fibrous connective tissue.
• Gomphoses: Occur only between teeth and adjacent bone. Ligaments hold the teeth in their sockets.
• Syndesmoses: Two bones connected by ligament. Examples include the ligament connecting the radius and ulna in the forearm.

Cartilaginous Joints

• Synchondroses: Occur between developing bones, like growth plates. Cartilage separates the bones until they fuse.
• Symphyses: Two bones are separated by cartilage. Examples include the pubic symphysis and intervertebral discs between vertebrae.

Movements at Synovial Joints

• Flexion: Bending a body part.
• Extension: Straightening a body part.
• Abduction: Moving a limb away from the midline.
• Adduction: Moving a limb towards the midline.
• Medial Rotation: Turning a limb towards the midline.
• Lateral Rotation: Turning a limb away from the midline.
• Circumduction: Moving a limb in a circular motion while maintaining its point of contact.
• Inversion: Moving the sole of the foot inward.
• Eversion: Moving the sole of the foot outward.
• Dorsiflexion: Moving the top of the foot toward the shin.
• Plantar flexion: Moving the heel of the foot towards the ground.
• Supination: Rotating the forearm so the palm faces anteriorly.
• Pronation: Rotating the forearm so the palm faces posteriorly.

Muscle Actions

• Muscles need nerves to function.
• Muscles produce movement by crossing over joints.
• Muscles are attached to bones via attachments called the origin and insertion.
• Insertion generally moves toward the origin when a muscle contracts.