Chapter 8 The Skeletal System: Joints

Chapter 8: The Skeletal System - Joints

Joints

• Definition: Articulations of bones.

• Functions of Joints:

  • Hold bones together securely.

  • Provide mobility to the rigid skeleton.

Classification of Joints

Functional Classification

• Focus: Amount of movement allowed.

• Types of joints classified primarily in the axial skeleton, emphasizing firm attachment and internal organ protection:

  • Synarthroses: Immovable joints.

  • Amphiarthroses: Slightly movable joints.

• Joints that predominate in limbs, emphasizing mobility:

  • Diarthroses: Freely movable joints.

Structural Classification

• Basis: Whether fibrous tissue, cartilage, or a joint cavity separates the bony regions.

• General rules:

  • Fibrous Joints: Generally immovable.

  • Cartilaginous Joints:

  • Some are immovable (synarthrotic).

  • Most are slightly movable (amphiarthrotic).

  • Synovial Joints: Freely movable (diarthrotic).

Fibrous Joints

• Description: Bones united by fibrous tissue.

• Types:

  • Sutures: Irregular edges of bone interlock, bound tightly by connective tissue fibers; essentially no movement.

  • Syndesmoses: Connecting fibers are longer and allow more give.

  • Example: Joint connecting the distal ends of the tibia and fibula.

Cartilaginous Joints

• Description: Bone ends connected by cartilage.

• Types:

  • Slightly movable (amphiarthrotic):

  • Examples: Pubic symphysis, intervertebral joints.

  • Immovable (synarthrotic):

  • Examples: Hyaline cartilage epiphyseal plates of growing long bones, cartilaginous joints between the 1st ribs and the sternum.

Synovial Joints

• Description: Articulating bones are separated by a joint cavity filled with synovial fluid.

Features of Synovial Joints

• Articular cartilage: Hyaline cartilage covers ends of bones forming the joint.

• Fibrous articular capsule: Lined with a smooth synovial membrane, enclosing joint surfaces.

• Joint cavity: Filled with lubricating synovial fluid.

• Ligaments: Surround the capsule and reinforce the joint.

Structures Associated with the Synovial Joint

• Bursae: Flattened fibrous sacs lined with synovial membranes, filled with synovial fluid. Not part of the joint but reduce friction (act like ball bearings).

  • Common Locations: Where ligaments, muscles, skin, tendons, or bones rub together.

• Tendon Sheath: Elongated bursa that completely wraps around a tendon subjected to friction.

Types of Synovial Joints Based on Shape

• Plane Joint: Articular surfaces are essentially flat, allowing only short, gliding movements.

  • Type: Nonaxial; no rotation.

  • Example: Intercarpal joints of the wrist.

• Hinge Joint: Cylindrical end of one bone fits into a trough-shaped surface of another bone, allowing angular movement in one plane.

  • Type: Uniaxial; allows movement around one axis only.

  • Examples: Elbow, ankle, joints between phalanges.

• Pivot Joint: Rounded end of one bone fits into a sleeve or ring of bone (and possibly ligaments).

  • Type: Uniaxial; can only turn around its long axis.

  • Examples: Proximal radioulnar joint, joint between the atlas and the dens of the axis.

• Condyloid Joint (Ellipsoid Joint): Egg-shaped articular surface of one bone fits into the oval concavity of another bone.

  • Movement: Allows the moving bone to travel side to side and back and forth, but not rotation.

  • Type: Biaxial; movement around two axes.

  • Example: Metacarpophalangeal joints (knuckles).

• Saddle Joint: Each articular surface has both convex and concave areas, resembling a saddle.

  • Type: Biaxial; like condyloid joints.

  • Example: Carpometacarpal joints in the thumb.

• Ball & Socket Joint: Spherical head of one bone fits into a round socket of another.

  • Movement: Multiaxial joint; movement in all axes including rotation.

  • Examples: Shoulder and hip joints.

Inflammatory Conditions Associated with Joints

• Bursitis: Inflammation of a bursa, usually caused by a blow or friction.

• Tendonitis: Inflammation of tendon sheaths.

• Arthritis: Inflammatory or degenerative diseases of joints, with over 100 different types. It is the most widespread crippling disease in the United States.

Clinical Forms of Arthritis

• Osteoarthritis: Most common chronic arthritis, likely related to normal aging processes.

• Rheumatoid Arthritis: An autoimmune disease where the immune system attacks joints. Symptoms begin with bilateral inflammation of certain joints and often lead to deformities.

• Gouty Arthritis: Inflammation of joints caused by deposition of urate crystals from the blood, controllable usually by diet.

Body Movements

• Flexion: The process of bending or the state of being bent.

• Extension: The act of straightening or extending a flexed limb.

• Hyperextension: Flexion of a limb or part beyond its normal range.

• Rotation: The process of turning around an axis.

• Abduction: To draw away from the median plane or, in the case of digits, away from the axial line of a limb.

• Adduction: To draw toward the median plane or, in the case of digits, toward the axial line of a limb.

• Circumduction: Movement of a part in a circular direction.

• Dorsiflexion: Turning of the foot or toes upward.

• Plantar Flexion: Extension of the ankle resulting in the forefoot moving away from the body.

• Inversion: Turning inward.

• Eversion: Turning outward.

• Supination: Applied to hand; the act of turning the palm forward or upward, involving lateral rotation of the forearm.

  • Applied to foot; it generally implies movements resulting in raising of the medial margin of the foot.

• Pronation: Applied to hand; the act of turning the palm backward or downward, involving medial rotation of the forearm.

  • Applied to foot; a combination of eversion and abduction movements in tarsal and metatarsal joints, resulting in lowering of the medial margin of the foot.

• Opposition: Unique to the thumb, allowing it to oppose or turn back against the other four fingers, enabling refined grip when holding objects.