Joints 8

Joints (Articulations) Weakest parts of the skeleton Articulation – site where two or more bones meet Functions of joints Give the skeleton mobility Hold the skeleton together

Classification of Joints: Structural Structural classification focuses on the material binding bones together and whether or not a joint cavity is present The three structural classifications are: Fibrous Cartilaginous Synovial

Fibrous Structural Joints The bones are joined by fibrous tissues There is no joint cavity Most are immovable There are three types – sutures, syndesmoses, and gomphoses

Fibrous Structural Joints: Sutures Occur between the bones of the skull Comprised of interlocking junctions completely filled with connective tissue fibers Bind bones tightly together, but allow for growth during youth

Fibrous Structural Joints: Sutures Figure 8.1a

Fibrous Structural Joints: Syndesmoses Bones are connected by a fibrous tissue ligament Movement varies from immovable to slightly variable Examples include the connection between the tibia and fibula, and the radius and ulna

Fibrous Structural Joints: Syndesmoses Figure 8.1b

Fibrous Structural Joints: Gomphoses The peg-in-socket fibrous joint between a tooth and its alveolar socket The fibrous connection is the periodontal ligament

Articulating bones are united by cartilage Lack a joint cavity Cartilaginous Joints Articulating bones are united by cartilage Lack a joint cavity Two types – synchondroses and symphyses

Cartilaginous Joints: Synchondroses A bar or plate of hyaline cartilage unites the bones All synchondroses are synarthrotic Examples include: Epiphyseal plates of children Joint between the costal cartilage of the first rib and the sternum

Cartilaginous Joints: Synchondroses Figure 8.2a, b

Cartilaginous Joints: Symphyses Hyaline cartilage covers the articulating surface of the bone and is fused to an intervening pad of fibrocartilage Amphiarthrotic joints designed for strength and flexibility Examples include intervertebral joints and the pubic symphysis of the pelvis

Cartilaginous Joints: Symphyses Figure 8.2c

All are freely movable diarthroses Synovial Joints Those joints in which the articulating bones are separated by a fluid-containing joint cavity All are freely movable diarthroses Examples – all limb joints, and most joints of the body

Synovial Joints: General Structure Synovial joints all have the following Articular cartilage Joint (synovial) cavity Articular capsule Synovial fluid Reinforcing ligaments

Synovial Joints: General Structure Figure 8.3a, b

Synovial Joints: Friction-Reducing Structures Bursae – flattened, fibrous sacs lined with synovial membranes and containing synovial fluid Common where ligaments, muscles, skin, tendons, or bones rub together Tendon sheath – elongated bursa that wraps completely around a tendon

Synovial Joints: Movement The two muscle attachments across a joint are: Origin – attachment to the immovable bone Insertion – attachment to the movable bone Described as movement along transverse, frontal, or sagittal planes

Synovial Joints: Range of Motion Nonaxial – slipping movements only Uniaxial – movement in one plane Biaxial – movement in two planes Multiaxial – movement in or around all three planes

Types of Synovial Joints Plane joints Articular surfaces are essentially flat Allow only slipping or gliding movements Only examples of nonaxial joints Figure 8.7a

Types of Synovial Joints Hinge joints Cylindrical projections of one bone fits into a trough-shaped surface on another Motion is along a single plane Uniaxial joints permit flexion and extension only Examples: elbow and interphalangeal joints

Types of Synovial Joints Figure 8.7b

Only uniaxial movement allowed Pivot Joints Rounded end of one bone protrudes into a “sleeve,” or ring, composed of bone (and possibly ligaments) of another Only uniaxial movement allowed Examples: joint between the axis and the dens, and the proximal radioulnar joint

Pivot Joints Figure 8.7c

Condyloid, or Ellipsoidal, Joints Oval articular surface of one bone fits into a complementary depression in another Both articular surfaces are oval Biaxial joints permit all angular motions Examples: radiocarpal (wrist) joints, and metacarpophalangeal (knuckle) joints

Condyloid, or Ellipsoidal, Joints Figure 8.7d

Similar to condyloid joints but allow greater movement Saddle Joints Similar to condyloid joints but allow greater movement Each articular surface has both a concave and a convex surface Example: carpometacarpal joint of the thumb

Saddle Joints Figure 8.7e

Ball-and-Socket Joints A spherical or hemispherical head of one bone articulates with a cuplike socket of another Multiaxial joints permit the most freely moving synovial joints Examples: shoulder and hip joints

Ball-and-Socket Joints Figure 8.7f

One flat bone surface glides or slips over another similar surface Gliding Movements One flat bone surface glides or slips over another similar surface Examples – intercarpal and intertarsal joints, and between the flat articular processes of the vertebrae

Flexion — bending movement that decreases the angle of the joint Angular Movement Flexion — bending movement that decreases the angle of the joint Extension — reverse of flexion; joint angle is increased Dorsiflexion and plantar flexion — up and down movement of the foot Abduction — movement away from the midline Adduction — movement toward the midline Circumduction — movement describes a cone in space

Gliding Movement Figure 8.5a

Angular Movement Figure 8.5b

Angular Movement Figure 8.5c, d

Angular Movement Figure 8.5e, f

The turning of a bone around its own long axis Rotation The turning of a bone around its own long axis Examples Between first two vertebrae Hip and shoulder joints Figure 8.5g

Supination and pronation Inversion and eversion Special Movements Supination and pronation Inversion and eversion Protraction and retraction Elevation and depression

Special Movements Figure 8.6a

Special Movements Figure 8.6b

Special Movements Figure 8.6c

Special Movements Figure 8.6d