joints.docx

Joints Joints (Articulations) • Weakest parts of the skeleton • Articulation – site where two or more bones meet • Functions • 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 Classification of Joints: Functional • Functional classification is based on the amount of movement allowed by the joint • The three functional class of joints are: • Synarthroses – immovable • Amphiarthroses – slightly movable • Diarthroses – freely movable Fibrous Structural Joints • The bones are jointed 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 CT fibers • Bind bones tightly together, but allow for growth during youth • In middle age, skull bones fuse and are called synostoses 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: Gomphoses • The peg-in-socket fibrous joint between a tooth and its alveolar socket • The fibrous connection is the periodontal ligament 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: 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 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: 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: Stability • Stability is determined by: • Articular surfaces – shape determines what movements are possible • Ligaments – unite bones and prevent excessive or undesirable motion • Muscle tone is accomplished by: • Muscle tendons across joints are the most important stabilizing factor • Tendons are kept tight at all times by muscle tone Synovial Joints: Movement • Muscle attachment across a joint • 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 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 Angular Movement • Flexion • Extension • Dorsiflexion and plantar flexion of the foot • Abduction • Adduction • Circumduction Rotation • The turning of a bone around its own long axis • Examples: • Between first two vertebrae • Hip and shoulder joints Special Movements • Supination and pronation • Inversion and eversion • Protraction and retraction • Elevation and depression • Opposition Types of Synovial Joints • Plane joints • Articular surfaces are essentially flat • Allow only slipping or gliding movements • Only examples of nonaxial 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 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 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 Saddle Joints • Similar to condyloid joints but with greater movement • Each articular surface has both a concave and a convex surface • Example: carpometacarpal joint of the thumb Ball-and-Socket Joints • A spherical or hemispherical head of one bone articulates with a cuplike socket of an