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Joints (Articulations) Chapter The Weakest parts of the skeleton Articulation – site where two or more bones meet Functions of joints Joints 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 Give the skeleton mobility Hold the skeleton together Classification of Joints: Functional Functional classification is based on the amount of movement allowed by the joint The three functional classes of joints are: Synarthroses – immovable Amphiarthroses – slightly movable Diarthroses – freely movable Fibrous Structural Joints: Sutures The bones are joined by fibrous tissues Occur between the bones of the skull There is no joint cavity Most are immovable Comprised of interlocking junctions completely filled with connective tissue fibers There are three types – sutures, syndesmoses, and gomphoses Bind bones tightly together, but allow for growth during youth In middle age, skull bones fuse and are called synostoses 1 Fibrous Structural Joints: Sutures 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 Figure 8.1a Fibrous Structural Joints: Syndesmoses Fibrous Structural Joints: Gomphoses The peg-in-socket fibrous joint between a tooth and its alveolar socket The fibrous connection is the periodontal ligament Figure 8.1b Cartilaginous Joints Cartilaginous Joints: Synchondroses Articulating bones are united by cartilage A bar or plate of hyaline cartilage unites the bones Lack a joint cavity All synchondroses are synarthrotic Two types – synchondroses and symphyses Examples include: Epiphyseal plates of children Joint between the costal cartilage of the first rib and the sternum 2 Cartilaginous Joints: Synchondroses 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 Figure 8.2a, b 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: 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: General Structure Synovial joints all have the following Articular cartilage Joint (synovial) cavity Articular capsule Synovial fluid Reinforcing ligaments Synovial Joints: Friction-Reducing Structures Figure 8.4 3 Synovial Joints: Stability Stability is determined by: Articular surfaces – shape determines what movements are possible Ligaments – unite bones and prevent excessive or undesirable motion Synovial Joints: Movement Muscle tone is accomplished by: Muscle tendons across joints acting as stabilizing factors Tendons that are kept tight at all times by muscle tone 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 Angular Movement Flexion — bending movement; decreases the joint angle Extension — reverse of flexion; joint angle is increased Dorsiflexion — up movement of the foot Plantar flexion — down movement of the foot Abduction — movement away from the midline Adduction — movement toward the midline Circumduction — movement describes a cone in space 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 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 Special Movements Supination and pronation Inversion and eversion Protraction and retraction Elevation and depression Opposition 4 Plane Joint Types of Synovial Joints Plane joints Hinge joints Articular surfaces are essentially flat Cylindrical projections of one bone fits into a trough-shaped surface on another Allow only slipping or gliding movements Motion is along a single plane Uniaxial joints permit flexion and extension only Examples: elbow and interphalangeal joints Only examples of nonaxial joints Figure 8.7a Hinge 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 Figure 8.7b Pivot Joints 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 Figure 8.7c 5 Condyloid or Ellipsoidal Joints 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 Figure 8.7d Saddle Joints 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 Figure 8.7e Ball-and-Socket Joints Synovial Joints: Knee Largest and most complex joint of the body Allows flexion, extension, and some rotation Three joints in one surrounded by a single joint cavity Femoropatellar joint Lateral and medial tibiofemoral joints Figure 8.7f 6 Synovial Joints: Knee Ligaments and Tendons – Anterior View Tendon of the quadriceps femoris muscle Lateral and medial patellar retinacula Fibular and tibial collateral ligaments Patellar ligament Synovial Joints: Knee – Other Supporting Structures Anterior cruciate ligament Posterior cruciate ligament Medial meniscus (semilunar cartilage) Lateral meniscus Figure 8.8c Synovial Joints: Knee – Other Supporting Structures Synovial Joints: Knee – Posterior Superficial View Adductor magnus tendon Articular capsule Oblique popliteal ligament Arcuate popliteal ligament Semimembranosus tendon Figure 8.8b Synovial Joints: Elbow Hinge joint that allows flexion and extension only Radius and ulna articulate with the humerus Ligaments of the Elbow Annular ligament Ulnar collateral ligament Radial collateral ligament Figure 8.8e Synovial Joints: Shoulder (Glenohumeral) Ball-and-socket joint in which stability is sacrificed to obtain greater freedom of movement Head of humerus articulates with the glenoid fossa of the scapula 7 Synovial Joints: Shoulder Stability Synovial Joints: Shoulder Stability Weak stability is maintained by: Thin, loose joint capsule Four ligaments – coracohumeral, and three glenohumeral Tendon of the long head of biceps, which travels through the intertubercular groove and secures the humerus to the glenoid cavity Rotator cuff (four tendons) that encircles the shoulder joint and blends with the articular capsule Figure 8.11a Synovial Joints: Shoulder Stability Synovial Joints: Hip (Coxal) Joint Ball-and-socket joint Head of the femur articulates with the acetabulum Good range of motion, but limited by the deep socket and strong ligaments Figure 8.11b Synovial Joints: Hip Stability Acetabular labrum Iliofemoral ligament Pubofemoral ligament Ischiofemoral ligament Ligamentum teres Temporomandibular Joint Mandibular condyle articulate with the temporal bone Two types of movement Hinge – depression and elevation of mandible Side to side – (lateral excursion) grinding of teeth 8
