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Structural classification—joints are named according to one of the following:
- Type of connective tissue that joins bones together (fibrous or cartilaginous joints)
- Presence of a fluid-filled joint capsule (synovial joint)
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Functional classification—joints are named according to degree of movement allowed:
- •Synarthroses —immovable joint
- •Amphiarthroses —slightly movable
- •Diarthroses —freely movable
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Synarthroses (Fibrous joints)
- bones of joints fit together closely, allowing little or no movement (Figure 9-1)
- –Syndesmoses —joints in which ligaments connect two bones
- –Sutures —found only in skull; toothlike projections from adjacent bones interlock with each other
- –Gomphoses —between root of a tooth and the alveolar process of the mandible or maxilla
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Amphiarthroses (Cartilaginous joints)
- bones of joints are joined together by hyaline cartilage or fibrocartilage; allow very little motion (Figure 9-2)
- Synchondroses —hyaline cartilage present between articulating bones
- Symphyses —joints in which a pad or disk of fibrocartilage connects two bones
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Synovial joints (diarthroses)—freely movable joints (Figure 9-3)
- •Joint capsule —sleevelike casing around ends of bones, binding them together
- •Synovial membrane —lines joint capsule and also secretes synovial fluid
- •Articular cartilage— hyaline cartilage covering articular surfaces of bones
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Structures of synovial joints
- • Joint cavity —small space between the articulating surfaces of the two bones of the joint
- • Menisci (articular disks) —pads of fibrocartilage located between articulating bones
- • Ligaments —strong cords of dense, white, fibrous tissue that hold bones of synovial joint more firmly together
- • Bursae —synovial membranes filled with synovial fluid; cushion joints and facilitate movement of tendons
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Uniaxial joints
synovial joints that permit movement around only one axis and in only one plane
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Hinge joints
articulating ends of bones form a hinge-shaped unity that allows only flexion and extension ex. Elbow and knee joints
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Pivot joints
a projection of one bone articulates with a ring or notch of another bone, ex. C1, C2 joint (dens of axis rotating against atlas) and head of radius and ulna
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Biaxial joints
synovial joints that permit movements around two perpendicular axes in two perpendicular planes
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Saddle joints
synovial joints in which the articulating ends of the bones resemble reciprocally shaped miniature saddles; only occurrence in body is in thumbs (carpo-metacarpal joint)
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Condyloid (ellipsoidal) joints
synovial joints in which a condyle fits into an elliptical socket. Ex. Atlanto-occipital joint
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Multiaxial joints
synovial joints that permit movements around three or more axes in three or more planes
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Ball and socket (spheroid) joints
most movable joints; ball-shaped head of one bone fits into a concave depression. Ex. Shoulder and hip joints
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Gliding joints
- relatively flat articulating surfaces that allow limited gliding movements along various axes.
- ex. Facet joints between articular processes of vertebrae
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Humeroscapular joint (Figure 9-5)
- Shoulder joint, a ball and socket joint
- Multiaxial joint
- Most mobile joint because of the shallowness of the glenoid cavity
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Glenoid labrum
- narrow rim of fibrocartilage around glenoid cavity that lends depth to the cavity
- Structures that strengthen the shoulder joint are ligaments, muscles, tendons, and bursae
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Humeroradial joint
lateral articulation of capitulum of humerus with head of radius
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Humeroulnar joint
medial articulation of trochlea of humerus with trochlear notch of ulna
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Proximal radioulnar joint
- between head of radius and medial notch of ulna
- –Stabilized by annular ligament
- –Permits rotation of forearm
- –Dislocation of radial head called “pulled elbow”
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Distal radioulnar joint
- point of articulation between ulnar notch of radius and head of ulna
- Together with proximal radioulnar joint, permits pronation and supination of forearm
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Radiocarpal (wrist) joints (Figure 9-7)
- Only radius articulates directly with carpal bones distally (scaphoid and lunate)
- –Joints are synovial
- –Scaphoid bone is fractured frequently
- –Portion of fractured scaphoid may become avascular
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