Joints (Articulations)

1. 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

2. 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

3. 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

4. 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

5. 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 • In middle age, skull bones fuse and are called synostoses

6. Fibrous Structural Joints: Sutures Figure 8.1a

7. 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

8. Fibrous Structural Joints: Syndesmoses Figure 8.1b

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

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

11. 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

12. 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

13. 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

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

15. Synovial Joints: General Structure Figure 8.3a, b

16. 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

17. Synovial Joints: Friction-Reducing Structures Figure 8.4

18. Synovial Joints: Stability • Stability is determined by: • Articular surfaces – shape determines what movements are possible • Ligaments – unite bones and prevent excessive or undesirable motion

19. Synovial Joints: Stability • Muscle tone is accomplished by: • Muscle tendons across joints acting as stabilizing factors • Tendons that are kept tight at all times by muscle tone

20. 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

21. 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

22. 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

23. 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

24. Angular Movement • Abduction — movement away from the midline • Adduction — movement toward the midline • Circumduction — movement describes a cone in space

25. Gliding Movement Figure 8.5a

26. Angular Movement Figure 8.5b

27. Angular Movement Figure 8.5c, d

28. Angular Movement Figure 8.5e, f

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

30. Special Movements • Supination and pronation • Inversion and eversion • Protraction and retraction • Elevation and depression • Opposition

31. Special Movements Figure 8.6a

32. Special Movements Figure 8.6b

33. Special Movements Figure 8.6c

34. Special Movements Figure 8.6d

35. Special Movements Figure 8.6e