JOINTS

1. JOINTS Chapter 9

2. Introduction • Joints or articulations are sites where two or more bones meet • Joints have two fundamental functions: • provide for skeletal mobility • hold the skeleton together • Weakest parts of the skeleton, yet have a remarkable ability to resist the forces that tear them apart

3. Classification of Joints • Structural classification • focuses on the material binding the bones together and whether or not there is a joint cavity (fibrous, cartilaginous, synovial) • Functional classification • based on the amount of movement allowed at the joint (synarthroses, amphiarthoroses, diarthroses)

4. Functional Classification • Synarthroses • Immovable joints • Amphiarthroses • Slightly movable joints • Diarthroses • Freely movable joints

5. Structural Classification • Fibrous • Joined by fibrous tissue • Cartilaginous • Joined by cartilage • Synovial • The bones are joined and surrounded by a joint cavity • Note: • Structural classification is the system used in your text

6. Summary of Joint Classes • Fibrous joints • Suture • Syndesmoses • Gomphoses • Cartilaginous joints • Synchondroses • Symphyses • Synovial • Gliding, hinge, pivot, condyloid, saddle, and ball and socket

7. Fibrous Joints In fibrous joints the bones are joined by fibrous tissue; no joint is present. The three types of fibrous joints are. . . • Sutures • Dense fibrous connective tissue • Syndesmosis • A cord or band of connective tissue • Gomphosis • Peg-in-socket arrangement surrounded by fibrous tissue or peridontal ligament

8. Suture Joint • Occurs only between bones of the skull • Wavy articulating bone edges interlock • Junction is filled by connective tissue • Rigid splices bind bones of the skull together tightly

9. Syndesmosis • Longer fibrous tissue occurs as a sheet or membrane • Longer fibrous tissue permits the joint to “give” or flex • True movement is not possible

10. Gomphosis • Fibrous tissue holds teeth in their sockets • Teeth embedded in sockets of bone • Anchored by fibers of periodontal ligament

11. Cartilaginous Joints In cartilaginous joints, the articulating bones are united by cartilage, there is no joint cavity • Synchondroses • Hyaline cartilage unites the bones • Symphyses • Fibrocartilage unites the bones

12. Synchondroses • Hyaline cartilage unites the bones • Epiphyseal plates in growing children • Provide for bone growth • When growth ends all synchondroses become immovable Epipyseal Plate

13. Synchrondroses • Sternocostal joint between the manubrium and rib 1 is a immovable hyaline cartilage joint

14. Symphyses • Bone surfaces are covered with articular hyaline cartilage which is fused to a pad of fibrocartilage • Fibrocartilage is resilient and acts as a shock absorber and permits limited movement

15. Synovial Joints • In synovial joints articulating bones are located within a fluid containing joint cavity • Synovial joints permit substantial range of motion • All synovial joints have similar features

16. Structures of Synovial Joint • Articular cartilage • Hyaline cartilage on opposing bone surfaces • Joint (synovial) cavity • Space filled with fluid • Articular capsule • Capsule to confine fluid • Synovial fluid • Fluid to lubricate joints • Reinforcing ligaments • Maintain joint alignment

17. Articular Cartilage • Hyaline cartilage covers the bone surfaces • Cartilage absorbs the compression placed on the joint • Cartilage keeps the bone ends from being crushed

18. Joint (synovial) cavity • Joint spaces are unique to synovial joints • Joint spaces are filled with synovial fluid

19. Articular capsule • The joint cavity is enclosed by a double layered articular capsule • The external layer is a tough flexible fibrous capsule • The inner synovial membrane

20. Synovial Fluid • Synovial fluid fills the entire joint • Slippery fluid lubricates joint • Weeping lubrication squeezes synovial fluid into and out of the cartilage nourishing the cells Synovial Fluid

21. Reinforcing ligaments Extracapsular Ligament • Ligaments reinforce joints • Intrinsic ligaments reinforce capsule • Extracapsular are outside capsule • Intracapsular are inside capsule Intracapsular Ligament

22. Features of Select Synovial Joints • Certain synovial joints have additional structural features • Fatty pads cushion the knee and hip joints • Fibrocartilage articular discs separates articular surfaces (menisci) • Articular discs improve the fit between the articulating surfaces (knee, jaw)

23. Bursae and Tendon Sheaths • Bursae and tendon sheaths are closely associated with synovial joints • Essentially sacs of lubricant • Function as “ball bearings” to reduce friction between adjacent structures • Reduces friction during joint activity

24. Bursae • Bursae are flattened fibrous sacs lined with synovial membrane and containing a thin film of synovial fluid • Common at sites where ligaments, skin, muscles or tendons rub against a bone

25. Bursae: Anomolies • A bunion is an enlarged bursae at the base of the big toe • False bursae may develop at any site where there is excessive motion • Function similar to a true bursae

26. Tendon Sheaths Tendon Sheath • An elongated bursa that wraps completely around a tendon subjected to friction • Tendon slides within this lubricated sleeve • Common at sites where the tendon is subject to friction from other tendons or bone features

27. Retinaculum Retinaculum • Retinaculum function to confine tendons to a specific line of pull • Muscle exerts a force around a skeletal feature • Similar to a pulley or gear changing the angle of force exerted by a machine

28. Factors Influencing Synovial Joint Stability • The stability of a synovial joint depends on three factors . . . • The nature of the articular surfaces • The number and positioning of the ligaments • The tone and strength of the muscles acting upon the joint

29. Articular Surfaces • The surfaces determine what movements are possible at a joint, but play a minimal role in joint stability • Many joints have shallow, “misfit” surfaces • Larger surfaces or deeper sockets vastly improve stability • Ball and socket joints are very stable because of their articular surfaces

30. Articular Surfaces • The knee is a hinge joint by classification • The knee is an example of a joint that allows for “extra” movements • The joint surfaces allow for some anterior - posterior sliding, sliding, as well as a slight amount of rotation at full extension

31. Ligaments • Ligaments unite the bones of a joint • Ligaments help to direct bone movement and prevent excessive or undesirable motion • As a rule, the more ligaments a joint has the stronger it is • Ligaments can stretch due to undue tension or trauma • Ligaments can stretch only 6% of its length before it snaps

32. Supporting Ligaments • The supporting ligaments of the elbow allow flexion / extension and restrict movement in any other plane • The Annular ligament allows for rotation of the head of the radius but restricts other movements

33. Muscle Tone • In most joints the muscles that act upon a joint are the most important stabilizing factor • The tendons of the muscles keep the joint taunt and provide dynamic support • Muscle tone is extremely important in reinforcing the shoulder and knee joint as well as the arches of the foot • The articular capsule and the ligament have extensive sensory nerve endings providing reflexive contraction of supporting muscles

34. Muscle Tone • The knee is a joint that features movement over stability • The knee is very dependent upon the muscles to provide dynamic stability to the joint while it moves • Note: Rehab

35. Movements Allowed by Synovial Joints • Nonaxial • Biaxial • Multiaxial

36. Gliding Movements • Simplest type of joint movement • Bone surface glides or slips over another similar surface • Occur at the intercarpal and intertarsal joints as well as articular processes of vertebrae

37. Flexion/Extension • Flexion • A bending movement that decreases the angle of the joint • Extension • A movement that increases the angle of the joint

38. Flexion/Extension/Hyperextension • Flexion • A bending movement that decreases the angle of the joint • Extension • A movement that increases the angle of the joint • Hyperextension • Bending beyond the upright position

39. Flexion • Flexion • A bending movement that decreases the angle of the joint and brings the two articulating bones closer together • Movement usually occurs in the sagittal plane • Illustrated • Flexion of the arm • Flexion of the leg

40. Extension • Extension • A movement that increases the angle of the joint that moves the two articulating bones farther apart • Movement within the sagittal plane • Illustrated • Extension of the leg and arm

41. Dorsiflexion and Plantar Flexion • Dorsiflexion • Lifting the foot so that its superior surface nears the shin • Plantar flexion • Depressing the foot or pointing the toes downward

42. Ab/Adduction/Circumduction • Abduction • Movement of a limb away from midline or a spreading of the digits of the hand or foot • Adduction • Movement of a limb toward midline or in the case of the digits toward the midline of the hand or foot • Circumduction • Movement of a limb in a circle

43. Rotation • Rotation is the turning of a bone around its own long axis • Only movement possible between C1 & C2 • Common at the hip and shoulder joints • Medial or lateral is a function of whether rotation results in the anterior surface of the limb moving toward or away from the midline of the body

44. Supination and Pronation

45. Inversion and Eversion

46. Protraction and Retraction

47. Elevation and Depression

48. Opposition

49. Types of Synovial Joints • Although all synovial joints have the same features they do not have a common structural plan • Based on the shape of their articular surfaces there are six major categories of synovial joints • Plane, hinge, pivot, condyloid, saddle, and ball and socket

50. Plane Joint • A plane joint is the only example of a nonaxial joint • Articular surfaces are essentially flat • Allow only short slipping or gliding movements