Joints

1. Joints Dr. Anderson GCIT

2. Joints • Where two or more bones meet • Function • Connection (ligaments) • Movement (muscles) • Protection (joint capsule)

3. Joint Classification

4. Sutures • Fibrous joints, slightly mobile in youth, immobile as adult (e.g. cranial sutures) • Limited mobility allows brain to grow during development • Immovability as adult serves as a protective function Top of Skull (newborn baby)

5. Syndesmoses • Bones connected exclusively by ligaments • Movement varies according to length of the ligaments forming the joint, e.g.: • Very limited movement between tibia and fibula • Very pronounced movement of ulna around radius

6. Gomphoses • Peg-in-socket, fibrous joint • Only example is the teeth in their alveolar cavities connected by the periodontal ligament

7. Cartilaginous Joints • Articulating bones are united by cartilage • Synchondroses and symphyses

8. Synchondroses • Cartilage that unites two bones (such as the epiphyses to the diaphyses in the long bones of children and young adults) • E.g. Epiphyseal plates

9. Symphyses • Where articulating bones are lined with cartilage, which is fused to a pad or plate of fibrocartilage • E.g. – intervertebral discs, pubic symphysis

10. Synovial Joints • Features 1. Articular cartilage – covers opposing bone surface 2. Synovial cavity – space that contains synovial fluid 3. Articular Capsule – provides tensile strength and covers all surfaces not lines with cartilage 4. Synovial fluid – provides joint lubrication, released from the cartilage itself during activity (weeping lubrication) 5. Reinforcing ligaments 6. Nerves and blood vessels -

11. Joint Structure

12. Articular Discs (Menisci) • Fibrocartilage pads that partially or completely divide the synovial cavity • (Knee, jaw meniscus) • Improve the fit of some articular surfaces in the joint

13. Bursae and Tendon Sheaths • Fibrous connective tissue that serves as a pliable “ball bearing” for some joints (e.g. shoulder) and closely packed tendons (e.g. wrist) • Bursa rolls in opposing direction of movement

14. What holds joints together? • Articular Surfaces -Deeply fitting articulations more stable than shallow ones • Ligaments – “cables” of dense regular connective tissue that hold the joint together • Relatively little stretch (can snap) • Muscle Tone – low levels of contractile activity – more tone = more stable joints

15. Synovial Joint Structure

16. Joint Movements • Originates from muscle contraction (of course) • Degree of joint movement is called “range of motion” • Three main types • Gliding • Angular • Rotation

17. Gliding joints • Simplest movement • One or more flat (usually) bone surfaces glide over another • Wrist bones • Ankle bones • Between vertebrae

18. Angular Movement • Flexion – pulling the joint angle closed • Extension – opening the joint angle • Hyperextension – greater than normal extension • Abduction – moving a limb away from the median line of the body • Adduction – moving a limb toward the median line of the body • Circumduction – moving a limb in a cone-shaped path in space

19. Rotation • Turning of a bone around its long axis • Medial rotation – turning toward the midline • Lateral rotation – turning away from the midline

20. Supination and Pronation • Refer to movement of radius around the ulna • With arms down at sides: • Supination is a lateral rotation of the palms (palms anterior or up) • Pronation is a medial rotation of the palms (palms face posteriorly, radius and ulna cross each other, forming an ‘X’)

21. Ankle and Foot Movement • Dorsi flexion – moves foot up (superiorly) • Plantar flexion – moves foot down (inferiorly) • Inversion – sole of foot turns medially • Eversion – sole turns laterally

22. Jaw movements • Protraction and retraction – jutting jaw out and bringing it back, respectively • Elevation and Depression – Moving a body part superiorly or inferiorly (e.g. jaw)

23. Synovial Joint Types • Plane(Gliding) – allow only short, gliding movements (wrist and ankle) • Hinge (One angular direction) - allows motion only along a single plane (flexion and extension only) • Pivot (Rotation)– allows the bone to rotate around its axis • Condyloid(All angular directions)– Oval articulating surfaces that permit movement in all directions • Saddle (All angular directions)– both articular surfaces have a convex AND a concave side that articulate together • Ball-and-Socket - (Universal movement)allows movement in all directions, including limited rotation

24. Knee Joint • Very Complex • 4 bones • Femur, tibia, fibula, patella • Ligaments often injured in sports or accidents

25. Knee Injuries • Cruciate Ligaments • ACL (anterior) • PCL (posterior) • Deep in joint cavity of knee (intracapsular) • Can tear and separate femur from the tibia • Most often happens when the knee is rotated during full extension Torn ACL (Arthroscopic view)

26. Knee Injuries • Most dangerous injuries are lateral blows to the fully extended knee • Torn menicsi • Torn collateral ligaments • Tibial (Medial or MCL)– outside hit • Fibular (Lateral or LCL)– inside hit

27. Jaw Joint Problems • Jaw Joint (mandible and mandibular fossa) is called the tempero-mandibular joint (TMJ) • Loosely connected – has a greater range of motion than other hinge joints • Condyle of mandible can move out of the fossa, (anterior disarticulation)