1. Joints
Part A 8

2. 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

3. 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

4. Fibrous Structural Joints: Sutures
Figure 8.1a

5. Fibrous Structural Joints: Syndesmoses
Figure 8.1b

6. Cartilaginous Joints: Synchondroses
Figure 8.2a, b

7. Cartilaginous Joints: Symphyses
Figure 8.2c

8. Examples – all limb joints, and most joints of the body
Synovial Joints
Those joints in which the articulating bones are separated by a fluid-containing joint cavity
All are freely movable
Examples – all limb joints, and most joints of the body

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

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

11. 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

12. Synovial Joints: Friction-Reducing Structures
Figure 8.4

13. Synovial Joints: Stability
Stability is determined by:
Articular surfaces – shape determines what movements are possible
Ligaments – unite bones and prevent excessive or undesirable motion
Muscle tone:
Muscle tendons across joints acting as stabilizing factors
Tendons that are kept tight at all times by muscle tone

14. Types of Synovial Joints
1. Plane joints
Articular surfaces are essentially flat
Allow only slipping or gliding movements
Only examples of nonaxial joints
Figure 8.7a

15. Gliding Movement
Figure 8.5a

16. Types of Synovial Joints (continue)
2. Hinge joints
Cylindrical projections of one bone fits into a trough-shaped surface on another
Motion is along a single plane
Uniaxial joints permit flexion and extension only
Examples: elbow and interphalangeal joints

17. Types of Synovial Joints
Figure 8.7b

18. Only uniaxial movement allowed
3. 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

19. 4. 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

20. 5. 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

21. 6. 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

22. Selected 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
Lateral and medial tibiofemoral joints

23. 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
Figure 8.8c

24. Synovial Joints: Knee – Other Supporting Structures
Anterior cruciate ligament
Posterior cruciate ligament
Medial meniscus (semilunar cartilage)
Lateral meniscus

25. Synovial Joints: Knee – Other Supporting Structures
Figure 8.8b

26. Synovial Joints: Knee – Posterior Superficial View
Adductor magnus tendon
Articular capsule
Oblique popliteal ligament
Arcuate popliteal ligament
Semimembranosus tendon
Figure 8.8e

27. Selected Synovial Joints: Shoulder (Glenohumeral) joint
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

28. 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

29. Synovial Joints: Shoulder Stability
Figure 8.10a

30. Synovial Joints: Shoulder Stability
Figure 8.10b