I. Joints and Their Classification (p. 308; table 10.1)

A. Arthrology is the science concerned with joints. (p. 308)

B. Joints are classified according to their relative freedom of movement. (p. 308; figs. 10.1, 10.2; TR 270)

1. A diarthrosis is freely movable.

2. An amphiarthrosis is slightly movable.

3. A synarthrosis is immovable.

C. Joints are also classified according to how the adjacent bones are joined: fibrous, cartilaginous, bony, or synovial. (p. 308)

II. Fibrous, Cartilaginous, and Bony Joints (p. 309)

A. Fibrous Joints (p. 310; fig, 10.3; TR 271

1. At fibrous joints, fibers of collagen join two bones.

2. Sutures are immovable fibrous joints limited to the skull. (fig. 10.4; TR 272)

a. Serrate sutures form wavy lines.

b. Lap (squamous) sutures occur where two bones have overlapping beveled edges.

c. Plane (butt) sutures occur where two bones have straight, nonoverlapping edges.

3. Gomphoses occur at the point where a tooth attaches into its bony socket and is held in place by a fibrous periodontal membrane.

4. Syndesmoses are the most movable of the fibrous joints and are joined by an interosseous ligament. Example: tibia and fibula connection at the ankle.

B. Cartilaginous Joints (p. 311; fig. 10.5; TR 273-275)

1. In cartilaginous joints, two bones are joined by cartilage.

2. In a synchondrosis, the bones are joined by hyaline cartilage. Example: the attachment of a rib to the sternum.

3. In a symphysis, two bones are joined by a fibrocartilage pad. Example: an intervertebral disc.

C. Bony Joints (Synostoses) (p. 311)

1. Some fibrous and cartilaginous joints ossify with age, and the gap between adjacent bones fills with osseous tissue until the bones become one (a synostosis).

III. Synovial Joints (p. 312)

A. General Anatomy (p. 313; fig. 10.6; TR 276-277)

1. The bones of a synovial joint are separated by a joint cavity containing lubricating synovial fluid. The adjoining surfaces of bones are covered with hyaline cartilage, further reducing friction within the joint.

2. A joint capsule encloses the cavity and is made up of an outer fibrous capsule lined with synovial membrane.

3. Certain joints contain a pad of fibrocartilage called a meniscus that absorbs shock and pressure.

4. Synovial joints are reinforced on the outside by tendons and ligaments and sometimes on the inside by ligaments.

5. Fluid-filled bursae underlie certain muscles, helping tendons glide easily over joints. (fig. 10.7; TR 278-279)

B. Types of Synovial Joints (p. 313)

1. Ball-and-socket joints are highly movable, multiaxial joints. Examples: the shoulder and hip joints.

2. Hinge joints are monaxial, like a door hinge. Examples: the knee, finger, and toe joints.

3. The body's single saddle joint occurs at the base of the thumb. Each bone in the joint is concave in one direction and convex in the other. This joint is the hallmark of primate anatomy: the opposable thumb.

4. In pivot joints, one bone has a knobby projection that fits into the ringlike ligament on the other. Example: between the first two vertebrae.

5. In gliding (plane) joints, articular surfaces are mostly flat. Example: between the carpal or tarsal bones.

6. Condyloid (ellipsoid) joints exhibit an oval convex surface on one bone that fits into a similar depression on the next. Example: the metacarpophalangeal joints.

C. Movements of Diarthroses (p. 316; fig. 10.8; TR 280; table 10.2)

1. Flexion is movement that decreases the angle of a joint; extension straightens the joint; and hyperextension increases the angle beyond 180 degrees. (fig. 10.9; TR 281)

2. Abduction is movement of a body part away from the midsagittal line, while adduction is movement toward the midsagittal line. (fig. 10.10; TR 282)

3. Elevation is movement that raises a bone vertically (e.g., by opening the mouth), and depression is the opposite. (fig. 10.11; TR 283)

4. Protraction is movement of a bone anteriorly, while retraction is movement posteriorly.

5. Lateral and medial excursion refer to the side-to-side movements associated with mastication.

6. During circumduction, one end of an appendage remains stationary while the other end makes a circular motion. (fig. 10.12; TR 284)

7. Rotation is a movement in which a bone turns on its longitudinal axis.

8. Supination and pronation are limited to the forearm. (fig. 10.13; TR 285)

a. Supination is rotating the arm so the palm is upward.

b. Pronation is rotating the arm so the palm is downward.

9. Opposition is movement of the thumb toward the fingers, and reposition is movement back to anatomical position.

10. Dorsiflexion and plantar flexion are limited to the feet. (fig. 10.14a,b,c; TR 286)

a. Dorsiflexion is a movement in which the toes are raised.

b. Plantar flexion is hyperextension of the foot so that the toes point downward.

11. Inversion and eversion are also limited to the feet. (fig. 10.14d,e)

a. Inversion is a movement in which the soles turn medially.

b. Eversion is a turning of the soles laterally.

D. Range of Motion (p. 320; fig. 10.15; TR 287)

1. Range of motion of joints varies considerably, depending on the structure and action of muscles, structure of the articular surfaces of the bones, and strength and tautness of ligaments, tendons, and the joint capsule.

E. Levers and Biomechanics of the Joints (p. 322)

1. A lever is an elongated, rigid object that rotates around a fixed point called the fulcrum. (fig. 10.16; TR 288)

2. The function of a lever is to confer an advantage.

3. When an effort applied to one point on the lever overcomes a resistance at some other point, rotation occurs.

4. The part of a lever from the fulcrum to the point of effort is called the effort arm, and the part from the fulcrum to the point of resistance is the resistance arm.

5. The mechanical advantage of a lever is the ratio of its output force to its input force. (fig. 10.17; TR 289)

6. In a first-class lever, the fulcrum is in the middle; in a second-class lever, the resistance is in the middle; and in a third-class lever, the effort is applied between the fulcrum and the resistance. (fig. 10.18; TR 290-292)

IV. Anatomy of Selected Diarthroses (p. 323)

A. The Temporomandibular Joint (p. 323; fig. 10.19; TR 293, 294)

1. The temporomandibular joint (TMJ) is the insertion of the mandibular condyle into the mandibular fossa of the temporal bone.

2. The synovial cavity of the TMJ is divided into superior and inferior chambers by the articular disc (a meniscus).

3. Two ligaments support the joint: the temporomandibular ligament and the sphenomandibular ligament.

B. The Humeroscapular Joint (p. 325; fig. 10.20; TR 295, 296)

1. The shoulder joint (also called the humeroscapular or glenohumeral joint) is the most freely movable joint in the body as well as one of the most commonly injured.

2. The joint is enclosed in a loose capsule, and the glenoid cavity is a shallow socket made deeper by a ring of fibrocartilage (the glenoid labrum).

3. Three glenohumeral ligaments support the joint; the other two principal ligaments are the coracohumeral ligament and the transverse humeral ligament.

4. Tendons of four muscles form the rotator cuff: the subscapularis, supraspinatus, infraspinatus, and teres minor.

5. Four bursae are associated with the shoulder: the subdeltoid, subacromial, subcoracoid, and subscapular.

C. The Elbow Joint (p. 327; fig. 10.21; TR 297, 298)

1. The elbow is a hinge joint composed of two articulations: the humeroulnar joint and the humeroradial joint.

2. A prominent bursa, the olecranon bursa, eases tendons over the elbow.

3. Side-to-side motions of the elbow are restricted by the radial collateral ligament and the ulnar collateral ligament.

4. The proximal radioulnar joint also occurs at the elbow where the head of the radius rotates within the annular ligament.

D. The Coxal Joint (p. 327; figs. 10.22, 10.23; TR 299, 300)

1. The coxal (hip) joint occurs where the head of the femur fits into the acetabulum of the os coxae.

2. The hip joint has a deeper socket and is much more stable than the shoulder. An acetabular labrum serves to further deepen the socket.

3. Ligaments that support the coxal joint are: the iliofemoral, pubofemoral, ischiofemoral, and transverse acetabular ligaments, plus the ligamentum teres at the fovea capitis.

E. The Knee Joint (p. 327; figs. 10.24, 10.25; TR 301-304)

1. The knee joint (tibiofemoral joint) is the largest and most complex diarthrosis of the body.

2. The patella and patellar ligament also form a gliding patellofemoral joint with the femur.

3. The joint cavity contains two cartilages, called the lateral meniscus and the medial meniscus, joined by a transverse ligament.

4. The posterior "pit" of the knee, called the popliteal region, is supported by intracapsular (anterior and posterior cruciate) ligaments inside the capsule, and extracapsular (oblique popliteal, arcuate, popliteal, lateral collateral, and medial collateral) ligaments outside.

5. The human ability to "lock" the knee is important in bipedalism.

6. The knee has at least 13 bursae to stabilize it.

F. The Ankle Joint (p. 331; figs. 10.26, 10.27; TR 305)

1. The ankle (talocrural) joint includes an articulation between the tibia and talus and another between the fibula and talus.

2. Several ligaments strengthen the ankle: the anterior and posterior tibiofibular ligaments, deltoid ligament, and lateral collateral ligament.

3. Sprains are especially common at the ankle.

G. A summary of common joint disorders, including sprains, is given in table 10.3 (p. 334).