Chapter 10 - Joints
I. Joints and Their Classification (p. 295; Figs. 10.1, 10.2; Transp. 153)
A. Arthrology is the science concerned with joints.
B. Joints are classified according to their relative freedom of movement.
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.
a. In fibrous joints, collagen fibers cross the gap between two bone matrices and join them.
b. In cartilaginous joints, the two bones are held together by cartilage.
c. In synovial joints, the bones are separated by lubricating synovial fluid.
II. Fibrous, Cartilaginous, and Bony Joints (p. 296)
A. Fibrous Joints (p. 296; Fig. 10.3; Transp. 154)
1. At fibrous joints, fibers of collage join two bones.
2. Sutures (p. 297; Fig. 10.4; Transp. 155)
a. Sutures are limited to the skull.
b. Serrate sutures form wavy lines.
c. Lap (squamous) sutures occur where two bones have overlapping beveled edges.
d. Plane (butt) sutures occur where two bones have straight, nonoverlapping edges.
3. Gomphoses (p. 298)
a. Where a tooth attaches into its bony socket is a gomphosis. The tooth is held in place by a fibrous periodontal membrane.
4. Syndesmoses (p. 298)
a. 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. 298)
1. In cartilaginous joints, the two bones are joined by cartilage.
2. Synchondroses (p. 298; Fig. 10.5; Transp. 156)
a. In a synchondrosis, the bones are joined by hyaline cartilage (such as the attachment of a rib to the sternum).
3. Symphyses (p. 298)
a. In a symphysis, two bones are joined by a fibrocartilage pad, such as an intervertebral disc.
C. Synostoses (Bony Joints) (p. 298)
1. Some fibrous and cartilaginous joints ossify with age. The gap between adjacent bones fills with osseous tissue until the bones become one. This type of joint is a synostosis.
III. Form and Function of Synovial Joints (p. 299)
A. General Anatomy (p. 299; Figs. 10.6, 10.7; Transps. 157, 158)
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 inside by ligaments.
5. Fluid-filled bursae underlie certain muscles, helping tendons glide easily over joints.
B. Types of Synovial Joints (p. 300; Fig. 10.8; Transp. 159; Table 10.1)
1. Ball-and-socket joints occur at the shoulder and hip and are highly movable, multiaxial joints. Examples include the shoulder and hip joints.
2. Hinge joints are monaxial, like a door hinge. Examples include the knee, finger and toe joints.
3. Condyloid (ellipsoid) joints exhibit an oval convex surface that fits into a similar depression on the next. The metacarpophalangeal joints are an example.
4. The body's only 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.
5. In pivot joints, one bone has a knobby projection that fits into the ring-like ligament on the other, such as between the first two vertebrae.
6. In gliding joints, articular surfaces are mostly flat, such as between the carpal or tarsal bones.
C. Movements of Diarthroses (p. 303)
1. Flexion, Extension, and Hyperextension (p. 303; Figs. 10.9, 10.10; Transps. 160, 161)
a. Flexion is movement that decreases the angle of a joint.
b. Extension straightens the joint.
c. Hyperextension increases the angle beyond 180o.
2. Abduction and Adduction (p. 303; Fig. 10.10; Transp. 161)
a. Abduction is movement of a body part away from the midsagittal line.
b. Adduction is movement toward the midsagittal line.
3. Elevation and Depression (p. 303; Fig. 10.11; Transp. 162)
a. Elevation is movement that raises a bone vertically.
b. Depression is the opposite of elevation.
4. Protraction and Retraction (p. 305)
a. Protraction is movement of a bone anteriorly.
b. Retraction is movement posteriorly.
5. Lateral and Medial Excursion (p. 305)
a. Lateral and medial excursion refer to the side-to-side movements associated with mastication.
6. Circumduction (p. 305; Fig. 10.12; Transp. 163)
a. During circumduction, one end of an appendage remains stationary while the other end makes a circular motion.
7. Rotation (p. 306; Fig. 10.12; Transp. 163)
a. Rotation is a movement in which a bone turns on its longitudinal axis.
8. Supination and Pronation (p. 306; Fig. 10.13; Transp. 164)
a. Supination and pronation are limited to the forearm.
b. Supination is rotating the arm so the palm is upward.
c. Pronation is rotating the arm so the palm is downward.
9. Opposition and Reposition (p. 306)
a. Opposition is movement of the thumb toward the fingers.
b. Reposition is movement back to anatomical position.
10. Dorsiflexion and Plantar Flexion (p. 306; Fig. 10.14; Transp. 165)
a. These movements are limited to the feet.
b. Dorsiflexion is a movement in which the toes are raised.
c. Plantar flexion is hyperextension of the foot so that the toes point downward.
11. Inversion and Eversion (p. 306)
a. These movements are also limited to the feet.
b. Inversion is a movement in which the soles turn medially.
c. Eversion is a turning of the soles laterally.
D. Range of Motion (p. 307; Fig. 10.15)
1. Range of motion of joints varies considerably, depending on 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. 307; Figs. 10.16 - 10.19; Transps. 166, 167)
1. A lever is an elongated, rigid object that rotates around a fixed point called the fulcrum. The function of a lever is to confer an advantage.
2. Rotation occurs when an effort applied to one point on the lever overcomes a resistance located at some other point.
3. The part of a lever from the fulcrum to the point of effort is called the fulcrum arm.
4. The mechanical advantage of a lever is the ratio of its output force to its input force.
5. A first-class lever is one with the fulcrum in the middle.
6. A second-class lever is one in which the resistance is in the middle.
7. A third-class lever has the effort applied between the fulcrum and the resistance.
IV. Anatomy of Selected Diarthroses (p. 310)
A. The Temporomandibular Joint (p. 311; Fig. 10.20; Transp. 168)
1. The temproromandibular 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 (as meniscus).
3. Two ligaments support the joint: the temporomandibular ligament and the sphenomandibular ligament.
B. The Humeroscapular Joint (p. 311; Fig. 10.21; Transp. 169)
1. The shoulder joint is called the humeroscapular or glenohumeral joint. It 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 of the five principle ligaments support the joint. These are all called glenohumeral ligaments. The other two are the coracohumeral ligament and the transverse humeral ligament.
4. Tendons of four muscles form the rotator cuff: subscapularis, supraspinatus, infraspinatus, and teres minor.
5. Four bursae are associated with the shoulder: subsapular, subacromial, subcoracoid, and subscapular.
C. The Elbow Joint (p. 313; Fig. 10.22; Transp. 170)
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. 313; Figs. 10.23, 10.24; Transp. 171)
1. The coxal (hip) joint occurs where the head of the femur fits into the acetabulum of the os coxae. The hip joint has a deeper socket and is much more stable than the shoulder. An acetabular labrum serves to further deepen the socket.
2. Ligaments that support the coxal joint are: iliofemoral, pubofemoral, ischialfemoral and transverse acetabular ligaments, plus the ligamentum teres at the fovea capititis.
E. The Knee Joint (p. 314; Figs. 10.25, 10.26; Transps. 172, 173)
1. The knee joint (tibiofemoral joint) is the largest and most complex diarthosis of the body. The patella and patellar ligament also form a gliding patellofemoral joint with the femur.
2. The joint cavity contains two cartilages called lateral meniscus and medial meniscus, joined by a transverse ligament.
3. 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.
4. The human ability to "lock" the knee is important to bipedalism.
5. The knee has at least 13 bursae to stabilize it.
F. The Ankle Joint (p. 317; Figs. 10.27, 10.28; Transp. 174; Tables 10.2, 10.3)
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. These are: anterior and posterior tibiofibular ligaments, deltoid ligament, and the lateral collateral ligament.
3. Sprains are especially common at the ankle.
CHAPTER ESSAY: Arthritis and Artificial Joints (p. 321; Figs. E.1, E.2)
i. Arthritis refers to painful, inflamed joints. It is the most crippling disease in the United States.
ii. Osteoarthritis is the most common form, resulting from wear and tear of the joints through excess use and aging.
iii. Rheumatoid arthritis results from an autoimmune disorder.
iv. Ankylosis refers to fused, immobilized joints.
v. Joint replacements (via arthroplasty) are a last resort, and occur in a variety of forms.
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