Chapter 9 - Joints

Question 0

What are the different types of joints?

Answer 0

A. Bony joints (synostosis)
B. Fibrous joints (synarthrosis)
C. Cartilaginous joints (amphiarthrosis)

Question 1

What are joints?

Answer 1

Any point where the bones meet. Joints are named from the bones involved.

Question 2

What is are bony joints (synostosis)?

Answer 2

1. An immovable joint formed when bones ossify and become a single bone.
2. Bony joints can form by ossification of fibrous or cartilaginous joints.
3. Examples include fusion of newborn frontal and mandibular bones, some cranial sutures, epiphyses and diaphyses of long bones.

Question 3

What are fibrous joints (synarthrosis)?

Answer 3

1. A point where adjacent bones are bound by collagen fiber that span the space between them.
2. Sutures - fibrous joint that closely bind the bones of the skull.
3. Gomphosis - periodontal ligament attachment between tooth and jaw.
4. Syndesmosis - fibrous joint at which two bones are bound together by long fibers such as interosseous membrane.

Question 4

What are cartilaginous joints (amphiarthrosis)?

Answer 4

1. Two bones linked by cartilage.
2. Synchondrosis - bones are joined by hyaline cartilage such as the joint between epiphysis and diaphysis of long bones of children.
3. Symphysis - two bones are joined by fibrocartilage such as at the public symphysis and the intervertebral discs.

Question 5

What is the general anatomy of synovial joints (diarthrosis)?

Answer 5

1. Articular cartilage - hyaline cartilage covering the surface of the bones.
2. Joint cavity - the space separating the cartilage.
3. Synovial fluid - slippery lubricant in the joint cavity.
4. Joint capsule - CT that encloses the cavity and retains the fluid.
5. Articular disc - a fibrocartilage pad that forms between articulating bones.
6. Meniscus - cartilage in the knee joint that absorbs shock and pressure, etc.
7. Tendon - CT that attaches a muscle to bone and stabilizes the joint.
8. Ligament - CT that attaches bone to bone.
9. Bursa - a fluid filled sac between the adjacent muscles, between tendon and bone, or between bone and skin to cushion muscles or help tendons slide more easily.
10. Tendon sheath - elongated bursa wrapped around a tendon which enables the tendon to move back and forth more freely.

Question 6

What are the joints and lever systems?

Answer 6

1. A lever is an elongated, rigid object that rotates around a fixed point called the fulcrum.
2. Rotation occurs when an effort applied overcomes a resistance.

Question 7

What causes resistance?

Answer 7

a. Effort arm - the part of the lever from the fulcrum to the point of effort.
b. Resistance arm - the part of the lever from the fulcrum to the point of resistance.
c. In the body the fulcrum is a joint, the effort is applied by a muscle, and the resistance is an object the body is working against, the weight of the limb, or tension of an opposing muscle.

Question 8

What is Mechanical Advantage (MA)?

Answer 8

The ratio of the length of the effort arm (LE) to the length of the resistance arm (LR) (MA = LE/LR).

a. The function of a lever is to produce a gain in the speed/distance, or force of a motion.
b. If MA is greater than 1.0 the lever produces more force.
c. If MA is less than 1.0 the lever produces more speed or distance.

Question 9

What are the types of levers?

Answer 9

a. First-class lever - the fulcrum is in the middle like a see-saw; ex. the atlanto-occipital joint.
b. Second-class lever - the resistance is in the middle like a wheelbarrow; ex. hip joint.
c. Third-class lever - the effort is in the middle like paddling a canoe; ex. elbow joint.

Question 10

What are the factors affecting range of motion - degrees through which a joint can move?

Answer 10

a. Structure of the articular surfaces - the olecranon process of the ulna prevents movement beyond 180° at the elbow.
b. Strength and tautness of ligaments - the ligaments in the fingers prevent flexion of the knuckles beyond 90°.
c. Action of the muscles and tendons - extension of the knee is limited by the hamstring muscles.

Question 11

What are the classes of synovial joints? These are distinguished by the shape of their articular surfaces and their degrees of freedom.

Answer 11

a. Ball-and-socket joint - multi-axial joint that consists of a bone with a hemispherical head that fits into a cup like socket of another.
b. Condylar (ellipsoid) joint - biaxial joint, an oval convex surface fits into a complementary-shaped depression on another bone.
c. Saddle joint - biaxial joint in which both bones have a saddle-shaped surface.
d. Plane (gliding) joint - biaxial joint with limited movement in which the bone surfaces are flat.
e. Hinge joint - monaxial joint in which one bone has a convex surface and fits into a concave depression on the other bone.
f. Pivot joint - monaxial joint in which a bone spins on its longitudinal axis against another bone.

Question 12

What are the movements of synovial joints?

Answer 12

1. Flexion - decreases a joint angle.
2. Extension - straightens the joint and returns the body part to zero position.
3. Abduction - movement away from the midline of the body.
4. Adduction - movement back toward midline.
5. Elevation - raises a body part vertically.
6. Depression - lowers a body part vertically.
7. Protraction - anterior movement.
8. Retraction - posterior movement.
9. Circumduction - one end of an appendage makes a circular motion.
10. Rotation - a bone spins on its longitudinal axis.
11. Supination - movement that turns the palm facing anterior.
12. Pronation - movement that turns the palm facing posterior.
13. Lateral excursion - movement to the left or right of zero position.
14. Medial excursion - movement back to the median.
15. Opposition - movement of the thumb to touch the tip of another finger.
16. Reposition - return the thumb to zero position.
17. Dorsiflexion - movement to elevate the toes.
18. Plantar flexion - movement to point the toes downward.
19. Inversion - tips the soles medially.
20. Eversion - tips the soles laterally.

Question 13

What is the anatomy of the jaw (temporomandibular) joint?

Answer 13

1. The synovial cavity divides into superior and inferior by an articular disc.
2. The lateral ligament prevents posterior displacement of the mandible.

Question 14

What is the anatomy of the shoulder (glenohumoral/humeroscapular) joint?

Answer 14

1. The loose joint capsule and shallow glenoid cavity sacrifices stability for freedom of movement.
2. Glenoid labrum - a ring of fibrocartilage that makes the cavity deeper.
3. Rotator cuff - tendons of the supraspinatus, infraspinatus, teres minor, and subscapularis that help stabilize the shoulder.
4. Ligaments that support the joint - glenohumoral, coracohumoral and transverse humeral ligaments.
5. 4 bursar located under tendons and ligaments help reduce the friction of movement.

Question 15

What is the anatomy of the elbow (humeroulnar and humeroradial) joint?

Answer 15

1. The two joints are enclosed in a single joint capsule.
2. The olecranon bursa, on the posterior side, eases the movement of the tendons over the joint.
3. The radial collateral and ulnar collateral ligaments restrict side-to-side motions of the elbow joint.
4. The anular ligament encircles the radial head and holds it in the radial notch of the ulna (proximal radioulnar joint).

Question 16

What is the anatomy of the hip (coxal) joint?

Answer 16

1. The acetabular labrum attaches to the rim of the acetabulum, increases the depth of the socket and prevents dislocation of the femur.
2. The iliofemoral, pubofemoral and ischiofemoral ligaments twist when standing and pull the head of the femur tightly into the acetabulum.
3. Round ligament arises in the fovea capitis and attaches to the acetabulum and contains an artery that supplies the head of the femur.
4. The transverse acetabulum ligament bridges a gap in the inferior margin of the acetabular labrum.

Question 17

What is the anatomy of the knee (tibiofemoral and patellofemoral) joint?

Answer 17

1. Anteriorly, the joint is covered by the patellar ligament and the patellar retinacula, extensions of the quadriceps tendon which stabilize the joint.
2. The menisci in the joint cavity absorb the shock of the body weight on the knee and prevent the femur from rocking side-to-side on the tibia.
3. The transverse ligament joins the menisci together.
4. The collateral ligaments prevent the knee from rotating when the joint is extended.
5. The cruciate ligaments, crossing between the condyles, prevents the knee from hyperextending and prevents the femur from sliding off of the tibia.
6. 13 bursae ease movement of the tendons and ligaments.

Question 18

What is the anatomy of the ankle (talocrural) joint?

Answer 18

1. Two joints enclosed in a single joint capsule.
2. The malleoli of the tibia and fibula overhang the talus and prevent side-to-side motion.
3. The tibiofibular ligaments bind the tibia to the fibula.
4. The medial ligament binds the tibia to the foot on the medial side.
5. The lateral ligament binds the fibula to the foot on the lateral side.
6. The calcaneal tendon plantarflexes the foot.

Question 19

What are the joint disorders?

Answer 19

1. Bursitis - inflammation of the bursa, usually due to overexertion.
2. Dislocation - displacement of a bone from its normal position at a joint.
3. Gout - uric acid crystals accumulate in the joint and irritate the cartilage and synovial membrane.
4. Sprain - torn ligament or tendon.
5. Strain - overstretching of a tendon or muscle.
6. Synovitis - inflammation of the joint capsule.
7. Tendinitis - the tendon sheath is inflamed.
8. TMJ syndrome - psychological tension and malocclusion causing facial pain, clicking sounds, limitation movement, headaches, vertigo, and tinnitus.
9. Osteoarthritis - the articular cartilages soften and degenerate with age exposing the bone, it can develop bone spurs restricting movement and causing pain.
10. Rheumatoid arthritis - autoimmune attack on the synovial membranes which leads to degradation of the articular cartilage, thickening of the synovial membrane, fluid accumulation, and ossification of the bones.