Chapter 8 Articulations Chapter Outline

Module 8.1 Classification of Joints A. Functional Classification: joints can be classified by how much motion they allow. Describe the three functional joint classifications. 1. Synarthrosis:

2. Amphiarthrosis:

3. Diarthrosis:

B. Structural Classification: joints can be classified based on their structural features into the following categories: 1.

joints are fastened together by dense regular collagenous connective tissue without a joint space between articulating bones. These joints can be

or

2.

functionally.

joints are fastened together with cartilage without a joint space. These joints can be

or

functionally. 3.

joints have a layer of hyaline cartilage on the articulating surface of each bone. The joint space is a fluid-filled cavity found between articulating bones. These joints are

functionally.

Module 8.2 Structural Classification: Fibrous Joints (Figure 8.1) A. Describe sutures.

(Figure 8.1a) B. Describe gomphoses.

(Figure 8.1b)

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C. Describe syndesmoses.

(Figure 8.1c) Module 8.3 Structural Classification: Cartilaginous Joints (Figure 8.2) A. Synchondroses: a synchondrosis consists of bones linked together by hyaline cartilage. The following are examples, which are

functionally

(Figure 8.2a): 1. Epiphyseal plates are composed of

cartilage that connects the

diaphyses and epiphyses of developing long bones, which is replaced with bone during maturation (Figure 8.2a). 2. First sternocostal and costochondral joints are synchondroses that persists into adulthood (Figure 8.2b). B. Symphyses: a symphysis is a joint where the bones are united by a fibrocartilaginous pad or plug, which is functionally an

.

The following are examples of this type of articulation (Figure 8. 2 b, c, d): 1. The

joints founded between adjacent vertebral bodies

of the spinal column (Figure 8.2c). 2. The

is found between pubic bones of the pelvic

girdle (Figure 8.2d). Module 8.4 Structural Classification: Synovial Joints (Figures 8.3, 8.4) A. Structural Elements (Figure 8.3): 1. The joint cavity, or synovial cavity, is a space found between articulating bones with the following three structural features: , and

, .

2. The articular capsule is a double-layered structure that has the following features (Figure 8.3): a. The outer fibrous layer keeps the articulating bones from being pulled apart and isolates the joint from the rest of the body.

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b. The inner layer is called the

membrane that lines the

entire inner surface except where hyaline cartilage is present. What do the cells in this membrane secrete? 3. Synovial fluid is an thick liquid with the following three main functions: a.

b.

c.

4. Articular cartilage is composed of a thin layer of hyaline cartilage and covers all exposed articulating bones within a joint. a. This thin layer provides a smooth surface for articulating bones to interact, which reduces wear and tear created by friction. b. Articular cartilage is avascular, isolated with the capsule. How does articular cartilage obtain oxygen, nutrients, and remove wastes?

5. Other components of a synovial joint include adipose tissue, nerves, and blood vessels. B. Stabilizing and Supporting Factors: synovial joints allow more mobility but are less stable than the other joint types. The following structures provide additional stabilization (Figure 8.4): 1. A

is a strand of dense regular collagenous connective

tissue that links one bone to another, which provides additional strength and reinforcement to a joint. 2. A

is a structural component of skeletal muscle, composed of

dense regular collagenous connective tissue, which connects muscle to bone. a. Tendons cross joints that they move when muscles are contracted, which provides stabilization to the joint itself. b. Muscle tone, a continuous level of muscle contraction, provides a stabilizing force to the joint.

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3. Bursae and tendon sheaths also provide stabilization forces to the joints where they are found. a. A bursa is a synovial-filled fibrous structure that is found in high stress regions. What is the function of a bursa?

b. A tendon sheath is a long bursa that surrounds tendons in high-stress regions associated with joints. What do tendon sheaths protect?

C. Arthritis is defined as

of one or more joints that result in pain

and limitations of joint movement. The following are three common types of arthritis: 1.

is the most common form generally associated with wear and tear, injuries, and advanced age, which is characterized by pain, joint stiffness, and lost mobility.

2.

arthritis is associated with joint destruction mediated by the individual’s own immune system.

3.

arthritis causes joint damage by generating an inflammatory reaction to uric acid crystal deposits.

Module 8.5 Function of Synovial Joints (Figure 8.5–8.10) A. Functional Classes of Synovial Joints: bones in a synovial joint move in different planes around an axis or axes. Describe the motion each of the following possible different joint configurations allows: 1. Nonaxial joints allow motion

2. Uniaxial joints allow motion 3. Biaxial joints allow motion 4. Multiaxial (triaxial) joints allow motion B. Movements at Synovial Joints: the following 4 general types of movement can take place at a synovial joint (Figures 8.5–8.10):

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1. Gliding movements: gliding is a sliding motion between articulating surfaces that is nonaxial (Figure 8.5). 2. Angular movements increase or decrease the angle between articulating bones and includes the following specific types of motion (Figures 8.6, 8.7): a. Flexion decreases the angle between articulating bones by bringing the bones closer to one another. This movement is paired with (Figure 8.6). b. Extension increases the angle between articulating bones, which is the opposite of

, where articulating bones move away

from one another. c. Hyperextension is extension beyond anatomical position of the joint. d. Abduction is the motion of a body part

the

midline of the body or another reference point. This movement is paired with

(Figure 8.7).

e. Adduction is the motion of a body part

the

midline of the body or another reference point. This movement is the opposite of

.

f. Circumduction is the only unpaired angular movement where a freely moveable distal bone moves on a fixed proximal bone in a coneshaped motion. This complex movement is a combination of the two angular motion pairs:

and (Figure 8.7e).

3. Rotation is a nonangular motion in which one bone rotates or twists on an imaginary line running down its middle

axis (Figure

8.8). 4. Special Movements: this group of paired movements includes those types not otherwise defined by previous categories (Figure 8.9): a. Opposition and reposition: opposition of the thumb at the 1st carpometacarpal joint allows the thumb to move across the palmar surface of the hand.

is the opposite movement that

returns the thumb to its anatomical position (Figure 8.9a, b).

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b. Depression and elevation: depression is the movement of a body part in an

direction while elevation moves a body part in a direction (Figure 8.9c, d).

c. Protraction and retraction: protraction moves a body part in an direction while retraction moves a body part in a direction (Figure 8.9e, f). d. Inversion and eversion: inversion is a rotational motion in which the plantar surface of the foot rotates

toward the midline

of the body. Eversion rotates the foot

away from

the midline (Figure 8.9g, h). e. Dorsiflexion and plantarflexion: dorsiflexion is a movement where the angle between the foot and leg between the foot and leg

. The angle during plantarflexion

(Figure 8.9i, j). f. Supination and pronation are rotational movements of the wrist and ankle regions (Figure 8.10). C. Range of Motion: the range of motion of a joint is the amount of movement it is capable of under normal circumstances. Module 8.6 Types of Synovial Joints (Figures 8.11–8.16) A. A

joint (gliding joint) is the most simple and least mobile

articulation between the flat surfaces of two bones (Figure 8.11a). B. In a

joint the convex articular surface of one bone interacts with the

concave depression of a second bone, which allows for movement around a single axis (uniaxial) (Figure 8.11b). C. A

joint is a where the rounded end surface of one bone fits into a

groove on the surface of a second bone allowing for movement around one axis (uniaxial) in which one bone pivots or rotates around the other (Figure 8.11c). D. A

or ellipsoid joint is a biaxial joint where the oval,

convex surface of one bone fits into a shallow, concave articular surface of a second bone (Figure 8.11d).

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joint each bone’s articulating surface has both a concave and

E. In a

convex region that allows each bone to fit together allowing for a great deal of motion for a biaxial joint (Figure 8.11e). F. A

joint is a multiaxial articulation in which the

articulating surface of one bone is spherical and fits into a cup-shaped depression in the second bone. This allows for a wide range of motion in around all three available axes (Figure 8.11f). G. Specific Hinge Joints: The Elbow and the Knee (Figures 8.13, 8.14) 1. The elbow, a very stable hinge joint, is composed of the following two articulations and three strong ligaments that support the articular capsule (Figure 8.13): a. The humeroulnar joint, the larger of the two joints, is the articulation between the

of the humerus and the of the ulna.

b. The humeroradial joint is the articulation between the of the humerus and the c. The

of the radius.

ligament (lateral collateral supports the

lateral side of the joint. d. The

ligament (medial collateral ligament)

supports the medial side of the joint. e. The

ligament binds the head of the radius to the neck

of the ulna, which stabilizes the radial head in the elbow joint. 2. The knee is a large complex modified hinge articulation composed of two separate joints, which allows for a small degree rotation and lateral gliding in addition to flexion and extension. The following are anatomical features associated with this joint and the patella (Figure 8.14): a. The articular capsule is absent from the anterior aspect of the joint where instead it is covered by the patella. This anatomical feature leaves the knee joint without a single continuous joint cavity. b. The patella is surrounded by the tendon of the quadriceps femoris muscle group.

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c. The

ligament, the distal continuation of the

quadriceps tendon, connects the distal patella to the anterior tibia. d. The

joint is the articulation between the

femoral and tibial condyles. e. The

joint is the articulation between the

posterior surface of the patella and the anterior patellar surface of the femur. f. The medial meniscus and lateral meniscus are c-shaped fibrocartilaginous pads found femoral and tibial condyles. What function do these pads serve?

g. The tibial collateral ligament (medial collateral) connects the femur, medial meniscus, and tibia to one another to provide medial joint stabilization. What is the function of this ligament?

h. The fibular collateral ligament (lateral collateral) connects the femur with the fibula. What is the function of this ligament?

i. The anterior cruciate ligament (ACL), found inside the joint cavity, links the anterior tibia with the posterior femur. What is the function of this ligament?

j. The posterior cruciate ligament (PCL), also within the joint cavity, links the posterior tibia with the anterior femur. What is the function of this ligament?

H. Specific Hinge Joints: The Shoulder and the Hip (Figures 8.15, 8.16)

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1. The shoulder (glenohumeral joint) is a component of the articulations of the pectoral girdle that connect the upper extremity with the axial skeleton. This joint is composed of the ball-shaped head of the glenoid cavity on the lateral

and the

. The shoulder joint has the

following anatomical features (Figure 8.15): a. The glenoid labrum is a fibrocartilaginous ring that increases the depth of the glenoid cavity to provide more stability to this multiaxial joint. b. The biceps brachii tendon provides a stabilizing force as it passes over the joint, which helps keep the head of the humerus within the glenoid cavity. c. The tendons of the following muscles form the rotator cuff, which provides most of the joints structural stabilization and strength: the , , and

, .

2. The hip (coxal joint) is a very stable, multiaxial articulation between the acetabulum and the ball-shaped head of the femur. The hip joint has the following anatomical features that make it stable enough for its weightbearing responsibilities (Figure 8.16): a. The acetabular labrum is a fibrocartilaginous ring. What is the function of the acetabular labrum?

b. Retinacular fibers are intracapsular ligaments that surround the neck of femur, which reinforce the joint capsule. c. The iliofemoral ligament is a Y-shaped structure that reinforces anterior aspect of the external joint capsule. d. The ischiofemoral ligament is a spiral-shaped structure. What is the function of this ligament?

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e. The pubofemoral ligament is a triangular-shaped structure. What is the function of this ligament?

f. The ligament of the head of the femur is a small ligament that connects the head of the femur with the acetabulum. What is the function of this ligament?

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