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Chapter 8

Chapter 8:  Joints of the Skeletal System

 

I.  Introduction

A.  Joints are also called articulations.

B.  Joints bind parts of the skeletal system, make possible bone growth, permit parts of the skeleton to change shape during childbirth and enable the body to move in response to skeletal muscle contractions.

II.  Classification of Joints

A.  Introduction

1.  Three general groups of joints are fibrous, cartilaginous, and synovial.

2.  Joints can also be grouped according to the degree of movement possible at the bony junctions.

3.  Immovable joints are called synarthrotic.

4.  Slightly movable joints are called amphiarthrotic.

5.  Freely movable joints are called diarthrotic.

B.  Fibrous Joints

1.  Fibrous joints are so named because the dense connective tissue holding them together contains many collagenous fibers.

2.  The three types of fibrous joints are syndesmosis, suture, and gomphosis.

3.  In syndesmois, bones are bound together by long fibers of connective tissue that form an interosseous ligament.

4.  An example of a syndesmosis is at the distal ends of the tibia and fibula, where they join to form the tibiofibular articulation.

5.  Because a syndesmosis permits slight movement, it is called amphiarthrotic.

6.  Sutures are only between flat bones of the skull.

7.  A sutural ligament is thin layer of dense connective tissue that joins flat bones of the skull together.

8.  Fontanels allow the skull to change shape slightly during childbirth.

9.  An example of a suture is the parietal suture.

10.  Because sutures are immovable, they are called synarthrotic.

11.  A gomphosis is a joint formed by the union of a cone-shaped bony process in a bony socket.

12.  A periodontal ligament is a structure that firmly attaches a tooth to the jaw.

13.  An example of a gomphosis is a tooth in a socket.

C.  Cartilaginous Joints

1.  Bones of cartilaginous joints are joined by hyaline cartilage or fibrocartilage.

2.  Two types of cartilaginous joints are synchondroses, and symphyses.

3.  In a synchondrosis, bands of hyaline cartilage unite bones.

4.  Many synchondroses are temporary structures and disappear during growth.

5.  Two examples of synchondroses are epiphyseal plates and the joint between the first rib and manubrium.

6.  Synchondroses do not permit movement and are therefore synarthrotic.

7.  In a symphysis, the articular surfaces of bones are covered with a thin layer of hyaline cartilage and the cartilage is attached to a pad of springy fibrocartilage.

8.  Two examples of symphyses are the symphysis pubis and intervertebral joints.

D.  Synovial Joints

1.  Most joints are synovial.

2.  Synovial joints allow free movement and are called diarthrotic.

3.  Synovial joints consist of articular cartilage, a joint capsule, and a synovial membrane

III.  General Structure of a Synovial Joint

A.  Articular cartilage is a thin layer of hyaline cartilage that covers the ends of bones.

B.  The joint capsule is a tubular structure that holds together the bones of a synovial joint.

C.  The outer layer of the joint capsule consists of dense connective tissue.

D.  The inner layer of the joint capsule consists of a synovial membrane.

E.  Ligaments reinforce the joint capsule.

F.  The synovial membrane is a shiny, vascular layer of loose connective tissue.

G.  Synovial fluid comes from the synovial membrane.

H.  Besides secreting synovial fluid, the synovial membrane may also store adipose tissue and form movable fatty pads with the joint.

I.  Synovial fluid has a consistency of uncooked egg white and functions to moisten and lubricate the smooth cartilaginous surfaces within the joint.

J.  Menisci are discs of fibrocartilage.

K.  Menisci function to cushion articulating surfaces.

L.  Bursae are fluid filled sacs associated with synovial joints.

M.  Bursae are located between the skin and underlying bony prominences.

N.  Bursae function to cushion and aid the movement of tendons that glide ofver bony parts of over other tendons.

O.  The names of bursae reflect locations.

IV.  Types of Synovial Joints

A.  The six major types of synovial joints are ball-and-socket, condyloid, gliding, hinge, pivot, and saddle.

B.  A ball-and-socket joint consists of a bone with a globular head that articulates with a cup-shaped cavity of another bone.

C.  A ball-and-socket joint allows a wider range of motion than any other type of joint.

D.  Examples of ball-and-socket joints are the hip joint and shoulder joint.

E.  The structure of a condyloid joint is an ovoid condyle of one bone fitting into the elliptical cavity of another bone.

F.  An example of a condyloid joint is between the metacarpals and phalanges.

G.  The articulating surfaces of gliding joints are nearly flat or slightly curved.

H.  Examples of gliding joints are joints within the wrists and ankles.

I.  The structure of a hinge joint is a convex surface of one bone fitting into the concave surface of another bone.

J.  An example of a hinge joint is the elbow joint.

K.  The structure of a pivot joint is a cylindrical surface of one bone rotating within a ring formed of bone and fibrous tissue of a ligament.

L.  Examples of pivot joints are the joint formed between the proximal ends of the radius and ulna, and the joint between the dens of the axis and ring of the atlas.

M.  The structure of a saddle joint is a convex surface of one bone articulating with a concave surface of another bone.

N.  An example of a saddle joint is the joint between the trapezium and the metacarpal of the thumb.

V.  Types of Joint Movements

A.  An insertion of a muscle is its movable end.

B.  The origin of a muscle is its fixed end.

C.  Flexion is bending of a body part.

D.  Extension is straightening of a body part.

E.  Hyperextension is excess extension of a body part beyond the anatomical position.

F.  Dorsiflexion is bending of the foot at the ankle upward.

G.  Plantar flexion is the bending of the foot downward at the ankle.

H.  Abduction is moving a part away from the midline of the body.

I.  Adduction is moving a part toward the midline of the body.

J.  Rotation is moving a body part around an axis; also known as twisting.

K.  Circumduction is moving a body part in a circular path.

L.  Supination is turning the palm of the hand up.

M.  Pronation is turning the palm of the down.

N.  Eversion is turning the sole of the foot laterally.

O.  Inversion is turning the sole of the foot medially.

P.  Protraction is moving a body part forward.

Q.  Retraction is moving a body part backward.

R.  Elevation is raising a body part.

S.  Depression is lowering a body part.

VI.  Examples of Synovial Joints

A.  Shoulder Joint

1.   The shoulder joint is a ball-and-socket joint that consists of the rounded head of the humerus and the shallow glenoid cavity of the scapula.

2.  The shoulder joint capsule is very loose.

3.  Muscles and tendons reinforce the shoulder joint capsule.

4.  The four ligaments that help prevent displacement of the shoulder joint are coracohumerual, glenohumeral, transverse humeral, and the glenoid labrum.

5.  The coracohumeral ligament strengthens the superior portion of the joint capsule.

6.  The glenohumeral ligament extends from the edge of the glenoid cavity to the lesser tubercle and the anatomical neck of the humerus.

7.  The transverse humeral ligament runs between the lesser and the greater tubercles of the humerus.

8.  The glenoid labrum functions to deepen the glenoid cavity.

9.  The four major bursae associated with each shoulder joint are subscapular, subdeltoid, subacromial, and subcoracoid.

10.  The shoulder joint is capable of a wide range of movement due to the looseness of its attachments and the relatively large atricular surface of the humeurs compared to the shallow depth of the glenoid cavity.

B.  Elbow Joint

1.  The articulations of the elbow joint are a hinge joint between the trochlea of the humerus and the trochlear notch of the ulna and a gliding joint between the capitulum of the humerus and a shallow depression on the head of the radius.

2.  The ulnar collateral ligament is located on the medial wall of the capsule.

3.  The ulnar collateral ligament attaches the medial epicondyle of the humerus to the medial margin of the coronoid process of the ulna; it also attaches the medial epicondyle of the humerus to the olecranon process of the ulna.

4.  The radial collateral ligament is located between the lateral epidondyle of the humerus and the annular ligament of the radius.

5.  The radial collateral ligament strengthens the lateral wall of the joint capsule.

6.  Fatty pads of the elbow joint protect nonarticular bony areas during joint movements.

7.  The only movements that occur at the elbow joint are flexion and extension.

C.  Hip Joint

1.  The hip joint is a ball-and-socket joint.

2.  The hip joint consists of the head of the femur and the cup-shaped acetabulum.

3.  The acetabular labrum is a ring of fibrocartilage and functions to     deepen the cavity of the acetabulum.

4.  The major ligaments of the hip joint are iliofemoral, pubofemoral, and ischiofemoral.

5.  The iliofemoral ligament attaches the anterior inferior iliac spine to the intertrochanteric line.

6.  The pubofemoral ligament extends between the superior portion of the pubis and the iliofemoral ligament.

7.  The ischiofemoral ligament connects the ischium to the joint capsule.

8.  The hip joint has less freedom of movement than the shoulder joint.

9.  Muscles surround the capsule of the hip joint.

D.  Knee Joint

1.  The largest and most complex of the synovial joints is the knee joint.

2.  The knee joint consists of the medial and lateral condyles at the distal end of the femur and the medial and lateral condyles at the proximal end of the tibia. 

3.  The femur articulates with the patella anteriorly.

4.  The knee functions as a modified hinge joint.

5.  The articulation between the femur and tibia is a condyloid joint.

6.  The articulation between the femur and patella is a gliding joint.

7.  The knee joint is greatly strengthened by ligaments and tendons of several large muscles.

8.  The 5 ligaments of the knee joint are patellar, oblique popliteal, arcuate, tibial collateral, and fibular collateral.

9.  The patellar joint extends from the margin of the patella to the tibial tuberosity.

10.  The oblique popliteal ligament connects the lateral condyle of the femur to the margin of the head of the tibia.

11.  The arcuate popliteal ligament connects the lateral condyle of the femur to the head of the fibula.

 12.  The tibial collateral ligament connects the medial condyle of the femur to the medial condyle of the tibia.

13.  The fibular collateral ligament connects the lateral condyle of the femur to the head of the fibula.

14.  Two ligaments within the knee joint are called cruciate ligaments.

15.  The anterior cruciate ligament connects the anterior intercondylar area of the tibia to the lateral condyle of the femur.

16.  The posterior cruciate ligament connects the posterior intercondylar area of the tibia to the medial condyle of the femur.

17.  Two menisci separate the articulating surfaces of the femur and tibia.

18.  Three bursae associated with the knee joint are suprapatellar, prepatellar, and infrapatellar.

VII.  Life-Span Changes

A.  Changes in collagen lie behind joint stiffness.

B.  The fibrous joints are the first to change.

C.  Synchondroses that connect epiphyses to diaphyses in long bones disappear as the skeleton grows.

D.  Ligaments lose their elasticity as collagen fibers become more tightly cross-linked.

E.  In the intervertebral discs, less water diminishes the flexibility of the vertebral column and impairs the ability of the discs to absorb shocks.

F.  Loss of function of synovial joints begins in the third decade of life.

G.  Fewer capillaries serving the synovial membrane slow the circulation of synovial fluid, and the membrane may become infiltrated with fibrous material and cartilage.

 

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