Articulations

I. Classification of Joints

A. Structural classification

1. Based on material binding bones together and presence or absence of a cavity

2. Types

            a. Fibrous

            b. Cartilaginous

            c. Synovial

B. Functional classification

1. Based on amount of movement permitted

2. Types

            a. Synarthroses

                        i. Immoveable

            b. Amphiarthroses

                        ii. Slightly moveable

            c. Diarthroses

                        iii. Freely moveable

 

II. Characteristics of Joints

A. Fibrous

1. Joined by fibrous tissue only; no cavity

2. Most are synarthrotic

3. Types

            a. Sutures (bones of skull)

 

                        i. Overlapping or interlocking bone edges

ii. Junction filled with connective tissue that penetrates into articulating bones

iii. Ossified in adults (synostoses)

 

           

 

            b. Syndesmoses: bones connected by a cord or sheet of fibrous tissue

 

                        i. Ligament or interosseous membrane

                        ii. Movement proportionate to length of connecting fibers

                        iii. Example: distal end of tibia and fibula (synarthrosis)

           

            c. Gomphoses—peg-in-socket

 

                        i. Tooth

 

 

B. Cartilaginous joints—articulating bones connected by cartilage; no joint cavity

 

1. Types

            a. Synchondroses—bar or plate of hyaline cartilage

                        i. Site for bone growth

                        ii. Become ossified and immoveable (synarthrotic)

iii. Epiphyseal plate connecting epiphysis and diaphysis regions of long bones

            b. Symphysis

                        i. Articulating surfaces are covered with articulating cartilage

                        ii. Cartilage (hyaline) is fused to an intervening pad of fibrocartilage

                        iii. Shock absorption with little movement

                        iv. Amphiarthrotic joints—strong with flexibility

                        v. Intervertebral discs

 

 

C. Synovial joints

 

1. Articulating bones separated by a fluid cavity

2. Freely moveable diarthrotic joints

3. General structure

            a. Articular cartilage

                        i. Covers opposing bones

                        ii. Shock absorption

            b. Synovial cavity

                        i. Fluid filled (synovial fluid)

            c. Articular capsule

                        i. Double-lined fibrous capsule

                        ii. Continuous with periostea of the articulating bones

                        iii. Inner synovial membrane line fibrous capsule internally

                        iv. Covers all non-hyaline internal joint surfaces

            d. Synovial fluid

                        i. Occupies all free space

                        ii. Reduces friction between cartilages

iii. Weeping lubrication—load based release of synovial fluid into and out of cartilage during movement

            e. Reinforcing ligaments

                        i. Intrinsic (capsular)—thickened parts of fibrous capsule

                        ii. Extracapsular—outside capsule

                        iii. Intracapsular—deep to capsule

4. Other structural features

            a. Fatty pads between fibrous capsule and synovial membrane

b. Articular discs (menisci)—fibrocartilage separating articulating surfaces of opposing bones

5. Associated structures

            a. Bursae—sacs of lubricant

                        i. Flattened fibrous sacs lined with synovial membrane with synovial fluid

            b. Tendon sheath—elongated bursa surrounding a tendon

6. Factors affecting synovial joint stability

            a. Shape of articulating surfaces

                        i. Shape determines type of movement but does not determine stability

                        ii. Bones usually “misfit”

            b. Ligaments

                        i. Unite bones

                        ii. Direct and limit movement

                        iii. Joints comprised of only ligaments are not stabile

            c. Muscle tone—major stabilizing factor

                        i. Tendons crossing joints are taut due to tone

                        ii. Sensory receptors monitor and maintain tone

 

III. Synovial Joint Movement

A. Background

1. Skeletal muscles have a minimum of two attachment points

            a. Origin—immoveable bone

            b. Insertion—moveable bone

2. Contraction across joint moves insertion towards origin

3. Directional terms

            a. Monaxial—slipping or sliding

                        i. No axis

            b. Uniaxial

            c. Biaxial

            d. Multiaxial

4. Types of movement

            a. Gliding (simple)

                        i. Surfaces slip or glide over another similar surface

            b. Angular—increase or decrease angle between bones

                        i. Flexion—decrease angle on sagittal plane

                        ii. Extension—increase angle on sagittal plane

                        iii. Abduction—away from midline

                        iv. Adduction—toward midline

                        v. Circumduction—movement describing a conical space

                        vi. Rotation—turn bone along its own long axis

vii. Supination and pronation—movement of radius and ulna; s. parallel; r. radius over ulna

viii. Inversion and eversion—sole of foot medial or lateral

ix. Protraction and retraction—non-angular anterior and posterior movement in transverse plane

x. Elevation and depression—lift body part superiorly

xi. Opposition—thumb

 

IV. Types of Synovial Joints

 

A. Categories

1. Plane—articulating surfaces are flat

            a. Slipping and gliding

                        i. Intracarpal joints

2. Hinge—projection of one bone fits into the trough of another bone

            a. Uniplanar movement

            b. Flexion and extension only

3. Pivot—conical end of one bone fits into sleeve of another

            a. Uniaxial rotation

4. Condyloid (knucklelike)—oval surfaces fit into complimentary concavity

            a. Permits angular movement

5. Saddle

            a. Greater movement than condyloid

            b. Both concave and convex surface

6. Ball and Socket—spherical head articulates with cuplike socket

            a. Multiaxial

            b. Most freely moving

 

V. Glenoid joint

 

1. Stability reduced to permit free movement

 

 

2. Ball and socket

 

            a. Humerus—ball

            b. Glenoid—socket

                        i. 1/3 size of humeral head

                                    ii. Deepened by rim of fibrocartilage (glenoid labrum)

3. Reinforcing ligaments

            a. Coracohumeral

                        i. Thickens capsule

                        ii. Supports weight of upper limb

            b. Glenohumeral (3)

                        i. Strengthen front of capsule

            c. Transverse humeral

4. Muscles and tendons

            a. Superstabilizer

                        i. Long head of biceps brachii

                        ii. Superior margin of glenoid, through joint cavity, to head of humerus

            b. Rotator cuff (4 tendons)—encircles joint

 

VI. Coxal Joint (hip)

 

1. Good range of motion; movement in all planes; limited by ligaments and socket depth

2. head of femur articulates with cupped acetabulum of coxal bone

3. Socket depth incrased by acetabulum labrum

            a. Fibrocartilage

            b. Diameter smaller than femur head

                        i. Snug fit

4. Ligament—reinforce capsule; screw femur head into acetabulum

            a. Iliofemural

                        i. V-shaped; anterior

            b. Pubofemoral

                        i. Triangular; inferior

            c. Ischiofemoral

                        i. Spiral posteriorly

 

VII. Knee Joint

 

 

A. Movement

1. Extension

2. Flexion

3. Rotation (limited)

B. Structure—three joints

1. Femoropetallar joint: patella to femur

2. Tibiofemoral joints (2)

            a. Lateral

                        i. Semilunar cartilage (menisci)

            b. Medial

C. Ligaments—extensions of quadriceps

1. Patellar ligament

2. Medial and lateral retinacula

D. Extracapsular ligaments—prevent hyperextension (do not know names)

E. Intracapsular ligaments—cruciate ligaments

1. Prevent anterior/posterior displacement of articulating surfaces

2. Anterior cruciate

a. Ant. intercondyle area of tibia and medial side of lateral condyle of femur

3. Posterior cruciate

a. Post. intercondyle area of tibia and lateral side of medial condyle of femur

F. Knee movements—slide, roll, spin

 

VIII. Elbow Joint

 

A. Movement—hinge joint

1. Flexion and extension

            a. No rotation

B. Structure

1. Radius and ulna articulate with humerus

2. Hinge formed by trochlear notch of ulna

3. Capsule (limited) between humerus and ulna and surrounding head of radius

4. Side to side motion is prevented by collateral ligaments of ulna and radius

 

IX. Joint Injuries

A. Mechanical

1. Sprain

            a. Mild sprains involve overstretching muscles

            b. Severe sprains involve partial rupture of tendon, ligament and/or blood vessels

 

2. Dislocation (luxation)—bones forced out of normal position

            a. Partial

            b. Dislocation

B. Inflammatory and Degenerative

1. Bursitis—inflammation of bursa

            a. Direct injury or friction

2. Tendonitis—inflammation of tendons

3. Arthritis—inflammatory disease of joints

            a. Osteoarthritis—most common

                        i. Degenerative aging of articular cartilage

                        ii. Restricts movement but is not crippling

            b. Rhematoid arthritis—chronic inflammatory disease

                        i. Autoimmune disease

                        ii. Begins as synovitis

                        iii. Membrane thickens into pannus

                        iv. Inflammatory cells in pannus release enzymes that erode cartilage

                        v. Scar tissue forms and connects bones

                        vi. Scar tissue ossifies

4. Gouty arthritis—uric acid crystallizes and gets deposited into soft tissue of joints