Joints (Articulations)

Copyright © 2010 Pearson Education, Inc.

Joints (Articulations)

• Articulation—site where two or more bones meet

• Functions of joints:

• Give skeleton mobility

• Hold skeleton together

Case: Hyaluronic acid injections for knee osteoarthritis

Joseph, a 45 year old construction worker has osteoarthritis. His knees have

been bothering him and his physician recommended injections of hyaluronic acid.


Functional Classification of Joints

• Based on amount of movement allowed by the joint

• Three functional classifications:

• Synarthroses—immovable

• Amphiarthroses—slightly movable

• Diarthroses—freely movable


Structural Classification of Joints

• Based on material binding bones together and whether or not a joint cavity is present

• Three structural classifications:

• Fibrous

• Cartilaginous

• Synovial


Fibrous Joints

• Bones joined by dense fibrous connective tissue

• No joint cavity

• Most are synarthrotic (immovable)

• Three types:

• Sutures

• Syndesmoses

• Gomphoses


Fibrous Joints: Sutures

• Rigid, interlocking joints containing short connective tissue fibers

• Allow for growth during youth

• In middle age, sutures ossify and are called synostoses


Crouzon's and Apert's SyndromeCrouzon and Apert syndromes are the most common of the craniosynostosis syndromes. Craniosynostosis refers to the early closing of one or more of the sutures of an infant's head. The skull is normally composed of bones which are separated by sutures. This diagram shows the different sutures which can be involved.

As an infant's brain grows, open sutures allow the skull to expand and develop a relatively normal head shape. If one or more of the sutures has closed early, it causes the skull to expand in the direction of the open sutures. This can result in an abnormal head shape. In severe cases, this condition can also cause increased pressure on the growing brain.

Copyright © 2010 Pearson Education, Inc. Figure 8.1a

Densefibrousconnectivetissue

Sutureline

(a) Suture

Joint held together with very short,interconnecting fibers, and bone edges

interlock. Found only in the skull.


Fibrous Joints: Syndesmoses

• Bones connected by ligaments (bands of fibrous tissue)

• Movement varies from immovable to slightly movable

• Examples:

• Synarthrotic distal tibiofibular joint

• Diarthrotic interosseous connection between radius and ulna

Copyright © 2010 Pearson Education, Inc. Figure 8.1b

Fibula

Tibia

Ligament

(b) Syndesmosis

Joint held together by a ligament.Fibrous tissue can vary in length, but

is longer than in sutures.


Fibrous Joints: Gomphoses

• Peg-in-socket joints of teeth in alveolar sockets

• Fibrous connection is the periodontal ligament

Copyright © 2010 Pearson Education, Inc. Figure 8.1c

Root oftooth

Socket ofalveolarprocess

Periodontalligament

(c) Gomphosis

“Peg in socket” fibrous joint. Periodontalligament holds tooth in socket.


Cartilaginous Joints

• Bones united by cartilage

• No joint cavity

• Two types:

• Synchondroses

• Symphyses


Cartilaginous Joints: Synchondroses

• A bar or plate of hyaline cartilage unites the bones

• All are synarthrotic


Epiphysealplate (temporaryhyaline cartilagejoint)

Sternum(manubrium)

Joint betweenfirst rib andsternum(immovable)

(a) Synchondroses

Bones united by hyaline cartilage


Ischiopubic Joint


Asymmetric Closure of Ischiopubic Synchondrosis in Pediatric Patients: Correlation with Foot Dominance

OBJECTIVE. The enlarged ischiopubic synchondrosis is a well-known anatomic structure; however, little is

known about its physiology. In early childhood, enlargement of this synchondrosis occurs bilaterally, whereas before

complete ossification, it is frequently found unilaterally. In most children, the unilateral enlarged ischiopubic

synchondrosis is observed in the left hemipelvis, a finding that was hitherto unexplained. During common athletic

activi- ties, increased ground reaction forces are exerted on the weight-bearing nondominant limb, which in up to

87% of the general population is the left leg. The asymmetric exertion of these forces may explain the distinct

closure sequence of this temporary joint. The purpose of this study was to correlate unilateral enlarged ischiopubic

synchondrosis with foot dominance.

MATERIALS AND METHODS. The study cohort comprised 32 children who had un- dergone unenhanced

radiography, CT, or MRI for reasons other than bone disorders and who presented with enlarged ischiopubic

synchondroses. In these children, the distribution of enlarged ischiopubic synchondrosis and foot dominance were

evaluated either retrospectively (n = 11) or prospectively (n = 21).

RESULTS. In this cohort, 78% of patients were right-footed and 22% were left-footed. Nine of the 32 children

presented with unilateral enlarged ischiopubic synchondrosis (left, seven [78%] of nine; right, two [22%] of nine).

All children with enlarged left ischiopubic synchondrosis were right-footed, and all children with enlarged right

ischiopubic synchondrosis were left-footed.

CONCLUSION. Unilateral enlarged ischiopubic synchondrosis is closely correlated with foot dominance. The

asymmetric ossification pattern of the ischiopubic synchondrosis indicates delayed ossification of this anatomic

structure due to asymmetrically applied mechanical forces to the nondominant limb.


Cartilaginous Joints: Symphyses

• Hyaline cartilage covers the articulating surfaces and is fused to an intervening pad of fibrocartilage

• Strong, flexible amphiarthroses


Fibrocartilaginousintervertebraldisc

Pubic symphysis

Body of vertebra

Hyaline cartilage

(b) Symphyses

Bones united by fibrocartilage


Diastasis symphysis pubis is the separation of normally joinedpubic bones, as in the dislocation of the bones, without a fracture.


Synovial Joints

• All are diarthrotic

• Include all limb joints; most joints of the body


Synovial Joints

Distinguishing features:

1. Articular cartilage: hyaline cartilage

2. Joint (synovial) cavity: small potential space


Synovial Joints


3. Articular (joint) capsule:

• Outer fibrous capsule of dense irregular connective tissue

• Inner synovial membrane of loose connective tissue


Synovial Joints


4. Synovial fluid:

• Viscous slippery filtrate of plasma + hyaluronic acid

• Lubricates and nourishes articular cartilageCase: Hyaluronan is also used to treat osteoarthritis of the knee. Such treatments, called viscosupplementation, are administered as a course of injections into the knee joint, and are believed to supplement the viscosity of the joint fluid, thereby lubricating the joint, cushioning the joint, and producing an analgesic effect.


Osteoarthritis is caused by 'wear and tear' on a joint.

Cartilage is the firm, rubbery tissue that cushions your bones at the joints, and allows bones to glide over one another.

Cartilage can break down and wear away. As a result, the bones rub together, causing pain, swelling, and stiffness.

Bony spurs or extra bone may form around the joint, and the ligaments and muscles become weaker and stiffer.

Copyright © 2010 Pearson Education, Inc. Figure 8.3

Periosteum

Ligament

FibrouscapsuleSynovialmembrane

Joint cavity(containssynovial fluid)

Articular (hyaline)cartilage

Articularcapsule


Synovial Joints


5. Three possible types of reinforcing ligaments:

• Capsular (intrinsic)—part of the fibrous capsule

• Extracapsular—outside the capsule

• Intracapsular—deep to capsule; covered by synovial membrane


Synovial Joints


6. Rich nerve and blood vessel supply:

• Nerve fibers detect pain, monitor joint position and stretch

• Capillary beds produce filtrate for synovial fluid


The cause of RA is unknown. It is an autoimmune disease, which means the body's immune system mistakenly attacks healthy tissue.RA can occur at any age, but is more common in middle age. Women get RA more often than men.Infection, genes, and hormone changes may be linked to the disease.


Synovial Joints: Friction-Reducing Structures

• Bursae:

• Flattened, fibrous sacs lined with synovial membranes

• Contain synovial fluid

• Commonly act as “ball bearings” where ligaments, muscles, skin, tendons, or bones rub together


CoracoacromialligamentSubacromialbursa

Cavity inbursa containingsynovial fluidBursa rollsand lessensfriction.Humerus headrolls medially asarm abducts.

(b) Enlargement of (a), showing how a bursaeliminates friction where a ligament (or otherstructure) would rub against a bone

Humerusresting

Humerusmoving


Prepatellar bursitis, also known as Housemaid's knee, is a common cause of swelling and pain above the patella (kneecap), and is due to inflammation of the prepatellar bursa. This structure is a superficial bursa with a thin synovial lining located between the skin and the patella. The bursa develops within the first years of life as a result of mechanical pressure and friction, and it serves the purpose of reducing friction on underlying structures and allowing maximal range of motion in the knee. Aseptic prepatellar bursitis is commonly caused by repetitive work in a kneeling position, hence the name "housemaid's knee"...


Synovial Joints: Friction-Reducing Structures

• Tendon sheath:

• Elongated bursa that wraps completely around a tendon


Acromionof scapula

Joint cavitycontainingsynovial fluid

Synovialmembrane

Fibrouscapsule

Humerus

Hyalinecartilage

CoracoacromialligamentSubacromialbursa

Fibrousarticular capsuleTendonsheath

Tendon oflong headof bicepsbrachii muscle

(a) Frontal section through the right shoulder joint


Stabilizing Factors at Synovial Joints

• Shapes of articular surfaces (minor role)

• Ligament number and location (limited role)

• Muscle tone, which keeps tendons that cross the joint taut

• Extremely important in reinforcing shoulder and knee joints and arches of the foot


Synovial Joints: Movement

• Muscle attachments across a joint:

• Origin—attachment to the immovable bone

• Insertion—attachment to the movable bone

• Muscle contraction causes the insertion to move toward the origin

• Movements occur along transverse, frontal, or sagittal planes


Synovial Joints: Range of Motion

• Nonaxial—slipping movements only

• Uniaxial—movement in one plane

• Biaxial—movement in two planes

• Multiaxial—movement in or around all three planes


Summary of Characteristics of Body Joints

Consult Table 8.2 for:

• Joint names

• Articulating bones

• Structural classification

• Functional classification

• Movements allowed


Movements at Synovial Joints

1. Gliding2. Angular movements:

• Flexion, extension, hyperextension• Abduction, adduction• Circumduction

3. Rotation• Medial and lateral rotation


Movements at Synovial Joints

4. Special movements• Supination, pronation• Dorsiflexion, plantar flexion of the foot• Inversion, eversion• Protraction, retraction• Elevation, depression• Opposition


Gliding Movements

• One flat bone surface glides or slips over another similar surface

• Examples:

• Intercarpal joints

• Intertarsal joints

• Between articular processes of vertebrae


Gliding

(a) Gliding movements at the wrist


Angular Movements

Movements that occur along the sagittal plane:

• Flexion—decreases the angle of the joint

• Extension— increases the angle of the joint

• Hyperextension—excessive extension beyond normal range of motion


(b) Angular movements: flexion, extension, and hyperextension of the neck

Hyperextension Extension

Flexion


Hyperextension Flexion

Extension

(c) Angular movements: flexion, extension, andhyperextension of the vertebral column


Angular Movements

Movements that occur along the frontal plane:

• Abduction—movement away from the midline

• Adduction—movement toward the midline

• Circumduction—flexion + abduction + extension + adduction of a limb so as to describe a cone in space


Rotation

• The turning of a bone around its own long axis

• Examples:

• Between C1 and C2 vertebrae

• Rotation of humerus and femur


Special Movements

• Movements of radius around ulna:

• Supination (turning hand backward)

• Pronation (turning hand forward)


Supination(radius and ulna are parallel)

(a) Pronation (P) and supination (S)

Pronation(radius rotatesover ulna)


Special Movements

• Movements of the foot:

• Dorsiflexion (upward movement)

• Plantar flexion (downward movement)


Dorsiflexion

Plantar flexion

Dorsiflexion

Plantar flexion

(b) Dorsiflexion and plantar flexion


Special Movements

• Movements of the foot:

• Inversion (turn sole medially)

• Eversion (turn sole laterally)


EversionInversion

(c) Inversion and eversion


Special Movements

• Movements in a transverse plane:

• Protraction (anterior movement)

• Retraction (posterior movement)


Special Movements

• Elevation (lifting a body part superiorly)

• Depression (moving a body part inferiorly)


Special Movements

• Opposition of the thumb

• Movement in the saddle joint so that the thumb touches the tips of the other fingers

Joints (Articulations)

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