JointsChapter 8

Joints (Articulations)

• Articulation—site where two or more bones meet

• Functions of joints:– Give skeleton mobility– Hold skeleton together

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 binding material and joint cavity• 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

Fibrous Joints: Syndesmoses

• Bones connected by ligaments

• Movement varies from immovable to slightly movable

• Examples: – Synarthrotic distal

tibiofibular joint– Diarthrotic interosseous

connection between radius and ulna

Fibrous Joints: Gomphoses

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

• Fibrous connection is the periodontal ligament

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

Cartilaginous Joints: Symphyses

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

• Strong, flexible amphiarthroses

Synovial Joints

• All are diarthrotic• Include all limb joints; most joints of the body• Distinguishing features:

1. Articular cartilage: hyaline cartilage2. Joint (synovial) cavity: small potential space3. Articular (joint) capsule: outer fibrous capsule of dense

irregular connective tissue, inner synovial membrane of loose connective tissue

4. Synovial fluid: viscous slippery filtrate of plasma + hyaluronic acid – lubricates and nourished articular cartilage

Figure 8.3

Periosteum

Ligament

Fibrouscapsule

Synovialmembrane

Joint cavity(containssynovial fluid)

Articular (hyaline)cartilage

Articularcapsule

Synovial Joints

Distinguishing features cont: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

6. Rich nerve and blood vessel supply:• Nerve fibers detect pain, monitor joint position and stretch• Capillary beds produce filtrate for synovial fluid

Synovial Joints: Friction-Reducing Structures

• Bursae:– Flattened, fibrous sacs lined with synovial

membranes – Contain synovial

fluid

Synovial Joints: Friction-Reducing Structures

• Tendon sheath:– Elongated bursa that wraps completely around a

tendon

Stabilizing Factors at Synovial Joints

• Shapes of articular surfaces (minor role)• Ligament number and location (limited role)• Muscle tone– 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

Synovial Joint Movement:

• Gliding: one flat bone surface glides or slips over another similar surface

• Examples:– Intercarpal joints– Intertarsal joints– Between articular processes of vertebrae

Synovial Joint Movement:

• Angular: (1)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

Synovial Joint Movement

• Angular: (2)movements that occur along the frontal plane:– Abduction—movement

away from the midline– Adduction—movement

toward the midline– Circumduction

Synovial Joint Movement

• Rotation: The turning of a bone around its own long axis– Examples:• Between C1 and C2

vertebrae• Rotation of humerus and

femur

Synovial Joints: Special Movements

• Movements of radius around ulna:– Supination (turning hand

backward)– Pronation (turning hand forward)

• Movements of the foot:– Dorsiflexion (upward movement) – Plantar flexion (downward

movement)

Synovial Joints: Special Movements

• Movements of the foot:– Inversion (turn sole medially)– Eversion (turn sole laterally)

• Movements in a transverse plane:– Protraction (anterior

movement)– Retraction (posterior

movement)

Synovial Joints: Special Movements

• Elevation (lifting a body part superiorly)

• Depression (moving a body part inferiorly)

• Opposition of the thumb– Movement in the saddle

joint so that the thumb touches the tips of the other fingers

Classification of Synovial Joints

• Six types, based on shape of articular surfaces:– Plane– Hinge– Pivot– Condyloid– Saddle– Ball and socket

Plane Joints

• Nonaxial joints• Flat articular surfaces• Short gliding movements

Hinge Joints

• Uniaxial joints • Motion along a single plane• Flexion and extension only

Pivot Joints

• Rounded end of one bone conforms to a “sleeve,” or ring of another bone

• Uniaxial movement only

Condyloid (Ellipsoidal) Joints

• Biaxial joints• Both articular surfaces are oval• Permit all angular movements

Saddle Joints

• Biaxial• Allow greater freedom

of movement than condyloid joints

• Each articular surface has both concave and convex areas

Ball-and-Socket Joints

• Multiaxial joints• The most freely moving synovial joints

Knee Joint• Largest, most complex joint of body• Three joints surrounded by a single joint cavity:– (1)Femoropatellar joint:• Plane joint• Allows gliding motion during knee flexion

– (2,3)Lateral and medial tibiofemoral joints between the femoral condyles and the C-shaped lateral and medial menisci (semilunar cartilages) of the tibia• Allow flexion, extension, and some rotation when knee

is partly flexed

Figure 8.8a

(a) Sagittal section through the right knee joint

Femur

Tendon ofquadricepsfemoris

SuprapatellarbursaPatellaSubcutaneousprepatellar bursaSynovial cavityLateral meniscus

Posteriorcruciateligament

Infrapatellarfat pad Deep infrapatellarbursaPatellar ligament

Articularcapsule

Lateralmeniscus

AnteriorcruciateligamentTibia

Figure 8.8b

(b) Superior view of the right tibia in the knee joint, showing the menisci and cruciate ligaments

Medialmeniscus

Articularcartilageon medialtibialcondyle

Anterior

Anteriorcruciateligament

Articularcartilage onlateral tibialcondyle

Lateralmeniscus

Posteriorcruciateligament

Knee Joint

• At least 12 associated bursae• Capsule is reinforced by muscle tendons:– E.g., quadriceps and semimembranosus tendons

• Joint capsule is thin and absent anteriorly• Anteriorly, the quadriceps tendon gives rise to:– Lateral and medial patellar retinacula– Patellar ligament

Figure 8.8c

Quadricepsfemoris muscle

Tendon ofquadricepsfemoris muscle

Patella

Lateral patellarretinaculum

Medial patellarretinaculum

Tibial collateralligament

Tibia

Fibularcollateralligament

Fibula

(c) Anterior view of right knee

Patellar ligament

Knee Joint

• Capsular and extracapsular ligaments– Help prevent hyperextension

• Intracapsular ligaments: – Anterior and posterior cruciate ligaments– Prevent anterior-posterior displacement– Reside outside the synovial cavity

Figure 8.8d

Articular capsule

Oblique poplitealligament

Lateral head ofgastrocnemiusmuscle

Fibular collateralligament

Arcuate poplitealligament

Tibia

Femur

Medial head ofgastrocnemiusmuscle

Tendon ofsemimembranosusmuscle

(d) Posterior view of the joint capsule,including ligaments

Popliteusmuscle (cut)

Tendon ofadductor magnus

Bursa

Tibial collateralligament

Figure 8.8e

Fibularcollateralligament

Posterior cruciateligament

Medial condyle

Tibial collateralligament

Anterior cruciateligament

Medial meniscus

Patellar ligament

Patella

Quadriceps tendon

Lateral condyleof femur

Lateralmeniscus

Fibula

Tibia

(e) Anterior view of flexed knee, showing the cruciateligaments (articular capsule removed, and quadricepstendon cut and reflected distally)

Figure 8.9

Lateral Medial

Patella(outline)

Tibial collateralligament(torn)

Medialmeniscus (torn)

Anteriorcruciateligament (torn)

Hockey puck

Shoulder (Glenohumeral) Joint

• Ball-and-socket joint: head of humerus and glenoid fossa of the scapula

• Stability is sacrificed for greater freedom of movement

Figure 8.10a

Acromionof scapula

Synovial membraneFibrous capsule

Hyalinecartilage

CoracoacromialligamentSubacromialbursa

Fibrousarticular capsuleTendonsheath

Tendon oflong headof bicepsbrachii muscle

Synovial cavityof the glenoidcavity containingsynovial fluid

Humerus

(a) Frontal section through right shoulder joint

Shoulder Joint

• Reinforcing ligaments:– Coracohumeral ligament—helps support the

weight of the upper limb– Three glenohumeral ligaments—somewhat weak

anterior reinforcements

Shoulder joint• Reinforcing muscle tendons:–Tendon of the long head of biceps:• Travels through the intertubercular

groove • Secures the humerus to the glenoid

cavity– Four rotator cuff tendons encircle the

shoulder joint:• Subscapularis• Supraspinatus• Infraspinatus• Teres minor

Figure 8.10c

Acromion

CoracoacromialligamentSubacromialbursaCoracohumeralligament

Greatertubercleof humerusTransversehumeralligamentTendon sheath

Tendon of longhead of bicepsbrachii muscle

Articularcapsulereinforced byglenohumeralligaments

Subscapularbursa

Tendon of thesubscapularismuscle

Scapula

Coracoidprocess

(c) Anterior view of right shoulder joint capsule

Figure 8.10d

Acromion

Coracoid process

Articular capsule

Glenoid cavity

Glenoid labrum

Tendon of long headof biceps brachii muscle

Glenohumeral ligaments

Tendon of thesubscapularis muscle

ScapulaPosterior Anterior

(d) Lateral view of socket of right shoulder joint,humerus removed

Elbow Joint

• Radius and ulna articulate with the humerus• Hinge joint formed mainly by trochlear notch

of ulna and trochlea of humerus• Flexion and extension only

Figure 8.11a

Articularcapsule

Synovialmembrane

Synovial cavity

Articular cartilage

Coronoid process

Tendon ofbrachialis muscle

Ulna

Humerus

Fat pad

Tendon oftricepsmuscle

Bursa

Trochlea

Articular cartilageof the trochlearnotch

(a) Median sagittal section through right elbow (lateral view)

Elbow Joint

• Anular ligament—surrounds head of radius• Two capsular ligaments restrict side-to-side

movement:– Ulnar collateral ligament– Radial collateral ligament

Figure 8.11b

Humerus

Lateralepicondyle

Articularcapsule

Radialcollateralligament

Olecranonprocess

Anularligament

Radius

Ulna

(b) Lateral view of right elbow joint

Figure 8.11d

Articularcapsule

Anularligament

Coronoidprocess

(d) Medial view of right elbow

Radius

Humerus

Medialepicondyle

Ulnarcollateralligament

Ulna

Hip (Coxal) Joint

• Ball-and-socket joint• Head of the femur articulates with the

acetabulum• Good range of motion, but limited by the deep

socket • Acetabular labrum—enhances depth of socket

Figure 8.12a

Articular cartilage

Coxal (hip) bone

Ligament ofthe head of the femur (ligamentum teres)

Synovial cavity

Articular capsule

Acetabularlabrum

Femur

(a) Frontal section through the right hip joint

Hip Joint

Reinforcing ligaments:• Iliofemoral ligament• Pubofemoral ligament• Ischiofemoral ligament• Ligamentum teres

Figure 8.12c

Ischium

Iliofemoralligament

Ischiofemoralligament

Greatertrochanterof femur

(c) Posterior view of right hip joint, capsule in place

Figure 8.12d

Anterior inferioriliac spine

Iliofemoralligament

Pubofemoralligament

Greatertrochanter

(d) Anterior view of right hip joint, capsule in place

Temporomandibular Joint (TMJ)

• Mandibular condyle articulates with the temporal bone

• Two types of movement– Hinge—depression and elevation of mandible– Gliding—e.g. side-to-side (lateral excursion)

grinding of teeth• Most easily dislocated joint in the body

Figure 8.13a

Zygomatic process

Mandibular fossaArticular tubercle

Infratemporal fossa

Externalacousticmeatus

Articularcapsule

Ramus ofmandible

Lateralligament

(a) Location of the joint in the skull

Figure 8.13b

Articularcapsule

Mandibularfossa

Articular discArticulartubercle

Superiorjointcavity

Inferior jointcavity

Mandibularcondyle

Ramus ofmandible

Synovialmembranes

(b) Enlargement of a sagittal section through the joint

Figure 8.13c

Lateral excursion: lateral (side-to-side) movements of the mandible

Outline ofthe mandibularfossa

Superior view

Common Joint Injuries• Sprains– The ligaments are stretched or torn– Partial tears slowly repair themselves– Complete ruptures require prompt surgical repair

• Cartilage tears– Due to compression and shear stress– Fragments may cause joint to lock or bind– Cartilage rarely repairs itself– Repaired with arthroscopic surgery

Common Joint Injuries

• Dislocations (luxations)– Occur when bones are forced out

of alignment– Accompanied by sprains,

inflammation, and joint immobilization

– Caused by serious falls or playing sports

• Subluxation—partial dislocation of a joint

Inflammatory and Degenerative Conditions

• Bursitis– An inflammation of a bursa, usually caused by a

blow or friction– Treated with rest and ice and, if severe, anti-

inflammatory drugs• Tendonitis– Inflammation of tendon sheaths typically caused

by overuse– Symptoms and treatment similar to bursitis

Arthritis

• >100 different types of inflammatory or degenerative diseases that damage joints

• Most widespread crippling disease in the U.S.• Symptoms; pain, stiffness, and swelling of a

joint• Acute forms: caused by bacteria, treated with

antibiotics• Chronic forms: osteoarthritis, rheumatoid

arthritis, and gouty arthritis

Osteoarthritis (OA)

• Common, irreversible, degenerative (“wear-and-tear”) arthritis

• 85% of all Americans develop OA, more women than men

• Probably related to the normal aging process• More cartilage is destroyed than replaced in badly

aligned or overworked joints• Exposed bone ends thicken, enlarge, form bone spurs,

and restrict movement• Treatment: moderate activity, mild pain relievers,

capsaicin creams, glucosamine and chondroitin sulfate

Rheumatoid Arthritis (RA)

• Chronic, inflammatory, autoimmune disease of unknown cause

• Onset: 40 -50 years• 3x more women• Signs and symptoms include joint pain and

swelling (usually bilateral), anemia, osteoporosis, muscle weakness, and cardiovascular problems

Rheumatoid Arthritis

• Synovitis, inflammation, pannus formation, cartilage erosion, scar tissue forms, bones connect (ankylosis)

Gouty Arthritis

• Uric acid crystals in joints and soft tissues, inflammation

• More common in men • Typically affects the joint at the base of the great toe

• In untreated gouty arthritis, the bone ends fuse and immobilize the joint

• Treatment: drugs, plenty of water, avoidance of alcohol

Lyme Disease

• Caused by bacteria transmitted by the bites of ticks

• Symptoms: skin rash, flu-like symptoms, and foggy thinking

• May lead to joint pain and arthritis• Treatment: antibiotics

Developmental Aspects of Joints

• By embryonic week 8, synovial joints resemble adult joints

• A joint’s size, shape, and flexibility are modified by use

• Advancing years take their toll:– Ligaments and tendons shorten and weaken– Intervertebral discs become more likely to

herniate– Most people in their 70s have some degree of OA

• Exercise!!!!!!