JOINTS

Chapter 9

Introduction Joints or articulations are sites where two

or more bones meet Joints have two fundamental functions:

– provide for skeletal mobility– hold the skeleton together

Weakest parts of the skeleton, yet have a remarkable ability to resist the forces that tear them apart

Classification of Joints

Structural classification– focuses on the material binding the bones

together and whether or not there is a joint cavity (fibrous, cartilaginous, synovial)

Functional classification– based on the amount of movement allowed at

the joint (synarthroses, amphiarthoroses, diarthroses)

Functional Classification Synarthroses

– Immovable joints Amphiarthroses

– Slightly movable joints Diarthroses

– Freely movable joints

Structural Classification

Fibrous– Joined by fibrous tissue

Cartilaginous– Joined by cartilage

Synovial– The bones are joined and surrounded by a

joint cavity Note:

– Structural classification is the system used in your text

Summary of Joint Classes Fibrous joints

– Suture– Syndesmoses– Gomphoses

Cartilaginous joints– Synchondroses– Symphyses

Synovial– Gliding, hinge, pivot, condyloid, saddle, and

ball and socket

Fibrous JointsIn fibrous joints the bones are joined by

fibrous tissue; no joint is present. The three types of fibrous joints are. . .

Sutures– Dense fibrous connective tissue

Syndesmosis– A cord or band of connective tissue

Gomphosis– Peg-in-socket arrangement surrounded by

fibrous tissue or peridontal ligament

Suture Joint Occurs only

between bones of the skull

Wavy articulating bone edges interlock

Junction is filled by connective tissue

Rigid splices bind bones of the skull together tightly

Syndesmosis Longer fibrous

tissue occurs as a sheet or membrane

Longer fibrous tissue permits the joint to “give” or flex

True movement is not possible

Gomphosis Fibrous tissue

holds teeth in their sockets

Teeth embedded in sockets of bone

Anchored by fibers of periodontal ligament

Cartilaginous Joints

In cartilaginous joints, the articulating bones are united by cartilage, there is no joint cavity

Synchondroses– Hyaline cartilage unites the bones

Symphyses– Fibrocartilage unites the bones

Synchondroses

Hyaline cartilage unites the bones

Epiphyseal plates in growing children

Provide for bone growth

When growth ends all synchondroses become immovable

EpipysealPlate

Synchrondroses Sternocostal

joint between the manubrium and rib 1 is a immovable hyaline cartilage joint

Symphyses Bone surfaces are

covered with articular hyaline cartilage which is fused to a pad of fibrocartilage

Fibrocartilage is resilient and acts as a shock absorber and permits limited movement Pubic Symphysis

Synovial Joints

In synovial joints articulating bones are located within a fluid containing joint cavity

Synovial joints permit substantial range of motion

All synovial joints have similar features

Structures of Synovial Joint Articular cartilage

– Hyaline cartilage on opposing bone surfaces Joint (synovial) cavity

– Space filled with fluid Articular capsule

– Capsule to confine fluid Synovial fluid

– Fluid to lubricate joints Reinforcing ligaments

– Maintain joint alignment

Articular Cartilage Hyaline cartilage

covers the bone surfaces

Cartilage absorbs the compression placed on the joint

Cartilage keeps the bone ends from being crushed

Joint (synovial) cavity

Joint spaces are unique to synovial joints

Joint spaces are filled with synovial fluid

Articular capsule The joint cavity is

enclosed by a double layered articular capsule

The external layer is a tough flexible fibrous capsule

The inner synovial membrane

Synovial Fluid Synovial fluid fills

the entire joint Slippery fluid

lubricates joint Weeping

lubrication squeezes synovial fluid into and out of the cartilage nourishing the cells

SynovialSynovialFluidFluid

Reinforcing ligaments Ligaments

reinforce joints Intrinsic

ligaments reinforce capsule

Extracapsular are outside capsule

Intracapsular are inside capsule

ExtracapsularExtracapsularLigamentLigament

IntracapsularLigament

Features of Select Synovial Joints

Certain synovial joints have additional structural features– Fatty pads cushion the knee and hip joints– Fibrocartilage articular discs separates

articular surfaces (menisci)– Articular discs improve the fit between the

articulating surfaces (knee, jaw)

Bursae and Tendon Sheaths Bursae and tendon sheaths are closely

associated with synovial joints Essentially sacs of lubricant Function as “ball bearings” to reduce

friction between adjacent structures Reduces friction during joint activity

Bursae Bursae are

flattened fibrous sacs lined with synovial membrane and containing a thin film of synovial fluid

Common at sites where ligaments, skin, muscles or tendons rub against a bone

Bursae: Anomolies A bunion is an enlarged bursae at the

base of the big toe False bursae may develop at any site

where there is excessive motion Function similar to a true bursae

Tendon Sheaths An elongated bursa

that wraps completely around a tendon subjected to friction

Tendon slides within this lubricated sleeve

Common at sites where the tendon is subject to friction from other tendons or bone features

TendonSheath

Retinaculum

Retinaculum function to confine tendons to a specific line of pull

Muscle exerts a force around a skeletal feature Similar to a pulley or gear changing the angle of force

exerted by a machine

Retinaculum

Factors Influencing Synovial Joint Stability

The stability of a synovial joint depends on three factors . . . – The nature of the articular surfaces– The number and positioning of the ligaments– The tone and strength of the muscles acting

upon the joint

Articular Surfaces The surfaces determine what movements

are possible at a joint, but play a minimal role in joint stability

Many joints have shallow, “misfit” surfaces

Larger surfaces or deeper sockets vastly improve stability

Ball and socket joints are very stable because of their articular surfaces

Articular Surfaces The knee is a hinge joint

by classification The knee is an example

of a joint that allows for “extra” movements

The joint surfaces allow for some anterior - posterior sliding, sliding, as well as a slight amount of rotation at full extension

Ligaments Ligaments unite the bones of a joint Ligaments help to direct bone movement

and prevent excessive or undesirable motion

As a rule, the more ligaments a joint has the stronger it is

Ligaments can stretch due to undue tension or trauma

Ligaments can stretch only 6% of its length before it snaps

Supporting Ligaments The supporting

ligaments of the elbow allow flexion / extension and restrict movement in any other plane

The Annular ligament allows for rotation of the head of the radius but restricts other movements

Muscle Tone In most joints the muscles that act upon a

joint are the most important stabilizing factor The tendons of the muscles keep the joint

taunt and provide dynamic support Muscle tone is extremely important in

reinforcing the shoulder and knee joint as well as the arches of the foot

The articular capsule and the ligament have extensive sensory nerve endings providing reflexive contraction of supporting muscles

Muscle Tone The knee is a

joint that features movement over stability

The knee is very dependent upon the muscles to provide dynamic stability to the joint while it moves

Note: Rehab

Movements Allowed by Synovial Joints

Nonaxial Biaxial Multiaxial

Gliding Movements Simplest type of

joint movement Bone surface

glides or slips over another similar surface

Occur at the intercarpal and intertarsal joints as well as articular processes of vertebrae

Flexion/Extension

Flexion– A bending

movement that decreases the angle of the joint

Extension– A movement

that increases the angle of the joint

Flexion/Extension/Hyperextension

Flexion– A bending movement

that decreases the angle of the joint

Extension– A movement that

increases the angle of the joint

Hyperextension– Bending beyond the

upright position

Flexion

Flexion– A bending movement

that decreases the angle of the joint and brings the two articulating bones closer together

– Movement usually occurs in the sagittal plane

Illustrated– Flexion of the arm

– Flexion of the leg

Extension Extension

– A movement that increases the angle of the joint that moves the two articulating bones farther apart

– Movement within the sagittal plane

Illustrated– Extension of the

leg and arm

Dorsiflexion and Plantar Flexion

Dorsiflexion– Lifting the

foot so that its superior surface nears the shin

Plantar flexion– Depressing

the foot or pointing the toes downward

Ab/Adduction/Circumduction Abduction

– Movement of a limb away from midline or a spreading of the digits of the hand or foot

Adduction– Movement of a limb

toward midline or in the case of the digits toward the midline of the hand or foot

Circumduction– Movement of a limb in a

circle

Rotation Rotation is the turning

of a bone around its own long axis– Only movement possible

between C1 & C2

– Common at the hip and shoulder joints

– Medial or lateral is a function of whether rotation results in the anterior surface of the limb moving toward or away from the midline of the body

Supination and Pronation

Inversion and Eversion

Protraction and Retraction

Elevation and Depression

Opposition

Types of Synovial Joints Although all synovial joints have the

same features they do not have a common structural plan

Based on the shape of their articular surfaces there are six major categories of synovial joints– Plane, hinge, pivot, condyloid, saddle, and

ball and socket

Plane Joint A plane joint is the

only example of a nonaxial joint

Articular surfaces are essentially flat

Allow only short slipping or gliding movements

Plane Joints No rotation

around an axis Examples

– Intercarpals

– Intertarsals

– Vertebrae

Plane joints

Hinge Joints In hinge joints a

cylindrical shaped projection of bone fits into a trough shaped surface of another bone

Motion is within a single plane

Joint components resemble that of a mechanical hinge

Hinge Joints The elbow joint is

an example of a hinge joint

It allows for movement (flexion and extension) in only one plane

Other example– Knee

Pivot Joints The rounded end of

a bone protrudes into a ring of bone and ligaments on another bone

Only movement allowed is rotation of bone around long axis

Pivot Joints An example is the

joint between the atlas and axis, which allows your head to move side to side

Another example is the proximal radioulnar joint, where the head of the radius rotates within the annular ligment

Condyloid Joints In condyloid joints

the oval articular surface of one bone fits into a comple- mentary concavity in another

Both articulating surfaces are oval shaped

Condyloid Joints The biaxial joints

permits all angular motions– flexion / extension

– abduction adduction

– Circumduction Metacarpo-

phalangeal joints

Saddle Joints Resemble condyloid

joints, but allow greater freedom of movement

Each surface has both a concave and a convex surface that fit together

Each surface is shaped like a saddle

Saddle Joints The best example of

a saddle joint in the body are the carpo-metacarpal joints of the thumb

Saddle Joint

Ball and Socket Joint The spherical head

of one bone articulates with the cuplike socket of another

These joints are multiaxial and the most freely moving synovial joints

Ball and Socket Joints Movements in all

planes is allowed All axis and planes Examples

– Shoulder

– Hip

Head of Femur fits

AcetabulumOf pelvis

Shoulder (Glenohumeral) Joint The shoulder

joint has sacrificed stability for mobility

Shoulder (Glenohumeral) Joint The glenoid

labrum deepens the cavity

The articular capsule is thin and loose to contribute to movement

Shoulder (Glenohumeral) Joint Ligaments

reinforce primarily the anterior aspect– Coracohumeral

– Glenohumeral

– Transverse humeral

Shoulder (Glenohumeral) Joint Muscles

crossing the joint provide most of the stability

Long head of the biceps is the most important stabilizer

Shoulder (Glenohumeral) Joint Four tendons

of the rotator cuff encircle the joint, blend with the capsule – Subscapularis

– Supraspinatus

– Infraspinatus

– Teres minor

Shoulder Joint The joint lacks structural stability and

shoulder dislocations are quire common Since the shoulder is weakest anteriorly

and inferiorly, the humerous tends to dislocate forward and downward

Hip Joint This ball and socket

joint has good range of motion but the motion is limited by the deep socket and the joint ligaments

Deep acetabulum is enhanced by circular acetabular labrum

Ligamentum teres provides internal support to the joint

Hip Joint This ball and socket

joint has good range of motion but the motion is limited by the deep socket and the joint ligaments

Deep acetabulum is enhanced by circular acetabular labrum

Ligamentum teres provides internal to the joint

Hip Joint

Thick articular capsule encloses the joint Several strong ligaments support the joint

– Iliofemoral, Pubofemoral, Ischiofemoral Ligaments are arranged in such a manner that

they screw the head of the femur into the acetabulum when standing erect

Elbow Joint

The ulna and humerus provide a stable hinge joint that allow flexion and extension

The Annular ligament anchors the head of the radius

Supported laterally and medially by ligaments

Knee Joint Largest and most

complex joint Allows for flexion

extension and some rotation

C-shaped menisci deepen the tibial articular surface

Menisci prevent side to side rocking and act a shock absorbers

Knee Joint The intracapsular

ligaments of the knee cruciates are located within the intercondylar notch

Ligaments restrict anterior / posterior displacement

Ligaments are named for their tibial attachment sites

Knee Joint Posteriorly the

joint is reinforced by the oblique popliteal ligament

Gastrocnemius has two head that cross the joint posteriorly and provide dynamic stability

Analysis of Knee Movements Weight bearing begins with

the femur sliding posteriorly on the posterior aspect of the condyles

During extension the femoral condyles travel forward until restricted by the anterior cruciate ligament

Finally the lateral condyle stops before the medial spinning the joint into a locked position

Analysis of Knee Movements When extending the

knee as in kicking the same movements occur but in this case the tibia does the moving

Analysis of Knee Injuries Knee is vulnerable to

horizontal forces or high tension twisting movements

These factors lead to– Isolated meniscus

tears

– Isolated medial collateral ligament tears

– Isolated cruciate tears

– Triad of O’Donahue

Orthopedic Injuries to Joints Sprains - Ligament supporting a joint

are stretched or torn Strains - Tendons or muscle fibers are

stretched or torn Cartilage - Tear or fragmentation of the

cartilaginous tissue Dislocation - Bones are forced out of

their normal alignments at a joint Bursitis/Tendonitis - Inflammation

caused by trauma or more frequently overuse

Degenerative Conditions of Joints Arthritis

– A general reference to over 100 different types of inflammatory or degenerative diseases of the joints

Osteoarthritis– A degenerative disease related to the aging

process (wear-and-tear arthritis) Rheumatoid Arthritis

– A chronic inflammatory disorder alters the synovival membrane

– Can lead to changes in articular cartilage and bone tissue of the joints

Degenerative Conditions of Joints Gouty Arthritis

– Abnormal amount of Uric acid contribute to the deposition of urate crystals in the soft tissues of joints

– Lead to agonizingly painful joints – If untreated can lead to fusion and

immobilization of the joint

End of Chapter

Chapter 8