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1. Joints
Siteswhere twoormore bonesmeetare calledjointsorarticulations.
Two basicfunctionsof jointsare to give ourskeletonmobilityandholdittogether.
ClassificationofJoints
Structural classificationfocusesonthe material bindingthe bonestogetherandwhetherornota joint
cavityis present.
In fibrousjointsthe bonesare joinedtogetherbyfibroustissue andlackajointcavity.
In cartilaginousjointsthe bonesare joinedtogetherbycartilage andtheylacka jointcavity.
In synovial joints,the articulatingbonesare separatedbyafluid-containingjointcavity.
Functional classificationisbasedonthe amountof movementallowedatthe joint.
Synarthrosesare immovablejoints.
Amphiarthrosesare slightlymovable joints.
Diarthrosesare freelymovablejoints.
FibrousJoints
Sutures
Suturesoccur betweenbonesof the skull anduse veryshortconnective tissuefiberstoholdthe bones
together.
Syndesmoses
In syndesmoses,the bonesare connectedbyaligament,whichisacord or bandof fibroustissue.

2. Gomphoses
A gomphosisisapeg-in-socketfibrousjoint.
CartilaginousJoints
Synchondroses
Synchondrosesinvolveabar or plate of hyaline cartilage unitingthe bones,suchasthe epiphyseal plate.
Symphyses
In symphyses,suchasthe pubicsymphysis,the articularsurfacesare coveredwitharticularcartilage
that isthenfusedtoan interveningpadorplate of fibrocartilage.

3. Synovial Joints
General Structure
The general structure of a synovial jointcontainsfivedistinguishing features.
Articularcartilage coversthe endsof the articulatingbones.
The joint(synovial)cavityisaspace that isfilledwithsynovial fluid.
The two-layeredarticularcapsuleenclosesthe jointcavity.
Synovial fluidisaviscous,slipperyfluidthatfillsall free space withinthe jointcavity.
Reinforcingligamentscrosssynovial jointstostrengthenthe joint.

4. Bursae and Tendon Sheaths
Bursae and tendonsheathsare bagsof lubricantthatreduce frictionatsynovial joints.

5. Factors Influencingthe Stability ofSynovial Joints
ArticularSurfaces
The shapesof the articularsurfacesof bonesfoundat a synovial jointdetermine the movementsthat
occur at the joint,butplaya minimal role instabilizingthe joint.
Ligaments
Ligamentsata synovial jointpreventexcessiveorunwantedmovementsandhelptostabilizethe joint;
the greaterthe numberof ligamentsatthe jointthe greaterthe stability.
Muscle Tone
Muscle tone keepstendonscrossingjointstaut,whichisthe mostimportantfactorstabilizingjoints.
MovementsAllowedbySynovial Joints
GlidingMovements
In glidingmovementsone flat,ornearlyflat,bone surface glidesorslipsoveranother.
AngularMovements
Angularmovementsincrease ordecrease the angle betweentwobones.
Flexiondecreasesthe angle of the jointandbringsthe articulatingbonesclosertogether.
Extensionincreasesthe angle betweenthe articulatingbones.
Dorsiflexiondecreasesthe angle betweenthe topof the foot(dorsal surface) andthe anteriorsurface of
the tibia.
Plantarflexiondecreasesthe angle betweenthe sole of the foot(plantarsurface) andthe posteriorside
of the tibia.
Abductionisthe movementof alimb(orfingers) awayfromthe midlinebody(orof the hand).
Adductionisthe movementof alimb(orfingers) towardthe midline of the body(orthe hand).
Circumductionismovingalimbsothat it describesacone inthe air.
Rotation
Rotationisthe turningof a bone alongitsownlongaxis.
Special Movements
Supinationisrotatingthe forearm laterallysothatthe palmfacesanteriorlyorsuperiorly.

6. Pronationisrotatingthe arm mediallysothatthe palmfacesposteriorlyorinferiorly.
Inversionturnsthe sole of the footsothat it facesmedially.
Eversionturnsthe sole of the footso that it faceslaterally.
Protractionmovesthe mandible anteriorly,jutsthe jaw forward.
Retractionreturnsthe mandible toitsoriginal position.
Elevationmeansliftingabodypartsuperiorly.
Depressionmeanstomove anelevatedbodypartinferiorly.
Oppositionoccurswhenyoutouchyourthumbto the fingersonthe same hand.
Types ofSynovial Joints
Plane jointshave flatarticularsurfacesandallow glidingandtransitionalmovements.
Hinge jointsconsistof a cylindrical projectionthatnestsinatrough-shapedstructure,andallow
movementalongasingle plane.
Pivotjointsconsistof aroundedstructure that protrudesintoasleeve orring,andallow uniaxial
rotationof a bone aroundthe longaxis.
Condyloid,orellipsoid,jointsconsistof anoval articularsurface that nestsina complementary
depression,andpermitall angularmovements.
Saddle jointsconsistof eacharticularsurface bearingcomplementaryconcave andconvex areas,and
allowmore freedomof movementthancondyloidjoints.
Ball-and-socketjointsconsistof aspherical orhemispherical structure thatarticulateswithacuplike
structure.Theyare the mostfreelymovingjointsandallow multiaxial movements.

7. SelectedSynovial Joints
Knee Joint
Enclosedinone jointcavity,the knee jointisactuallythree jointsinone:the femoropatellarjoint,the
lateral andmedial jointsbetweenthe femoral condyles,andthe menisci of the tibia,knowncollectively
as the tibiofemoraljoint.
Many differenttypesof ligamentsstabilizeandstrengthen the capsuleof the knee joint.
The knee capsule isreinforcedbymuscle tendonssuchasthe strong tendonsof the quadricepsmuscles
and the tendonof the semimembranosus.

9. Shoulder(Glenohumeral) Joint

10. Stabilityhasbeensacrificedtoprovide the mostfreelymovingjointinthe body.
The ligamentsthathelptoreinforce the shoulderjointare the coracohumeral ligamentandthe three
glenohumeral ligaments.
The tendonsthat crossthe shoulderjointandprovide the moststabilizingeffectonthe jointare the
tendonof the longheadof the bicepsbrachii andthe four tendonsthatmake upthe rotator cuff.

11. ElbowJoint
The elbowjointprovidesastable andsmoothlyoperatinghingejointthatallowsflexionandextension
only.
The ligamentsinvolved inprovidingstabilitytothe elbow jointare the annularligament,the ulnar
collateral ligament,andthe radial collateral ligament.
Tendonsof several armmuscles,the bicepsandthe triceps,alsoprovide additional stabilitybycrossing
the elbowjoint.
Hip (Coxal) Joint
The hip jointisa ball-and-socketjointthatprovidesagoodrange of motion.
Several strongligamentsreinforce the capsule of the hipjoint.

12. The muscle tendonsthatcross the jointcontribute tothe stabilityandstrengthof the joint,butthe
majorityof the stabilityof the hipjointisdue tothe deepsocketof the acetabulumandthe ligaments.
TemporomandibularJoint
The temporomandibularjointallowsbothhinge-like movementandside-to-sidelateral excursion.
The jointcontainsan articulardiscthat dividesthe synovial cavityintocompartmentsthatsupporteach
type of movement.
The lateral aspectof the fibrouscapsule containsalateral ligamentthatreinforcesthe joint.

13. Homeostatic Imbalancesof Joints
Common JointInjuries
Cartilage Tears

14. Sprains
Dislocations
Inflammatory and Degenerative Conditions
BursitisandTendonitis
Bursitis,aninflammationof the bursa,isusuallycausedbya blow or friction;tendonitisisinflammation
of the tendons,andisusuallycaused byoveruse.
Arthritis
Arthritisdescribesmanyinflammatoryordegenerativediseasesthatdamage the joints,resultingin
pain,stiffness,andswellingof the joint.
Osteoarthritisisthe mostcommonchronicarthritis.Itisthe resultof breakdownof articularcartilage
and subsequentthickeningof bone tissue,whichmayrestrictjointmovement.
Rheumatoidarthritisisachronicinflammatorydisorderthatisan autoimmune disease.
Gouty arthritisresultswhenuricacidisdepositedinthe softtissues of the joints.

15. Lyme Disease
Lyme disease isabacterial disease transmittedbyticksthatnormallylive onmice anddeer.Itcausesa
charachteristic"bulls-eye rash,flu-like symptoms,andmaybe accompaniedbydisruptionsincognition
and jointpainandarthritis.
Withouttreatment(antibiotics) itcanprogressto neurological disordersandirregularheartbeat.
Developmental AspectsofJoints
Jointsdevelopatthe same time asbones,resemblingadultformbyeightweeksgestation.
At late middle age and beyond,ligamentsandtendonsshortenandweaken,intervertebral discsbecome
more likelytoherniate,andthere isonsetof osteoarthritis.