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