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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

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Chapter 9

  • 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
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
Functional Classification
  • Synarthroses
    • Immovable joints
  • Amphiarthroses
    • Slightly movable joints
  • Diarthroses
    • Freely movable joints
structural classification
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
Summary of Joint Classes
  • Fibrous joints
    • Suture
    • Syndesmoses
    • Gomphoses
  • Cartilaginous joints
    • Synchondroses
    • Symphyses
  • Synovial
    • Gliding, hinge, pivot, condyloid, saddle, and ball and socket
fibrous joints
Fibrous Joints

In 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
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
  • Longer fibrous tissue occurs as a sheet or membrane
  • Longer fibrous tissue permits the joint to “give” or flex
  • True movement is not possible
  • Fibrous tissue holds teeth in their sockets
  • Teeth embedded in sockets of bone
  • Anchored by fibers of periodontal ligament
cartilaginous joints
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
  • Hyaline cartilage unites the bones
  • Epiphyseal plates in growing children
  • Provide for bone growth
  • When growth ends all synchondroses become immovable



  • Sternocostal joint between the manubrium and rib 1 is a immovable hyaline cartilage joint
  • 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
synovial joints
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
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
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 (synovial) cavity
  • Joint spaces are unique to synovial joints
  • Joint spaces are filled with synovial fluid
articular capsule
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
  • Synovial fluid fills the entire joint
  • Slippery fluid lubricates joint
  • Weeping lubrication squeezes synovial fluid into and out of the cartilage nourishing the cells



reinforcing ligaments
Reinforcing ligaments



  • Ligaments reinforce joints
  • Intrinsic ligaments reinforce capsule
  • Extracapsular are outside capsule
  • Intracapsular are inside capsule



features of select synovial joints
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
  • 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 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
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
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


  • 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
factors influencing synovial joint stability
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
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 surfaces30
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 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
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
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 tone34
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
Movements Allowed by Synovial Joints
  • Nonaxial
  • Biaxial
  • Multiaxial
gliding movements
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
    • 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
    • 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 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 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
types of synovial joints
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
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
Plane Joints



  • No rotation around an axis
  • Examples
    • Intercarpals
    • Intertarsals
    • Vertebrae
hinge 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 joints53
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
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 joints55
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
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 joints57
Condyloid Joints
  • The biaxial joints permits all angular motions
    • flexion / extension
    • abduction adduction
    • Circumduction
  • Metacarpo- phalangeal joints
saddle 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 joints59
Saddle Joints



  • The best example of a saddle joint in the body are the carpo-metacarpal joints of the thumb
ball and socket 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
Ball and Socket Joints
  • Movements in all planes is allowed
  • All axis and planes
  • Examples
    • Shoulder
    • Hip

Head of

Femur fits


Of pelvis

shoulder glenohumeral joint
Shoulder (Glenohumeral) Joint
  • The shoulder joint has sacrificed stability for mobility
shoulder glenohumeral joint66
Shoulder (Glenohumeral) Joint
  • The glenoid labrum deepens the cavity
  • The articular capsule is thin and loose to contribute to movement
shoulder glenohumeral joint67
Shoulder (Glenohumeral) Joint
  • Ligaments reinforce primarily the anterior aspect
    • Coracohumeral
    • Glenohumeral
    • Transverse humeral
shoulder glenohumeral joint68
Shoulder (Glenohumeral) Joint
  • Muscles crossing the joint provide most of the stability
  • Long head of the biceps is the most important stabilizer
shoulder glenohumeral joint69
Shoulder (Glenohumeral) Joint
  • Four tendons of the rotator cuff encircle the joint, blend with the capsule
    • Subscapularis
    • Supraspinatus
    • Infraspinatus
    • Teres minor
shoulder joint
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
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 joint72
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 joint73
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
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
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 joint76
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 joint77
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
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 movements79
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
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
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
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 joints83
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