Chapter 9
Joints
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INTRODUCTION
• Joint = point of contact
– between 2 bones
– between cartilage and bone
– between teeth and bone
• Joints hold bones together but permit movement
• Arthrology = study of joints
• Kinesiology = study of motion
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I.
Classification of Joints
• Structural classification based on:
– presence or absence of a synovial (joint) cavity
– type of connective tissue
– three structural classifications
• fibrous
– do not have synovial cavity
– held together by fibrous C.T. (lots of collagen)
• cartilaginous
– no synovial cavity
– bones held together by cartilage
• synovial
– bones forming joint have a synovial cavity
– dense irreg. C.T. & accessory ligaments of articular
capsule holds bones together
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I.
•
Classification of Joints
Functional classification based on degree of movement
allowed by joint:
1) Synarthrosis = immovable
2) Amphiarthrosis = slightly movable
3) Diarthrosis = freely movable
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II. A. Fibrous Joints
• No synovial cavity
• Articulating bones held closely
together by fibrous C.T.
• Allow limited movement
• 3 structural types
– sutures
– syndesmoses
– gomphoses
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Sutures
• Thin layer of dense fibrous connective tissue uniting bones
of the skull
• Irregular/interlocking edges give added strength & prevent
fracture
• Synarthrosis because immovable
• Synostosis = suture that has fused completely & been
replaced by bone
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Syndesmoses
• Greater distance btwn articulating bones & more fibrous
C.T. than sutures
• Arrangements of C.T.
– bundles = ligament
– sheets = inteross. memb.
• Amphiarthrosis: limited movement
• Examples
– Anterior tibiofibular joint
– Interosseous membranes in forearm and leg
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Gomphoses
• Dentoalveolar joints: cone-shaped pegs in bony socket
• Synarthrosis
• Only example = teeth in alveolar processes of maxillae
and mandible
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B.
Cartilaginous Joints
• Lack a synovial cavity
• Allows limited movement
• Articulating bones tightly connected by fibrocartilage or
hyaline cartilage
• 2 types
– synchondroses
– symphyses
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Synchondrosis
• Connecting material = hyaline cartilage
• Synarthrosis
• Examples:
– epiphyseal plates
– articulation of first rib w/ manubrium of sternum
– become synostoses when bone replaces cartilage
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Symphysis
• Ends of articulating bones covered w/ hyaline cartilage
• Thin disc of fibrocart. connects bones
• All occur in midline of body
• Amphiarthrosis
• Examples:
– intervertebral disc
– pubic symphysis
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C.
Synovial Joints
• Synovial cavity separates articulating bones
• Freely moveable (diarthroses)
• Articular cartilage covers articulating bones
– reduces friction
– absorbs shock
• Three structural components:
– Articular capsule
– Synovial membrane/fluid
– Accessory ligaments/discs
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Structural Components: Articular Capsule
• Surrounds joint, encloses synovial cavity, & unites
articulating bones
• Two layers
– outer fibrous capsule
• usually dense irregular C.T.
• attaches periosteum of articulating bones
• flexibility permits considerable movement, but
tensile strength prevents dislocation
• forms ligaments (dense CT) when arranged in bundles
– inner synovial membrane
• secretes a lubricating synovial fluid
• sometimes contains articular fat pads
– EX: infrapatellar fat pads
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Structural Components, ctd
• Synovial fluid
– Mixture of hyaluronic acid secreted by synovial
membrane & interstitial fluid
– Lubricates joints & absorbs shock
– Provides nutrients to/removes wastes from
articular capsule
– Phagocytes remove microbes
– Immobility of joint increases viscosity, activity
decreases viscosity
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Structural Components, ctd
• Accessory ligaments & articular discs/menisci
– extracapsular ligaments lie outside joint capsule
– intracapsular ligaments lie within capsule
– articular discs (menisci) = pads of fibrocartilage
btwn bones
• attached to capsule
• allow 2 bones of different shape to fit tightly
• maintain stability of joint
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Nerve and Blood Supply of Synovial Joints
• Nerves to joints are branches of nerves that supply
muscles that move joint
• Many nerve endings distributed to articular capsule &
accessory ligaments
– sense pain
– relay information about degree of stretch/movement
• Many components are avascular but arteries can
penetrate ligaments/capsule
– deliver nutrients to joint
– veins remove CO2 & wastes
• pass from chondrocytes to synovial fluid to vein
• pass directly from all other joint structure to vein
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Bursae and Tendon Sheaths
• Bursae
– Fluid-filled saclike structures that alleviate friction in some
joints
– Resemble joint capsules
• Walls consist of C.T. & synovial membrane
– Fluid similar to synovial fluid
– Located between:
• Skin/bone
• Tendon/bone or ligament/bone
• Muscle/bone
• Bursitis = chronic inflammation of a bursa
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Bursae and Tendon Sheaths
• Tendon sheaths = tubelike bursae that wrap around
tendons that experience large amounts of friction
– where tendon enters synovial cavity
• Biceps brachii @ shoulder
– where many tendons come together in small space
• Wrist/ankle
– where there is considerable movement
• Fingers/toes
• Bursae & tendon sheaths reinforce the articular capsule
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Types of Movements at Synovial Joints
Four main categories of joint movement (Table 9.1)
1) Gliding movements
• flat bone surfaces move back and forth & side to side
with respect to one another
•
no significant alteration of angle between bones
•
limited in range because of structure of
capsule/ligaments
•
Ex: intercarpal or intertarsal joints (planar joints)
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Types of Movements at Synovial Joints
2) Angular movements
• Increase or decrease in angle btwn articulating bones
•
Measured with respect to anatomical position
•
Covered in lab
•
Flexion/extension, lateral extension, hyperextension
•
Abduction/adduction, circumduction
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Types of Movements at Synovial Joints
4) Special movements
– Occur only at certain joints
– 11 different special movements
• Elevation/depression: upward/downward motion
• Protraction/retraction: movement in transverse plane
• Inversion/eversion: movement of soles medially/laterally
• Dorsiflextion/plantarflexion: bending of ankle in direction
of superior/inferior surfaces
• Supination/pronation: movement of prox/distal
radioulnar joints which turns palms anteriorly/posteriorly
• Opposition: movement of carpometacarpal joint in which
thumb touches fingers of same hand
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Types of Synovial Joints
• ***These will be covered in lab, so they will be minimally
discussed in lecture. However the notes may be useful to
you in studying for the lab exam.***
• Varying shapes of bones/joints allow numerous movements
• 6 types
– Planar
– Hinge
– Pivot
– Condyloid
– Saddle
– Ball & socket
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1. Planar Joint
• Articulating surfaces flat or slightly curved
• Primarily allow gliding movements
• Rotation prevented by ligaments
• Nonaxial because motion does not occur around axis or
along plane
• Examples
– intercarpal or intertarsal joints
– sternoclavicular joint
– vertebrocostal joints
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2. Hinge Joint
• Convex surface of one bone fits into concave surface of
another
• Monaxial: allows motion around single axis
– produces angular opening & closing
– flexion/extension only
• Examples
– Knee, elbow, interphalangeal joints
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3. Pivot Joint
• Rounded/pointed surface of bone articulates with ring formed
by 2nd bone & ligament
• Monaxial: rotation around own axis
• Examples
– Proximal radioulnar joint
• supination
• pronation
– Atlanto-axial joint
• nodding head “no”
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4. Condyloid (Ellipsoidal) Joint
• Convex oval-shaped projection articulates with oval depression
• Biaxial: allows motion along two axes
– flexion/extension
– abduction/adduction/circumduction
• Examples: wrist & metacarpophalangeal joints for digits 2 to 5
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5. Saddle Joint
• Articulating surface of one bone saddled-shaped; other bone
fits into “saddle”
• Modified condyloid joint
• Biaxial
– Circumduction allows tip of thumb travel in circle
– Opposition allows tip of thumb to touch tip of other fingers
• Example: carpo/metacarpal joint of wrist/thumb
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6. Ball and Socket Joint
• Ball-like head of long bone fits into a cup-like socket
• Multiaxial: motion around 3 axes & all directions in between
– flexion/extension
– abduction/adduction
– rotation
• Examples:
– shoulder joint: humerus in glenoid
– hip joint: femur in acetabulum
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III. CONTACT & RANGE OF MOTION
AT SYNOVIAL JOINTS
•
•
Range of motion (ROM) = range (measured in degrees of
circle) thru which bones of joint can move
Several factors contribute to keeping articular surfaces in
contact & affect ROM:
1)
2)
3)
4)
5)
6)
Structure and shape of the articulating bone
Strength and tautness of the joint ligaments
Arrangement and tension of the muscles
Contact of soft parts
Hormones
Disuse
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IV. ETC…
• Arthroscopy = examination of joint w/ pencil-sized instrument
– removes torn knee cartilages & repair ligaments
– requires only small incision
• Arthroplasty = joint replacement
– hip & knee replacements common
• Dislocation of a joint = luxation
– refers to displacement of a bone from a joint
– torn tendons, ligaments, capsules accompany dislocation
– subluxation = partial dislocation
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ETC…
• Sprain
– forcible twisting of joint that stretches or tears
ligaments
– no dislocation of the bones
– may damage nearby blood vessels, muscles or
tendons or nerves
– swelling & hemorrhage from damaged blood vessels
– ankle & back are common sprain sites
• Strain
– overstretched or partially torn muscle
– results from sudden, powerful contraction
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DISORDERS: HOMEOSTATIC IMBALANCES:
• Osteoarthritis
– degenerative joint disease commonly known as “wearand-tear” arthritis
– characterized by deterioration of articular cartilage and
bone spur formation
– noninflammatory
– primarily affects weight-bearing joints
• Gouty arthritis
– sodium urate crystals deposited in soft tissues of joints
causing inflammation, swelling, and pain
– If not treated, bones @ affected joints eventually fuse,
rendering joints immobile
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Rheumatoid Arthritis
• Autoimmune disorder: body attacks its own cartilage & joint
linings
• Inflammation of synovial membrane
– accumulation of synovial fluid causes swelling, pain &
loss of function
– eventually, fibrous tissue in joints becomes ossified 
joint becomes immovable
• Occurs bilaterally
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