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Articulations

Terms in this set (61)

Articulations (ROM & Anatomical structure)
--Site where 2 or more bones come into contact
--Allow movement( Rigid bones →no movement)
--Provide mechanical support
--Anatomical structures characterize a joint(Type of movement, range of motion (ROM))
--Joints overall function reflects need for: (Strength or structure; Mobility)
Types of Articulations
Classifications based on Motion:
1. Synarthrosis (no movement)
2. Amphiarthrosis (little movement)
3. Diarthrosis (freely moveable)
1) Synarthrosis
--Bones are tightly congruent
--No movement
--Extremely strong joints
--Very simple in structure
a) Sutures b) Gomphosis
c) Synchondrosis d) Synostosis
1a) Sutures
--Sewn together
--Between flat bones of the skull
--Irregularly shaped
--Dense fibrous CT
--VERY STRONG for protection
1b) Gomphosis
--Bolted together
--Binds teeth to the bony sockets in the mandible and maxillae
--Dense fibrous CT
1c) Synchondrosis
--Rigid cartilaginous bridge
--1st pair of ribs to the sternum
--Open epiphyseal growth plate
1d) Synostosis
--Totally rigid, immovable joint
--Fusion of 2 bones(Even boundary disappears)
--Frontal bone
--Ossified epiphyseal growth plates of long bones
2) Amphiarthrosis
--Bones connected by collagen fibers or cartilage
--Allows slight movement
--More motion than synarthrosis
--Stronger than diarthrosis
--Simple in structure
a) Syndesmosis b)Symphysis
2a) Syndesmosis
--Bones connected by a fibrous band or ligament
--Distal articulations between tibia and fibula
--Interosseous membranes
--Strong
2b) Symphysis
--Bones separated by a wedge or pad of fibrous cartilage
--Pubic symphysis
--Intervertebral joints
3) Diarthrosis (Synovial Joints)
--Freely moving joints
--Permit much wider range of motion than synarthrosis or amphiarthrosis
--Very complex in structure
--Typically located at the ends of long bones ( Upper and lower extremities)
Types of Articulations
Classified based on Structure:
1. Fibrous(Suture, Gomphosis, Syndesmosis)
2. Cartilaginous(Synchondrosis, Symphysis)
3. Synovial(Diarthrosis or Synovial)
Synovial Joint Structure
--Bones separated by fluid filled joint cavity
--Fluid and articular cartilage prevent bones from contacting
--Freely movable
--Most joints in the body
Joint Capsule
--Dense, fibrous
--Often reinforced by ligaments, tendons, etc.
--Contains the articulation
Articular Cartilage
--Covers articulating surfaces of bones
--Reduces friction
--Prevents wear to ends of bones
Synovial Membrane
--Thin layer between joint capsule and cavity
--Lines interior of joint cavity(Except where there is articular cartilage)
--Produces synovial fluid
Synovial Fluid
--Thick slippery fluid;Contained w/in joint capsule
Functions:
1. Lubrication:(Hydrostatic Pressure; Extremely low coefficient of friction)
2. Nutrient Supply:(Circulates nutrient and waste to and from avascular cartilage; Movement is critical)
3. Shock Absorption: (Distributes high impact forces evenly; Shear thickening fluid)
Accessory Structures of Synovial Joints
...
Articular Discs
--Fibrous cartilage situated b/t opposing bones
Example: menisci
--Increase joint congruity (Distribute forces)
Bursa and Tendon Sheaths
--Fluid filled sacs - synovial fluid
--Around many joints
--Acts as cushion between:Ligaments, tendons, muscles, bones, etc.
--Minimize friction
Glenoid or Acetabular Labrum
--Lip of fibrocartilage around articulation
--Deepened the socket(Increases joint congruency)
--Increase joint stability
Motion of Joints
--3 Unique ways to move:
1. Gliding
2. Rotation
3. Angular Motion
a) Circumduction
Gliding
--Pencil remains upright and slides across surface
--Pure linear translation
--Can glide in any direction across the plane of the surface
--Point of contact changes
Rotation
--Pencil remains upright at one point of contact on surface (No translation or gliding)
--Pencil rotates about its long axis
Angular Motion
--Pencil remains at one point of contact on surface(No translation or gliding; No rotation about long axis)
--Can move pencil about the fixed point of contact in any direction
Circumduction
--Special case used to describe complex angular motion
--Pencil still fixed point of contact on surface
--Pencil tilted off the vertical axis
--Rotated about point in a circular motion
Types of Synovial Joints
--classified based on type of motion permitted
--6 Classifications:
1. Gliding
2. Hinge
3. Pivot
4. Ellipsoid
5. Saddle
6. Ball-and-Socket
Gliding Joint
--Only permits gliding or translation
--No rotation or angular motion
--Very simple joint
Examples:Intercarpal and intertarsal; Sternoclavicular; Intervertebral facets
Hinge Joint
--Only permits angular motion in one direction
--Rotates about a hinge
--No translation
--Very simple joint
Examples:Elbow joint; Interphalangeal joints; Knee Joint; Ankle Joint
Pivot Joint
--Only permits rotation about long axis of bones (axial rotation)
--Twisting or rotating motion
--Very simple
Examples:Proximal radio-ulnar joint; Atlas/Axis (C1 and C2 vertebrae)
Ellipsoid Joint
--Permits angular motion in multiple directions
--No translation
--No rotation
--More complicated
Examples:Radio-carpal joints; Metacarpophalangeal joints; Metarsophalangeal joints
Saddle Joint
--Interlocking saddle shapes
--Permits variety of motion
--Angular motion,Translation
--No axial rotation
--More complicated
Examples: First carpometacarpal joint (thumb)
Ball-and-Socket Joint
--Interlocking ball and cup shapes
--Permits variety of motion (No translation)
--Allow for most motion of all joint types
--Most complicated
Examples: Shoulder Joint; Hip Joint
Body Motions
...
Flexion and Extension
--Occurs in sagittal plane
--Flexion: reduces angle b/t articulating elements
--Extension:increases angle b/t articulating elem
--Hyperextension: extension past neutral A.P
Abduction and Adduction
--Occurs in frontal plane
--Abduction: away from longitudinal axis of body
--Adduction: towards longitudinal axis of body
Rotation
--Occurs in transverse plane
--Medial/Internal: Anterior surface of limb moves towards mid-line
--Lateral/External: Anterior surface of limb moves away from mid-line
--Left/Right: For motions about mid-line of body
Example: head rotation
Circumduction
--Movement of a limb in a circular motion
Foot Motions
--Dorsiflexion(Reduces angle between foot and leg;Similar to flexion)
--Plantar Flexion(Increases angle between foot and leg; Similar to extension)
--Inversion(Twisting of foot to turn sole inward)
--Eversion(Twisting of foot to turn sole outward)
Hand Motions
--Pronation(Palm turned posteriorly; Radius crosses over ulna)
--Supination (Palm turn anteriorly)
--Opposition(Movement of thumb towards surfaces of palm or other fingers)
Body Motions
--Elevation(Movement of body part superiorly)
--Depression(Movement of body part inferiorly)
--Protraction(Movement of body part anteriorly)
--Retraction(Movement of body part posteriorly)
Shoulder Joint
--Glenohumeral joint(Glenoid fossa of scapula + head of humerus)
--Ball-and-socket
--Greatest range of motion of any joint in body
--Frequently dislocated
--Minimal bony congruency
--Many ligaments hold bones together
--Numerous bursae aid to reduce friction for the large amounts of motion
--Glenoid labrum increases bony congruity by deepening socket
--Relatively large and loose articular capsule allows for large amounts of glenohumeral motion
--All of the many muscles crossing the joint offer dynamic stability
Hip Joint
--Acetabulum + head of femur
--Sturdy ball-and-socket
--Major weight bearing joint
--Permits wide ROM (Much less than shoulder)
--Limited bony congruency
--Acetabular labrum, or rim of fibrous cartilage deepens joint socket to increase bony congruity
--Broad, thick ligaments span from coxal bone to femoral neck to support joint and limit end range motion
--Numerous, LARGE muscle groups span the hip joint to provide dynamic stability to the joint
Intervertebral Discs
--Pads of fibrocartilage between vertebrae
--Act as cushion to support body weight and external forces
--Allows for slight movement between vertebrae
--Account for ¼ of the length of vertebral column
--High water content
--Water helps for disc to act as cushion
--Lose water with age(Shortening with age, Higher risk of injury)
Intervertebral Disc Components
--Nucleus Pulposus(Soft, elastic, gelatinous core; Shock absorption)
--Anulus Fibrosus(Tough outer layer of collagen fibers; Contain Nucleus Pulposus; Attach to adjacent vertebrae)
Intervertebral Disc Injuries
--Slipped Disc(Compressed nucleus pulposus pushes annulus fibrosus into vertebral canal
--Herniated Disc(Nucleus pulposus breaks through anulus fibrosus into vertebral canal)
Knee Joint
--Femur, tibia, and patella
--Essentially a hinge joint(Mainly flexion/extension)
--Largest synovial joint in body
--Major weight bearing joint
--Large range of motion
Knee Joint Articulations
--Tibiofemoral joint(Tibial condyles with femoral condyles; Weight bearing)
--Patellofemoral joint (Patella on patellar surface of femur)
Knee Joint Ligaments
1. Anterior Cruciate Ligament (ACL)
2. Posterior Cruciate Ligament (PCL)
3. Medial Collateral Ligament (MCL)
4. Lateral Collateral Ligament (LCL)
--Collectively act to stabilize the tibio-femoral joint
Cruciate Ligaments
--Cruciate = crus = cross
--Act together to prevent excessive rotations and tibial-femoral translation(ACL restraints anterior tibial translation; PCL restrains posterior tibial translation)
Collateral ligaments
--Act together to prevent medial/lateral translation
--Lateral prevents lateral translation
--Medial prevents medial translation
Menisci
--Fibrocartilage pads on tibial condyles
--Enhance joint congruity
--Provide cushioning
--Aid in distributing forces across joint
--Meniscal degradation and meniscectomy
↓ contact area
Nearly doubles stress on cartilage
High risk of subsequent degeneration
Knee Joint
--Large muscle groups crossing the knee(Dynamic stability; Increase forces across knee)
Knee Joint Structure vs. Motion
--Large ROM(160 in total, 60 during walking)
--Major weight bearing joint
Joint Loading
--Compressive forces on knee joint:
1x to 2x BW during gait
3x to 4x BW during running
Can be much higher during other activities
--Large muscle groups crossing the knee → large joint contact forces
Factors Affecting Joint Loading
--Body Weight
↓ 1 lb. yields ↓ 4 lbs. joint load
=7,000 steps per day
--Tibiofemoral Alignment(Location of loading; Medial compartment loading)
Articular Cartilage
--Hyaline cartilage(Avascular)
--Function:Smooth transmission and distribution of loading
Cartilage Mechanics
--Collagen extracellular matrix
--Hydrophilic PG's
--Fluid flow
--Sponge analogy
Synovial Fluid
--Multifunctional:Provide joint lubrication;μ ≈ 0.005, 10x better than man-made lubricants
--Shock absorption(Shear-thickening fluid)
--Cartilage nutrition
Osteoarthritis
--Degenerative joint disease(Metabolic imbalance of chondrocyte activity)
--Genetics, trauma, developmental
In US: ≈ 27 million (2008) to ≈ 67 million (2030)
↑ age,↑ obesity
--Outliving cartilage lifespan
--Radiographs(K-L Grades 0 to 4; Many factors)
--Osteophytes
--Joint space narrowing
Total Knee Arthroplasty (TKA)
--When to TKA: Pain,Age
--Procedure:
1. Extension Cuts
2. Flexion Cuts
3. Femoral Component
4. Tibial Component
5. Patella Component
--Materials:Ti or Co/Cr Alloy
--Key constraints:Biocompatible;Strong;Wear resistant
--Sacrifices both ACL and PCL
--Post and cam interlock to prevent tibial-femoral translation(Design acts as ACL/PCL)
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