A&P 1: Joint Structure & Function

Joint/Articulation

Place on contact between bones, bone & cartilage or bones & teeth; bones articulate with each other at a joint

Classified by structural and functional characteristics

Inverse relationship between stability & mobility

Fibrous joint

No joint cavity; bones held together by dense regular (fibrous) connective tissue

Synarthrosis or amphiarthrosis; typically for stability

Gomphosis, suture, syndesmosis

Cartilaginous joint

No joint cavity; cartilage pad wedged between bones

Synarthrosis or amphiarthrosis; typically for shock absorption

Synchondrosis, symphysis

Synovial joint

Joint cavity filled with synovial fluid enclosed within connective tissue capsule separating articular surfaces

Supported by lligaments, blood vessels, sensory receptors for proprioception (movement, strength, postion) and nociception (pain)

Bones attached by ligaments; typically for movement; diarthrosis

Plane, hinge, pivot, condylar, saddle, ball-and-socket

Synarthrosis

Immobile joint; fibrous or cartilaginous

amphiarthrosis

Slightly mobile joint; fibrous or cartilaginous

Diarthosis

Freely mobile joint; synovial

Gomphosis

“Peg in a socket”; articulates tooth root, alveolar process

Held by fibrous periodontal membranes; synarthrosis

Suture

Fibrous joint found in skull to permit growth (ossifies in adulthood, becoming synostoses)

Interlocking, irregular edges; synarthrosis

Syndesmoses

Fibrous joint with sheet (interosseous membrane/ligament) which functions as a pivot; amphiarosis

Composed of long strands of dense regular connective tissue joining bones

Found in radius/ulna, tibia/fibula

Synchondrosis

Bones joined by hyaline cartilage; typically synarthrosis

Epiphyseal plate, spheno-occipital synchondosis, costochondral joints, sternocostal joint

Symphysis

Pad of fibrocartilage between articulating bones; resists compression & tension; arphiarthrosis

Public symphysis, intervertebral joints

Articular capsule/joint capsule

Outer fibrous layer of dense connective tissue to prevent joint separation

Inner layer is synovial membrane (synovium) secretes synovial fluid; covers internal joint surfaces not covered by cartilage

Articular cartilage

Thin layer of hyaline cartilage covering articulating surfaces of synovial joints

Reduce friction, cushions to absorb compression, protects articulating ends of bones

Lacks perichondrium

Joint cavity

Space that permits separation of articulating bones; lined with cartilage and synovial fluid

Synovial fluid

Viscous, oily product of synovial membrane cells and blood plasma filtrate

Lubricates articular cartilage

Nourishes chrondocytes and removes wastes when circulating (from movement) in/out of cartilage matrix

Absorbs shock as synovial fluid distributes stress & force evenly across surfaces when pressure suddenly increases

Ligaments

Dense regular connective tissue connecting bone to bone

Stabilize, strengthen, reinforce synovial joints

Intrinsic ligament

Thickening of articular capsule; extracapsular (outside) or intracapsular (inside)

Extrinsic ligament

Outside of, physically separate from articular capsule

Tendon

Dense regular connective tissue connects bone to muscle; pass across/around joint for stability, sometimes limiting range of motion

Bursa

Fibrous, saclike structure containing synovial fluid to relieve friction

Occur where other structures overlie and rub

Connected to or separate from joint cavity

Tendon sheath

Elongated bursa wrapping around tendon commonly found in tight spaces i.e. digital

Fat pad

Packing material/protection distributed along synovial joint periphery; often fill spaces forming when bones move and the joint cavity changes

Uniaxial

Bone move in one plane/axis

Plane, hinge, pivot

Biaxial

Bone moves in two planes/axes

Condylar, saddle

Multiaxial/triaxial

Bones move in multiple planes/axes

Ball-and-socket

Plane

Planar/gliding joint; simplest, least mobile

Limited side-to-side movement; no rotational or angular movement

Intercarpal, intertarsal

Hinge

Convex surface of one bone fits into concave depression in other; movement confined to single axis like hinge of door (uniaxial)

Elbow, knee, interphalangeal (IP)

Pivot

One bone with rounded surface fits into ring formed by ligament & bone

First bone rotes on longitudinal axis relative to second bone; uniaxial

Proximal radioulnar, atlantoaxial joint (atlas/axis)

Condylar

Conyloid/ellipsoid joint; biaxial with oval convex surface on bone articulating with concave surface

2 axes; i.e. back/forth, side/side

Metacarpophalangeal joints (MP)

Saddle

Articular surfaces have saddle-shaped concave/convex regions

Biaxial with greater movement than condylar

Carpometacarpal (thumb)

Ball-and-socket

Multiaxial with spherical articulating head fit into rounded, cuplike socket

Coxal, glenohumeral (shoulder)

Gliding

Simple movement with 2 opposing surfaces sliding back and forth or side to side with respect to each other

Bone angle does not change; limited motion in any direction; typical of plane joint

Angular motion

Increase/decrease angle between two bones

flexion or lateral flexion/extension, abduction/adduction, circumduction

Flexion

Movement between anterior/posterior (AP) plane that decreases angle between bones

Extension

Movement in anterior/posterior (AP) plane that increases angle between articulating bones

Hyperextension

Extension of joint beyond normal range of motion due to hypermobility or injury

Lateral flexion

Trunk of body moves in coronal plane laterally away from body midline

I.e. side bend/vertebral movement, radial deviation

Circumduction

Sequence of movements where distal end of appendage makes circular movement around relatively stationary proximal end

I.e. arm/leg circle

Rotation

Pivoting motion where bone turns on its own longitudinal axis

Atlantoaxial joint

May be lateral (external) or medial (internal); i.e. humerus/femur

Pronation/supination

Pronation

Medial rotation of forearm, palm directed posterior/inferior

Supination

Lateral rotation of forearm, palm directed anterior/superior

Depression

Inferior movement of body part

I.e. opening mouth (mandible depression), lowering shoulders

Elevation

Superior movement of body part

I.e. shrugging shoulders

Dorsiflexion

Talocrural joint bent with dorsum (superior surface) & toes move toward leg

Plantar flexsion

Talocrural joint bent with toes pointing inferiorly

Eversion

Sole of foot turns to face laterally/outward at intertarsal joints

Inversion

Sole of foot turns to face medially/inward at intertarsal joints

Protraction

Anterior movement of body part from anatomic position

I.e. jutting TMJ, hunching shoulder to cross arms

Retraction

Posterior movement of body part from anatomic position

I.e. jaw retraction

Opposition

Thumb moves toward palmar tips crossing palm of hand; allows grasping

Reposition

Thumb moves away from palmar tips back toward neutral position; reverse of opposition

Lever/fulcrum

Rigid object rotates around a fixed point when effort exceeds resistance

Effort arm

Part of lever from point of effort to fulcrum

Resistance arm

Part of lever from fulcrum to point of resistance

First-class lever

Fulcrum in middle between effort and resistance; scissors

Atlanto-occipital joint

Second-class lever

Resistance is between the fulcrum and applied effort; wheelbarrow lift

Rare; plantar flexion

Third-class lever

Effort applied between resistance and fulcrum; picking up with foreceps

Most common type in body; elbow, TMJ (bite)

Development

Process begins in week 6 with progressive development during fetal period

Mesenchyme differentiates based on joint type

Synovial joints develop joint capsule, ligaments from laterally placed mesenchyme and central mesenchyme reabsorbed or forming menisci/articular discs

Childhood injuries (subluxation/fracture of epiphysis) can affect development

Arthritis

Disease involving damage to articular cartilage

Osteoarthritis: chronic degeneration of aging joints; may be caused by wear and tear

Gouty: crystals in synovial fluid & membrane, can cause fusion; mostly middle aged/older males affected

Rheumatoid: autoimmune disorder with synovial membrane inflammation, swelling, thickening, erosion; causes pain, joint swelling, weakness, osteoporosis with heart/vessel; mostly younger/middle-aged women affected

Ankylosis

Scar tissue in joint forms and ossifies; bone ends fuse