ch5outline

PED 351 BIOMECHANICS LECTURE OUTLINE
Chapter 5

Skeletal Articulations: Joint Architecture

Classification according to MOVEMENT:

Synarthrosis - immovable, fibrous joints

sutures - bone sheets mate closely and held by fibers (skull)
syndemosis - held by ligaments (mid-radioulnar, mid-tibiofibular)

Amphiarthrosis - slightly movable, cartilaginous joint

synchondroses - held by thin layer of hyaline cartilage (sternocostal, epiphyseal plate)
symphyses - thin plate of hyaline cartilage separates disc of fibrocartilage from bone (vertebral, pubic symphysis)

Diarthroses - freely movable, synovial joints

Articular cartilage - protective layer of dense white connective tissue covering articulating bone surfaces that spreads load over wider are, therby reducing contact stress

Articular capsule - double layered membrane that surrounds the joint

Synovial fluid - clear, slightly yellow liquid that provides lubrication inside the articular capsule

Bursae (and tendon sheath) - small capsules filled with synovial fluid that reduce friction between tendon and bone

Meniscus - articular fibrocartilage (soft tissue that intervenes between articulating bones) that may

distribute load over wider area
improve "fit" of articulating surfaces
limit translation ("slip") of one bone in relation to another
protection of periphery of joint
lubrication
shock absoprtion

Tendons (muscle to bone) and Ligaments (bone to bone)

Types include

gliding (plane; arthrodial) - allows non-axial gliding only (intermetatarsal, intercarpal, facet joints of vertebrae)
hinge (ginglymus) - convex vs. concave (humeroulnar, interphalangeal)
pivot (screw; trochoid) - allows rotation around one axis (proximal and distal radioulnar, atlanto-axial [between first and second cervical vertebrae])
condyloid (ovoid; ellipsoidal) - modified ball-and-socket (not as deep) (radiocarpal, 2-5 metacarpophalangeal)
saddle (sellar) - shape of riding saddle (carpometacarpal of thumb)
ball and socket (spheroidal) - reciprocally convex and concave (hip and shoulder)

Click here to download a page that contains examples of each of the diarthrodial joints.

Major joints in Human Body

shoulder (glenohumeral) - articulation of glenoid fossa and humerus (ball-and-socket)
elbow (humeroulnar) -articulation of humerus and ulna (hinge)
wrist (radiocarpal) -articulation of radius and carpals (condyloid)
hip (acetabularfemoral) -articulation of acetabulum and femoral head (ball-and-socket)
knee (tibiofemoral) - articulation of femur and tibia (hinge)
ankle (talocrural) - articulation of tibia and fibula with talus (hinge)
spine (intervertebral) - intervertebral disc (symphysis - amphiarthrosis)
forearm (proximal and distal radioulnar) - articulation of heads of radius and ulna (pivot)
neck (atlanto-occipital and atlanto-axial)

atlanto-occipital - articulation of atlas (C1) and occipital bone (skull) = condyloid joint
atlanto-axial - articulation of atlas (C1) and axis (C2) = pivot joint

Functional Aspects of the Joint

Joint Stability - ability to resist abnormal displacement of articulating bones

prevents injuries to surrounding ligaments, muscles, and tendons
high stability is desired

Factors affecting joint stability:

Joint structure

reciprocally shaped = tend to fit tightly together

Contact area

wide contact area = high stability (shoulder vs. hip)
different among joints and among individuals
change in joint angle --> change in contact area --> change in stability

maximal area of contact at the close-packed position

Connective tissues

weak and lax connective tissues = low stability
strengthening of tissues --> increase in stability
muscle activity and fatigue --> decrease in stability

Example: illiotibial tract of fascia latae crosses lateral aspect of knee and contributes to knee stability

Joint Flexibility - range of motion (ROM) allowed at a joint

ROM - the angle through which a joint moves from anatomical position to the extreme limit of segment motion
is joint specific

Factors affecting joint flexibility:

shapes of articulating bone surfaces
intervening muscle or fatty tissue
laxity
extensibility of the collagenous tissue and muscles
fluid contens in cartilagenous disc
temperature of collagenous tissues (warm-up?)
stretching program

Flexibility vs. injury

sources of injury

extremely low flexibility = high chance of tear or rupture
extremely high flexiblity = low stability
imbalance between dominant and non-dominant sides

injury prevention - high strength and flexibility desired

stretching program

Golgi Tendon Organs (GTO's) - sensory receptors that sense tension

when activated cause antagonist to contract and muscle being stretched to relax

Muscle Spindles - sensory receptors that monitor changes in length of muscle

when activated cause contraction of muscle being stretched and inhibit tension developement in antagonist

Goal of stretching program is to maximize GTO effect and minimize muscle spindle effect

regular stretching --> flexibility increases
active (produced by active tension in antagonist muscle) vs. passive (produced by force other than muscles)
ballistic vs. static vs. proprioceptive neuromuscular facilitation (PNF) stretching

Common joint Injuries and Pathologies

Sprains - stretching or tearing of connective tissue around a joint
Dislocations - displacement of articulating bones
Bursitis - inflammation of bursa sacs
Arthritis -inflammation of joint with pain and swelling

rheumatoid - most debilitating and painful (immune system attacks healthy tissues)
osteoarthritis - cartilage becomes rough and wears away

Chapter 5 Key Terms:

active stretching (131)	the stretching of muscles, tendons, and ligaments produced by active development of tension in the antagonist muscles
articular capsule (119)	double layered membrane that surrounds every synovial joint
articular cartilage (119)	protective layer of dense white connective tissue covering the articulating bone surfaces at diarthrodial joints
articular fibrocartilage (121)	soft tissue discs or menisci that intervene between articulating bones
ballistic stretching (132)	a series of quick, bouncing-type stretches
close-packed position (123)	joint orientation for which the contact between the articulating bone surfaces is maximum
Golgi tendon organ (129)	sensory receptor that inhibits tension development in a muscle
joint flexibility (125)	a term indicating the relative ranges of motion allowed at a joint
joint stability (123)	the ability of a joint to resist abnormal displacement of the articulating bones
loose-packed position (123)	any joint orientation other than the close-packed position
muscle spindle (130)	sensory receptor that provokes reflex contraction in a stretched muscle and inhibits tension development in antagonist muscles
passive stretching (131)	the stretching of muscles, tendons, and ligaments produced by a stretching force other than tension in the antagonist muscles
proprioceptive neuromuscular facilitation (132)	a group of stretching procedures involving alternating contraction and relaxation of the muscles being stretched
range of motion (125)	the angle through which a joint moves from anatomical position to the extreme limit of segment motion in a particular direction
reciprocal inhibition (130)	the inhibition of the antagonist muscles resulting from activation of muscle spindles
static stretching (132)	maintaining a slow, controlled, sustained stretch over time, usually about 30 seconds
stretch reflex (130)	a monosynaptic reflex initiated by stretching of muscle spindles and resulting in immediate development of muscle tension
synovial fluid (119)	clear, slightly yellow liquid that provides lubrication inside the articular capsule at synovial joints