Joints• Joints (articulations) - the sites where two or

more bones meet; weakest parts of skeleton.Two fundamental functions:– Give skeleton mobility– Hold skeleton together; sometimes playing a

protective role.

• Joints are classified by structure & function: – Structure: focused on the material that binds the

bones together & whether a joint cavity is present– Function: Based on the amount of movement

allowed at the joint.

Joints: Structural Classification• Focuses on material binding joint and whether or not a joint

cavity is present• Three structural categories:– Fibrous:

• joined by fibrous tissue, no joint cavity, generally immovable or only slightly movable (based on length of connective tissue fibers)

• 3 Types of Fibrous Joints: Sutures, Syndesmoses & Gomphoses

– Cartilaginous: • articulating bones are united by cartilage, lack a joint cavity• 2 Types of Cartilaginous Joints: Synchondroses or Symphyses

– Synovial:• articulating bones are separated by a fluid-containing joint cavity,

permits substantial freedom of movement. Freely movable diarthroses

• majority of joints fit into this category including all limb joints

Fibrous Joints• Sutures (“seams”)

– Only between bones of skull– Completely filled with short connective tissue continuous w/ periosteum

to prevent movement but allow for growth– Ossifies at middle age and become “synostoses” (bony junctions); moving

cranial bones would damage brain – protective adaptation. • Syndesmoses (syndesmos = ligament)

– Bones connected by a ligament, length can vary & determines movement– Prevents true movement, fuctionally an immovable joint/synarthrosis– Ex: tibia/fibula (some “give”) v. radius/ulna (rotation permitted)

• Gomphoses– “peg-in-socket” fibrous joint– Only example – articulation of teeth in bony alveolar sockets– Fibrous connection is short periodontal ligament

Cartilaginous Joints• Synchondroses:

– Bar or plate of hyaline cartilage unites bones @ synchondrosis (junction of cartilage)

– Ex: ephipheseal plates connecting diaphysis & epiphysis in long bones of children (eventually become synostoses) and immovable joint of 1st rib costal cartilage to manubrium

• Symphyses: (“growing together”)– Articular surfaces of bone are covered with articular hyaline

cartilage which is fused to pad or plate of fibrocartilage– Fibrocartilage acts as a shock absorber and permits limited

movement, for strength and flexibility– Ex) Intervertebral disks and pubis symphysis of pelvis

The Synovial JointThe Synovial Joint

Five Distinct Features1.Articular cartilage2.Joint (synovial) cavity3.Articular capsule4.Synovial fluid5.Reinforcing ligaments

Structures Associated with the Synovial JointStructures Associated with the Synovial Joint

Bursae – flattened fibrous sacs

Lined with synovial membranes

Filled with thin film of synovial fluid

Not actually part of the joint

Generally found in places of prone to friction. Ex: shoulder joint

Tendon sheath

Elongated bursa that wraps around a tendon

Types of Synovial Joints Based on Shape ITypes of Synovial Joints Based on Shape I

Types of Synovial Joints Based on Shape IITypes of Synovial Joints Based on Shape II

Movements Allowed by Synovial Joints

Joints: Functional Classification

• Based on amount of movement allowed in the joint• Three functional categories:

– Synarthroses: immovable • majority of fibrous• some cartilaginous

– Amphiarthroses: slightly movable • some cartilaginous

– Diarthroses: freely movable • All synovial

Joint Injuries• Sprains: ligaments reinforcing a joint are

stretched or torn; common in lumbar region of spine, the ankle & the knee

• Cartilaginous injuries: overuse damage to articular cartilage or tearing of knee menisci, usually due to intense athletic use; often hear “snap & pop” noise

• Dislocations: bones are forced out of alignment; usually accompanied by sprains, inflammations & joint immoblilization; Usually the result of a serious fall or contact injury

Inflammatory & Degenerative Conditions

• Bursitis: inflammation of bursa; usually due to a physical blow or friction

• Tendonitis: inflammation of tendon sheaths; usually due to overuse

• Arthritis: broad term applying to >100 types of inflammatory/degenerative diseases that damage joints; combined it is the most widespread, crippling disease in the U.S.

Arthritis• Osteoarthritis (OA): most common chronic arthritis; “wear &

tear” arthritis; develops in ~85% of Americans; probably related to normal aging process, believed that normal joint use promotes the release of metalloproteinase enzymes that break down articular cartilage

• Rheumatoid Arthritics (RA): Autoimmune disease, immune system attacks bodily tissue; Initial trigger unknown, may be linked to streptococcus bacterium, affects ~1% of Americans will be affected; starts off with joint tenderness and stiffness, onset is usually bilateral; periods of “flare-ups” & “remissions”

• Gouty Arthritis: Increase in uric acid in blood sometimes results in needle-like urate crystals in the soft tissues of joints; this triggers an inflammatory response or a “gout attack”; typically affects one joint, usually base of the big toe