1. 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.

2. 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

3. 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

4. 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 1 st 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

5. The Synovial Joint Five Distinct Features 1.Articular cartilage 2.Joint (synovial) cavity 3.Articular capsule 4.Synovial fluid 5.Reinforcing ligaments

6. Structures 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

7. Types of Synovial Joints Based on Shape I

8. Types of Synovial Joints Based on Shape II

9. Movements Allowed by Synovial Joints

10. 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

11. 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

12. 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.

13. 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