1. Joints Joints (articulations), the sites where two or more bones meet, have two fundamental functions: – Give skeleton mobility – Hold skeleton together 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) Sutures, Syndemoses & Gomphoses – Cartilaginous: articulating bones are united by cartilage, lack a joint cavity Synchondroses or Symphyses – Synovial: articulating bones are separated by a fluid-containing joint cavity, substantial freedom of movement 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 to prevent movement but allow growth – Ossifies at middle age and become “synostoses” (bony junctions) Syndesmoses – Connected by a ligament, length can vary and determine mvmnt – Ex) tibia/fibula (some “give”) v. radius/ulna (rotation permitted) Gomphoses – “peg-in-socket” – Only example is teeth in bony alveolar socket – Fibrous connection is short periodontal ligament

4. Cartilaginous Joints Synchondroses: – Bar or plate of hyaline cartilage unites bones – Ex) ephipheseal plates in long bones of children (eventually become synostoses) and immovable joint of 1 st rib costal cartilage to manubrium Symphyses: (“growing together”) – Articular surfaces 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

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 synovial fluid  Not actually part of the 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