JointsJoints (articulations), the sites where two or more bones meet, have two fundamental functions:Give skeleton mobilityHold skeleton together Joints are classified by structure & function: Structure: focused on the material that binds the bones together & whether a joint cavity is presentFunction: Based on the amount of movement allowed at the joint.

Joints: Structural ClassificationFocuses on material binding joint and whether or not a joint cavity is presentThree 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 & GomphosesCartilaginous: articulating bones are united by cartilage, lack a joint cavitySynchondroses or SymphysesSynovial: articulating bones are separated by a fluid-containing joint cavity, substantial freedom of movementmajority of joints fit into this category including all limb joints

Fibrous JointsSutures (seams) Only between bones of skullCompletely filled with short connective tissue to prevent movement but allow growthOssifies at middle age and become synostoses (bony junctions) Syndesmoses Connected by a ligament, length can vary and determine mvmntEx) tibia/fibula (some give) v. radius/ulna (rotation permitted)Gomphosespeg-in-socketOnly example is teeth in bony alveolar socketFibrous connection is short periodontal ligament

Cartilaginous JointsSynchondroses:Bar or plate of hyaline cartilage unites bonesEx) ephipheseal plates in long bones of children (eventually become synostoses) and immovable joint of 1st rib costal cartilage to manubrium

Symphyses: (growing together)Articular surfaces covered with articular hyaline cartilage which is fused to pad or plate of fibrocartilageFibrocartilage acts as a shock absorber and permits limited movement, for strength and flexibilityEx) Intervertebral disks and pubis symphysis

The Synovial JointFive Distinct FeaturesArticular cartilageJoint (synovial) cavityArticular capsuleSynovial fluidReinforcing ligaments

Structures Associated with the Synovial JointBursae flattened fibrous sacsLined with synovial membranesFilled with synovial fluidNot actually part of the jointTendon sheathElongated bursa that wraps around a tendon

Types of Synovial Joints Based on Shape I

Types of Synovial Joints Based on Shape II

Movements Allowed by Synovial Joints

Joints: Functional ClassificationBased on amount of movement allowed in the jointThree functional categories:Synarthroses: immovable majority of fibroussome cartilaginousAmphiarthroses: slightly movable some cartilaginousDiarthroses: freely movable All synovial

Joint InjuriesSprains: ligaments reinforcing a joint are stretched or torn; common in lumbar region of spine, the ankle & the kneeCartilaginous injuries: overuse damage to articular cartilage or tearing of knee menisci, usually due to intense athletic use; often hear snap & pop noiseDislocations: 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 ConditionsBursitis: 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.

ArthritisOsteoarthritis (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

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