Articulations Chapter 9

9.1 Introduction to Articulations A. Joints- where two bones interconnect 1. compare function & form 2. movements of skeleton can occur only at articulations B. Categorized by range of motion or anatomical organization 1. Functional scheme- based on amount of movement possible, or range of motion 2. Anatomical scheme- relies on anatomical organization of joint, not motion of joint

C. Functional Categories 1 C. Functional Categories 1. synarthrosis- immovable joint, can be fibrous or cartilaginous 2. amphiarthrosis- slightly moveable joint, and be fibrous or cartilaginous 3. diarthrosis- freely moveable, referred to as a synovial joint

D. Types of Synarthroses- bony edges are close together, may interlock; extremely strong joints, found where movement btwn bones must be prevented 1. sutures- bones of skull, connected by fibrous connective tissue 2. gomphosis- binds teeth to maxillae & mandible 3. snychondrosis- ridgid, cartilaginous bridge btwn 2 bones, connection between 1st pair of ribs and sternum 4. synostosis-totally rigid joint, formed when 2 bones fuse & boundary disappears, frontal suture of frontal bone

E. Types of Amphiarthoris- (allow more movement than synarthrosis joints, but are stronger than freely moveable joints) 1. syndesmosis-bones connected by a ligament, (distal artic. btwn tibia and fibula- pg 260) 2. symphysis- bones are separated by a wedge/pad of fibrous cartilage (vertebrae, pubic symphysis)

F. Diarthrosis- (synovial) permit wider range of motion, typically at ends of long bones (like those of upper and lower limbs) 1. joint is surrounded by articular capsule, a synovial membrane lines the walls & synovial fluid fills joint cavity. 2. classified by the planes of movement each joint will allow

9.2 II. Synovial Joints (Diarthrosis) A. Components 1. articular cartilages- bony surfaces don’t come in contact because articulating surfaces are covered by cartilage a. slick surface reduces friction during joint movement b. surfaces of cartilage don’t touch even when pressure is applied-separated by a thin layer of synovial fluid w/ in the cavity

c. this fluid acts as a lubricant- reduces friction d c. this fluid acts as a lubricant- reduces friction d. normal joint function is hindered if articular cartilages are damaged - slick surface changes to rough meshwork of collagen fibers, increasing friction in joint drastically 2. Synovial Fluid- resembles interstitial fluid, has 3 functions

a. lubrication- fluid squeezed out of cartilage upon application of pressure (like sponge) b. nutrient and waste distribution - as joint moves, fluid is pumped into & out of cartilage matrix, allowing for waste removal and nutrient diffusion for cartilage cells c. shock absorption- fluid cushions shocks in joints subjected to compression - knee, hip & ankle joints are compressed as you walk and more in running. -Synovial fluid distributes shock evenly across articular surfaces, reducing overall shock to joint.

3. Accessory structures a. cartilages and fat pads i 3. Accessory structures a. cartilages and fat pads i. meniscus -pad of cartilage positioned btwn bones w/in a synovial joint. ii. fat pads- present in many joints (knee), between opposing articular surfaces. Pads protect articular cartilages.

b. Ligaments- accessory ligaments (connect bone to bone) support and strengthen synovial joints and are very strong. c. Tendons- (connect muscle to bone) not part of the articulation, but may limit joint’s range of motion & provide support-example: tendons in arm provide bracing for shoulder joint

d. bursae- fluid filled pockets in connective tissue, contain synovial fluid. -Form where a ligament rubs against other tissues, reduce friction and act as a shock absorbers i. synovial tendon sheaths – tubular bursae, surround tendons in locations where they cross bony surfaces ii. adventitious bursae- bursae that develop in abnormal locations due to stresses iii. bursitis- inflamed bursae, caused by repetitive motion or pressure on joint (tennis elbow, bunions:)

B. Stabilizing Factors- joint is either very strong OR highly moveable 1.in moveable joints (diarthrosis), ROM must be limited to prevent joint damage 2. limitations include a. collagen fibers and ligaments b. shapes of articulating surfaces and menisci-prevent movement in certain directions c. presence of bones, muscles, or fat pads around joint d. tension in tendons, limiting direction of movement

3. injuries -Articulating surfaces forced out of position a. Dislocation (luxation) -Articulating surfaces forced out of position -Damages articular cartilage, ligaments, joint capsule b. Subluxation -A partial dislocation, less severe

9.3 III. Properties and movements of synovial joints A. Types of Dynamic Motion 1. Linear motion (gliding) 2. Angular motion- shaft changes angle while pivot point remains stationary 3. Rotation-angle doesn’t change, shaft spins around axis B. Planes (Axes) of Dynamic Motion 1. Monaxial (1 axis) 2. Biaxial (2 axes) 3. Triaxial (3 axes)

C. Classification of Synovial Joints by Shape -Gliding -Hinge -Pivot -Ellipsoid -Saddle -Ball-and-socket 1. Gliding Joints a. Flattened or slightly curved faces b. Limited motion (nonaxial) 2. Hinge Joints a. Angular motion in a single plane (monaxial) 3. Pivot Joints a. Rotation only (monaxial)

6. Ball-and-Socket Joints 4. Ellipsoid Joints Oval articular face within a depression Motion in two planes (biaxial) 5. Saddle Joints Two concave, straddled (biaxial) 6. Ball-and-Socket Joints Round articular face in a depression (triaxial)

7. A joint cannot be both mobile and strong a 7. A joint cannot be both mobile and strong a. The greater the mobility, the weaker the joint b. Mobile joints are supported by muscles and ligaments, not bone-to- bone connections