Chapter 8: Joints

Types of Angular Movement

-Abduction: movement along frontal plane, away from the midline -Adduction: movement along frontal plane, toward the midline -Circumduction •Involves flexion, abduction, extension, and adduction of limb •Limb describes cone in space

Special movements: Dorsiflexion and Plantar Flexion

-Dorsiflexion and plantar flexion of foot •Dorsiflexion: bending foot toward shin •Plantar flexion: pointing toes -Inversion and eversion of foot •Inversion: sole of foot faces medially

Special Movements: Elevation

-Elevation and depression of mandible •Elevation: lifting body part superiorly -Example: shrugging shoulders•Depression: lowering body part -Example: opening jaw -Opposition: movement of thumb •Example: touching thumb to tips of other fingers on same hand or any grasping movement

Other features of some synovial joints

-Fatty pads •For cushioning between fibrous layer of capsule and synovial membrane or bone -Articulardiscs (menisci) •Fibrocartilage separates articular surfaces to improve "fit" of bone ends, stabilize joint, and reduce wear and tear

Three general types of movements

-Gliding -Angular movements -Rotation

2. Angular Movements

-Increase or decrease angle between two bones -Movement along sagittal plane -Angular movements include: •Flexion: decreases the angle of the joint •Extension: increases the angle of the joint -Hyperextension: movement beyond the anatomical position

Range of motion allowed by synovial joints

-Nonaxial: slipping movements only -Uniaxial: movement in one plane -Biaxial: movement in two planes -Multiaxial: movement in or around all three planes

1. Gliding Movements

-One flat bone surface glides or slips over another similar surface -Examples •Intercarpal joints •Intertarsal joints •Between articular processes of vertebrae

Special movements: Supination

-Supination and pronation: rotation of radius and ulna •Supination: palms face anteriorly -Radius and ulna are parallel •Pronation: palms face posteriorly -Radius rotates over ulna

Three factors determine stability of joints to prevent dislocations

1. Shape of articular surface (minor role) •Shallow surfaces less stable than ball-and-socket 2. Ligament number and location (limited role) •The more ligaments, the stronger the joint 3. Muscle tone keeps tendons taut as they cross joints (most important) •Extremely important in reinforcing shoulder and knee joints and arches of the foot

1. Articular Cartilage

consists of hyaline cartilage covering ends of bones •Prevents crushing of bone ends

2. Joint (synovial) cavity

small, fluid-filled potential space that is unique to synovial joints

3. Rotation

turning of bone around its own long axis, toward midline or away from it -Medial: rotation toward midline -Lateral: rotation away from midline-Examples •Rotation between C1 and C2 vertebrae •Rotation of humerus and femur

3. Articular (joint) capsule

two layers thick •External fibrous layer: dense irregular connective tissue •Inner synovial membrane: loose connective tissue that makes synovial fluid

4. Synovial Fluid

viscous, slippery filtrate of plasma and hyaluronic acid •Lubricates and nourishes articular cartilage •Contains phagocytic cells to remove microbes and debris

Movements Allowed by Synovial Joints

•All muscles attach to bone or connective tissue at no fewer than two points -Origin: attachment to immovable bone -Insertion: attachment to movable bone •Muscle contraction causes insertion to move toward origin •Movements occur along transverse, frontal, or sagittal planes

Bursae and Tendon Sheaths

•Bags of synovial fluid that act as lubricating "ball bearing" -Not strictly part of synovial joints, but closely associated •Bursae: reduce friction where ligaments, muscles, skin, tendons, or bones rub together •Tendon sheaths: elongated bursae wrapped completely around tendons subjected to friction

Synchondroses

•Bar or plate of hyaline cartilage unites bones •Almost all are synarthrotic (immovable) •Examples -Temporary epiphyseal plate joints •Become synostoses after plate closure -Cartilage of 1st rib with manubrium of sternum

Syndesmoses

•Bones connected by ligaments, bands of fibrous tissue •Fiber length varies, so movement varies -Short fibers offer little to no movement •Example: inferior tibiofibular joint -Longer fibers offer a larger amount of movement •Example: interosseous membrane connecting radius and ulna

Fibrous Joints

•Bones joined by dense fibrous connective tissue •No joint cavity •Most are immovable -Depends on length of connective tissue fibers •Three types of fibrous joints -Sutures -Syndesmoses -Gomphoses

Synovial Joints

•Bones separated by fluid-filled joint cavity •All are diarthrotic (freely movable) •Include almost all limb joints •Characteristics of synovial joints -Have six general features -Have bursae and tendon sheaths associated with them -Stability is influenced by three factors -Allow several types of movements -Classified into six different types

Cartilaginous Joints

•Bones united by cartilage •Like fibrous joints, have no joint cavity •Not highly movable •Two types -Synchondroses -Symphyses

5. Different types of reinforcing ligaments

•Capsular: thickened part of fibrous layer •Extracapsular: outside the capsule •Intracapsular: deep to capsule; covered by synovial membrane

Special Movements: Eversion

•Eversion: sole of foot faces laterally -Protraction and retraction: movement in lateral plane •Protraction: mandible juts out •Retraction: mandible is pulled toward neck

Symphyses

•Fibrocartilage unites bone in symphysis joint -Hyaline cartilage also present as articular cartilage on bony surfaces •Symphyses are strong, amphiarthrotic (slightly movable) joints •Examples -Intervertebral joints -Pubic symphysis

Classification of Joints

•Joints, also called articulations: sites where two or more bones meet •Functions of joints: give skeleton mobility and hold skeleton together •Two classifications: 1. Structural: three types based on what material binds the joints and whether a cavity is present •Fibrous •Cartilaginous •Synovial 2.Functional classifications: three types based on movement joint allows •Synarthroses: immovable joints •Amphiarthroses: slightly movable joints •Diarthroses: freely movable joints •Structural classifications are more clear cut, so these will be used here

6. Nerves and blood vessels

•Nerves detect pain; monitor joint position and stretch •Capillary beds supply filtrate for synovial fluid

Gomphoses

•Peg-in-socket joints •Only examples are the teeth in alveolar sockets •Fibrous connection is the periodontal ligament -Holds tooth in socket

Sutures

•Rigid, interlocking joints of skull •Allow for growth during youth -Contain short connective tissue fibers that allow for expansion •In middle age, sutures ossify and fuse -Immovable joints join skull into one unit that protects brain -Closed, immovable sutures referred to as synostoses

General Structure of the synovial joint

•Synovial joints have six general features: 1. Articular cartilage: 2. Joint (synovial) cavity: 3. Articular (joint) capsule: 4. Synovial Fluid 5. Different types of reinforcing ligaments 6. Nerves and blood vessels

Types of Synovial Joints

•There are six different types of synovial joints -Categories are based on shape of articular surface, as well as movement joint is capable of •Plane •Hinge •Pivot •Condylar •Saddle•Ball-and-socket