Joints of the Body

Definition Joints are junctions between bones A joint is the point of contact, or articulation, between two bones Joints hold bones together Many of them permit flexibility and movement

How Joints Are Held Together Both ligaments and tendons help to hold joints together Ligaments – connect bones to bones Tendons – connect muscle to bone Joints are also surrounded and held together by thick connective tissue called a capsule, which is a lot like Saran-Wrap Joints are cushioned by bursae Bursa sacs are fluid-filled sacs that keep tendons and ligaments from rubbing against bony processes, which could cause shredding and tearing, as well as bony irritation

Classification of Joints Joints are classified according to the degree of movement that they permit 3 categories Synarthroses (sin’-ar-throw’-sees) Amphiarthrosis (am’-fee-ar-throw’-sees) Diarthroses (dye’-ar-throw’-sees); also known as synovial joints

Synarthroses Joints Do not permit movement Bones are connected by a thin layer of fibrous connective tissue that may be replaced by bone in the adult Example: The sutures that join skull bones are synarthroses

Amphiarthroses Joints Permit slight movement and help absorb shock Bones are joined by cartilage Example: The pubic symphysis of the pelvis and the intervertebral joints of the vertebral column

Diarthroses (Synovial) Joints Referred to as freely movable joints, though the amount of flexibility varies Most of the body’s joints are diarthroses 6 types Gliding Condyloid Saddle Pivot Hinge Ball-and-socket

Make-up of a Diarthrosis Joint Ends of bones that form these joints are covered with hyaline (articular) cartilage, which lacks nerves and blood vessels The joint is surrounded by a connective tissue capsule, called the joint capsule Made of tough, fibrous connective tissue that is continuous with the covering of the bone The joint capsule is reinforced with ligaments, which connect the bones, and limit movement at the joint

Make-up, continued The joint capsule is lined with a membrane that secretes a lubricant called synovial fluid Reduces friction during movement and absorbs shock Fluid-filled sacs called bursae are located between bone and tendons and between bone and some other tissues to cushion the movement of the bone over other tissues

Gliding Joints Shape: Flat or slightly curved Range of movement: One bone glides over another without circular movement Example: Carpal joints of wrist and tarsal joints of ankle

Condyloid Joints Shape: Oval-shaped condyle fits into elliptical cavity Range of movement: Angular movement Example: Joints between metacarpals and phalanges

Saddle Joints Shape: Saddle shaped Range of movement: Permits wide range of movement Examples: Carpo-metacarpal joint of thumb

Pivot Joints Shape: Small projection of one bone pivots in ring-shaped socket of another bone Range of movement: Rotation Example: Atlanto-axial joint of 1st & 2nd cervical vertebrae; radio-ulnar joint of elbow

Hinge Joints Shape: Convex surface of one bone fits into concave surface of another bone Range of movement: Motion in one plane only; permits only flexion and extension Examples: Elbow; knee

Ball-and-Socket Joints Shape: Ball-shaped end of one bone fits into cup-shaped socket of another bone Range of movement: Permits widest range of movement, including rotation Examples: Shoulder; hip joint

Naming Joints Joints are named according to the 2 structures that are being joined Examples: The clavicle joins with the acromion process on the scapula This is called the acromio-clavicular joint (a-c joint) Carpals join with metacarpals Called the carpo-metacarpal joints Metacarpals join with phalanges Called the metacarpo-phalangeal joints (MP joints) Phalanges join with each other Called interphalangeal joints (IP joints)

A Few Things To Remember Hip ball-and-socket joint Femoral head (ball) fits into Acetabulum of the ischium (socket) Shoulder ball-and-socket joint Humeral head (ball) fits into Glenoid fossa of the scapula (socket) Called the “gleno-humeral joint” Jaw joint – saddle joint Mandible fits into Temporal bone Called the temporo-mandibular joint (TMJ)