Joints Also called articulations Functional junctions between bones Functions: Bind parts of the skeleton together Make bone growth possible Permit parts of the skeleton to change shape during childbirth Enable the body to move in response to skeletal muscle contractions

Classification of Joints If classified by function (the degree of movement they make possible): Synarthrotic or immovable Amphiarthrotic or slightly movable Diarthrotic or freely movable If classified by structure (the type of tissue that binds the bones together at each junction): Fibrous Cartilaginous Synovial Currently, the structural classification is more commonly used.

Fibrous Joints Lie between bones that closely contact each other The type of tissue that joins the bones is a thin layer of dense connective tissue Examples: Sutures of the skull (synarthrotic) Between the distal ends of the tibia and fibula (amphiarthrotic)

Cartilaginous Joints Joined by either hyaline cartilage or fibrocartilage Allow only limited movement (amphiarthrotic) as when the back is bent forward or to the side, or when twisted. Examples: Intervertebral discs separate vertebrae of the spinal column and function to absorb shocks and equalize pressure between adjacent vertebrae when the body moves. Symphysis pubis functions to separate the pubis bones anteriorly.

Cartilaginous Joints

Synovial Joints Allow free movement (diarthrotic) Most common type of joint in the body More structurally complex than fibrous or cartilaginous joints Contain a joint capsule made of dense connective tissue Composed of an outer layer of ligaments to hold the joint in place Inner lining called a synovial membrane secretes a thick jelly-like fluid called synovial fluid that lubricates the joints

Synovial Joints Some synovial joints contain special structures: Menisci are flattened pads of fibrocartilage found between articulating surfaces of bones Act as shock-absorbers Bursae are fluid-filled sacs lined with synovial membrane Commonly located between tendons and underlying bony prominences Aid the movement of tendons that glide over these bony parts or other tendons.

Synovial Joints – Ball & Socket Consists of a bone with a globular or slightly egg-shaped head that articulates with the cup-shaped cavity of another bone Allows a wider range of motion than any other type of joint Permits movements in all planes as well as rotational movement around a central axis Examples: Shoulder joint Hip joint

Synovial Joints – Condyloid Also called ellipsoidal joint Oval-shaped condyle of one bone fits into an elliptical cavity of another bone Permits a variety of movements in different planes No rotational movement Examples: Joint between the metacarpals and the phalanges

Synovial Joints – Gliding Also called plane joint Nearly flat or slightly curved Allow twisting or sliding movements Examples: Most of the joints of the ankle and wrist Joints between the articular processes of adjacent vertebrae Sacroiliac joint Joints formed by ribs 2 through 7 connecting with the sternum

Synovial Joints – Hinge Convex surface of one bone fits into the concave surface of another Permits movement in one plane only Resembles the hinge of a door Examples: Joints of the phalanges Elbow The knee is considered to be a modified hinge joint because it also allows some rotation in addition to extension and flexion

Synovial Joints – Pivot Cylindrical surface of one bone rotates within a ring formed of bone and ligament Movement is limited to rotation around a central axis Examples: Joint between the proximal ends of the radius and ulna Joint between the first and second vertebrae (atlas and axis)

Synovial Joints – Saddle Forms between bones whose articulating surfaces have both concave and convex regions The surface of one bone fits the complementary surface of the other Permits a variety of movements Example: Joint between the carpal (trapezium) and metacarpal bones of the thumb

Synovial Joints

Arthritis Group of disorders that cause inflamed, swollen, and painful joints More than a hundred different types world-wide Most common types: Rheumatoid arthritis – most painful and debilitating type Synovial membrane becomes inflamed and thickened Articular cartilage is damaged and fibrous tissue infiltrates, interfering with joint movement Joints may ossify, fusing the articulating bones Autoimmune disorder in which the immune system attacks the body’s healthy tissues

Arthritis Osteoarthritis degenerative disorder that occurs as a result of aging. An inherited form exists Articular cartilage softens and disintegrates gradually Joints become painful and restrict movement Most often affects joint used the most such as the fingers, hips, knees, and lower vertebral column.

Types of Joint Movements Skeletal muscle action produces movements at synovial joints. One end of a muscle is attached to a relatively fixed part on one side of a joint, while the other end of the muscle is fastened to a movable part on the other side. When the muscle contracts, its fibers pull its moveable end toward the fixed end and movement occurs at the joint.

Types of Joint Movements Flexion Bending parts at a joint so that the angle between them decreases and the parts come closer together Example: Bending the elbow Extension Straightening parts at a joint so that the angle between them increases and the parts move further apart Straightening the elbow

Types of Joint Movements Dorsiflexion Movement at the ankle that brings the foot closer to the shin Example: Walking on the heels Plantarflexion Movement at the ankle that brings the foot further from the shin Walking or standing on the toes

Types of Joint Movements Hyperextension Extension of the parts at a joint beyond the anatomical position Often used to describe an abnormal extension beyond the normal range of motion, resulting in injury Examples: Bending the head back beyond the upright position Bending the knee beyond vertical

Types of Joint Movements Abduction Moving a part away from the midline Example: Lifting the upper limb horizontally to form a right angle with the side of the body Adduction Moving a part toward the midline Returning the upper limb from the horizontal position to the side of the body.

Types of Joint Movements Rotation Moving a part around an axis Example: twisting the head from side to side Circumduction Moving a part so that its end follows a circular path Example: moving the finger in a circular motion without moving the hand

Types of Joint Movements Pronation Turning the hand so that the palm is downward or facing posteriorly Supination Turning the hand so that the palm is upward or facing anteriorly

Types of Joint Movements Eversion Turning the foot so that the plantar surface faces laterally Inversion Turning the foot so that the plantar surface faces medially

Types of Joint Movements Retraction Moving a part backward Example: Pulling the chin backward Protraction Moving a part forward Example: Thrusting the chin forward

Types of Joint Movements Elevation Raising a part Example: shrugging the shoulders Depression Lowering a part Example: drooping the shoulders

Arthroscopy Procedure used to diagnose and treat injuries to joints such as the elbow, shoulder, and knee Enables a surgeon to visualize the interior of a joint and perform diagnostic or therapeutic procedures guided by the image on a video screen The surgeon inserts the device through a small incision in the joint capsule Less invasive than conventional surgery