Types of Joints and the Anatomy of the Synovial Joint

What is an Articulation (Joint)  Point of contact between two bones **There are three types of joints

1. Fibrous Joints  Also called “sutures” ZERO  These joints are bound tightly together by connective tissue and allows ZERO movement (immovable joint)  Ex. Interlocking bones of the skull

2. Cartilaginous Joints SLIGHT  Occur where the body of one bone connects to the body of another bone by means of cartilage and allows SLIGHT movement  Ex. Intervertebral discs

3. Synovial Joints  Occurs where bony surfaces are separated by a lubricating fluid (synovia) and by cartilage  Also joined by ligaments, which enclose the ends of articulating bones and form the synovial-containing capsule MOST  Allows MOST movement

Examples of Synovial Joints

Parts of Synovial Joint

1. Articulating Cartilage  Allow for smooth contact surface  Acts as a shock absorber

2. Joint Cavity  Located between two bony articulating surfaces  Filled with synovial fluid (joint lubricant)  Essential in reducing friction and providing nutrients for articulating cartilage

3. Joint Capsule  Fibrous structure that consist of the:  Synovial membrane (allows certain nutrients to pass through to synovial fluid)  Fibrous capsule (keeps synovial fluid from leaking) ** Membrane is medial to capsule

4. Bursae  Small flattened sacs  Prevents friction between tendons, ligaments and bones

Intrinsic Ligaments  Thick bands of fibrous connective tissue  Helps thicken and reinforce the joint capsule  Ex. Forming the joint capsule or the meniscus of the knee

Extrinsic Ligaments  Separate from the joint capsule and help to reinforce the joint by attaching bones together

Types of Synovial Joints

Gliding Joint  Also known as a “plane” or “arthrodial” joint  Connects flat or slightly curved bone surfaces  Ex. Joints between tarsals  Ex. Joints between carpals

Hinge Joints  Also known as a “ginglymus” joint  Think of the hinge of a door…  Convex portion of one bone fitting into a concave portion of another  Allows movement on one plane  Ex. Joint between phalanges  Ex. Joint between humerus and ulna  Ex. Joint between femur and tibia

Pivot Joints  Also known as a “trochoid” joint  Allows rotation in one plane (uni-axial)  A rounded point of one bone fits into a groove of another  Ex. Atlantoaxial joint (between atlas and axis– shake head “no”)  Ex. Between radius and ulna at humerus

Ellipsoid Joints  Allows movement on two planes (bi-axial)  Ex. Metaphalangeal joint

Saddle Joints  Allows movement in two planes  Movements include flexion/extension and abduction/adduction  Does not have a ball-and-socket rotation  Ex. Carpo-metacarpal articulation

Ball and Socket Joint  Also known as a “spherodial” joint  “Ball” at one bone fits into the “socket” of another, allowing movements around all three axis  Ex. Hip  Ex. Shoulder