Joint Mechanics

Joint ClassificationJoints classified according to movement capabilities or structure:

1. Synarthrosis Fibrous Joint Immovable tightly bound together by

connective tissue2. Amphiathrosis Cartilaginous Joint

Slightly moveable body of one bone connects to the body of another by cartilage

3. Diarthrosis Synovial Joint Allows greatest movement bony surfaces are

separated by lubricating fluid & cartilage

Fibrous Joint Cartilaginous Joint

Synovial Joint

Synovial Joint Characteristics

• Articulating cartilage– Protects ends of bones & allows for smooth contact when

they move (also known as hyaline cartilage)• Joint capsule– Fibrous structure that consists of synovial membrane

(nutrients) & fibrous capsule (keeps fluid from leaking)• Joint cavity– Between 2 bony articulating surfaces, filled with synovial

fluid (lubricant for joint) – help reduce friction

Synovial Joint Characteristics

• Bursae (Bursa – singular)– Small, flattened fluid sacs found at friction points

between tendons, ligaments & bones• Intrinsic ligaments– Thick bands of fibrous connective tissue that help

thicken & reinforce joint capsule• Extrinsic ligaments– Separate from joint capsule & help reinforce joint by

attaching bones together

Types of Synovial Joints

1. Pivot Joint2. Ball & Socket Joint3. Hinge Joint4. Ellipsoid Joint5. Saddle Joint6. Gliding Joint

• Quick Review of Terminology:

Pivot Joint• One bone rotates around another stationary

point• Movement is limited to rotation in one plane

Eg. Radius around ulna (pronation/supination) &1st vertebrae around 2nd vertebrae (turning neck)

Ball & Socket Joint

• Ball shaped head fits into concave socket• Provides widest range of motion with rotation

& movement occurring in all 3 planes

Eg. Hip joint & shoulder joint

Hinge Joint

• Convex surface fits into concave surface• Motion is limited to flexion & extension in a

single plane

Eg. Elbow joint, knee joint & distal phalanges

Ellipsoid Joint

• Oval, convex surface fits into an oval, concave depression

• Allows movement in 2 directions at right angles to each other & doesn’t allow for rotation

Eg. Wrist

Gliding Joint

• Flat & slides over one another

Eg. Intervertebral joint, carpals & tarsals

Saddle Joint• Concave surface in one direction & convex

surface in the other direction• Allows movement in 2 planes (flexion-extension

& adduction-abduction), no rotation

Eg. Thumb at the carpometacarpal joint