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