Functional Classification of Bone

Synarthroses (means the same think synonym)

  • Immovable joint

  • Bones are almost in direct contact and are held by dense CT or cartilage

3 types: Sutures (holding together the bones of the flat skull), Gomphosis (holding the teeth into the gums), Synchondrosis

  • Teeth are held in the alveolar processes by the periodontal ligament

  • Think scurvy: Pirates who didn’t get enough vitamin C would lose their teeth

Synchondrosis

  • Bones held via hyaline cartilage (ex: ribs are held onto sternum, epiphysial plate)

  • Epiphysial Plate: Temporary Hyaline Cartilage Joint that’s in place before an individual reaches terminal height

Amphiarthroses

  • Slightly movable joint

  • Bones held by fibrocartilage or dense CT

  • Think amphibian: can live in both water and land, the prefix amphi means both → The joint is slightly movable (it stays still and moves hence both)

  • 2 types: Symphyses, syndesmoses

Symphyses

  • Eventually this joint stops being flexible completely

  • ex: this helps in childbirth because it’s slightly flexible

Diarthroses

  • Freely movable joint with joint cavity (synovial joint)

Ball and Socket Joint

  • 3 degrees of freedom (3 different ways in which it can rotate in the socket)

  • Example: hip and shoulder

  • Multi/tri-axial: moves in all planes plus rotation

Ellipsoidal/Condyloid

  • Oval process that does not allow independent rotation of one with respect to the other

Think about the geometry, you can’t turn an oval inside another oval because egg shaped structures will crash into each other

  • Biaxial: Allows various movements but no rotation

  • Example: Our hands

Gliding/Planar

  • Nearly flat articulating surface

  • Example: Carpals and tarsals

  • Allows slight sliding movement - Biaxial

Hinge

  • Convex

Pivot

  • Radioulnar joint

  • Pivots around a single axis (1 axis of rotation)

Saddle

  • 2 degrees of freedom

  • articulating surfaces are convex and concave (example: metacarpal of thumb)

  • Biaxial

  • This type of joint allows the opposable thumb

Structural Classification

  • Fibrous joints

Sutures, gomphoses, syndesmoses

  • Cartilaginous joints

Synchondroses, symphyses

  • Synovial Joints

Synovial fluid that lubricates the joints

Flexion, Extension, and Hyperextension

  • Flexion: bending parts of a joint to lessen the angle between component bones

  • Extension: Straightening parts of a joint to raise the angle between bones

  • Hyperextension: you cannot hyperextend your knee without a trip to the ER

Dorsiflexion

  • Pointing the foot at ankle at an upward angle

Plantarflexion

  • Pointing your foot at a downward angle

Abduction

  • Moving away from the midline of the body (think abducted means taken away)

Adduction

  • Moving toward the midline of the body

Circumduction

  • Moving in a circular motion

  • You can do this with your fingers

Rotation

  • moving around an axis

Pronation

  • Moving the palms upward

Supination

  • Moving the palms downward

Inversion

  • Turning the sole of the foot inward (a lot of people sprain their ankle this way)

Protraction

  • Moving a part forward

Depression

  • Lowering a part

Synovial Joint Structure

  • Articular Cartilage: covers the articulating surface, and minimizes friction and reduces wear

  • We want to have articular cartilage to avoid inflammation, this is a layer of hyaline cartilage

Joint/Articular Capsule

  • Surrounds and encapsulates the joint

  • prevents excessive movement

  • 2 layers: fibrous capsule, synovial membrane

  • If you follow the fibrous capsule, it becomes the periosteum (contiguous)