Joints


The Joints is part of the Anatomy and Physiology section which provides High Yield information of different types of joints in the human body such as Cartilaginous, Fibrous, and Synovial joints that is needed for the USMLE and COMLEX exams.



Structural Classification

  • Structural Classification
    • – Based on whether there is a joint cavity and the type of CT
      • 1. cartilaginous joint
        • a. no cavity
        • b. cartilage holds bones together
      • 2. fibrous joint
        • a. no cavity
        • b. fibrous CT holds bones together
      • 3. synovial joint
        • a. has synovial cavity
        • b. articular capsule and ligaments hold bones together
Structural Classification of Joints
www.scientificanimations.com / CC BY-SA
(L to R): Cartilaginous joint here bones are attached by fibrocartilage/ hyaline cartilage. Fibrous joint are the ones where bones are bound by tough fibrous tissue. Joints filled with synovial fluid are called Synovial joint.

Functional Classification

  • – Based on movement allowed
    • 1. synarthroses are immovable
    • 2. amphiarthroses are partially movable
    • 3. diarthroses are freely movable

Fibrous Joints

  • – Sutures
    • 1. in skull
      • a. dense fibrous CT
      • b. functionally synarthrotic
    • 2. other sutures (synostoses)
      • a. complete fusion of bone
      • b. functionally synarthrotic
  • – Syndesmoses
    • 1. more CT than a suture (longer fibers)
    • 2. dense regular CT forms ligament or interosseous membrane
    • 3. functionally amphiarthrotic (depends on length of fibers)
  • – Gomphoses
    • 1. peg fits into a socket
    • 2. functionally synarthrotic

Cartilaginous Joints

  • – Synchondroses
    • 1. hyaline cartilage
    • 2. epiphyseal plate is functionally synarthrosis, later becomes synostosis
    • 3. sternum and rib 1 is synarthrosis
  • – Symphyses
    • 1. fibrocartilage
    • 2. functionally amphiarthrotic

Synovial Joints


  • – Basic structure
    • 1. ends of bones covered with articular cartilage (hyaline), which reduces friction and absorbs shock
    • 2. joint surrounded by articular capsule
      • a. fibrous capsule is outer layer
        • 1) mostly dense irregular CT
        • 2) helps stabilize joint
      • b. synovial membrane is inner layer
        • 1) areolar CT, elastic fibers, adipose
        • 2) secretes synovial fluid into synovial cavity, which lubricates (hyaluronic acid), supplies nutrients to articular cartilage and removes wastes (fluid is derived from plasma, coming from the blood vessels in the synovial membrane)
    • 3. accessory ligaments
      • a. some are intracapsular (part of articular capsule)
      • b. some are extracapsular
      • c. help stabilize joint
    • 4. articular discs (menisci)
      • a. fibrocartilage
      • b. allow better fit of bone surfaces
      • c. found in temporomandibular, knee, sternoclavicular, distal radioulnar
    • 5. rich nerve supply
      • a. same nerves that supply skeletal muscles that cause movement at that joint
      • b. sensory nerves for pain and body position
      • 6. rich blood supply
    • 6. bursae
      • a. sacs of CT lined with synovial membrane
      • b. provide extra cushioning between bones, tendons, ligaments, muscles and skin
    • 7. tendon sheaths
      • a. like bursae, but wrap around tendons where there’s lots of friction
      • b. around tendon of biceps at shoulder, at wrist and ankle
  • – Movements at synovial joints
    • 1. gliding
      • a. flat bone surfaces move back & forth, side to side
      • b. example: intercarpal
    • 2. angular
      • a. change in angle between bones
      • b. flexion (decrease in angle), example: bending elbow
      • c. extension (increase in angle), example: straightening elbow; hyperextension is continuing beyond anatomical position
      • d. abduction (moving bone away from midline), example: moving arm laterally
      • e. adduction (moving bone toward midline), example: moving arm medially
      • f. circumduction (moving in a circle, involving b-e), example: move arm in circle at shoulder
    • 3. rotation
      • a. movement of bone around its own longitudinal axis
      • b. example: turning head
    • 4. special movements
      • a. occur only at specific joints
      • b. elevation (upward motion), examples: closing mouth, shrugging shoulders
      • c. depression (downward motion), examples: opening mouth
      • d. protraction (anterior movement), examples: moving jaw forward, move clavicles forward
      • e. retraction (moving back from protracted position)
      • f. inversion (move soles of feet medially)
      • g. eversion (move soles of feet laterally)
      • h. dorsiflexion (move dorsum of foot toward tibia)
      • i. plantar flexion (move sole of foot to “point the toe”)
      • j. supination (turning palm anteriorly or superiorly)
      • k. pronation (turning palm posteriorly or inferiorly)
      • l. opposition (move thumb toward fingertips)
  • – Types of synovial joints
    • 1. gliding or plane
      • a. articulating surfaces usually flat
      • b. allows gliding movement
      • c. nonaxial (does not involve movement around an axis)
    • 2. hinge
      • a. convex surface fits into concave surface
      • b. allows flexion and extension
      • c. monaxial (allows movement in a single axis)
    • 3. pivot
      • a. rounded or pointed surface articulates with a ring of bone and ligament
      • b. allows rotation
      • c. monaxial
    • 4. condyloid
      • a. oval shaped projection fits into oval shaped depression
      • b. allows abduction, adduction, flexion, extension, circumduction
      • c. biaxial
    • 5. saddle
      • a. modified condyloid with more freedom of motion
      • b. allows abduction, adduction, flexion, extension, circumduction
      • c. biaxial
    • 6. ball & socket
      • a. ball shaped surface fits into a cup
      • b. allows abduction, adduction, flexion, extension, circumduction, and rotation
      • c. triaxial