What are the three types of joints, based on functional classification?

SYNARTHROSES, AMPHIARTHROSES, AND DIARTHROSES

JOINTS

A.Joints (articulations) are the functional junctions between bones. (where 2 bones meet) B. Joints enable a wide variety of body movements (give mobility, & hold skeleton together) C. Joints can be classified according to the degree of movement possible and can be immovable (synarthrotic), slightly movable (amphiarthrotic), or freely movable (diarthrotic). [Functional classification]

Synarthrotic Amphiarthrotic Diarthrotic

D.Joints can also classified according to the type of tissue that binds them together, and whether the joint cavity is present (structural classification).

STRUCTURAL CLASSIFICATION E.Fibrous Joints 1.Fibrous joints are held close together by dense connective tissue and are immovable (sutures of skull) or only slightly movable (joint between the distal tibia and fibula). There are 3 types:

FIBROUS JOINTS

a. syndesmosis: bound together by interosseous ligament that is flexible and may be twisted; the joint may permit slight movement, and thus is amphiarthrotic. Distal tibiofibular joint

FIBROUS JOINTS b. suture: only occur between flat bones of the skull which are united by a sutural ligament. (Sutures replace fontanels). Because they are immovable, sutures are synarthrotic joints

FIBROUS JOINTS c. gomphosis: joint formed by the union of a cone shaped bony process in a bony socket. They are synarthrotic joints. Example: peglike root of a tooth fastened to a jawbone by a periodontal ligament

STRUCTURAL CLASSIFICATION, CONTINUED F.Cartilaginous Joints 1.Hyaline cartilage or disks of fibrocartilage unite the bones in cartilaginous joints. They lack joint cavities

CARTILAGINOUS JOINTS 2. Intervertebral disks between vertebrae help absorb shock and are slightly movable

CARTILAGINOUS JOINTS CONT’D 3. Two types: a. synchondrosis: hyaline cartilage unites the bones. Many are temporary that disappear during growth.

CARTILAGINOUS JOINTS, SYNCHONDROSIS Example: Immature long bone - When ossification is complete, movement no longer occurs at the joint, making it synarthrotic.

OTHER EXAMPLE OF SYNCHONDROSIS Other example: between manubrium and the first rib, which are united directly by costal cartilage. This joint is permanent. (Joints between costal cartilages & the sternum of ribs 2 through 7 are usually synovial instead)

CARTILAGINOUS JOINTS, SYMPHYSIS b. symphysis: articular surfaces are covered by hyaline cartilage, which is attached to a pad of springy fibrocartilage. There is limited movement at this type of joint when forces compress or deform the pad.

EXAMPLES OF SYMPHYSES Example: symphysis pubis in the pelvis (allows maternal pelvic bones to shift for infant to pass through birth canal)

Other example: Each intervertebral disk is slightly flexible itself, so the combined movement of many of the joints in the vertebral column allow the back to bend forward or twist; because of the slight movement this allows, they are amphiarthrotic joints.)

G.Synovial Joints (diarthrotic) 1. Most joints of the skeleton are synovial joints, which are more complex than fibrous or cartilaginous joints.

SYNOVIAL JOINT

SYNOVIAL JOINTS, CONT’D 2. The articular ends of bone in a synovial joint are covered with hyaline cartilage

3. A joint capsule (articular capsule) holds together the bones of a synovial joint. Bundles of strong, tough collagenous fibers called ligaments reinforce the joint capsule & help bind the articular ends of the bones together. Ligaments help prevent excessive movement at the joint, and tighten when the joint is stressed.

4. A joint capsule consists of an outer layer of dense connective tissue that joins the periosteum, and an inner layer made up of synovial membrane. Synovial membranes surround a closed sac called the synovial cavity and secrete synovial fluid into it.

Besides filling spaces & irregularities of the joint cavity, the synovial membrane can – increase surface area – store adipose tissue – form movable fatty pads within the joint – reabsorb fluid (important when joint cavity is injured/infected.)

Synovial fluid has the consistency of egg whites and lubricates articulating surfaces within the joint.

5. Some synovial joints contain shock-absorbing pads of fibrocartilage called menisci. In the knee joint, menisci… cushion the articulating surfaces & help distribute body weight onto them.

COMMON KNEE INJURY: TORN MENISCUS

6. Some synovial joints have fluid-filled sacs called bursae which cushion and aid the movement of tendons that glide over bony parts or over other tendons. The names of the bursae show their locations.

BURSA

7. Based on the shapes of their parts and the movements they permit, synovial joints can be classified as follows:

a. A ball-and-socket joint consists of a bone with a globular or egg-shaped head articulating with the cup-shaped cavity of another bone; a very wide range of motion is possible; examples include the hip and shoulder joint.

b. A condyloid joint consists of an ovoid condyle fitting into an elliptical cavity, permitting a variety of motions; an example is the joint between a metacarpal & a phalange. Movement can be in different planes.

c. Gliding joints (or Plane Joints) occur where articulating surfaces are nearly flat or slightly curved, allowing a back-and-forth motion. Joints of the wrist and ankle, as well as those between vertebrae, are gliding joints.

Plane Joint (a.k.a. Gliding joint)

d. In a hinge joint, a convex surface fits into a concave surface, as is found in the elbow and phalange joints; movement is in one plane only

e. In a pivot joint, a cylindrical surface rotates within a ring of bone and fibrous tissue; examples include the joint between the proximal ends of the radius and ulna.

f. A saddle joint forms where articulating surfaces have both concave and convex areas, permitting a wide range of movements; the joint between the carpal and the metacarpal of the thumb is of this type.

H. Types of Joint Movements 1. When a muscle contracts, its fibers pull its movable end (insertion) toward its stationary end (origin), causing movement at a joint. 2. These terms describe movements that occur at joints: flexion, extension, dorsiflexion, plantar flexion, hyperextension, abduction, adduction, rotation, circumduction, pronation, supination, eversion, inversion, retraction, protraction, elevation, and depression.

3. Descriptions of each movement: a. flexion & extension-angle at joint decreased (flexion) or increased (extension)

b. hyperextension-excessive extension

c. dorsiflexion-bending foot upward at the ankle

d. plantar flexion-bending foot downward

e. abduction-moving a part away from the midline

f. adduction-moving a part toward the midline

g. rotation-around an axis

h. circumduction-end follows a circular path (moving a finger in a circular motion without moving the hand)

i. supination-palm upward j. pronation-palm downward

Question Q. Which hand position—pronation or supination—is characteristic of the anatomical position?

ANSWER: SUPINATION

k. eversion-sole outward l. inversion-sole inward

m. protraction-moving a part forward (chin forward) n. retraction-moving a part backward (pulling chin back)

o. elevation-raising a part p. depression-lowering a part