Basic Structure & Function of Joints (10/9b) [Biomedical]

Question 1

Arthrology

Answer 1

study of the classification, structure, and function of joints

Movement occurs through sequenced rotations around the joints

Joint surfaces transfer and disperse internal and external forces

Question 2

Classification of Joints by

Answer 2

Movement potential

• Synarthroses
• Diarthroses

Mechanical analogy
-Joint types

Question 3

Synarthrotic joints

Answer 3

Allow slight to essentially no movement

Stabilized by dense connective tissue with high concentration of collagen
- By flexible fibrocartilage or hyaline cartilage

Fibrous joints, cartilaginous joints
- EX: Symphysis pubis, intervertebral disc, syndesmosis, interosseous tissue

Function is to transfer forces between the bones

Question 4

Diarthrotic/Synovial joints

Answer 4

Allow moderate to extensive movement

Seven elements of all synovial joints

Question 5

Seven Elements of All Synovial Joints

Answer 5

Articular cartilage
Joint capsule
Synovial membrane
Synovial fluid
Ligaments
Blood vessels
Sensory nerves

Question 6

Articular cartilage

Answer 6

Cartilage that covers the articular surface of the bone

“Like a cap of low-friction paint on the end of your bone”

Question 7

Joint capsule

Answer 7

Connective tissue “envelope” that encloses the joint

2 histologically distinct layers

• Outer fibrous layer = dense connective tissue (has nerves that tell you about stretch)
• Inner layer = synovial membrane

Question 8

Synovial membrane

Answer 8

~ 3-10 cell layers thick

Specialized cells produce synovial fluid

Like someone saran-wrapped your joint and folded it up a lot

Highly innervated

Question 9

Synovial fluid

Answer 9

Contains hyaluronan and glycoproteins

Lubricates the joint surfaces

Provides nourishment to articular cartilage

When you move, the fluid gets squeezed out of synovial membrane to lubricate the joint

Question 10

Ligaments

Answer 10

Connective tissue that attach between bones

Prevent excessive joint movement

Capsular or Extracapsular ligaments

Question 11

Blood vessels

Answer 11

Penetrate capsule & extend to junction of fibrous and synovial layer

You need blood to heal

Question 12

Sensory nerves

Answer 12

Innervate external and internal capsular layers

Pain & proprioception

Question 13

Synovial Membrane - Synovitis

Answer 13

Inflamed capsule, occurs in synovial membrane

Also leads to inflammatory fluid in the synovial fluid → affects viscosity

Question 14

Ligaments - Capsular ligaments

Answer 14

Thickenings of joint capsule

Broad sheet of fibers

Resist movement in multiple planes

Question 15

Ligaments - Extracapsular ligaments

Answer 15

Cord like structure

Partially or completely separate from joint capsule

May resist movement in one or two planes

Question 16

Other Joint Support Elements

Answer 16

Intra-articular discs/menisci
Peripheral labrum
Fat pads
Bursae
Synovial plica

Question 17

Intra-articular Discs or Menisci

Answer 17

Fibrocartilage structures

Increase joint congruency → improves stability

Provide shock absorption

Highly mobile

Question 18

Peripheral Labrum

Answer 18

Fibrocartilage structure

Extend around the periphery of joint

Deepen joints concavity and support capsular attachment

Highly mobile

Like a rubber washer that seals and supports your joint

Question 19

Fat Pads

Answer 19

Reinforces capsule & fills in ‘recesses’ in the joint

Often interposed between fibrous layer & synovial membrane

Cushions surfaces to reduce forces

Fills space and is protective shock absorber

Question 20

Bursae

Answer 20

Extension or outpouching of synovial membrane

Spaces filled with a little synovial fluid

Cushions and prevents friction between moving tissue surfaces

Can palpate when they are inflamed

Related to folds in the capsule

Question 21

Synovial Plicae

Answer 21

Redundancy or folds in synovial membrane

Redundancy is necessary to prevent undue tension during motions

When inflamed, creates pathological synovial plicae

Becomes a mechanical block

Not all joints have plica (knee has it)

Question 22

Synovial Joint Types

Answer 22

Hinge
Pivot
Ellipsoid
Ball and Socket
Plane
Saddle
Condyloid

Question 23

Joint Type - Hinge

Answer 23

Single axis of rotation

Motion occurs perpendicular to axis of rotation (i.e. hinge)

EX: Humeral ulnar joint

Question 24

Joint Type - Pivot

Answer 24

Single axis of rotation

Rotation occurs parallel to the axis of rotation

EX: Humeral radial joint

Question 25

Joint Type - Ellipsoid

Answer 25

Two axes of rotation

One side elongated concave surface & other elongated concave surface

Biplanar motion flexion/extension & abduction/adduction

Limits spin motion at joint

EX: wrist

Question 26

Joint Type - Ball and Socket

Answer 26

3 axes of rotation

Spherical convex surface and cuplike concave surface

Allows 3 degrees of freedom for joint angular motion

EX: hip, shoulder

Question 27

Joint Type - Plane

Answer 27

Lack a definitive axis of rotation

Sliding and rotation of one surface on the other

EX: fingers

Question 28

Joint Type - Saddle

Answer 28

2 axes of rotation

Perpendicularly oriented convex and concave surfaces

Allows ample biplanar motion but limits spin motion

EX: thumb

Question 29

Joint Type - Condyloid

Answer 29

Primarily 2 axes of rotation

Spherical convex ball articulates with relatively flat or non-concave surface

Motions vary based on particular structure

EX: knee

Question 30

Ovid vs Saddle Joints

Answer 30

OVID

• Paired joint surfaces that are imperfectly spherical
• Shape of most synovial joints in the body

SADDLE

• Convex surface perpendicularly bisects concave surface
• Very few examples of this in the body

*Planar joints are exception to this binary classification

Question 31

Fixed axis of rotation

Answer 31

all points experience equal rotation

moment arm can be somewhat stable

in joints, axis of rotation is rarely fixed

Question 32

Instantaneous axis of rotation

Answer 32

the axis changes as the joint changes position

the moment arm and mechanical advantage of muscles changes as you change position

muscles are stronger in certain positions than others