Lecture 5 - Joints

Question 1

Joint classification: Fibrous

Answer 1

• bones held together by fibrous connective tissue
• no joint cavity
• little/no movement
  e. g. skull sutures

Question 2

Joint classification: Cartilaginous

Answer 2

• bones connected by cartilage
• fibrocartilage - slightly moveable (pubic symphysis)
• hyaline - immoveable (costal cartilage)

Question 3

Joint classification: Synovial

Answer 3

• bones connected by fluid filled cavity
• moderate to extensive movement
• structurally complex

Question 4

Types of synovial joint:

Answer 4

• pivot (neck cervical vertebrae) - 1 DOF (onAx)
• hinge (elbow) - 1 DOF (FE)
• ball and socket (hip) - 3 DOF (FE+AA+IRER)
• saddle (base of thumb) - 2 DOF
• plane (tarsal bones) - variable DOF (SorR)
• condyloid (wrist) - 2 DOF (FE+AA)

Question 5

Synovial joint structures:

Answer 5

Synovial membrane

• continuous with periosteum
• encloses joint cavity
• subintima + intima (cell layer - fibroblasts, macrophages, blood vessels)
• secretes synovial fluid

Synovial fluid

• hyaluronic acid, lubricin, proteinases, collegenases
• lubricate, absorb shock, supply nutrients, remove waste
• non-newtonian fluid
• healthy = 3.5mL (more in arthritic)
• joint cracking - gasses fill void of fluid, cavitation

Ligaments
- medial collateral, lateral collateral
Intra-articular ligaments
- ACL, PCL

Bursae

• sac filled with synovial fluid
• between muscles / where tendon passes over bone

Tendons
Menisci
Articular Cartilage
Labrum

Question 6

Joint functions

Answer 6

1. Load transfer

2. Low friction surface for motion

Question 7

Surface roughness

Answer 7

Statistical measure of peak and valley distribution

Question 8

Lubrication types

Answer 8

Fluid-film:(x>3)

• surfaces not in contact
• load transferred by thick film (thickness of film greater than combined surface roughness)
• low wear, low friction
• low load, high v (low viscosity)

Mixed/boundary: (1

Question 9

Surface separation

Answer 9

= lubricant film thickness / composite surface roughness

Question 10

What is the mechanism of boosted lubrication when a fluid film is not formed?

Answer 10

• water molecules diffuse into cartilage under load

- concentrated GAGs left behind –> supports for short time

Question 11

Biphasic lubrication

Answer 11

• load transfer from fluid to solid
• fluid within matrix supports load
• fluid exuded from matrix –> friction coefficient increases

Question 12

Factors affecting joint motion/stability

Answer 12

1. Bones (mating shapes)
2. Ligaments (formed where needed)
3. Muscles (contractile forces compress joint surfaces)

Question 13

Synovial Fluid Function

Answer 13

1. Lubricate joint
2. Absorb shock
3. Supply nutrients to cartilage
4. Remove metabolic waste from cartilage
   NOTE: its a non-newtonian fluid, so viscosity decreases as shear rate increases

Question 14

Surface Separation

Answer 14

Lubricant film thickness/composite surface roughness

Question 15

Lubrication Mechanisms

Answer 15

Film formation depends on speed and load. Load results in the deformation of cartilage (increasing the surface area, and reducing the pressure and local surface roughness)