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
• hinge (elbow) - 1 DOF
• ball and socket (hip) - 3 DOF
• saddle (base of thumb) - 2 DOF
• plane (tarsal bones) - variable DOF
• condyloid (wrist) - 2 DOF

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:

• 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:

• two surfaces rub (molecules attached to surface of cartilage act as lubricant - lubricin)
• thin film (nm)
• high wear, high friction
• high load, low v (high viscosity)

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