Week 1: Bone

Question 1

Describe the structural organisation of bone:

Answer 1

• Strong and rigid CT
• Provide support and protection to the body, involved in load bearing and articulation

Question 2

Describe the structural organisation of the periosteum:

Answer 2

Dense fibrous connective tissue/outer condensed collagen layer - absent at articular surfaces & at points of insertion of tendons and ligaments (enthesis)

Question 3

Describe the structural organisation of the endosteum:

Answer 3

Cellular layer (osteoprogenitor cells, osteoblasts, osteoclasts etc.)

Question 4

Describe the role of the medullary cavity:

Answer 4

Site to store hemopoietic tissue (bone marrow) and fat

Question 5

Describe the overall structure of a long bone

Answer 5

Diaphysis, Metaphysis, Epiphysis

Question 6

Define epiphysis:

Answer 6

Expanded articular end - protected by a layer of articular cartilage which covers the articular surface

Question 7

Define diaphysis:

Answer 7

Shaft of the bone

Question 8

Define metaphysis:

Answer 8

Wider part of the developing bone where the diaphysis meets the epiphysis.
- Contains epiphyseal (growth) plate.
- Once growth is complete it ossifies.

Question 9

What is the role of compact/cortical bone?

Answer 9

• Give strength and rigidity
• Resist tensile forces/bending
• Limited to the outer parts of the bone (shaft of long bone) or to the cortex of mature bone

Question 10

What is the role of trabecular/cancellous bone?

Answer 10

• Provide support to the bone while minimizing the weight
• Resist compressive forces/ stress applied form different directions
• Seen in epiphysis, vertebral bodies

Question 11

Describe the distribution of cortical and cancellous bone in the diaphysis and epiphyses:

Answer 11

Diaphysis: cortical bone forms the dense walls of the diaphysis while a very small amount of cancellous bone occupies part of the central medullary cavity
Epiphyses: typically consist of a thin outer layer of compact bone while internally the bone is cancellous

Question 12

Describe the distribution of cortical and cancellous bone in human vertebrae.
Why does this arrangement exist?

Answer 12

Vertebrae are primarily composed of cancellous bone with a thin outer layer of cortical bone. This arrangement allows the vertebrae to sustain large compressive forces with a minimal amount of bone

Question 13

What is oteoporosis?

Answer 13

Loss of bone density - fracture, altered force distribution

Question 14

What is the extracellular matrix (osteoid) made up of?

Answer 14

1. Inorganic (60-70%)
   – Mineral salts, hydroxyapatite, calcium phosphate
   – Hard, resists compression, deformation
2. Organic (30-40%)
   – Collagen fibres (synthesised by osteoblasts)
   – Ground substance
   – Resists tension and bending forces

Question 15

What are the 3 bone cells?

Answer 15

• Osteoblasts: bone-forming cell, small, responsible for synthesis and secretion of organic matrix, osteoids, that undergoes mineralisation to form bone
• Osteocytes: mature bone cell derived from osteoblasts, gives integrity to bone, found in lacunae between layers of bone tissue
• Osteoclasts: bone-removing cell, large, multi-nucleated

Question 16

What are lamellae? Identify the 2 different types.

Answer 16

Layers of ossified extracellular matrix

• Interstitial - between Haversian systems
• Circumferential - Periphery of the bone is surrounded by circumferential lamellae

Question 17

What are haversian systems/osteons?

Answer 17

Bony tubes that lie parallel to each other along the long axis of the bones

Question 18

What is the haversian canal?

Answer 18

• Tube in the Haversian system
• Has 1 or 2 capillaries lined by fenestrated endothelium, and a few unmyelinated axons.

Question 19

What are the Volkmann’s canals?

Answer 19

• Communicate haversian canals with each other
• These channels connect with medullary and periosteal vessels.

Question 20

What are the lacuna?

Answer 20

• Spaces within the Harversian system
• Each space has an osteocyte
• The lacunae are interconnected by fine canals, the canaliculi (connect osteocytes through processes).

Question 21

What is the myotendinous junction?

Answer 21

The junction between the muscle and the tendon

Question 22

What is the osteotendinous junction

Answer 22

The junction between the bone and the tendon

Question 23

What is intramembranous ossification?

Answer 23

Direct formation of bones from mesenchymal stem cells that develops into osteoprogenitor cells
E.g., Skull bones, clavicle

Question 24

What is endochondral ossification?

Answer 24

Hyaline cartilage template model is formed, which is later converted to bone
Centres of Ossification:
* One primary (diaphysis) - appear between 7th and 12th week of intrauterine life.
* Several secondary (epiphysis) - appear after birth
E.g., long bones etc.

Question 25

Describe the process of bone elongation:

Answer 25

* Occurs at a growth or epiphyseal plate * Cartilage proliferates continuously - elongation of bone * Reaching maturity growth plates are replaced by bone

Question 26

What happens if a growth plate injury (fracture) occurs?

Answer 26

It alters normal growth and development

Question 27

A twelve year old netballer trips during a game, and falls heavily on her right leg, causing a fracture. The epiphyseal plate of her right tibia is severely damaged in the fracture. What are the possible consequences of such an injury?

Answer 27

As the patient is twelve years of age the epiphyseal plate is still patent, with growth still potentially occurring. Damage to the epiphyseal plate interferes with bone elongation. As a result, her tibia and therefore her leg may be shorter than normal

Question 28

What might happen if an epiphyseal plate was subjected to considerable shear force? An example is a “slipped capital femoral epiphysis”, which occurs from trauma.

Answer 28

The epiphyseal plate might separate (from either the diaphysis or the epiphysis) allowing the epiphysis to slip out of alignment with the diaphysis. This can cause lifelong joint problems if not carefully managed

Question 29

Why do epiphyseal (growth) plates appear as a ‘gap’ on radiograph?

Answer 29

Because growth plates are composed of cartilage

Question 30

How do bones grow in width?

Answer 30

* Periosteal (external) surface: osteoblasts * Endosteal (internal) surface: osteoclasts As bone is being added to the outer surface through appositional growth, osteoclasts are removing and recycling lamellae at the inner surface. As a result the medullary gradually enlarges as the bone increases in diameter.

Question 31

Describe 2 age-related and congenital changes in bone:

Answer 31

1. Osteopenia * Inadequate ossification 2. Osteoporosis * Reduction in bone mass * Microstructural changes The activity of osteoclasts is more than osteoblasts, so more bone is being resorbed than produced. Can lead to fracture and deformity.

Question 32

Why do injuries to bone typically heal quickly and well?

Answer 32

Because bone is well vascularised

Question 33

Why are disease processes (e.g. tumour) within bone painful?

Answer 33

Bone is innervated via nerves which run with the blood vessels

Question 34

What is the nutrient foramina?

Answer 34

Long bones often have a larger main artery (nutrient artery) entering the shaft. This supplies most of the marrow and cortex, its branches running in the Haversian canals of the compact bone.

Question 35

What is the vascular foramina?

Answer 35

The ends of long bones typically have several smaller arteries entering and several veins leaving, so numerous vascular foramina are usually visible on the epiphyses of dried bones.

Question 36

What is articular (hyaline) cartilage?

Answer 36

It is a tissue that has a high concentration of water and it covers the articulating surfaces (ends) of bones

Question 37

What are the main functions of chondrocytes?

Answer 37

Responsible for the manufacture, secretion and maintenance of articular cartilage, a tissue which has a high concentration of water

Question 38

What are 2 important functions of articular cartilage?

Answer 38

1. Allow relative movement of opposing joint surfaces with minimal friction and wear 2. Distribute loads, thereby decreasing stresses sustained by the contacting joint surfaces

Question 39

Does articular cartilage have an abundant or poor blood supply? What implications this have for healing?

Answer 39

Avascular tissue (reflected in its pale colour) – nourished by diffusion from synovial fluid of the joint cavity. If damaged it has limited (to no) capacity to heal

Question 40

What would you notice when looking at the articular cartilage from an individual with osteoarthritis compared to normal, healthy articular cartilage? What implications might this have on function of the joint?

Answer 40

Thinning and loss of cartilage; Cartilage softens and the smooth surface disrupted, becoming rough with gaps (fibrillation) in the tissue; changes in chondrocyte morphology and arrangement (haphazard) Functional implications – decreased capacity to distribute forces through the joint, and increased friction with joint movement