119 - Shoulder Trauma

Question 1

What is a dislocation?

Answer 1

Displacement from normal position of a joint - with complete loss of contact surfaces

Question 2

What is a subluxation?

Answer 2

Partial dislocation - bone ends are still in contact but misaligned

Question 3

In the shoulder what sort of dislocation is most common?

Answer 3

Anterior more common than posterior

Question 4

Why does the shoulder dislocate reasonably easily?

Answer 4

The humeral head is bigger than the glenoid fossa - only 1/3 in contact

Question 5

What complications can occur after recurrent shoulder dislocations?

Answer 5

Bankart lesion - damage to glenoid labrum (in 85% of traumatic dislocations)

Hill’s Sach’s lesion - Cortical depression/fracture of postero-lateral aspect of head of humerus

Auxillary nerve injury - traction as it is in contact with joint capsule

Question 6

What does an auxillary nerve injury cause?

Answer 6

Deltoid weakness

Reduced sensation in regimental badge area

Question 7

What adaptations does the shoulder have to improve stability?

Answer 7

Labrum - fibrocartillagenous cuff

Rotator cuff muscles - pull humerus into joint

Question 8

What position makes the shoulder weakest?

Answer 8

When arm abducts to 90 degrees and externally rotated

Question 9

What are bones?

Answer 9

Specialised form of connective tissue - Cells and mineralised ECM

Question 10

What is the function of bones?

Answer 10

Framework
Protection
Movement
Storage (Ca, Phosphorus)
Blood cell production

Question 11

What is the contents of bone?

Answer 11

40% Organic ECM

• 95% collagen (type 1)
• BMPs - bone morphogenic proteins
• Proteoglycans - secreted by osteoblasts
• Phosphoproteins + glycoproteins

60% inorganic ECM - mineral content is unique to bone

• Calcium hydroxyapatitie crystals
• Crystals either inside or outside collagen fibrils

Question 12

What are the 4 main bone cell types?

Answer 12

Osteoprogenitor - stem cells

Osteoblasts - bone forming - control minerilsation (mesenchymal stem cells)

Osteocytes - make bone, modified osteoblasts

Osteoclasts - remove bone - macrophage like, resporb bone. (haematopoietic stem cells)

Question 13

What is trabeculat/cancellous bone?

Answer 13

Skeletal bone
Ends of long bones
Spongy in middle
Lost 1st in osteoperosis

Question 14

What is compact bone/cortical bone?

Answer 14

Concentric layers of dense connective tissue
Hole in middle - less weight
Lamellae structure
Low turnover

Question 15

What is newly formed bone called?

Answer 15

Osteoid - unmineralised bone

Question 16

What hormones effect bone formation/resportion?

Answer 16

Parathyroid hormone
Calcitonin
Oestrogen
Testosterone
Growth Hormone
Vit D

Question 17

How do osteoblasts and osteoclasts communicate?

Answer 17

RANK-ORG system
Osteoblasts detect the hormones, releases either:
-RANK - > activates osteoclasts - > increase resorption
-OPG -> blocks osteoclast activation -> reduces resportion

Question 18

Where does bone growth occur?

Answer 18

At the ossification centre - epiphyseal plate

Or secondary eg. Greater trochanter- Apophysis

Question 19

What is articular cartilage?

Answer 19

Shock absorbers at synovial joint

Elastic and dampening

Question 20

What allows articular cartilage to have its elastic properties?

Answer 20

Osmotic pressure - as aggrecan holds water well

Question 21

What bone type is a network of thin, bony plates separated by wide marrow spaces.

Answer 21

canellous bone

Question 22

What is a Cavity in the bone matrix which is occupied by a bone cell.

Answer 22

lacuna

Question 23

What bone type is Often characteristic of bone diseases and fracture repair tissue.

Answer 23

Woven bone

Question 24

What in bone is a small channel which permeates the bone matrix and facilitates cell-to-cell communication.

Answer 24

Canaliculus

Question 25

What is the Dense, fibrous layer which covers the outer surface of bone.

Answer 25

periosteum

Question 26

What are the characteristics of articular cartillage?

Answer 26

Avascular
Aneural
Hypocellular
No lymphatics
No basement membrane

Question 27

What is the wet weight compositions of articular cartillage?

Answer 27

70% water
20% collagen
7% proteoglycan
2% cells

Question 28

What is the dry weight composition of articular cartilage?

Answer 28

75% collagen (mostly type II)
22% proteoglycans
3% other proteins

Question 29

What property does collagen give to articular cartilage? Which collagen types are in it?

Answer 29

Tensile and shear strength

94% type II - fibrilar, tensile strength
Type VI - pericellular matrix, in lacunae
Type IX - fibril associated, resists sheer forces
Type XI - inside type II fibrils, tensile strength

Question 30

What proteoglycans are in articular cartilage? What role do they play?

Answer 30

Immobilise water - so flow is resisted when compressed

• Large aggregating - eg. aggrecan

Small leucine rich - eg. decorin, biglucan, fibromodulin.

Question 31

What is young articular cartilage like?

Answer 31

Less matrix
More cells
No zonal morphology
No tidemark

Question 32

What is old articular cartilage like?

Answer 32

Extensive cross-linked matrix
Hypocellular
Tidemark present
shorter aggrecan

Question 33

How is articular cartillage degraded?

Answer 33

By matrix proteinases

• MMPS - matrix metalloproteinases
• Aggrecanases (ADAMTS)
• require Zn or Ca to work

Question 34

What 4 muscles make up the rotator cuff?

Answer 34

Supraspinatus
Infraspinatus
Subscapularis
Teres minor

Question 35

which germ layer does the skeletal system arise from?

Answer 35

Mesoderm