5.3 - Injury and Healing 1

Question 1

What makes up the musculoskeletal system?

Answer 1

• bone
• muscle
• connective tissue –> tendon, ligaments, cartilage

Question 2

What is a joint?

Answer 2

A junction between two or more separate bones

Question 3

How many bones are there in an adult vs a child?

Answer 3

• 206 in adults (+ sesamoids)
• 270 in children

Question 4

What are the two components to the skeleton?

Answer 4

• appendicular and axial skeleton
• appendicular - shoulder/pectoral girdle, upper and lower limbs, pelvic girdle
• axial - cranium, vertebral column, rib cage

Question 5

What are the functions of the skeleton?

Answer 5

1. support - helps you stand up
2. protection - protects your vital organs
3. movement - works with muscles so you can get around
4. mineral storage - stores calcium and phosphate
5. produces blood cells

Question 6

How do bones develop in utero? Overview

Answer 6

• intramembranous ossification (mesenchymal cells to bone) –> flat bones
• endochondral ossification (mesenchymal cells to cartilage to bone) –> long bones

Question 7

What bones are flat bones?

Answer 7

• skull
• clavicle
• mandible

Question 8

How are flat bones formed? Intramembranous ossification

Answer 8

1. clustering and condensation of mesenchymal stem cells which differentiate into osteoblasts –> ossification centre forms
2. secreted osteoid (unmineralised organic tissue) traps osteoblasts which become osteocytes
3. trabecular matrix (cancellous bone) and periosteum (outside connective tissue layer) form
4. compact bone develops superficial to cancellous bone, and crowded blood vessels condense into red bone marrow

Question 9

What bones are long bones?

Answer 9

• all bones below the skull
• development of long bone from a hyaline cartilage model

Question 10

What is a summary of endochondral ossification?

Answer 10

• bone collar formation
• cavitation
• periosteal bud invasion
• diaphysis elongation (primary ossification centre)
• epiphyseal ossification (secondary ossification centre)

Question 11

How are long bones formed? Endochondral ossification (detail not needed)

Answer 11

1. starts with a hyaline cartilage precursor, which then forms a ring of tissue around it called perichondrium
2. mesenchymal stem cells in cartilage differentiate into osteoblasts which gather at the diaphysis wall of the bone to form the bone collar
3. chondrocytes in central cavity form a calcified matrix which forms a primary ossification centre with a nutrient artery (periosteal bud invasion forms spongy bone by delivering osteoclasts that break down cartilage, and osteoblasts that deposit new spongy bone)
4. at primary ossification centre, osteoclasts then degrade centre of spongy bone to form medullary cavity where yellow bone marrow (fat) will be
5. you get a secondary ossification centre at the end of long bones - appear after birth to continue bone growth
6. junction between primary and secondary ossification centre is epiphyseal plate and cartilage at ends of bone only stays at surface to lubricate ends for joints

Question 12

What is the structure of long bones?

Answer 12

• diaphysis - primary ossification centre, long bone
• epiphysis - secondary ossification centre, at joint
• physis - growing area
• epiphysis (ends) –> physis –> metaphysis –> diaphysis (centre)
• periosteum - connective tissue covering
• outer cortex - compact bone
• cancellous bone
• medullary cavity - contains yellow bone marrow
• nutrient artery
• articular cartilage - on surface of bone at joint only

Question 13

What cells are in bone?

Answer 13

• osteogenic cell
• osteoblast
• osteocyte
• osteoclast
• osteogenic cell –> osteoblast –> osteocyte –> osteoclast

Question 14

What are osteogenic cells?

Answer 14

• bone stem cell
• found in deep layers of periosteum

Question 15

What are osteoblasts?

Answer 15

• bone forming cells
• secrete osteoid and catalyse osteoid mineralisation
• found in growing portions of bone including periosteum and endosteum

Question 16

What are osteocytes?

Answer 16

• mature bone cells
• formed when an osteoblast becomes embedded in their own secretions
• sense mechanical strain to direct osteoclast and osteoblast activity

Question 17

What are osteoclasts?

Answer 17

• bone breaking/consuming cells
• dissolve and resorb bone by phagocytosis
• derived from bone marrow
• found entrapped in matrix

Question 18

What makes up the bone matrix?

Answer 18

Organic component (40%):

• type I collagen (90%)
• ground substance (10%) - proteoglycans, glycoproteins, cytokine and growth factors

Inorganic component (60%):

• calcium hydroxyapatite
• osteocalcium phosphate

Question 19

What is immature bone?

Answer 19

• first bone type produced by body
• laid down in a ‘woven’ manner - relatively weak
• mineralised and replaced by mature bone

Question 20

What is mature bone?

Answer 20

• mineralised woven bone
• lamellar (layer) structure - relatively strong
• replaces immature bone

Question 21

What are the two types of mature bone?

Answer 21

• cortical/compact bone - compact and dense, suitable for weight bearing
• cancellous bone - spongy and honeycomb structure, not suitable for weight bearing
• both exist in same bone e.g. in flat bones, the cortical bones are on top and bottom layers with spongy bone sandwiched in the middle, in long bones there is a cortical shell with spongy bone in the centre

Question 22

What is an osteon?

Answer 22

• compact bone has osteons
• a structural unit of cortical bone
• has few spaces
• provides protection, support and resists stresses produced by weight of movement
• central part is Haversian canal containing blood vessels, nerves and lymphatics
• surrounded by concentric lamellae of bone laid down by osteoblasts, that get trapped within their mineralisation to become osteocytes
• lacunae - small spaces containing osteocytes - tiny canaliculi radiate from lacunae filled with extracellular fluid
• Volkmans canals - transverse perforating canals that join Haversian canals together

Question 23

How do bones grow?

Answer 23

• interstitial growth –> long bones, increased length
• appositional growth –> increase thickness and diameter

Question 24

What is interstitial growth?

Answer 24

• long bones increasing in length
• happens at the physis (physeal plate) - zone of elongation in long bone, contains hyaline cartilage
• epiphyseal side - active hyaline cartilage that divides to form hyaline cartilage matrix
• diaphyseal side - cartilage calcifies and dies and is replaced by bone

Question 25

What are the zones of the physis?

Answer 25

• reserve zone - they are resting, matrix production
• proliferative zone - high mitotic rate and divide
• they then mature and hypertrophy to become bigger = more lipid, glycogen and alkaline phosphatase filled
• they calcify into matrix + cell death
• zone of ossification (metaphysis)

Question 26

What is appositional growth?

Answer 26

• increase in thickness and diameter by depositing bone beneath periosteum
• can happen in growing bones in children but also healing bones after fracture

1. ridges in periosteum create groove for periosteal blood vessel
2. periosteal ridges fuse, forming an endosteum-lined tunnel
3. osteoblasts in endosteum build new concentric lamellae inward toward centre of tunnel, forming a new osteon
4. bone grows outwards as osteoblasts in periosteum build new lamella - osteon formation repeats as new periosteal ridges form over blood vessel

Question 27

What is the role of bone in calcium homeostasis?

Answer 27

• bone - stores 99% of total body calcium
• calcium hydroxyapatite - structural support
• calcium is deposited and withdrawn during bone remodelling
• regulated by PTH and calcitriol (kidneys)
• calcitonin (thyroid) - stimulates calcium uptake into bone
• vitamin D - helps body absorb and use calcium

Question 28

What are the mechanisms of bone fracture?

Answer 28

• trauma - low or high energy trauma (e.g. falling over vs car crash)
• stress - abnormal stresses on normal bone
• pathological - normal stresses on abnormal bone

Question 29

What is the stress mechanism for bone fracture?

Answer 29

• abnormal stresses on normal bone
• overuse of bones –> increased stress exerted on bone > bones capacity to remodel –> bone weakening through microfractures –> stress fracture –> risk of complete fracture

Question 30

What is the pathological mechanism for bone fracture?

Answer 30

• normal stresses on abnormal bone
• can cause an insufficiency fracture (type of stress fracture) i.e. if the bone is weak already due to an underlying abnormality
• underlying abnormality can be local in one bone or general in all bones

Question 31

What underlying abnormalities can lead to insufficiency fractures?

Answer 31

• osteoporosis - soft bone
• malignancy - primary or bone metastases
• vitamin D deficiency –> osteomalacia or rickets
• osteomyelitis
• osteogenesis imperfecta
• pagets

Question 32

What is osteopenia and osteoporosis?

Answer 32

• loss of bone density - osteopenia up to 2.5 SD from normal, osteoporosis > 2.5 SD
• osteoclast activity > osteoblast activity = disrupted microarchitecture
• associated with fragility fractures e.g. in hip, spine, wrist - where low energy trauma can cause fracture
• primary osteoporosis = senile osteoporosis, linked to age 70+
• secondary osteoporosis - any age, can be due to hypogonadism, glucocorticoid excess or alcoholism
• postmenopausal osteoporosis - women 50-70

Question 33

What does osteopenia/osteoporosis do to the bone?

Answer 33

• fewer trabeculae
• thinning of cortical bone
• widening of Haversian canals

Question 34

What is vitamin D deficiency?

Answer 34

• vitamin D facilitates calcium, magnesium and phosphate absorption
• dietary or synthesised from the sun
• inadequate calcium/phosphate –> defect in osteoid matrix mineralisation
• leads to soft bone = predisposed to fractures
• rickets in kids, osteomalacia in adults

Question 35

What is congenital osteogenesis imperfecta?

Answer 35

• brittle bone disease
• hereditary - autosomal dominant or recessive
• decreased type I collagen due to decreased secretion or production of abnormal collagen
• leads to insufficient osteoid production
• effects are bone weakening and negative effects on hearing, heart, sight

Question 36

What is Pagets disease?

Answer 36

• comes from genetic and acquired factors
• excess bone breakdown and disorganised remodelling –> deformity, pain, fracture or arthritis
• may transform into a malignant disease - can become osteosarcoma in chronic cases
• four stages - osteoclastic activity, mixed osteoclastic-osteoblastic activity, osteoblastic activity, malignant degeneration

Question 37

What are examples of primary bone cancers?

Answer 37

• osteosarcoma - cancer in osteoblasts
• chondrosarcoma - cancer in chondrocytes
• Ewing sarcoma
• lymphoma

Question 38

What are secondary bone cancers and give examples?

Answer 38

• where you have metastatic bone tumours from other tissues
• metastases can be blastic (bone forming) or lytic (bone eating) depending on which cancer they came from
• e.g. blastic - prostate
• e.g. lytic - kidney, thyroid, lung
• e.g. mixed - breast

Question 39

How do bone tissues heal generally speaking?

Answer 39

1. bleeding - blood products involved
2. inflammation - neutrophils and macrophages involved
3. new tissue formation - blasts (fibro-, osteo-, chondro-) involved
4. remodelling - macrophages, osteoclasts, osteoblasts involved

Question 40

How do fractures heal more specifically?

Answer 40

1. haematoma formation - bleeding between bone ends
2. inflammation - cytokines released & granulation tissue and blood vessel formation
3. repair - chondroblasts/osteoblasts make soft callus (type II collagen - cartilage), which is converted to hard callus (type I collagen - bone)
4. remodelling - callus responds to activity, external forces, functional demands and growth - osteoblasts heavily involved, excess bone is also removed

Question 41

What is Wolff’s law?

Answer 41

Bone grows and remodels in response to the forces that are placed on it

Question 42

What is primary bone healing?

Answer 42

• intramembranous healing
• mesenchymal stem cell goes straight to osteoblast and there is direct formation of woven bone
• occurs when you have a stable fracture and ends of bones are close together (absolute stability)

Question 43

What is secondary bone healing?

Answer 43

• endochondral healing
• results in more callus forming (endochondral ossification)
• involves responses in the periosteum and external soft tissues
• occurs when you have a relatively stable fracture (relative stability)
• mesenchymal stem cell goes to chondral precursor which produces bone cells

Question 44

How long does it take fractures in different bones to heal?

Answer 44

• phalanges: 3 weeks
• metacarpals: 4-6 weeks
• distal radius: 4-6 weeks
• forearm: 8-10 weeks
• tibia: 10 weeks
• femur: 12 weeks
• signs of healing visible on X-ray from 7-10 days
• generally, upper limbs heal quicker than lower limbs
• healing times vary depending on age, biology and comorbidities of patient

Question 45

What are the main principles of fracture management?

Answer 45

• reduction - bring fracture ends together
• hold - hold ends in the right position with metal or no metal
• rehabilitate - once bone has healed, limbs will still be weak and need rehabilitation

Question 46

What is closed reduction?

Answer 46

• pulling bones back together without opening skin
• can be through manipulation e.g. dinner fork traction
• can be through traction of skin or skeletal (pins in bone) - wrapping bandage around leg/putting pin in bone and attaching weight to other end to realign bones

Question 47

What is open reduction?

Answer 47

• mini-incision
• full exposure
• these are to realign bones

Question 48

What are the different ways of holding a fracture?

Answer 48

• plaster - closed
• traction (skin or skeletal) - closed
• fixation

Question 49

What are the different ways of fixating a fracture?

Answer 49

Internal:

• intramedullary through pins or nails
• extramedullary through plate/screws or pins

External:

• monoplanar
• multiplanar

Question 50

What are the different parts to rehabilitation?

Answer 50

• use - using the limb, retraining with physiotherapy and using pain relief if necessary
• move
• strengthen
• weight bear (in case of lower limb)

Question 51

What are the questions orthopaedic surgeons ask themselves when considering fracture management?

Answer 51

• is the fracture displaced?
• is it stable / unstable?
• is it at a joint surface?
• are the soft tissues okay?
• what other illnesses does the patient have?
• what does the patient think? do they want surgery or not?

Question 52

What might you expect to see when examining a patient for a fracture?

Answer 52

• inability to weight bear
• severe pain
• swelling and point tenderness
• deformity
• scrapes/abrasions
• wound if open fracture
• loss of movement
• loss of sensation if nerve injury