KEY NOTES CHAPTER 1: GENERAL PRINCIPLES (E) Healing and grafts: wound, bone, cartilage, nerve and tendon, haemostasis and thrombosis. Flashcards
What are the phases of wound healing?
- Haemostasis
- Inflammation
- Proliferation
- Remodelling
Tell me about haemostasis.
Haemostasis (immediate)
- thromboxanes and PG from damaged cells cause vasoconstriction
- platelets bind to exposed collagen forming platelet plug
- platelets degranulate and bind to fibrinogen
- membrane glycoprotein IIb/IIIa is modified (blocked by clopidogrel)
- PAF, vWF and TXA2 stimulate conversion of fibrinogen to fibrin
Thrombus propagates
- initially white thrombus (platelets only)
- red thrombus (red blood cells also trapped)
Tell me about inflammation
Inflammation (2-3 days after injury)
- stimulated by physical injury, Ab-Ag reaction or infection
- Platelets release growth factors (PDGF) and pro-inflammatory factors e.g. serotonin, bradykinin, PG, TXA2, histamine which increase cell proliferation and migration
- endothelial cells swell, vasodilate and cause egress of PMNs and monocytes
T lymphocytes
- migrate into wound
- secrete cytokines e.g. epidermal growth factor and basic fibroblast growth factor (bFGF)
- mediate cell immunity and antibody production
Tell me about proliferation
Proliferation (from day 2-3 for 2-4wks)
- monocytes mature to macrophages, release PDGF & TGF-B, chemoattractant to fibroblast
- fibroblasts enter wound,
secrete GAGs to produce ground substance
- produce collagen (type III initially) and elastin
- some fibroblasts become myofibroblasts and affect wound contraction
- angiogenesis occurs
Tell me about remodelling
Remodelling (From 2-4wks from injury to 1+years)
- Type III collagen is replaced by type I (stronger)
- haphazard collagen fibres are arranged in more organised manner
- tensile strength 50% at 3 months, 80% after remodelling
- scar initially red due to dense capillary network, apoptosis leads to a pale scar.
How does epithelialisation occur?
- Mobilisation.
- Migration.
- Mitosis.
- Cellular differentiation.
What occurs during mobilisation?
- Marginal epithelial cells elongate, flatten and form pseudopodia.
- Cells detach from neighbour and basement membrane.
What occurs during migration?
- decreased contact inhibition promotes cell migration.
- meanwhile marginal epi cells proliferate to replace them.
- when cells meet opposite migrating epi cells, contact inhibition is reinstituted and migration ceases.
What occurs during mitosis?
Epithelial cells
- proliferate.
- secrete proteins to form new BM.
- desmosomes and hemdesmosomes re-establish themselves and anchor the cells to BM and each other.
- becomes new stratum germinativum.
What occurs during cellular differentiation?
- normal structure of stratified squamous epithelium is re-established.
How is collagen made?
Hydroxyprolene, hydroxylysine Procollagen x3 Tropocollagen Collagen filaments Fibrils Fibres
Tell me about collagen.
- 30% of total body protein
- amino acids lysine and proline are hydroxylated by enzymes (require Vit C)
- procollogen (in cell)
- tropocollagen (outside cell)
- collagen - 3 polypetide chains wound in left handed helix, 2 chains wound in right handed coil to form basic tropocollagen unit
What inhibits collagen production?
- colchicine, penicillamine, steroids and Vit C and iron deficiency inhibits collagen formation.
- cortisol: stimulates collagen degradation
Name some common collagen types.
- 28 types of collagen (diff cross-linkages and hydroxyproline and hydroxylysine).
Type I: mature skin, bone tendon (90% total body collagen).
Type II: hyaline cartilage and cornea.
Type III: healing tissue (esp fetal wounds).
Type IV: BM.
Type V: BM, hair and placenta.
Normal skin I:III = 5:1.
What is a cytokine? What is a growth factor?
Cytokines are proteins required for cell defence that are secreted predominantly by immune cells.
They mediate in protective and reparative processes and also regulate cell growth and maturation.
Growth factors are polypeptides whose primary role is in regulation of cell growth and maturation.
What is the function of a macrophage?
- Derived from mononuclear leukocytes.
- Debrides tissue, removes micro-organisms.
- Co-ordinates angiogenesis and fibroblast activity by releasing growth factors: PDGF, FGF 1&2, TNF-a, TGF-b.
- Orchestrator of wound healing
What is the function of myofibroblasts?
- contains alpha-sooth muscle actin
- responsible for wound contraction
- increased numbers in fascia of Dupuytren’s disease
What secretes TGF-beta? What is it’s role in wound healing?
- Macrophages, fibroblasts, platelets, keratinocytes, endothelial cells.
Plays a central role in wound healing: - Chemoattractant for fibroblasts and macrophages.
- Induction of angiogenesis.
- Stimulation of extracellular matrix deposition.
- Keratinocyte proliferation.
3 isoforms identified
1&2 - promote wound healing and scarring (unregulated in keloids).
3 - decreases wound healing and scarring (possible factor for deceased inflammation and improved scarring in fetal wound healing)
How are factors affecting healing classified?
Systemic
- Congenital
- Acquired
Local
Systemic factors: congenital
Pseudoxanthoma elasticum Ehler-Danlos syndrome Cutis laxa Progeria Werner syndrome Epidermolysis bullosa
Systemic factors: acquired
Nutrition - Vitamins A, C (collagen synthesis), Vitamin E, zinc, copper, selenium (cofactors for enzymes), hypoalbuminaemia.
Pharmacological - steroids, NSAIDs, anti TNF-alpha drugs (RA), cytotoxics.
Endocrine abnormalities - diabetes, hypothyroidism.
Age - mitosis rate decreases.
Smoking - nicotine (vasoconstriction), CO (decreased O2 carriage by Hb), hydrogen cyanide.
Local factors
Infection
Radiation - endothelial cell, capillary and arteriole, lymphatic damage. Fibroblasts secrete less collagen and ECM.
Blood supply - decreased by low pO2, low Hb, low O2 transfer from Hb, poor tissue perfusion. Decreased tissue O2 reduces collagen formation, ECM deposition, angiogenesis and epithelialisation.
Trauma - neoepidermis disrupted.
Neural supply - possibly related to levels of chemoattractant neuropeptides in wound.
Tell me about skin grafts
Full or split thickness (of epidermis and dermis).
Donor sites differ.
Primary contraction - immediate recoil after harvest.
Secondary contracture - after skin graft has taken, and is due to myofibroblasts.
What do you know about fetal wound healing?
Foetus’ first 6 months - heals by regeneration, not repair, therefore no scarring.
- Reduced inflammation.
- Reduced platelet aggregation and degranulation.
- Reduced angiogenesis.
- More rapid epithelialisation.
- No myofibroblasts, no wound contraction.
- Type III > I collagen.
- Wound contains more water and hyaluronic acid.
More TGF-B3 than 1&2
How do skin grafts take?
- Adherence (fibrin) - immediate.
- Serum imbibition (absorption of fluid and nutrients) - D2-4.
- Revascularisation - D4.
- Inosculation.
- Revascularisation.
- Neovascularisation. - Remodelling.
What are the reasons for graft failure?
- Haematoma.
- Infection (if >100,000 organisms / gram, less if Group A B-haemolytic Strep, as streptokinase and hyaluronidase prevent adhesion)
- Seroma.
- Shear.
- Inappropriate bed (cartilage, tendon, bone).
- Technical error.
Describe nerve anatomy
Endoneurium (nerve cell - neurone, cell body, efferent axon, afferent dendrite)
Perineurium (fascicle)
Epineureum (peripheral nerve)
What nerve fibre groups are there?
A-C -
heavily myelinated → non-myelinated,
diameter 20-0.5 micrometres,
conduction speed 120-1.2 m/sec.
Group A o α fibres - motor o β fibres - touch, pressure o γ fibres → proprioception and motor tone o δ fibres → pain, temperature
Group B
o Myelinated , preganglionic autonomic (sympathetic) nerves
Group C
o Non-myelinated, postganglionic autonomic nerves - pain, temp (Chronic Pain – Gate Theory)
What is the MRC grading of nerve function?
Motor M0 = No contraction M1 = Flicker M2 = Movement with gravity eliminated M3 = Movement against gravity M4 = Movement against gravity and resistance M5 = Normal Sensory
S0 = No sensation S1 = Pain sensation S2 = Pain and some touch sensation, possible hypersensitivity S3 = Pain and touch with over-reaction – S2PD > 15mm S3+ = S2PD 7-15mm S4 = normal – S2PD 2-6mm
What is the classification of nerve injury?
Sunderland (1951) = 5,
Seddon (1947) = 3
Neuropraxia
1. 1st degree → Axon in continuity, conduction impaired, recovery complete
Axonotmesis
- 2nd degree → Axonal divided, distal Wallerian degeneration, connective tissue intact, recovery good.
- 3rd degree → axon and endoneurium divided. Perineurium and epineurium are intact. Recovery reasonable
- 4th degree → Complete division of all intraneural structures, epineurium intact. Recovery expected, may → neuroma in continuity
Neurotmesis
5. 5th degree → Nerve trunk completely divided
What happens in neuropraxia?
Critical pressure for nerve dysfunction is 30mmHg
What nerve graft sites do you know?
Sural (30cm) - post to lat malleolus
Lateral antebrachial cutaneous nerve (8cm) - cephalic vein, BR
Medial antebrachial cutaneous nerve (20cm) - basilic vein, b/t triceps biceps
Terminal br of PIN - radial side of 4th extensor compartment at wrist
How do you perform a nerve repair?
- Direct approximation of divided stumps
- Ends trimmed, epineural repair
- Fine sutures , magnification
- Align fascicles of nerve trunks
- min tension (nerve graft / vein conduit if needed)
- Knowledge of internal nerve topography → ulnar nerve = motor central bn the volar sensory from palm and dorsal sensory from dorsum.
How does bone form?
- Intramembranous ossification
→ Occurs by direct deposition of bone within a vascularized membranous template.
Flat bones of face, calvarium, ribs. - Endochondral ossification.
→ cartilage laid down first at epiphysis followed by ossification.
All long bones and iliac crest.
What is the blood supply of bone?
- Periosteal vessels at muscle attachments
- Apophyseal vessels at tendon and ligament attachments
- Nutrient arteries - medullary cavity
- Epiphyseal vessels - growth plates
How do bones heal?
Haematoma,
Inflammation,
Proliferation.
D1-7
Clotting cascade activated, fibrin coagulum b/t bone ends invaded by neutrophils, macrophages, fibroblasts to form granulation tissue.
Callus formation
Soft callus stage D3-4
Capillaries invade fibrin clot
Periosteal mesenchyme cells differentiate into chondrocytes.
Bridging callus is formed.
Chondrocytes further differentiate into osteoblasts and endochondral ossification of callus occurs
Hard callus is formed wk 3
Remodelling - over years
Woven bone is replaced by lamellar bone along lines of stress
Primary Healing = apposition and rigid fixation, no callus (e.g. phalanges)
Secondary Healing = callus and endochondral ossification
What are the complications of fracture healing?
Delayed union, Non-union, Mal-union, Infection, Avascular Necrosis (AVN), Shortening, Damage to adjacent structures
Healing of bone grafts
Incorporation,
Osteoinduction,
Osteoconduction,
Osteogenesis
Osteoinduction - pluripotential precursor cells present and are ‘induced’ → osteoblasts.
Osteoconduction - bone graft acts as scaffold for ingrowth of cells and capillaries. Old bone is reabsorbed and new bone deposited by ‘creeping substitution’.
Osteointegration - new bone formation by surviving cells within vascularised bone graft.
What factors affect take?
- Systemic
- Graft factors - intact periosteum.
- Graft bed - orthotopic (Graft placed in position normally occupied by bone) vs heterotopic (not normally occupied by bone), quality of bed, graft fixation.
- Mechanical stress
- Physiological loading speeds up union and creeping substitution.
Describe the anatomy of tendons
- dense, metabolically active connective tissue
- Collagen bundles arranged in regular spiralling fashion
- Most Type 1, small amount Type 3
- Few cells → Tenocytes, synovial cells, fibroblasts
- Endotenon → surrounds tendon, lie in synovial sheaths
- Paratenon → loose adventitial layer that surrounds tendons OUTSIDE synovial sheaths
What are the zones of flexor tendon injury?
Verdan Zone 1 → distal to FDS insertion Zone 2 → proximal tendon sheath → FDS Zone 3 → flexor sheath → flexor retinaculum Zone 4 → under flexor retinaculum Zone 5 → proximal to retinaculum
Zone 2 = ‘no mans land’ – Bunnell → poor results of repair
What are the zones of extensor tendon injury?
Zone 1 DIPJ Zone 2 Middle phalanx Zone 3 PIPJ Zone 4 Prox phalanx Zone 5 MCPJ Zone 6 between MCPJ and ext retinaculum Zone 7 under ext ret Zone 8 between ext ret and musculotendinous junction
How do tendons heal?
Extrinsic healing
- By cells recruited from synovial sheaths and surrounding tissues forming adhesions
- Depends on fibrous attachments forming between tendon sheath and tendon
Intrinsic healing
- by cells within tendon itself
- Depends on blood flow through long and short vinculae + diffusion from synovial fluid
- Lunborg → tendons heal if placed in semipermeable membrane to stop cells but allow passage of nutrients
- Post op EAM allowed
Tendons also heal by inflammation, cell proliferation (fibroplasia) and remodelling.
What are the phases of tendon healing?
Inflammation → 2-3 days
- inflammatory cells infiltrate wound, secrete growth factors which attract fibroblasts
Proliferation → 3 days → 3 weeks
- fibroblasts secrete collagen and GAGs
- Collagen initially randomly arranged and lacks tensile strength
Remodelling → 3 weeks+
- collagen organised
Early mobilisation limits formation of fibrous attachments with sheath, promotes intrinsic not extrinsic healing.
Tendons are stronger than extrinsically healed ones.
What is abnormal scarring?
Keloid and hypertrophic scarring
What is a keloid scar?
What is a hypertrophic scar?
Keloid - extend beyond original wound borders
Hypertrophic - scar elevated but within borders of original scar
Both characterised by excessive accumulation of collagen type III in particular
Tell me about keloid scarring hypertrophic scarring?
- limited to original wound margins, commoner than keloids.
- usually starts ~ 8wks.
- rapid growth for ~6mths, then gradually regresses (may be years).
- common around shoulders, neck, presternal area, knees, ankles.
Tell me about keloid scarring
- extend beyond original wound margins
dark skin more prone, family history
may suddenly develop anytime after injury. - persist, don’t tend to regress.
- can be painful, hypersensitive.
- common on anterior chest, shoulders, earlobes, upper arms, cheek.
- excision alone has high risk of recurrence.
- microscopy: type I and III collagen bundles are poorly organised with few myofibroblasts.
- expression of PCNA (proliferation cell nuclear antigen) and p53 upregulated.
What is the difference between hypertrophic and keloid scars
Keloid
- FHx - Blacks > Caucasians
- F>M
- appears months after injury, rarely subsides
- common: earlobes, chest, deltoid
- aetiology: possible autoimmune
Hypertrophic
- low FHx / racial / sex predilection
- appears soon after injury, subsides with time
- common - across tension / joints / infection, delayed healing areas
- aetiology: tension, timing of closure
What are the different treatments for adverse scarring?
intralesional steroids intralesional excision compression therapy silicone gel / sheets DXT 5FU bleomycin
What factors influence scarring?
Surgical
- atraumatic technique
- everted wound edges
- scar placement within RSTL
- U shaped scars tend to pincushion
Suture
- Braided more traumatic
- Absorbable more tissue inflammation
Patient factors
- Age
- Skin type and tendency to scar
- Region on body
What is the difference between contraction and contracture?
Contraction = physiological (due to myofibroblasts, specialised fibroblasts with contractile myofilaments and cellular adhesion structures
Contracture = pathological (may cause shortening, distortion, deformity and limit mvmt)
Primary contraction of skin graft = elastin
Secondary = myofibroblast
What are the 4 components of clotting and haemostasis?
Vasoconstriction
Activation of platelets
Coagulation
Fibrinolysis
What are the disorders of coagulation?
Congenital
Haemophilia
A Von Willebrands disease
Acquired
Vit K and warfarin (II, VII, IX, X)
Liver disease
DIC
What are the disorders of haemostasis?
Thrombocytopenia
- aspirin, clopidogrel
Blood vessel abnormalities
What are the hypercoagulability states?
Activated protein C resistance
Anti phospholipid antibody
Homocysteinaemia
Elevated FVIII and XI
Inherited blood clotting disorders for DVT
Mutated genes (such as factor V Leiden, factor II)
Decreased protein C, protein S, and antithrombin III
Increased levels of antiphospholipid or lupus anticoagulant
How are scars classified?
Mature scar Immature scar Linear hypertrophic Widespread hypertrophic Minor keloid Major keloid (>0.5cm)
What is the Vancouver Scar Scale?
Provides an objective measurement of burn scars and assists prognosis and management.
International clinical recommendations on scar management (Mustoe 2002)
- Steroids
- Silicone gel sheet
- Pressure therapy
- Surgery
Intralesional steroid (kenolog 40mg/ml)
- reduce inflammation, decrease collagen synthesis, increase collagenase activity
- response rate 50-100%, recurrence rate 9-50%.
- Risks e.g. skin atrophy, depigmentation, telangiectasia (63%)
Topical steroid - RCT showed no benefit.
Silicone gel sheet
- hydration
- met analysis showed significant benefit (no figures)
Pressure therapy (24-30mmHg for 6-12mths) - compliance difficult
Surgery
- alone (45-100% recurrence rate)
- surgery + steroid (
International clinical recommendations on scar management (Mustoe 2002)
- Radiotherapy
- Laser
- Cryotherapy
- Micropore tape
Radiotherapy
- alone controversial
Laser
- CO2
- Nd-YAG
- PDL
Cryotherapy
- 51-74% response
Micropore tape
What emerging evidence is available?
International clinical recommendations on scar management (Mustoe 2002)
Interferon
- post-op recurrence (19% vs 59% with steroids)
- painful: may req GA
5-FU + steroid
Bleomycin
Transforming growth factor beta modulators
Inhibitors of collagen synthesis
