5.4: Injury and healing (part 1 of 2) Flashcards
3 mechanisms of bone fracture
Trauma
Stress
Pathological
What 2 things are bones made up of
Cells
Matrix
How do bones develop in utero
Intramembranous (flat bones e.g. skill, clavicle, mandible) and
endochondral (long bones, ribs, vertebrae)
ossification
Process of Intramembranous ossification
Mesenchymal cells condensate, differentiate into osteoblasts and secrete osteoid
This traps osteoblasts which become osteocytes - collate and form ossification centre
Multiple ossification centres form and fuse, forming trabecular matrix and periosteum
Compact bone develops
Intramembranous ossification is
Bone development from fibrous membranes
Process of endochondral ossification
Bone collar formation
Cavitation
Periostea’s bud invasion
Diaphysis elongation
Epiphyseal ossification
Which bone formation takes a longer amount of time?
Endochondral ossification
Primary ossification centre of endochondral ossification
Diaphysis
What is the secondary ossification centre of endochondral ossification
Epiphysis
2 Different types of bone structure
Immature bone
Mature bone
Characteristics of immature bone
First bone that’s produced
Laid down in a woven manner - relatively weak
Mineralised and replaced by mature bone
Characteristics of mature bone
Mineralised woven bone
Lamellar structure - relatively strong
2 types of mature bone
Cortical
Cancellous
Characteristics of cortical bones
Compact - dense
Suitable for weight bearing
Characteristics of cancellous bone
Spongy - honeycomb structure
Not suitable for weight bearing
Organisation of cortical bone (compact)
Osteons found in compact bone, repeated structural units , around central Haversian canal which contains blood vessels, nerves and lymphatics
Structure of long bones
Diaphysis - long part of bone
Metaphysis- area that flares up
Physis- growth plate
Piphysis - distal or proximal part of bone
2 locations of Osteogenic cells
Marrow
Deep layers of periosteum
Where are osteoblasts found
Growth portions of bone :
Periosteum and endosteum
Where are osteoclasts formed
Bone surfaces and at sites of old, injured or unneeded bone
Where are osteocytes found
Entrapped in matrix
2 ways that bones can grow
Interstitial - increased length
Appositionsl -increased thickness and diameter
Where does Interstitial occur
In the physis
Where does appositional growth occur
Periosteum :
Osteoblasts add more and more bone cells
Role of bone in calcium homeostasis
Calcium hydroxyapatite- structural support
Calcium deposited and withdrawn during bone remodelling
Regulated by PTH and calcitriol
Calcitonin stimulates calcium uptake into bone
VitaminD helps body absorb and use calcium
Trauma causing bone to break
Low energy or high energy transfer
Stress fracture is
Abnormal stress on normal bone
A pathological fracture is
Normal stress on abnormal bone
How do stress fractures occur
Repetitive applications of forces on bone, results in stress exertion on localised region, excess remodelling capacity, bone weakening persists, stress fractures
When does a bone experience stress
When a force is loaded upon it , low levels of these forces cause bone to deform and place strain
4 weigh bearing bones in body
Femur, tibia, metatarsals, navicular
6 examples of conditions that can lead to a pathological/insufficiency fracture
Osteopenia and osteoporosis - Soft bone
Malignancy
Vitamin-D deficiency - Insufficient exposure to sunlight, reduced vitamin-D source → Osteomalacia + Ricket’s
Osteomyelitis
Osteogenesis Imperfecta - Collagen deficiency
Paget’s disease
What causes osteopenia and osteoporosis?
Bone remodelling imbalance → Osteoclast activity greater than osteoblast activity
Leads to disrupted microarchitecture
At what age do senile and postmenopausal osteoporosis occur?
- Senile osteoporosis: >70Postmenopausal osteoporosis: Women 50-70
-
Is osteoporosis more common in men or women
Women
4:1
What fractures is osteoporosis associated with?
Fragility fractures - Hip, spine, wrist
Low energy trauma fractures
What can secondary osteoporosis be caused by?
Hypogonadism - low oestrogen
Glucocorticoid excess - glucocorticoids inhibit insulin growth factor-1 which can directly or indirectly reduce osteoblast function
Alcoholism - increases PTH which leaches Ca2+ from the bone and excess alcohol can kill osteoblasts
What is the T-score of a person with osteoporosis and osteopenia respectively?
Osteoporosis: Equal to or less than -2.5
Osteopenia: Between -1 and -2.5
What does vitamin D facilitate
Calcium, magnesium and phosphate absorption
What can inadequate calcium or phosphate lead to in bones
Defect on osteoid matrix mineralisation
What can a Vitamin D deficiency cause in children and adults respectively?
Children - rickets
Adults - osteomalacia
What type of inheritance pattern does congenital osteogenesis imperfecta (OI) display?
Autosomal dominant or recessive
Explain the pathogenesis of congenital OI
Reduction in type I collagen secretion
Collagen is an ECM protein secreted by fibroblasts and osteoblasts and organised into insoluble fibres, comprising the ECM surrounding cells → Provides mechanical strength and rigidity to tissues and organs, especially to skeletal tissues: Bone cartilage, tendons and ligaments
What 4 things does congenital OI affect
Bones
Hearing
Heart
Sight
What is Paget’s disease
Excessive bone degradation and disorganised bone remodelling→ Deformity, pain, fracture or arthritis
May transform into malignant disease
4 stages of Paget’s disease
- Osteoclastic activity (Increased bone resorption)
- Mixed osteoclastic-osteoblastic activity (Imbalance) results in disorganised bone remodelling, considering the osteoid scaffold is disrupted and diverted through osteoclastic activity → Deformities arises
- Osteoblastic activity
- Malignant degeneration
4 primary bone cancers
Osteosarcoma
Chondrosarcoma
Ewing sarcoma
Lymphoma
What is secondary bone cancer
Metastatic bone tumour from other tissues
What are the types of secondary bone cancers that can lead to a pathological bone fracture?
Lytic - Bone eating; Kidney, thyroid, lung and breast
Blastic - Bone forming; Prostate and breast
3 ways to describe fractures
Soft tissue integrity : open or closed (skin remains intact)
Bony fragments (greenstick- partial fracture in which one side of bone is broken, simple, multifrahmentory)
Movement (displaced/undisplaced)
Process of fracture healing
1) Bleeding - release of cytokines causing inflammation
2) granulation - tissue deposited and blood vessel formation forms soft callus then forms a hard callus
3)bone remodelled through endochondral ossification
What is wolffs law
Bone grows and remodels in response to the forces that are placed on it
Outline the differences between primary and secondary bone healing
Primary: Intramembranous healing + Absolute stability
Mesenchymal stem cell goes to the bone cells in fracture to start replacing bone cells
Secondary: Endochondral healing involving responses in the periosteum and external soft tissues + Relative stability; Endochondral ossification → More callus
Mesenchymal stem cell goes to the chondral precursor to start producing new bone cells
When do you see signs of healing visibly on an X-ray?
From 7-10 days
What is the duration for each step in fracture/bone healing?
Inflammatory - Hours to days
Repair - Days to weeks
Remodelling - Months to years
3 general principles of fracture management?
Reduce → Closed, open
Hold → Metal; no metal
Rehabilitate → Move, physiotherapy, use
What is reduction in terms of fracture management
Involves restoring the anatomical alignment of a fracture or dislocation of derormed limbs
What is skin traction
Wrap bandage around fracture and the add a weight to bring limb into natural alignment
What is skeletal traction
Put a pin through bone and use a larger weight
2 different types of hold
Fixation
Closed - plaster and traction
4 methods to rehabilitate fractures
Use - Pain relief and strain
Move
Strengthen (Muscles)
Weight-bear
2 examples of soft tissue injury
Tendinopathy:
Tendinitis - Inflammation of tendon associated from overuse (In additions to infection or rheumatic disease). Swelling + pain → reduced mobility of tendon and muscle.
Tendinosis - Caused by overuse of a tendon → Abnormal thickening.
Rupture
(Mainly ligaments/tendons tearing)
List and explain ligament injury classifications
Grade I - Slight incomplete tear → No notable joint instability.
Grade II - Moderate/severe incomplete tear → Some joint instability. One ligament may be complete torn.
Grade III - Complete tear of 1+ ligaments → Obvious indication of stability of instability surgical requirement.
How can we treat tendon or ligament tears?
Immobilise - Plaster OR boot/brace
Surgical repair - Suture
Good effects of immobilisation on injured tissue
Less ligament laxity (lengthening)
Bad effects of immobilisation on injured tissue
Less overall length of ligament repair scar
Protein degradation exceeds protein synthesis
Production of inferior tissue by blast cells
Resorption of bone at site of ligament insertion
Decreased tissue tensile strength (50% in 6-9 weeks)
2 benefits of mobilisation on injured ligaments is tissue?
Ligament scars are wider, stronger and more elastic
Better alignment/quality of collagen
2 factors affecting tissue healing
Mechanical environment - Movement and forces
Biological environment - Blood supply, immune function, infection, nutrition
