Theory of tissue mechanics Flashcards
Bone healing
- Organic compound 20-25% of wet bone weight
- Inorganic compound 65-70% of wet bone weight
- Water component 10% of wet weight
Types of bones
Cortical bone: External part of long bone
Trabecular bone: Found in metaphases and epiphysis
Basic forces causing fractures
- Compression
- Tension
- Transverse loading
- Torsion
- Bone is anisotropic
Bone likes and dislikes
Like:
- Compression
Dislikes:
- Torsion
- Shear
Remodelling
Balancing between bone absorption by osteoclasts and bone formation
Osteoporosis
Increase porosity of bone, decrease in density and strength, increase vulnerability to fractures
Piezoelectric effect
Electrical potential created when collagen fibres in bone slip relative to another one, facilitates bone growth
Bone healing with fixation
- Pins and plates
- Prevent movement around…
- Reduce mechanotherapy
- Longer healing time
- More stability earlier
Bone healing without internal fixation
- Heal through callus formation
- Unstable in early stages
- No hardware issues
Two contractile proteins
- Actin: thin
- Myosin: thick
Muscle architecture
- Typical diameter 50-70
- Length varies from mm to 10cm+
- Attach to tendon plates
- Geometric arrangement differs
Types of contraction: Lengthening
- Addition of sarcomeres to muscle fibres
- In region on myotendinous junction
Types of contraction: Strength
- Max strength between 20-30yrs
- Cross sectional area of muscle is greatest
- Resistance training increases myofibrillar diameter
Types of contraction: Cross-sectional area
- Female is 75% of male
- Response to resistance training in males via hypertrophy
Muscle regeneration
- Satellite cells
- Fuse with adjacent myofibres to repair and regenerate muscles
- Restore and replace muscles cells damaged by injury
Tendons
- Similar to ligaments in composition
- Predominantly made of collagen 70-80%
- Lesser % of elastin
- Connect muscle to bone
- Synovial component to assist gliding
Tendon continuum
Reactive:
- PG absorb water
- Tenocytes change shape
- Fibres widen (swll)
Disrepair:
- Angiogensis
- Type I to Type III
- Increase PG
Degenerative:
- Less cellular
- Type III predominates
- More permanent
Tendon Recap
Tendons:
- Transmits muscle load
Failure:
- Bone-tendon
- Muscle-tendon
- Mid-tendon
Elastic region:
- 1.5-4% stretch
Plastic region:
- Causes 10-15% stretch
Ligament composition
- Similar to tendons in composition
- Predominantly made of collagen 70-80%
- Higher % of elastin
- Connects bone to bone
- Structure regulated by fibroblastic activity
Ligament immobilisarion
- Major deterioration occurs within a few weeks
- Ligament cells produce inferior quality ligament material
- Structural weakening of ligament complex
Aims of ligament healing
- Increase cross-sectional area
- To maintain ligamentous length
- Encourage remodelling
Cartilage
Layer of hydrated soft tissue covers the ends of bones of diathrodial joints
Articular cartilage reaction to force
- Cartilage has a natural tendency to swell
- Cartilage susceptible to constant load
- Excessive load can be destructive to matrix
