Bone L2: Biomechanics of Bone Flashcards
What are the 2 types of bone growth?
- Intramembranous ossification
- Endochondral ossification
What are the characteristics of bone modelling?
- Formation OR resorption (Reoccurring but not linked)
- Changes in bone shape
What are the characteristics of bone remodelling?
- Resorption AND formation (linked)
- Bone turnover
- Metabolic OR mechanical
- Releasing Ca2+ into blood stream
- Maintaining homeostasis
What is endochondral ossification?
- 3 bone ossification areas
- Remains through life = articular cartilage
What are the 6 steps to intramembranous ossification?
- Stem cells in mesenchyme
- Differentiate into osteoblasts (Obs)
- Secrete osteoid, engulfs Obs = osteocytes
- Mineralises (spongy bone around vessels)
- Periosteum forms, with Obs present
- Lamellar bone formation • Eg. lat clavicle, flat bones (cranial bones)
Bone growth is compromised of _______ and _______.
- Collagen type I
- Ground substances
What are osteoprogenitor cells?
- derived from mesenchymal stem cells
- give rise to osteoblasts
What are bone-lining cells?
- Derived from osteoblasts
- Maintenance of osteocytes
Osteocytes are _______, ________ or _______ in nature.
Osteocytes are quiescent, formative or resorptive in nature
What is osteocytic osteolysis?
- Internal degradation of of matrix
- Secretes matrix metalloproteinases (MMPs)
- Responsible for ion homeostasis
9 characteristics of skeletal development
- Begins in utero and continues for 25 years
- Adult has 204 bones
- Increased bone number
- Increased mineralisation
- baby’s bones are soft and compliant
- Increased bone size
- Bone proportion change
- Patterns and magnitudes of force change
- Physically- external and internal
- Newborn to adult o Increased mechnical demands
- Increased mechnical competence
- Adult to old age
- Decreased mechanical demands
- Decreased mechanical competence (abruptly due to menopause- hormone change)
Development of hand and wrist at 3 months
- Incomplete bone
- No carpal bones
- Radial head as cartilage
Development of hand and wrist at 2 years
Radial head
Development of hand and wrist at 4 years
Bony prominence = whiter = more dense
Hand increases ______ to general growth
proportion
Bone formation/modelling is accompanied by bone _______.
remodelling
What is bone modelling?
- Increased length at growth plate
- Increased diameter = lay down bone at periosteum surface
- Increased growth cavity = osteoclasts taking cavities (out of endosteum)
Why are bones curved?
• If compressed, has a predictable form/direction of loading when fractured • Cells can make the vulnerable side stronger
What is bone remodelling?
- Basic-multicellular unit erodes existing bone and then, after a period of time the eroded bone is replaced as a linked sequence of events.
- Referred to as A-R-F
- Basic-multicellular unit creating a secondary osteon, with subsequent mineralization
- The difference between resorption and formation (bone balance) determines whether bone is gained or lost during remodeling
- Osteoporosis- struts break, absorbed and lost
- Target remodeling occurs to replace damaged or won out bone that may be affected by micro damage at microscopic and sub-microscopic levels
What happens at cortical bone remodelling?
• Secondary osteon formation
What happens at cancellous bone surface remodeling?
- Osteoclasts dig a trench
- Osteoblasts start to refill the resorption cavity
Bone can change _____, _____ and _____ throughout life in order to be relevant to demands placed upon it
size, shape and density
- Increase load (eg. training) o Decreased load (eg. immobilization
What is Wolff’s Law?
- Bone will change in mass and geometry to meet physical demands
What is Mechanostat theory?
- Bone adapts to function mechanically as required by detecting and responding to mechanical loads o If bone load is small load continues bone
What is bone adaptation? Give an example.
- Applied torsion Polar moment of inertia increased
- Example: Humeral hypertrophy in response to exercise
- In tennis players
- Both CSA and cross sectional moment of inertia (strength) increased in dominant arm
Exercise for bone maintenance
- Optimise bone mass during childhood
- Include UL, LL, and trunk
- Effect is lost, when training is discontinued
- Weight-bearing exercise, aerobic and/or strength training
- Short regular sessions are more effective than few longer sessions
- Effects are site specific
Frequency and duration of exercise for bone maintenance
- 2-3 times/wk
- 15-60mins for aerobic work
- 8-10 reps , 1 set for strength work
Intensity of exercise for bone maintenance
- Moderate to intense
- Impulsive loading
- 80% VO2max for aerobic
- 8-10 RM for strength
