week 6 Flashcards
immobilisation
includes “quiet rest in bed for a prolonged period used in the treatment of disease OR the fixation of a body part usually to promote healing in normal structural relation
Wolff’s law
the effect of mechanical stresses on bone remodeling
Specific Adaptation to Imposed Demand (S.A.I.D.) principle
which describes the changes in body tissues other than bone
mechanostat
- bony change to meet mechanical demands
Immobilization affecting the degree of bone loss
Creates imbalance between bone formation and resorption
* Creates reduced bone mass in relation to bone volume
* Bone mineralization remains the same
* Causes cortical bone thinning
* Trabecular bone loss
* Initial bone loss is rapid in the first weeks but steadies after 6 months
* Skeletal response to disuse is greater than its response to loading ie: its faster
to lose bone than to gain it!!
Response to immobilisation of bone Mechanical Changes (monkeys)
Decrease to both strength & stiffness
* 3-fold reduction in load to failure
bone Response to training
- Bone deposition occurring in response to weight-bearing & as
a result of increased muscle force - Maintenance or enhancement bone mineral density
- Effect of loading particularly weight-bearing component of bone
and area of transferred muscle force
bone recovery
Smaller sessions separated by recovery periods when bone
mass is the goal
Hyaline Cartilage Response to immobilization
Within only a matter of weeks the thickness of cartilage may be reduced by as much as 50% with immobilization in cast -> cartliage reduce ability to withstand load or compression However, these changes can be reversed when load is restored because
the collagen matrix is intact → hence period of immobilisation
recommended for cartilage lesions.
Fibrocartilage Response to immobilization
Unloading results in increase in disc volume which in
turn results in:
* Increases annular fibre stress
* Decreased disc stiffness
(Belavy, 2008)
Astronauts show much higher incidence of
intervertebral disc herniation
Hyaline Cartilage Response to training
Static compressive loading reverses proteoglycan reduction in normal articular cartilage
* Periarticular muscle action also stimulates proteoglycan syntheses
* (Brandt, 2003)
* Health of articular cartilage depends on application and removal of compressive
loads
* However current evidence regarding hyaline cartilage appears to confirm that
whilst deloading changes volume of cartilage, increasing load does not increase
tissue mass after mechanical stimulation.
Fibrocartilage Response to training
Cartilage changes no load:
* Disc volume increase
* Disc height increase
* Lumbar spine length increased
With vibration:
Less severe increase in disc height & volume
Better recovery
Immobilization reduces the tensile force on ligaments and tendons
*Decreased strength (reduced ultimate
failure)
*Decreased stiffness (slope of line)
*Increased elongation at failure
*Avulsion at insertion more likely than
mid portion
Structural Changes to ligamanets and tendons i nresponse to immobilisation
minimal change in ligament CSA or mass ie not atrophy
* increased rate of collagen turnover ie; synthesis and degradation
* newly synthesized (immature) collagen more pliable
* Collagen not organized as no stress/load to stimulate orientation
* Decreased water content and total glycosaminoglycans (GAGs)
ligaments and tendons mechsnical changes in response To training
Increased tensile strength
* Increase stiffness tendon & ligaments
* Increase diameter of collagen fibers
* Increase collagen crosslinking
