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Biomechanics PT 3 - Coggle Diagram
Biomechanics PT 3
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factors that affect stability of external fixator:
-pin diameter: bending stiffness increasing by order of the 4th power as diameter increases
-# of pins used
-distance from the surface to the bone
-stiffness of the frame
-# of fixation plates
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fixation plate:
-stability determined by raising thickness to 3rd power and width to first power
-strength determined by raising thickness to 2nd power and width to the third power
Holes in bone affect its strength:
-decreases CSA and strength is decreased
-strength decreased by causing stress concentration point determined by geometry of the hole and bone
-hole 20% of bone diameter decreases strength by 50%
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Fracture fixation:
-strength of fixation determined by pullout strength of lag-screw
-40% incresae in strength over plating alone
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Length-tension relationship:
-amount of force that muscle can produce varies with length of muscle at time of contraction
-max force produced when muscle is at approximately its resting length
-when fibers shortened beyond force production decreases slowly first, then rapidly
-progressive decline as fibers are lengthened-explains why surgically lengthened muscles are weak post-operatively
Cartilage: morphological, biological, metabolic, and histologic differences in joints of LE
- in part explains why OA is more common in knee/hip and not ankle
Friction: is good or bad depending on context:
-force that is parallel to contact surface
-opposes motion between two objects
-magnitude depends on material characteristics
-lower if there is relative motion between the two surfaces
-friction needed for efficient motion, but can also lead to risk of ankle/knee injuries in sports
Tissues adapt to change at different rates:
-tendon (dec # of cells) and bone adapt slower than muscle
-ligs IV discs, and cartilage also believed to adapt slower, but less research
-muscle will regain strength prior to other tissues in rehab process and is not good indicator alone of rehab process
Spurt vs shunt muscle:
-spurt muscle has insertion close to joint, change in distal bone motion is large for a short change in muscle length (brachialis)
-shunt muscle has origin close to joint. small change in muscle length for small amount of distal bone motion (brachioradialis)
-spurt muscles are better at moving the joint, shunt muscles are better at stabilizing joint
Biomechanical factors that affect implant stability:
-initial stability: based on surgery technique and implant design
-late stability: determined by bone growth and remodeling of bone around implant
-stress shielding: affects bone around the implant as load typically goes through the stronger implant, not bone surrounding the implant
-wear of the implant: cobalt-chrome implants typically used to decrease wear
-changing anatomic alignment: by the manner in which the implant is installed