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Flashcards in Biomechanics of fractures Deck (14):

Bone strength

-Fractures occur when force applied exceeds bone strength
-Bone strength depends on bone density, metabolic, structural aspects of bone, and the modality of the force


Metabolic factors of bone strength

-Osteomalacia: disturbance in Ca metabolism (increased parathyroid hormone), leads to decreased Ca in matrix, but normal matrix amount
-Osteoporosis: Ca to matrix relationship is normal, matrix amount is low, leads to a decrease in bone quality


Physical properties that determine bone strength

-Cross-sectional diameter: small cross-sectional diameter w/ thick walls are strongest
-Age: over time bones loose wall thickness, and diameter increases (makes bones weaker)


Forces applied to bone

-Tension: forces separating bone
-Compression: forces collapsing bone
-Bone is weaker in tension than compression, thus bones will break on the OPPOSITE side of impact (tension force on opposite side, compression force on same side)


Rate of force application

-Rapid force: fracture
-Slower (relative) force: ligament failure


Locations of fractures

-Can be at diaphysis (middle of bone) or metaphysics (near ends of bone- could effect bone growth)
-Soft tissue integrity: open or closed fracture
-Types of fractures: transverse, oblique, butterfly, spiral, comminuted
-Loss of structural integrity (fractures) lead to muscle losing its resting tension and going into spasm


Avascular necrosis

-Carpal navicular
-Femoral neck: retrograde flow required (artery w/ ligament of femoral head not sufficient)
-These fractures are surgical emergencies in young, hip replacement in elderly
-Talus: also retrograde flow required


Wolf's law

-Bone constantly remodels itself to resist forces
-If a constant force is applied to a bone over time, the bone will re-organize to resist the force
-During bone healing, initial bone is woven (disorganized)
-Over time this bone becomes lamellar (organized) bone which is stronger


Fatigue failure of bone

-Fatigue failure is constant application of a certain movement leading to failure
-Bone is very resistant to this
-But it can fail from this
-Fatigue failure of bone results in stress fracture


Factors affecting bone healing

-Biologic (blood supply, metabolic)
-Mechanical: bolts or casts
-Primary bone healing (bolts): eliminates all motion, inflammation+repair stages skipped
-Callous formation (casts): motion required


Compartment syndrome

-Accumulation of fluid in a compartment of fixed volume leads to increase in pressure in that compartment
-5 Ps: pain, pressure, paralysis, pulselessness, pallor


Nerve injuries

-Fibular neck fractures can lead to common fibular nerve injury
-Shoulder (scapula) fractures: injury to the axillary nerve
-Humerus fracture: injury to the radial nerve


Vascular injuries

-Fractures of the distal femur: superficial femoral artery
-Knee dislocations: popliteal artery


Facture Rx

-Goals: achieve union in short time, restore function, maintain alignment, minimize complications
-Casts: less precise method of maintaining alignment, leads to micro movements which generate callous
-Internal fixation: using implants (screws, nails)