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Flashcards in Biomechanics of fractures Deck (14):
1

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

2

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

3

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)

4

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)

5

Rate of force application

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

6

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

7

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

8

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

9

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

10

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

11

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

12

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

13

Vascular injuries

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

14

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)