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63 Cards in this Set
- Front
- Back
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differ stress from strain
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stress; ratio of applied force to cross sectional area
strain: change in length of a material when stress is applied |
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what are two major regions of a stress-strain curve
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elastic region - initial straight portion of the curve (the material hasnt changed shape yet)
plastic region - non linear portion of the cirve (deformation of the material occurs) |
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what are 3 major points on a stress-strain curbe
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yield point; point where linear portion ends and non linear portion begins (deformation begins)
ultimate tensile strength: max stress that material can withstand on a curve failure strength: point where fracture occurs (aka fracture strength) |
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what is the modulus of elasticity of a material
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-the stiffness of a material
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what is fatigue failure
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delayed failure from fluctuating or cyclic stresses
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what type of sensitivity is observed with metal implants
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Type 4
-delayed response, cell mediated -osteolysis and dermatitis |
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what is the most common metal allergy and in what alloy can it be found
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-nickel is most common
- SS contains 15% nickel |
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what is stress shielding
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-phenomenon by which bone mass is decreased over period of time bc a rigid device takes the load and not the bone
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how can stress shielding be reduced in fracture fixation
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-use less rigid or flexible fixation devices
-use metal plates that are thinner -use metals that have a modulus of elasticity (stiffness) closer to that of bone |
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what is osteointegration
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process by which bone attaches to a material or device
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which type of bone are staples meant for
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cancellous; cortical is too hard to get staples through?
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for an oblique fracture, should the screw fixation be perpendicular to bone or fracture line
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-to the bone to rpevent sliding of the fragments on each other during axial load
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what is a herbert bone screw
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no head
pitch is different on either end of the screw |
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the primary advantage of cortical bone is stability; what is the advantage of cancellous
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facilitates osteogenesis
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list an xenograft
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coralline hydroxyapatite
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how long after skin grafitng will the area "pink up" and what is this process called
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- 48 hours later
-inosculation: graft is getting its new blood supply |
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what is the best suturing technique for areas of high tension
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mattress
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how do you relieve tension from the bases of a flap after performing an advancement flap
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cut Burow's triangles in tissue adjacent to the pivot point
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Bone morphogenic proteins (BMP) are growth factors needed for bone growth; who discovered them
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Urist in 1965
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what is lyophilization
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-process by which freeze dried bone reduces its antigenicity (used in allograft)
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name the non toxic dye used to asess the viability of skin flaps
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fluorescein
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what is the MC failure of skin flaps
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vascular embarrassment
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increase in length for a 60 degree Z plasty
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75%
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what is the minimum angle of a Z plasty
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35 degrees, any less then 45 though will impair blood flow to the flap
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what is a Gillies stitch
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-suture utilized at teh apical portions of incisions that does not penetrate the epidermis of teh apex, thus dec vascular damage
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what is the process by which skin grafts must heal when placed over an avascular area
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bridging; must get vascular supply from surrounding tissue
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how are the RSTL oriented on the plantar foot
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transversely
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give the thickness of thin, intermediate and thick STSG
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thin 0.008-0.012 inch
intermediate 0.012-0.016 thick 0.016-0.020 |
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how many cortices for syndesmotic screw
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3
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fixation for SH 4 fracture of distal tibia
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smooth k wire
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which method of fixation works best in Open wedge osteotomies
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staples because they maintain the size of osteotomy when graft is being resorbed
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cutting cone
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-is an osteon (composed of osteoclasts being chased by osteoblasts across the fx line)
-also resorption canal invaded by vascular buds |
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what is the first step in proper lag technique
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reduce the fracture with a bone clamp
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T or F: two crossed K wires provides compression
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False
K wires provide splintage not compression |
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how many threads of a screw should extend beyond the far cortex
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2
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when can a screw be used alone for internal fixation of a fracture
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when the fx is at least twice as long as the diam of the bone
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best type of fixation for pseudoarthrosis following debridement and graft placement
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neutralization plate
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how long for NWB of base osteo of 1st met
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6-8 weeks
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what is the cx of not overdrilling the proximal fragment
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distraction rather then compression
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when fixating a fracture, is the "load screw" perpendicular to the bone or fracture
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bone
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describe load screw technique (offset drilling)
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use the holes closet to teh fracture sight first, the first two screws are considered the "load screws"
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what are the 4 basic techniques of internal fixation
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-splinting
-neutralization -buttressing -interfrag compression |
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what is a transfixation screw
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-syndesmotic screw
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if pt has a nickel allergy, how would you fixate their CBWO
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bio absorbable screw
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5 weeks out; sclerosis it noted at an osteotomy site
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-beginning of non union
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which type of screw allows for percutaneous placement across the fracture sight
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cannulated
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what is Pauwels principle
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long bone eccentrically loaded is subjected to tension forces on teh convex side and compression on the concave side
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which effect is produced when using two different types of metals in close proximity to each other in the body
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galvanic corrosion
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what is the purpose of the posterior 1/3 semi tube plate in a distal oblique fib fracture
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anti glide plate that prevents proximal migration of distal fracture fragment
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T or F; threads of a lag screw should cross the fx line
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False
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K wire sizes
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0.035 inch
0.045 0.054 0.062 |
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steinman pin sizes
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5/64-12/64 except 11/64
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T or F; do lag screws provide dynamic interfrag compression
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no they provide static interfrag compression
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how is dynamic interfrac compression achieved; given an example in the foot
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-acheived with tension band fixation
-styloid fractures can be fixated with tension band -tension band harnesses forces generated at the level of the fracture when the bone comes under load |
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review screw sets and over under drill sizes
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.
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what is the primary function of a neutralization plate
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to protect interfrag compression lag screws deom bending, shearing, and torsional forces
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what is the primary purpose of a buttress plate
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to prevent axial deformity fron bending, shearing and torsion forces
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when appying bone screws should the depth gauge be used prior to tapping or after
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after. once the threads are tapped, teh depth gauge could disrupt the threads
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increased oxygen tension favors bone healing. what does a decreased oxygen tension promote
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cartilage formation instead of bone formation
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large (>6 cm) osseous defects are best treated by what special type of bone graft
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vascularized bone transfer
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how much of their inital strength will cortical grafts lose to osteoclastic activity
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30-40%
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what is the rate that cutting cones advance during bone healing
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50-80 micrometers/day
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how long does revascularization of a cortical and cancellous bone graft take, respectively
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cancellous - with in hours
cortical - after 6th day |
