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68 Cards in this Set

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What is the definition of a biomaterial?
Any substance of synthetic or natural origin, that can be used for any period of time, as whole or as part of a system that treats, augments, or replaces any tissue, organ or function of the body
What is the definition of a medical/surgical implant?
Foreign material placed in the body to assist or assume function of a body part
What are orthopedic implants made of?
Metals, polymers, ceramics & composites of these
What are the ideal characteristics of orthopedic implants?
Inert, sufficiently strong, good handling characteristics, easy to sterilize, nonallergenic, noncorrosive, nontoxic, nonteratogenic, resistant to infection & inexpensive
what are 3 types of metal implants?
1) Stainless steel & allows
-iron based, with chromium, nickel, molybdenum & minor elements
2) Titanium and alloys
3) cobalt based alloys
Compare stainless steel and alloy metal implants to titanium & alloy implants.
Titanium & allows have lower density, lighter weight, and a lower modulus of elasticity
How does a higher modulus of elasticity in an implant affect bone healing?
High module of elasticity results in less stress to the bone and results in stress shielding
-get stress shielding when implant is stronger than bone
What are cobalt-based alloy implants used for?
Primarily for prosthetic implants
-e.g. total hips, total knees, disc replacement
Why is it important not mix different types of metal implants?
Corrosion potential
-avoid mixing of stainless steel implants with unalloyed titanium, titanium alloys, & cobalt base alloy implants
What metals can normally be mixed without encountering serious galvanic corrosion problem?
Titanium, titanium alloy & cobalt base implants
Different metals can be placed in the same bone (e.g. stainless steel plate and titanium plate) as long as _______.
There's no direct contact w/ each other
What are the 3 advantages of metal implants?
1) high strength
2) ductility
3) resistance to wear
What are 3 disadvantages of metal implants?
1) Corrosion
2) Release of metal ions
3) Excess stiffness compared w/ surrounding tissues - can weaken bones
What causes corrosion, in general?
ionization, oxidation, hydroxylation associated with electrochemical and pH changes
What are the 4 types of corrosion?
1) Pitting corrosion: scratching or defects
2) Galvanic corrosion- dissimilar metals in contact with conductive media
3) Stress corrosion: metal subjected to opposing mechanical forces causing electrochemical potential leading to corrosion
4) Fretting corrosion: physical removal of metal by motion b/w components
What happens when metal implants release metal ions?
May stimulate neutrophils to release lysosomal enzymes leading to loosening, discomfort, allergic reactions
-wear particles can cause inflammatory reactions
What are ceramic implants used for?
Bone substitutes
-Osteoconductive: allows ingrowth of bone
What are two classes of ceramic implants?
-Calcium sulfates (CaS- plaster of paris)
-calcium phosphates (CaP-ceramic)
What are the advantages of ceramic implants?
Excellent biocompatibility, corrosion resistance, high compressive strength & resistance to wear, low frictional properties
What are the disadvantages of ceramic implants?
Brittle w/ low tensile strength and poor shear properties, low fracture strength, difficulty of fabrication, low mechanical reliability, lack of resiliency & high density
-Not used very often
What are 7 types of metal implants used for surgery?
1) Plates
2) Screws
3) Pins
4) Rods
5) Wires
6) Sutures
7) Joint replacements
What are most bone plates made of?
Stainless steel
What are the 3 types of bone plates?
1) Compression plates
2) Round-hole plates
3) Specialized plates
What are the 3 types of compression plates?
1) Dynamic compression plate (DCP)
2) Limited-contact dynamic compression plate (LC-DCP)
3) Locking compression plate (LCP)
What are 4 types of round-hole plates?
1) Straight plate
2) T-plate
3) L-plate
4) Reconstruction plates
What are 6 types of specialized plates?
Angled blade plate, dynamic condylar screw system, tubular, modified cobrahead, triple osteotomy, TPLO plates
What are 3 options when deciding on a bone plate?
1) Length of plate
-by number of holes- 2 to 26 or more
2) Size of plate (named by size of screw- 1.7mm to 5.5 mm)
3) Broad or narrow
Compare broad and narrow bone plates?
Broad generally has staggered screw holes & plate is thicker and stronger
-narrow has aligned screw holes and plate is thinner
Describe a dynamic compression plate.
Incline in screw hole, so screws can be placed in either load or neutral positions
What does the load position of a dynamic compression plate provide?
Interfragmentary compression
What type of screw angulation does a dynamic compression plate allow?
Longitudinal and transverse screw angulation
Describe how a limited-contact dynamic compression plate works.
Grooved undersurface provides limited contact b/w plate & bone
-hole is symmetrical & underside of hole is relieved to increase screw angulation
What does the strength of the DCP plate depend on?
Contact of plate and screws with the bone
When do we want to use DCP plates? When don't we?
-w/ large animals want complete contact under plate
-w/ smaller bones can lose blood supply this way - when use limited contact plates
What are 2 benefits of LC-DCP plates?
1) Minimizes chance for temporary osteoporosis under plate- doesn't compress bones like DCP
2) Allows periosteal callus formation at fractures site
What does conventional plating rely on to be effective?
Tightening of screws to full plate onto bone, creating frictional forces between plate & bone
*Forces holding plate on bone must be greater than load applied to bone by patient
-plate must be contoured to bone to maximize stability
Describe the screw placement in locking compression plates.
Screws can be locked into plate or placed in conventional manner
What is different about using a locking screw with a LCP?
Creates a fixed-angle construct, providing angular stability
True or false. LCP needs to be contoured to the bone.
False
Are LCPs very good at preserving periosteal blood supply? Explain.
Yes, because LCPs do not generate plate to bone compression
How do LCPs improve tissue viability?
Have a tapered end for submuscular plate insertion
Compare the strength of unicortical insertion of locking screws in a LCP to that of bicortical placement with conventional screws.
Unicortical insertion of locking screws provides a construct with AT LEAST as much strength as one created by bicortical placement of conventional screws
What must you do before placing locking screws in a LCP?
Must reduce fracture with lag screws if necessary BEFORE placement of locking screws in LCP
What plate provides the most strength, LC-DCP, DCP, LCP?
LCP-Have threads on plate & screw= very strong construct
What is the mode of failure for LCPs?
Fracturing of bone, very strong plates
What are bone screws made of?
Same materials as plates, most are stainless steel
What are 4 types of bone screws?
1) Cortical
2) Cancellous
3) Locking
4) Specialized
When do you use cortical bone screws?
For use in dense diaphyseal bone
When do you use cancellous bone screws?
For use in softer metaphyseal bone
When do you use locking bone screws?
For use with LCP
When do you use specialized bone screws?
Specialized bone screws such as cannulated screws are used for specialized applications
What are 4 options you have to decide when picking a bone screw?
1) Length of screw
-6mm to 100mm or more
2) Size (diameter of screw)
-1.5 mm to 5.5 mm
3) +/- self-tapping
4) Fully threaded or partially threaded
Describe a cancellous screw.
Fully threaded
Describe a locking screw.
Partially threaded so allows lagging in the middle
Describe a cannulated screw.
Have center drilled out so can put pin in to guide placement of the screw
What does self-tapping mean?
Means that don't have to cut threads for the screw hole, but most people do to get extra material out of there
-what most cortical screws are
Compare the size of the drill bit and screw necessary for a successful repair.
Drill bit always needs to be a little smaller than the screw
-screw size refers to size of screw WITH threads
-if drill same size as screw w/ threads then won't hold
What are Steinmann pins made of?
Stainless steel
What is the diameter of Steinmann pins? Length?
1/16 to 1/4 inch diameter
9 or 12 inches long
What threads are available for Steinmann pins?
Threaded or non-threaded
-threaded have positive or negative profile threads with positive being preferred
What are the 3 sharp tips that are available for Steinmann pins?
1) Trochar tip
-3 sides long bevel
2) Chisel tip
-2 sides, short bevel
3) Screw tip available
What are Kirschner wires (K-wires)? When are they used?
Small pins
Used in very small bones or for *fracture repair across a physis
What are 3 uses of pins & wires?
1) As intermedullary implants
-single or multiple
2) As transfixation pins in external fixation
3) Cross pinning of some fractures (SA)
What are interlocking nails made of?
Stainless steel or titanium
Describe an interlocking nail.
Nail has holes for transfixation screws
What are 2 applications for orthopedic (cerclage) wire?
1) fracture repair
-more common in SA than LA
2) Physeal growth retardation (LA)
What are 2 ways cerclage wire can be used to repair a fracture?
1) Auxillary fixation w/ IM pins or plating
2) Tension-band wiring (SA/ some LA)
What does a smaller gauge wire mean?
Larger the wire