Elec 371 - Surgical Instruments

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Surgical Instruments

Iron-Based Metal Compounds

Iron (Fe)

• Crystalline Structure– Atoms arranged in a lattice

• Alpha Iron– < 910° C

• Gamma Iron– 910°-1400° C

• Melting point– 1540° C

Ferrite (Steel)

• Iron Alloy– Fe + Other atoms

– At least 50% Fe

• Stainless steel– 11% to 30% Cr

– Up to 2% C

Elec 371 - Surgical Instruments

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Atomic Structure of Iron Crystal

Body CenteredFerrite (α iron)

Face CenteredAustenite (γ iron)

910° C(threshold temp)

Heat

Cool

Non-magneticLarger interstitial gaps

Magnetic

Alloys - Substitutional Atoms

• Similar size as Fe

• Replace Fe atoms• Chromium (Cr)

• Molybdenum (Mo)

• Nickel (Ni)

Elec 371 - Surgical Instruments

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Alloys - Interstitial Atoms

• Smaller than Fe

• Occupy gaps

• Greater solubility in Gamma

• Precipitate out during cooling• Carbon (C)

• Nitrogen (N)

Iron Alloy Atoms

Substitutional Atoms

• Chromium (Cr)– Corrosion Resistance

• Molybdenum (Mo)– Extra corrosion resistance

• Nickel (Ni)– Austenite

– Stabilizes Gamma at room temp

– Bright finish

Interstitial Atoms

• Carbon (C)– Smaller atomic radius than

substitutional atoms

• Nitrogen (N)– Smaller atomic radius than C

– Greater solubility

Elec 371 - Surgical Instruments

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Hardening

Quench Hardening– Heat to Gamma

• face centered

• higher C solubility

– Carburize• Add C and/or N

– Quench• Cool rapidly in oil bath

• Rapid transition traps C/N atoms

– Martensite• Disorganized crystal structure

Work Hardening– Mechanical manipulation

– Non-uniform

– Result• Low strain

• Brittle

Softening

Annealing• Heat

– Target temperature / long time– Gamma throughout

• Cool slowly– Carbon precipitates out

• 0.00005% to 2% (by weight)

• Result– Ductile throughout

Tempering• Heat

– High temperature / short time– Gamma surface / Alpha core

• Cool slowly– C precipitates from surface

• Result– Ductile surface– Hard interior

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Classes of Stainless Steel

• Ferrite– Fe + Cr

– Magnetic

– Ductile

– Low Cost

• Martensite– Fe + Cr + (C / N)

– Magnetic

– Hard

• Austenite– Fe + Cr + Ni (+ C / N)

– Non-magnetic

– May be quench hardened• Not as hard as Martensite

• Other– Duplex Austenitic-Ferritic

– Manganese-Substituted Austenitic

– Precipitation Hardened

Dissecting ForcepsMicro-Dissecting (normally open)

Cross Action (normally closed)

Adson

Cushing

Jansen

Alligator

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Hemostats (Clamps)

Reynolds - sturdy Mixter - delicate

Kelly - sturdy Mosquito - delicate

Scissors

McPherson-Vannas

Mayo - sturdy Metzenbaum - delicate

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Scissors

Blunt

Angled

Sharp Curved

Curved (side)

Sharp - blunt

Retractors

Rake Davis

BarraquerWeitlaner

Senn

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Scalpels

#3

#4#7

Miniature

Round

Needle Drivers

WebsterOlsen-Hegar

Driver/Scissor Combo

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Needles

Cross-SectionsTop = inside edge

Btm = outside edge

Opthalmic / micro-surgery

Most common

Tough tissue