Medicon reference

Almost all labels or surgical instruments give the Medicon reference at the end of the label. The reference has the following structure: 3 x 2 numbers separated by a dash e.g. 11-22-33.

The Medicon reference gives clear specifications for the article, but it remains an open article. Several sources (other than Medicon) are possible if the same quality level is met.

The reference of Medicon can also be used to view the article in their online catalogue (replace the dash by a dot to search in the Medicon catalogue).

Norms for surgical instruments

The technical commission 170 from ISO is responsible for the standardization in the field of surgical instruments

• ISO 7151:1988 (3rd edition is under development): Surgical instruments -- Non-cutting, articulated instruments -- General requirements and test methods
• specification of basic requirements for as well physical characteristics as workmanship, of the steel grades used and heat treatment of component parts, excluding rivets, screws and parts manufactured of material grade M.
• ISO 7153-1:2016: Surgical instruments -- Materials -- Part 1: Metals
• specifies metals commonly used to manufacture various types of standard surgical instruments, including but not limited to those used in general surgery, orthopaedics and dentistry.
• is not intended for surgical instruments used in special applications, such as implantology and minimally invasive surgery, parts of it might be applicable to those instruments.
• ISO 7740:1985 (reviewed and confirmed in 2021): Instruments for surgery -- Scalpels with detachable blades -- Fitting dimensions
• lays down the dimensions of two sizes of fitting features for detachable scalpel blades and the handles with which they are used. It secures a good fitting and interchangeability of detachable blades for scalpels
• ISO 7741: 1986 (reviewed and confirmed in 2017): Instruments for surgery -- Scissors and shears -- General requirements and test methods
• deals with materials, heat treatment and hardness of component parts, corrosion resistance, workmanship and cutting ability of scissors and shears used in the surgery and defines the test methods.
• ISO 13402:1995 (reviewed and confirmed in 2021): Surgical and dental hand instruments -- Determination of resistance against autoclaving, corrosion and thermal exposure

Metals used to manufacture surgical instruments

Since there are different requirements to various surgical instruments, there also have to be different requirements to the materials from which the instruments are manufactured. Not all of the materials are suited to use in every type of instrument.

For most types of surgical instruments materials which are known from experience to be suitable for those instruments are given in the tables of ISO 7153.

Surgical stainless steel

Surgical stainless steel is a grade of stainless steel used in biomedical applications. There is no formal definition on what constitutes a "surgical stainless steel", product manufacturers and distributors apply the term to refer to any grade of corrosion resistant steel.Table 4 of ISO 7153 lists the grades of stainless steels used in surgical instruments using the material number and short term according to EN 10088-1:2014.

The most common "surgical steels" are austenitic 316 stainless steels and martensitic 440 and 420 stainless steels.

440 and 420 stainless steels, known also by the name "Cutlery Stainless Steel", are high carbon steels alloyed with chromium. They have very good corrosion resistance compared to other cutlery steels, but their corrosion resistance is inferior to 316 stainless. Biomedical cutting instruments are often made from 440 or 420 stainless steel due to its high hardness coupled with acceptable corrosion resistance. This type of stainless steel may be slightly magnetic.

316 stainless steel, also referred to as marine grade stainless steel, is a chromium, nickel, molybdenum alloy of steel that exhibits relatively good strength and corrosion resistance.

Chemical composition of the stainless steels

Stainless steel is a steel alloy with a minimum of 10.5% chromium content by mass and a maximum of 1.2% carbon by mass.

Alloy steel is steel that is alloyed with a variety of elements in total amounts between 1.0% and 50% by weight to improve its mechanical properties.

The simplest steels are iron (Fe) alloyed with carbon (C): about 0.1% to 1%, depending on type. As the carbon percentage content rises, steel has the ability to become harder and stronger through heat treating; however, it becomes less ductile. Regardless of the heat treatment, a higher carbon content reduces weldability.

The term "alloy steel" is the standard term referring to steels with other alloying elements added deliberately in addition to the carbon.

• Si = silicium: increases the hardness and wear resistance
• Mn = manganese: can increase the tensile strength, could remove or improve the bad influence of Sulfur, could improve the hardening capacity of heat treatment. High content of Mn will cause worse welding capability and reduce the heat conductivity of steel = easier to cause cracks.
• Ni = nickel: could improve the tensile strength and toughness of cast steel, improve the hardening capacity of heat treatment. High content of Ni could improve the corrosion resistance and the properties of other alloys.
• P = phosphorus: reduces the plasticity and toughness of cast steel, especially at low temperature: better to keep it at less than 0.04%.
• S = sulfur: is the harmful impurity of cast steel, it causes fragility, especially after quenching heat treatment, and during machining at high temperature. A lower Sulfur is better (less than 0.04%).
• Mo = molybdenum: could improve the hardening capacity, and heat-resisting strength of heat treatment, = reducing the brittleness of quenching treatment. It can also improve the surface abrasive resistance.
• V = vanadium: promotes fine grain size, increases hardenability and improves wear resistance. Small amount of Vanadium increases the strength of steels significantly

Surgical stainless steels for families of products

Pressure force instruments and springs (haemostatic forceps, dissecting forceps, gripping forceps, surgical towel clamps, needle holding forceps, threading forceps, clamping forceps) ► martensitic steel

• The steel used must be springy and highly impact resistant.
• Carbon gives them hardness, while chromium gives them corrosion resistance.
• The steel have to undergo a complex, rigorous heat treatment which allows the steel to be hardened; otherwise they will bend the first time they are used.
• The steel must be carefully polished; the quality of the polishing determines the corrosion resistance.

Instruments that cut by shearing (scissors curettes, raspatories, gouge shears, cutting forceps) ► martensitic steel

• The steel used has a higher percentage of carbon than for the pressure force instruments in order to increase hardness.
• The percentage of chromium is the same to give corrosion resistance, while incorporation of molybdenum makes up the balance and improves the cutting qualities.

Instruments that cut by percussion (chisel shears, osteotomes, gouges) ⇒ martensitic steel

• For the cutting part, the heat treatment and polishing are the same as for instruments that cut by shearing.
• For the non cutting part, the heat treatment and polishing are the same as for pressure force instruments.

Static function instruments: self-retaining retractors, long-handles retractors, valves, specula, dilators) ► martensitic or austenitic steel

Miscellaneous instruments (instrument boxes, obstetrical hook, manual drill) ► austenitic steel

Hard metals used in surgical instruments

Alloy type used for instruments with wear protection (inserts or coating):

• cobalt-chrome-tungsten: for scissors
• tungsten carbide cobalt-binder: for forceps and needle holders
• tungsten carbide nickel-binder: for forceps, scissors and needle holders

Tungsten carbide is a chemical compound containing equal parts of tungsten and carbon atoms. It is approximately twice as stiff as steel and is double the density of steel—nearly midway between that of lead and gold.

Tungsten Carbide materials have a unique combination of properties, high compressive strength, hardness and resistance to wear, as well as an ability to withstand shock and impact.

The binder in most grades of Tungsten Carbide is cobalt. The other binder used is nickel. The binder is added as a percentage by weight varying from 3% to 30%. The amount of binder used is a very important factor in determining the properties of each grade. As a rule of thumb the lower the cobalt content the harder the material will become. However variation in grain size and additives can upset this rule.

Titanium used in surgical instruments

Different grades of pure titanium and titanium alloy are used in surgical instruments. Information about the quality can be found in ISO 5832 Implants for surgery -- Metallic materials

Retractors and probes: pure titanium = Unalloyed Commercially Pure (CP) Titanium, ISO implant quality 5832-2 grade 1, 2, 3 and 4. Grade 1 has the highest corrosion resistance, formability and lowest strength, grade 4 offers the highest strength and moderate formability.

A titanium alloy (ISO 5832-3) can be used for: forceps, scissors, retractors, probes, needle holders, springs, screws, rivets, guide pins.

Titanium is naturally a grey metal, but by anodizing the surgical instruments, manufacturers change the surface properties of the metal. Titanium surgical instruments are typically blue. The anodizing also makes the surgical instruments non-reflective so that there is no glare.

Titanium surgical instruments offer several advantages over stainless steel instruments:

• lightweight: reduces hand fatigue especially during long surgical procedures
• high tensile strength.
• durable, even after repeated autoclaving without damaging the surfaces or cutting edges
• corrosion resistant, non-ferrous (it will not rust), non-magnetic (=MRI compatible) and bio-compatible.