Implant manufacturing and conformity are governed by various standards and the cups, stem, heads and inserts have to meet these requirements.
The question is : are they sufficient or are they minimal standards. The answer is very simple. Not only are they minimal but many manufacturers just scrape through.
Now there are numerous questions, what do these standards fix as being acceptable, do they cover all aspects of implant manufacturing, do all implants meet these requirements and finally are the requirements sufficient.
The answers are rather and somewhat astonishing:
Now even standards change names or references, many people are still talking about ISO 9001 or EN 46001…..these are now out one has to talk about ISO 9001:2000 and ISO 13485. Do be careful about this as only last week were British companies trying to explain to us that they were ISO 9001….luckily they say were as that is the exact term to say that they are not up to date!
TITANUIM: Here we have one of the main features of implant manufacturing which is not covered by any standard whatsoever ! Indeed the composition of the titanium to be used for implant manufacturing is not governed by any standard!. There are standards indicating all the physical specifications that have to be met…but funnily enough no standard concerning the exact requirements of the chemical composition of the raw material !
Hydroxyapatite: is not far from being in the same situation as Titanium as there are no ISO standards for it either. The standards met are the French and American national standards…..this is not dramatic as these are often superior to the now aging ISO standards…..
Then having said that, are the required standards acceptable : well in fact they are rather poor and one can get away with a registration by just meeting minimum requirements which are not that brilliant.
Just to ascertain such a statement if you are using ceramic options be aware that there is a non official certification from CeramTec who test implants to see if they are worthy and reliable enough to accept Biolox inserts or heads…….as we have said this is a none official certification but many implants do not meet these CeramTec standards or requirements but on the other hand comply to CE registration or certification! Now if you are a ceramic user next time you speak with your supplier why not just ask him if he is Ceramtec ‘approved’?
For your information Scanos implants have been approved by Ceramtec for use in conjunction with Biolox ceramics, be it either for heads or inlays.
Then browsing through these standards further on, for interest sake, you will find the here and there some of the readings achieved by our Scanos implants compared to the accepted CE standards.
So lets say there are high standards and other standards……..and Scanos will supply any user upon request with their implant test results so that they may check what quality of implant they are using. Because as we have said above some implants just scrape through certification and nowhere is it specified if you are well above requirements……
STANDARDS TO BE MET FOR ACETABULAR CUPS.
Orthopaedic implant manufacturing is governed by ISO 8828 standards.
Hip implants COMPONENTS are governed by EN 12563 standards.
ISO 8828 standard: Implants for surgery. Guidance on Care and Handling of orthopaedic implants
EN 12563 standard: Non active surgical implants. Joint replacement implants. Specific requirements for hip joint replacement implants.
Quality is governed by two ISO standards ISO 9001:2000 and ISO 13485.
ISO 7206-2 for the bearing surfaces, both the heads and the inserts.
EN 12563 also deals with implant thickness tolerances.
4. Material OF THE METAL CUP
ISO 5832-3 standard covers high strength titanium TA6V ELI alloy (Titanium-aluminium 6-vanadium 4.Ti 6-Al 4V) the material from which acetabular cup components are generally manufactured from, In the case of TA6V alloy orthopaedic cups the titanium does not undergo a forging process. For this reason the mechanical properties of the metal differ from those of the same wrought alloy from which titanium femoral components and some cups are manufactured from. The variations are shown below:
ISO 5832-3Implants for surgery. Metallic materials.
Part 3: Wrought titanium 6-aluminium 4-vanadium
alloy 1996-07-01
WROUGHT TA6V (generally for femoral components)
Resistance to traction : minimum 860 Mpa
Elasticity limit : minimum 780 Mpa
Reciprocal value of modulus of elasticity : minimum 10%
Contraction coefficient : minimum 25%
NON-WROUGHT TA6V (generally for acetabular cups)
Resistance to traction : minimum 900 Mpa
Elasticity limit : minimum 820 Mpa
Reciprocal value of modulus of elasticity : minimum 15%
Acetabular orthopaedic cups comply to EN 12563 standards with regards to material thickness and to ISO 7206-2 standards for the articular surfacing.
EN 12563: Non active surgical implants. Joint replacement implants. Specific requirements for hip joint replacement implants.
EN 12563 establishes a minima for PE thickness for acetabular cup components. A minimum of 5mm of PE thickness is required for a PE insert and 6mm for a complete PE cup (Muller type).
ISO 7206-2: Implants for surgery. Partial and total hip joint prostheses. Part 2. Articulating surfaces made of metallic, ceramic and plastic materials.
PE inserts:Material: Polyethylene in compliance to ISO 5834 parts 1&2
ISO 5834-1: implants for surgery. Ultra High Molecular Weight Polyethylene. Part 1. Powder form.
ISO 5834-2: implants for surgery. Ultra High Molecular Weight Polyethylene. Part 2. Moulded forms.
UHMWPEA general description of UHMWPE rarely to be found in medical technical dossiers: A semi-crystalline, whitish opaque engineered thermoplastic which chemically has an extremely high molecular weight between 3-6 million HDPE. UHMWPE can only be processed by powder sintering methods. UHMWPE has outstanding strength, a very high cut and wear resistance plus a very high chemical resistance.
UHMWPE evidences very high tensile properties broadly similar to KEVLAR on a volume basis and even higher on a weight basis.
NB: just for information neither UHMWPE nor KEVLAR match carbon fibre properties on either basis.
For medical use UHMWPE is sterilized, this process not only sterilizes the implant but also cross-links the PE. (cross-linking: transformation of a linear polymer into a three-dimensional polymer by creating 3D molecular transversal liaisons, then scientifically referred to as being cross-linked).
Mechanical properties of UHMWPE:
Coefficient of friction0.1-0.2
Elongation at break (%)500
Hardness (Rockwell)R50-70
Izod impact strength (j m-1)>1000
Tensile modulus (gpa)0.2-1.2
Tensile strength (mpa)20-40
Physical properties:
Density (g cm3)0.94
Water absorption over 24hrs (%)<0.01
Femoral Head precision:
Metal femoral heads:
Sphericity less than -10µm of nominal diameter and a roughness less than Ra 0.05µm.
Ceramic femoral heads:
Sphericity must be within the limits of the nominal diameter and -0.2µm. Roughness must be less than Ra 0.02µm.
UHMW PE INSERTS:
Sphericity precision must be lower than 100µm of the nominal value and the inside diameter precision of the insert between +0.1mm and +0.3mm of the nominal value at a room temperature of 20°C.
Scanos cup inserts undergo mechanical resistance tests (crash tests) in order to resist to over 20 million load cycles [max force=14kN, min force = 0.5kN, frequency = 10 Hz, fluid test: Ringer solution RT]
The results obtained by Scanos cups are as follows:
Average 78kN (required value:>46kN)
Standard deviation obtained: 20kN
Minimum value requirement: 4kN
N° of pieces tested: 7
These tests comply to stem fatigue tests governed by ISO 7206-4 and 8 standards.
ISO 7206-4: Implants for surgery. Partial and total hip joint prostheses. Part 4.
Determination of endurance properties of stemmed femoral components with application of torsion.
ISO 7206-8: Implants for surgery. Partial and total hip joint prostheses. Part 8:
Endurance performance of stemmed femoral components with application of torsion
Coating
The CAPTIV® ELS titanium press-fit cup is fully coated externally with a 80µm APS plasma sprayed hydroxyapatite coating on a pre-prepared alumina corundum surface.[APS coating. Atmospheric Plasma Spray ]
Coating specifications :
Coating is in compliance with the following standards: ISO 13779-1 and ISO 13779-4 and with NFS 94-065 and 072 (French standards) and with ASTMF 1185-88 (American standards). These two standards are explicated in the paragraph Hydroxyapatite below.
ISO 13779-1: Implants for surgery--hydroxyapatite--Part 1: Ceramic hydroxyapatite.
ISO 13779-4: Implants for surgery--hydroxyapatite--Part 4: Determination of coating adhesion strength.
Technologyused for spraying: APS [Atmospheric Plasma Spray] Resistance to traction: 20Mpa. Surface roughness: 50µm.
12.Hydroxyapatite
Hydroxyapatite coating complies to French NFS standards NFS 94-065 and 072 and to US standard ASTM F1185-88
Crystallinity: 50%
Ca/P ratio: between 1.63 and 1.77[stoichiometric 1.667]
CaO: less than 5%
Metal contents: below readable level.(undetectable).
ASTM F1185-88 (R1993) Standard: Specification for Composition of Ceramic Hydroxylapatite for Surgical Implants.
Notice: FDA Modernization Act of 1997: Modification to the List of Recognized Standards.
Recognition List Number :007
Federal Register: October 2, 2002 (Volume 67, Number 191) Pages 61893-61910.
Docket No.: 97D-0530
AGENCY: FDA. Food and Drug Administration. HHS
13. Traceability
Traceability is ensured in compliance to EN 1041 standard governed by the general ISO 8828 standard.
EN 1041: Information supplied by the manufacturer with medical devices.
ISO 8828: Implants for Surgery. Guidance on Care and Handling of Orthopaedic Implants.
The required information is to be found engraved on the cup rim.
Engraving placed as such guarantees easy reading should the cup have be explanted.
Marks to be found:
On the metallic titanium cup itself: · Manufacturer’s name or logo.For the CAPTIV cups the logo is a triangle with an E inside the triangle (E stands for Evolutis)
·Material of the implant: in this case T (for titanium) · Lot n°: 2 numbers represent the year, 2 for the month and 3 numbers for the lot n°. On the PE inserts: The same as for the above metallic cup excepting that the T for titanium is here replaced by the engraving ISO 5834which stands for UHMWPE
Manufacturing certifications:ISO 9001:2000 / ISO 13485*
Implants are manufactured in compliance to: EC Guideline EC 42/93
*ISO 13485 (ex EN 46001): Quality systems--Medical devices--Particular requirements for the application of ISO 9001:2000.
