BS ISO 7206-12:2016 pdf download – Implants for surgery — Partial and total hip joint prostheses — Part 1 2: Deformation test method for acetabular shells
The clamping jaws holding the test specimen in place during loading shall possess a flat clamping surface (flatness according to ISO 2768-2:1989, K, avoiding cross forces due to tilting or sliding of the test specimen during loading and measuring. Certain acetabular component designs contain design elements for exceptional purposes such as complex revision surgery or specific patients’ demands, e.g. anchoring edges, anatomical shaped rim, etc. In case that such an acetabular component shall be tested, clamping jaws shall be used which are designed in a way that the specimen can be fixed and loaded.
The width of the clamping surface shall be at least 20 % of the outer diameter of the test specimen at the frontal face reference plane allowing the manual centring of the test specimen contact points on the clamping surfaces prior testing. Additional centring features or tools are not necessary. If centring features or tools are provided, ensure that the two-point loading and the deformation of the test specimen are not constrained. The load cell shall be capable of measuring an axial compressive force with an uncertainty of 1 %.
5.2 Test specimen selection The test specimen of that size of the acetabular component, which has been identified to be the worst- case size, shall be randomly selected being representative for manufacturing and shall have the same geometry and be made to the same material specification through the same process as the final product. NOTE In case of modular acetabular components, the worst-case size for the first step of testing (metal backing deformation) may be different from the worst-case size of the second step of testing (articulating surface deformation of the acetabular component). If there are different articulating surface materials offered for the modular acetabular components, then all insert articulating surface material and sizes shall be evaluated regarding identification of worst-case material and sizes. Design features, such as asymmetrically located screw holes, shall also be considered.
a) Prior to loading, measure the inner diameter, D 0 [mm], of the specimen for each of the planned loading directions by using a capable measurement device. The diameter shall be measured in the measurement plane inside the spherical socket. An uncertainty of the measurement of <5 μm is required. The diameter can additionally be measured at further positions in the same measurement plane, e.g. perpendicular to the loading direction, for acquisition of additional data on the general deformation behaviour of the test specimen.
b) Position the specimen in the testing set-up and apply and maintain an axial force of (1,00 ± 0,01) kN by steady turning the load adjustment screw. Avoid jerky loading. The contact points of the specimen with the loading surfaces of the load frame shall be located within the loading plane.
c) Measure the diameter D 1 (mm) of the specimen in the loading direction, within the same measurement plane and by use of the same measurement device as in a). The deformation of the cup is the difference D 0 − D 1 .
d) Unload the test specimen.
e) Measure the diameter, D 0 ’ [mm], of the specimen in the direction of c) again by using the same measurement device. If a remaining difference, D 0 ’ − D 0 , to the initial diameter from a) is determined, which is larger than the uncertainty of the measurement device and which is larger than 2 % of the deformation [ |(D 0 ’ − D 0 )/(D 0 − D 1 )| > 0,02 ] determined in c), then a plastic deformation of the specimen occurred. In that case, the test shall be stopped for that specimen and the testing proceeds taking the next specimen and starting at a).BS ISO 7206-12 pdf download.