A reliable in vitro approach to assess the stability of acetabular implants using digital image correlation

Abstract

The main cause of failure of the hip acetabular component is aseptic loosening. Preclinical test methods currently used to assess the stability of hip acetabular implants rely on crude simplifications. Normally, either one component of motion or bone strains are measured. We developed a test method to measure implant 3D translations and rotations and bone strains using digital image correlation. Hemipelvises were aligned and potted to allow consistent testing. A force was applied in the direction of the load peak during level walking. The force was applied in 100-cycle packages, each load package being 20% larger than the previous one. A digital image correlation system allowed measuring the cup-bone relative 3D displacements (permanent migrations and inducible micromotions) and the strain distribution in the periacetabular bone. To assess the test repeatability, the protocol was applied to six composite hemipelvises implanted with very stable cups. To assess the suitability of the method to detect mobilisation, six loose implants were tested. The method was repeatable: the interspecimen variability was 16 μm for the bone/cup relative translations, 0.04°for the rotations. The method was capable of tracking extremely loose implants (translations up to 4.5 mm; rotations up to 30°). The strain distribution in the bone was measured, showing the areas of highest strain. We have shown that it is possible to measure the 3D relative translations and rotations of an acetabular cup inside the pelvis and simultaneously to measure the full-field strain distribution in the bone surface. This will allow better preclinical testing of the stability of acetabular implants.

Primary Stability of Revision Acetabular Reconstructions Using an Innovative Bone Graft Substitute: A Comparative Biomechanical Study on Cadaveric Pelvises

“…This was justified by previous investigations. In particular, our study relied on an extensively validated testing method based on Digital Image Correlation, which provided very small measurement errors [ 22 ]. To overcome the inter-specimen variability, paired hemipelvises were used, allowing more powerful statistical analysis based on paired data.…”

“…The loading configuration was limited to a single direction, reducing the complexity of forces and moments acting in the acetabulum. Such an approach, already adopted by most authors, has been proved to induce cup motions comparable with ones clinically observed while granting a good robustness and reliability to the results (i.e., minimizing the sources of experimental error [ 22 ]). Moreover, as paired tests were performed, the effect of the loading configuration on the acetabular stability was reduced in comparison with the effect of the reconstruction material.…”

“…A validated protocol was used for the biomechanical testing [ 22 ]. Walking was selected among the recommended activities for post-op rehabilitation.…”

“…To compute the bone/implant motions (translations and rotations along/about cranio-caudal, antero-posterior and medio-lateral axes), the DIC-measured displacements were post-processed through a dedicated script in Matlab (2017 Edition, MathWorks, Natick, MA, USA) [ 22 ]. In particular, the permanent migration (i.e., the migration accumulated cycle after cycle), and the inducible micromotion (i.e., the recoverable motion between load peak and valley) were analyzed.…”

Primary stability of a press‐fit cup in combination with impaction grafting in an acetabular defect model

“…Motion increased with increasing load (Figure 4), which is in good accordance with previous primary stability studies under dynamic load. 26,35 in human donor specimens. Under uniaxial dynamic loading in the same direction as applied in the present study, they found that inducible displacements and migrations were slightly higher (but without statistically significant difference) for tetrapods + coll than for bone chips throughout all applied load packages from 0.5*BW to 3.0*BW, which corresponded to median values of approximately 387 and 2325 N based on the donors' weight.…”