Discussion
osteolysis, impingement, dislocation, THA
SECONDARY, ASEPTIC LOOSENING, STILL, OSTEOLYSIS
THA remains one of the most important and common procedures of healthcare systems around the world and despite advancements in surgical techniques and implant designs, revision rates remain concerning. Aseptic loosening of the prosthetic components is a known risk factor for revision surgery and latest implant designs have incorporated mechanisms to increase initial stability, such as available screw holes in most acetabular prostheses. Still, the use of screws to supplement acetabular fixation is unsettled in literature, leaving the choice to surgeon preference.Initial cup position is an important determinant of THA success since cup malposition increases the risk of revision surgery, as it can lead to impingement, reduced range of motion, dislocation, wear and osteolysis, loosening and cup failure.The results of this study revealed that the use of screws had a significant impact on the stability of the cup and resulted in increased proximal migration up to 2 years postoperatively. Previous RSA studies compared acetabular cup stability between press-fit cups fixated with no screws or with 2 or 3 screws and found no added benefit of screw fixation on cup stability.Some limitations can be noted in the presented study. Primarily, this study was a secondary analysis and was not designed to detect differences in acetabular cup migration. Still, the power calculation analysis showed sufficient power to compare patient groups and results of this study are of important clinical significance. Additionally, potential bias may be introduced since there was a difference in the operative techniques used between screw fixation groups. However, an expertise-based design has been reported to reduce challenges to expertise bias and ensured the best technique was used in all cases, as both surgeons are experts in their respective approaches.In conclusion, this study demonstrated that the use of screws had an impact on the primary stability of the acetabulum cup. Specifically, cups fixated with 1 screw resulted in greater migration than compared to no screws or 2 screws, though the mean magnitude of migration was well below the 1.0-mm threshold for unacceptable migration. 3 patients who received only 1 screw did exceed the threshold for unacceptable migration. As such, the results of this study show that two screws to supplement cup fixation can provide good implant stability that is equivalent to a secure press-fit component with no screws.